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Nonanal Gas Sensors Using Porous Glass as a Reaction Field for Ammonia-Catalyzed Aldol Condensation
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  • Masato Tsujiguchi*
    Masato Tsujiguchi
    Development Division, Research and Development Group, Nippon Electric Glass Co., Ltd., 7-1, Seiran 2-chome, Otsu, Shiga 520-8639, Japan
    *Email: [email protected]
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    Orcidhttps://orcid.org/0000-0002-7629-7838
  • Yasushi Kii
    Yasushi Kii
    Evaluation Division, Research and Development Group, Nippon Electric Glass Co., Ltd., 7-1, Seiran 2-chome, Otsu, Shiga 520-8639, Japan
    More by Yasushi Kii
  • Takashi Aitoku
    Takashi Aitoku
    Development Division, Research and Development Group, Nippon Electric Glass Co., Ltd., 7-1, Seiran 2-chome, Otsu, Shiga 520-8639, Japan
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  • Masaru Iwao
    Masaru Iwao
    Development Division, Research and Development Group, Nippon Electric Glass Co., Ltd., 7-1, Seiran 2-chome, Otsu, Shiga 520-8639, Japan
    More by Masaru Iwao
  • Yasuko Yamada Maruo
    Yasuko Yamada Maruo
    Department of Applied Chemistry and Environment, Faculty of Engineering, Tohoku Institute of Technology, 35-1, Yagiyama, Kasumicho, Taihakuku, Sendai 982-8577, Japan
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ACS Omega

Cite this: ACS Omega 2023, 8, 8, 7874–7882
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https://doi.org/10.1021/acsomega.2c07622
Published February 13, 2023

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Abstract

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Transmittance in porous-glass gas sensors, which use aldol condensation of vanillin and nonanal as the detection mechanism for nonanal, decreases because of the production of carbonates by the sodium hydroxide catalyst. In this study, the reasons for the decrease in transmittance and the measures to overcome this issue were investigated. Alkali-resistant porous glass with nanoscale porosity and light transparency was employed as a reaction field in a nonanal gas sensor using ammonia-catalyzed aldol condensation. In this sensor, the gas detection mechanism involves measuring the changes in light absorption of vanillin arising from aldol condensation with nonanal. Furthermore, the problem of carbonate precipitation was solved with the use of ammonia as the catalyst, which effectively resolves the issue of reduced transmittance that occurs when a strong base, such as sodium hydroxide, is used as a catalyst. Additionally, the alkali-resistant glass exhibited solid acidity because of the incorporated SiO2 and ZrO2 additives, which supported approximately 50 times more ammonia on the glass surface for a longer duration than a conventional sensor. Moreover, the detection limit obtained from multiple measurements was approximately 0.66 ppm. In summary, the developed sensor exhibits a high sensitivity to minute changes in the absorbance spectrum because of the reduction in the baseline noise of the matrix transmittance.

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Introduction

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The progressive increase in both the global birthrate and aging populating has attracted increased interest in the development of new medical solutions, particularly in post-illness treatment and preventive medicine. Hence, new diagnostic methods for the early detection of diseases are currently being researched and developed. In the early 1970s, Pauling et al. reported that human-exhaled breath contained over 200 volatile organic compounds (VOCs); (1) subsequent studies have since identified over 3500 VOCs. (2) The composition of these VOCs has been widely adopted as an indicator of health status. (3−7) Thus, as diseases can be diagnosed from exhaled breath, non-invasive and rapid means of detecting VOCs could be very useful in the field of medical diagnosis. (6,7)
Cancers are a leading cause of death, among which lung cancer has a particularly high mortality rate. This is mainly because of the difficulty in detecting cancer disease markers in the early stages of illness. Thus, there is a growing need for convenient and sensitive detection of VOC markers for lung cancer. Several studies have compared the VOC concentration in the exhaled breath of lung cancer patients and healthy individuals; (8−13) significant differences in the concentration of nonanal have been reported. (11−13) Nonanal is an oxidative decomposition product of oleic acid; (14−17) it is generally accepted that as oleic acid oxidation progresses in lung cancer patients, the nonanal concentration in the exhaled air increases. Thus, nonanal can be a promising VOC marker for lung cancer diagnosis. Although several methods have been reported for sensing nonanal, including semiconductor sensing, (18) chemosensitive property variability, (19) and quartz crystal microbalance (QCM) measurements, (20,21) these methods demonstrate poor gas selectivity or sensitivity. Semiconductor gas sensors can detect nonanal at a level of several dozen parts per billion (ppb), but they must be loaded with a noble metal, such as platinum, to detect aliphatic hydrocarbon gas with high sensitivity and gas selectivity. (18) Chemosensitive and QCM sensors cannot detect sub-ppm levels of nonanal and do not show gas selectivity for aldehydes, which have structures similar to that of nonanal. (19−21)
We have previously reported a nonanal sensor utilizing porous glass and an aldol condensation reaction between nonanal and vanillin under alkaline conditions. (22) Because porous glass contains translucent nanopores, changes in the reactant color due to the chemical reactions occurring inside the pores can be easily detected. (22−24) In addition, porous glass has an inner-wall surface functionalized with silanol groups, which retains a thin water film because of its hydrophilicity. Thus, porous glass is a suitable nanoporous material for homogeneously supporting condensation reagents. Furthermore, the material has the potential to function as a reaction field for trace-level gas detection reactions. We therefore proposed to use it as a reagent carrier and reaction field for gas sensors, using the change in the absorption spectra of the condensation reagents as the detection mechanism. For this purpose, we had prepared alkali-resistant porous glass using sodium hydroxide as an alkali catalyst. The limit of detection (LOD) was found to be in the order of 102 ppb; however, the gas sensor exhibited a low transmittance. (22) Nevertheless, the sensor was able to detect changes in absorbance caused by the aldol condensation of vanillin and nonanal within the inner surfaces of the porous glass. However, detecting minute changes in absorbance becomes challenging when the transmittance of the porous glass decreases. In addition, the resulting increase in the lower LOD value becomes disadvantageous.
To address these shortcomings, we investigated the factor responsible for decreasing the transmittance of sodium hydroxide-loaded porous glass gas sensors. To achieve this, we employed ammonia as an alternative catalyst and compared its performance to that of the hydroxide-loaded sensor. Through the findings discussed herein, we suggest measures that may overcome the detection issues in nonanal gas sensors.

Experimental Section

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Porous Glass Preparation

Porous glass was prepared by a phase-separation method, as shown in Figure S1. (22) Soda borosilicate glass was subjected to heat treatment at the glass transition temperature (or higher) and separated into silica and soda boron oxide phases. The soda boron oxide phase was leached with an acid solution to produce pores, whereas the silica phase was not leached, forming a skeleton. (26,27)
In addition to the conventional borosilicate components for porous glass (SiO2, B2O3, and Na2O), (26,27) raw materials included K2O, Al2O3, CaO, P2O5, TiO2, and ZrO2. In particular, ZrO2 was added to improve the alkali resistance of the glass. The materials were placed in a platinum crucible and melted at 1773 K. The molten glass was then rolled, molded on an iron plate to form a plate, and gradually cooled. The glass sample was processed to a size of 5 × 5 × 0.5 mm and subjected to a phase heat treatment at 968 K. The fractional glass sample was then leached with 1 mol/L aqueous nitric acid.
The glass sample was further leached with 1.5 mol/L aqueous sulfuric acid followed by 0.5 mol/L aqueous sodium hydroxide and then washed with ion-exchanged water.

Porous Glass Evaluation

Scanning electron microscopy (SEM) was performed using a field emission scanning electron microscope (SU-8820, Hitachi, Japan) at an accelerating voltage of 1.6 kV. The ultraviolet–visible (UV–Vis) spectra of the porous glass samples were obtained using a spectrophotometer (UH-4150, Hitachi High-Tech, Japan) in a wavelength range of 300–800 nm. The pore-size distribution of the porous glass was determined using a nitrogen adsorbent and a surface/pore-size analyzer (Quadrasorb SI, Anton Paar, Austria).

Estimation of Changes in the Absorption Spectra

For the sodium hydroxide-loaded and ammonia-loaded porous glass samples, the relationship between their absorption spectra and the elapsed time after base treatment was estimated. For these spectra, the samples were measured between 300 and 800 nm after exposure time intervals of 0.05 (3 min), 1, 3, and 6 h. The hydroxide-loaded sample was also subjected to X-ray diffraction (XRD) and cross-sectional SEM observations after each time interval. The ammonia-loaded sample was subjected to XRD measurements only after the 6 h interval, in addition to the SEM observation. The XRD analysis was performed at 2θ = 35–40° using a powder X-ray diffractometer (Smart-Lab, Rigaku, Japan).

Solution System Evaluation

A solution system was tested to investigate the spectra of vanillin, nonanal, and the reaction products. Vanillin (C8H8O3, 0.5 g, Wako special grade, FUJIFILM Wako Pure Chemical Corporation, Japan) was dissolved in a solution containing 6.5 mL of ion-exchanged water and 33.5 mL of aqueous ammonia (30 wt %, Wako special grade, FUJIFILM Wako Pure Chemical Corporation, Japan). Subsequently, 2.7 mmol/L of an ethanol solution of nonanal was prepared using pure ethanol (C2H5OH, Wako special grade, FUJIFILM Wako Pure Chemical Corporation) and nonanal (CH3(CH2)7CHO, Wako first grade, FUJIFILM Wako Pure Chemical Corporation). Then, 1 mL of an ethanol solution of nonanal was added to the vanillin-ammonia solution. The solution was then transferred to an Erlenmeyer flask, sealed, and heated in a water bath at 373 K for 1 h; this solution was then used for the UV–Vis spectroscopic analysis. The measurement range was 350–700 nm. Nonanal and vanillin were dissolved in acetonitrile and water, respectively, to obtain their reference absorption spectra.

Evaluation of the Ammonia-Supporting Ability and Nonanal-Adsorbing Capacity of Porous Glass

The amount of ammonia supported on the sensor chip was measured by thermal desorption spectrometry (TDS). The sensor chip sample was placed in a quartz glass container, which was filled with helium gas and externally heated from 323 to 773 K. The gas released from the glass container during the temperature increase was analyzed using a quadrupole mass spectrometer (M-101QA-TDM, Canon-Anelva, Japan). The amount of ammonia on the sensor was evaluated using ion currents with a mass-to-charge ratio of 17. The spectrometer ion current was calibrated to the expected value by subtracting the current corresponding to the fragments from water. The spectrometer ion current was obtained at standard temperature and pressure (STP; 273 K, 1 atm). The amount of ammonia supported per unit surface area in the pores of the porous glass was expressed by converting it into a gas at STP.
Vanillin (0.1 g) was dissolved in 10 mL of deionized water to prepare a 1 wt % aqueous solution, which was then mixed with 5 mL of aqueous ammonia (30 wt %, Kanto Chemical, special grade, Kanto Chemical Co., Inc., Japan). Subsequently, the porous glass was immersed in 20 μL of the mixed solution using a microdispenser (Dialamatic 3-000-250, Drummond Scientific, USA). The sample was then dried at 298 K for 24 h under vacuum to obtain a sensor chip. The absorption spectrum and microstructure of the sensor chip were analyzed by UV–Vis spectroscopy and SEM, respectively.
The nonanal-adsorbing capacity of the porous glass was also evaluated using 1 L atmosphere. At first, a 50-L Tedlar bag (1-2711-08, Asone, Japan) was filled with nitrogen (Industrial Grade, Iwatani, Japan). Subsequently, 0.125 mL of nonanal was diluted to 50 mL with ethanol; 40 μL of this solution was then placed in the Tedlar bag to achieve a nonanal atmosphere of 0.28 ppm. Then, 1 L of atmosphere was adjusted by subdividing 50 L of nonanal atmosphere of 0.28 ppm as described above, and the porous glass was in a polytetrafluoroethylene (PTFE) mesh film was hung in the 1 L Tedlar bag. After a predetermined time (every 30 min), the sensor was removed from the Tedlar bag, and the nonanal concentration in the bag was measured using a sensor gas chromatograph (SGVA-P3-A, Nissha FIS Inc., Japan).

Nonanal Sensing Test

The nonanal-sensing ability of the prepared sensor was also investigated (Figure 1). 50 liter Tedlar bags were filled with nitrogen in the same manner as described previously. Various concentrations of nonanal (0, 250, 500, and 750 μL) were diluted to 50 mL with ethanol. Each resulting nonanal solution (40 μL) was placed in a Tedlar bag to achieve a nonanal atmosphere of 0, 0.5, 1.0, or 1.5 ppm. After this, 575 mL of deionized water was placed in the Tedlar bag to achieve a relative humidity of 50%. For each nonanal concentration, a sensor chip was wrapped in a PTFE mesh bag and hung with Teflon thread inside the Tedlar bag for 24 h. This exposure time was selected because the sensing mechanism is based on accumulation of nonanal inside the sensor chip; (22) in our previous study, it was confirmed that the sensor sensitivity increased until 24 h. After this period, the sensor was removed from the Tedlar bag and heated at 373 K for 1 h on a hot plate to promote the aldol condensation reaction. The absorption spectrum of the sensor chip was then obtained using UV–Vis spectroscopy.

Figure 1

Figure 1. Illustration of a nonanal sensor chip preparation process and a subsequent nonanal sensing test.

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Results and Discussion

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Evaluation of Alkali-Resistant Porous Glass Sample

The appearance and microstructure of the obtained glass sample, its transmission spectrum, and the pore distribution are shown in Figure 2. The exterior photograph (Figure 2a) shows that the sensor is translucent, while the transmission spectrum (Figure 2c) confirms that the sensor transmittance is between 10% and 90% in the wavelength range of visible light (400–800 nm). In particular, the transmittance at approximately 420 nm, where the absorption of vanillin is expected, (22) is approximately 10%. At shorter wavelengths, the transmittance decreases because of Rayleigh scattering in the porous structure. (28) Notably, if the pore size decreases, the transmittance increases; however, it then becomes difficult for the gas to diffuse into the pores. The calculated mean free path of nonanal was 9 nm according to the Maxwell–Boltzmann approximation. (22) If the pore size is reduced further to increase the transmittance, Knudsen diffusion occurs, which causes the rate of gas diffusion into the pores to become very low as the mean free path and pore size become equivalent. (29)

Figure 2

Figure 2. (a) Exterior photograph and (b) SEM image of an alkali-resistant porous glass sample; (c) UV–Vis transmittance spectrum of the sample; (d) pore-size distribution of the sample as determined by a nitrogen adsorption method.

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An SEM photograph of the microstructure (Figure 2b) shows a porous structure arising from the spinodal phase. In the pore-size distribution determined by the nitrogen adsorption method (Figure 2d), the median pore diameter was found to be approximately 35 nm, and 80% of the pores were between 20 and 50 nm in size. SEM observations also confirmed this distribution range. Therefore, the obtained pore sizes are sufficiently large for nonanal gas diffusion when considering the mean free path. Consequently, the resulting porous glass is a suitable material for a gas sensor matrix that combines desirable light transmission and gas diffusibility.

Evaluation of the Absorption Changes upon Sodium Hydroxide and Ammonia Treatment

A porous glass treated with sodium hydroxide exhibits a considerably reduced transmittance compared to a non-treated glass, as reported in a previous study. (22) Hence, the sodium hydroxide-loaded porous glass sample was subjected to absorption, cross-sectional SEM, and XRD measurements at exposure to an air atmosphere at designated time intervals to investigate the factor responsible for the decreased transmittance. These results are presented in Figure 3.

Figure 3

Figure 3. (a) UV–Vis absorption spectra and (b) XRD patterns of sodium hydroxide-loaded glass after several time intervals of NaOH exposure; (c) cross-sectional SEM image of the sodium hydroxide-loaded porous glass.

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After vacuum drying, the sodium hydroxide-loaded glass exhibited an increase in absorbance with exposure time (Figure 3a). Furthermore, the intensity of the diffraction peak corresponding to sodium carbonate also increased with exposure time (Figure 3b). This result is attributed to the reaction of sodium hydroxide with carbon dioxide from the air inside the pores, which generates sodium carbonate. (30) In addition, the cross-sectional SEM observation confirmed the precipitation of coarse particles within the porous glass sample after an elapsed time period post drying (Figure 3c), which can be attributed to the growth of sodium carbonate crystals. From these results, it can be concluded that the sodium hydroxide treatment of the porous glass generates coarse particles of sodium carbonate within the pores; these particles then scatter the incident light, which decreases the sensor transmittance. As the transmittance of the porous glass decreases (and the absorbance increases), the sensor sensitivity to minute absorbance changes during the aldol condensation reaction also decreases. Measures to prevent this deterioration in transmittance were therefore required.
As an alternative, a porous glass was produced utilizing weakly alkaline ammonia as the alkali catalyst instead of the strongly alkaline sodium hydroxide. Figure 4a shows the absorbance changes of the ammonia-loaded porous glass with exposure time. After vacuum drying, the absorbance at wavelengths of above 370 nm barely changed with each time interval. In addition, crystal-derived diffraction peaks were not observed after the longest exposure period (Figure 4b). Furthermore, the cross-sectional SEM image (Figure 4c) revealed that the ammonia-loaded porous glass differs considerably from the sodium hydroxide-loaded sample; no precipitation of coarse particulate crystals can be observed within the material. The above results therefore suggest that the transmittance of the ammonia-loaded porous glass is unchanged with exposure time because of the lack of precipitation of coarse carbonate crystal particles.

Figure 4

Figure 4. (a) UV–Vis absorption spectra and (b) XRD patterns of ammonia-supported glass after several time intervals of ammonia exposure; (c) cross-sectional SEM image of the ammonia-loaded porous glass.

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Evaluation of the Solution System Reaction between Nonanal and Vanillin Using an Ammonia Catalyst

Ammonia was used in a solution system to confirm its role as a catalyst in the reaction between nonanal and vanillin, which was used as a nonanal-detecting reagent in our previous study. (22) The changes in the absorbance spectra of different reagent mixtures due to heating (when applied to promote the aldol condensation reaction) are illustrated in Figure 5. When only vanillin and ammonia were mixed as a control system, an absorbance of approximately 0.003 was observed at 500 nm (Figure 5a); this did not change notably (0.006 at 500 nm) when ethanol was added to the mixed solution. However, the absorbance changed after the solution was heated to 373 K for 1 h (0.086 at 500 nm); this is caused by the formation of side products from the reaction of vanillin and ammonia, owing to the high reactivity of the hydroxy group in vanillin at elevated temperatures (Figure S2) and the possible spontaneous reaction of ammonia with the aldehyde group. (31) While such a change is likely to decrease the sensor sensitivity, the subsequently measured calibration curve (Figure 10) shows that the transmittance was still higher than that of the sodium hydroxide-loaded sensor by an order of magnitude. When diluted nonanal was added to the vanillin/ammonia system, the absorbance remained approximately constant before heating (Figure 5b); however, the change after heating (0.14 at 500 nm) was notably greater than that observed for the control solution (as seen in Figure 5c). This additional absorbance increase across the studied wavelength range indicates a formation of a product from the reaction between nonanal and vanillin.

Figure 5

Figure 5. Absorption spectra of solution systems before and after heating at 373 K for 1 h: (a) vanillin and ammonia mixed with ethanol, and (b) vanillin and ammonia mixed with ethanol-diluted nonanal; comparisons of the post-reaction absorbance spectra of (c) the control and nonanal-mixed ammonia-catalyzed solutions and (d) the nonanal mixed ammonia- and sodium hydroxide-catalyzed solutions.

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Figure 5d illustrates the difference between the absorption spectra of the reaction product mixture when either sodium hydroxide or ammonia was used as the catalyst. While the sodium hydroxide-catalyzed reaction mixture showed a large absorbance with a narrow range of approximately 400–480 nm, the ammonia-catalyzed mixture showed a larger absorbance across a broader wavelength band of approximately 480–700 nm. This may be attributed to the products formed from the additional side reactions of ammonia with vanillin.

Ammonia-Supporting Ability and Nonanal-Adsorbing Capacity of Porous Glass

Next, the ammonia-supporting ability of the porous glass was evaluated. Figure 6 shows the TDS profile of ammonia released from a gas sensor element carrying ammonia and vanillin. Two peaks appear at 423 and 543 K; these positions are identical to those observed previously in TDS profiles of ammonia released from solid acidic porous materials such as zeolite. (32) The peak at 423 K is caused by the desorption of the physically adsorbed ammonia, whereas the peak at 543 K arises from the desorption of ammonia from the acidic sites in the porous structure. These results suggest that ammonia adsorbs to the glass by two means: weak physisorption and acid–base interactions.

Figure 6

Figure 6. Thermal desorption spectra of ammonia released from alkali-resistant porous glass and conventional porous glass exposed to a mixed ammonia/vanillin solution.

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The ammonia TDS profile of a control sample in which ammonia and vanillin were supported in a conventional porous glass product (26,27) is also shown in Figure 6. Only a small peak in the spectrum can be observed at a peak temperature of 383 K. Thus, as the conventional product does not contain acidic sites, only the physically adsorbed ammonia is retained in the pores.
In addition, when the amount of adsorbed ammonia (obtained from the peak area by integrating the TDS curve) was compared between the two samples, the treated product was found to contain approximately 50 times more ammonia than the conventional product. This finding suggests that the treated product retains more ammonia because of the acidic sites in its pores. It has been reported that the composite oxides of SiO2 and ZrO2, which are the main components of porous glass, have high acidity. (33,34) Similarly, the acidity of SiO2 was strong, even in porous glasses containing SiO2 and ZrO2, and the peak splits into two as ammonia adsorption increases to the acid point, thereby indicating an increase in the retention amount of ammonia.
In addition, the evaluation results of the nonanal-adsorbing performance of the porous glass are shown in Figure 7. The evaluation was performed on both pristine and ammonia-loaded porous glass samples. The nonanal adsorption rate was larger in the pristine glass compared to that of the ammonia-supported sample, owing to the strongly acidic pore surfaces in the pristine glass. It is assumed that the carbonyl groups in nonanal interacted with the acidic pore surfaces; as the carbonyl carbon is positively charged due to the polarization induced by oxygen, (35) these groups should therefore have a strong affinity to the negatively charged acidic sites under aqueous conditions. Conversely, when ammonia was supported on the pores, the surface acidity of the pores was neutralized by the basic ammonia, thus weakening the overall acidity in the material. These modified sites should therefore become positively charged in aqueous conditions, thus reducing the overall negative charge on the glass surface and weakening the carbonyl interactions.

Figure 7

Figure 7. Amount of nonanal adsorbed on pristine and ammonia-loaded alkali-resistant porous glasses.

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Nonanal Gas Detection Test and Sensor Calibration Curve

Figure 8 shows three absorption spectra of the porous glass sensor chip: the sensor chip before loading, the sensor with vanillin and ammonia supported in the pores, and the sensor after exposure to nonanal with subsequent heating for 1 h. Nonanal concentration, exposure time, and heating conditions were 1 ppm, 24 h, and 373 K, respectively. Notably, the absorption of the original porous glass increases at lower wavelengths owing to Rayleigh scattering caused by the microstructure. (29) When the gas detectors were loaded with ammonia and vanillin, the absorption remained unchanged over 450 nm; however, the absorption below 450 nm increased owing to the absorption of light by the supported vanillin. This conclusion is supported by the previously confirmed fact that crystal precipitation does not occur in the sensor when exposed to ammonia. These spectral changes therefore demonstrate the formation of a gas detection layer within the porous structure. After exposure to nonanal and heating, the sensor absorption below 450 nm increased, suggesting the occurrence of aldol condensation between vanillin and nonanal inside the sensor pores. This result also supports the observations seen on the solution system experiments.

Figure 8

Figure 8. Absorption spectra (300–800 nm) of the gas sensor chip before loading, after vanillin and ammonia loading, and after exposure to 1 ppm nonanal gas for 24 h followed by subsequent heating (373 K, 1 h).

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Figure 9 illustrates the visual appearance of the sensor chips before and after the nonanal gas exposure and heating process. The vanillin-loaded sensor chip became slightly yellow due to the absorbance of vanillin at below 400 nm. The color then intensified after nonanal gas exposure and heating, which is in accordance with the absorption spectrum change. The color also darkened after zero nonanal gas exposure and heating, which can be attributed to the side reaction of vanillin and ammonia at the heating stage. However, the color change in the sensor chip exposed to nonanal was still distinct enough to be identified.

Figure 9

Figure 9. Photographs of (a) untreated alkali-resistant porous glass, (b) nonanal sensor chip after vanillin and ammonia loading, and nonanal sensor after exposure to (c) 0 or (d) 1 ppm nonanal with subsequent heating.

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Figure 10 illustrates the relationship between the nonanal concentration and the change in sensor absorbance at 420 nm. The amount of aldol condensation, which determines the absorbance change, depends on the amount of vanillin and nonanal gas accumulated on the chip. The amount of nonanal gas accumulated on the sensor chip was proportional to the nonanal concentration in the atmosphere and exposure time. (22) Therefore, the amount of aldol condensation is proportional to the amount of vanillin, nonanal concentration of the atmosphere, and exposure time. In this study, the amount of vanillin and exposure time were constant. Thus, the absorbance shift linearly increased with the nonanal concentration. The proportionality constant can be obtained from the slope in Figure 10. A large constant was obtained because of the large specific surface area of the glass, which leads to an increase in its adsorption capacity

Figure 10

Figure 10. Calibration curve illustrating the relationship between nonanal concentration and the change in absorbance at 420 nm.

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The absorbance change was evaluated at 420 nm because absorbances obtained at wavelengths less than 420 nm increase sharply owing to the absorbance of vanillin. If a wavelength less than 420 nm is chosen, the error of subtraction becomes relatively large; however, if a wavelength greater than 420 nm is chosen, the change in absorbance would decrease significantly because the absorbance decreases with increasing wavelength.
The sensitivity of the developed sensor was also analyzed. The obtained calibration curve shows a one-to-one correspondence in a concentration range of 0.1–1.5 ppm; thus, the sensor can measure sub-ppm nonanal concentrations. The standard deviation and coefficient of variation obtained from multiple blank measurements were 0.022 and 18%, respectively. The three-sigma value was 0.066, which corresponds to the LOD of the absorbance change after considering the experimental variation. The absorbance change per unit of concentration (ppm) was approximately 0.1; thus, an absorbance change of 0.066 is equivalent to 0.66 ppm of nonanal. Consequently, the LOD of the developed nonanal sensor is 0.66 ppm. This sensitivity is comparable to those obtained with other types of gas sensors, which range between several dozen ppb to several ppm. (17−20,36,37)
The limit of quantification (LOQ) of the sensor was determined from the ten-sigma value and gradient of the calibration curve, where LOQ = ten-sigma/gradient. (38) For the developed sensor, the ten-sigma value was 0.22, while the curve gradient was 0.1, giving the LOQ of 2.2 ppm. However, this value is insufficient for diagnosing lung cancer, which requires a sensitivity in the order of several ppb. (11−13)
In this study, we focused on increasing the transmittance of the sensor chip because the accuracy of an absorbance measurement increases with transmittance. The absorption measurement resolution of spectrometers is generally less than or equal to 0.005 a.u. when the transmittance is higher than 10%. In this study, it was confirmed that transmittance through the sensor chip can exceed 10% when ammonia is used as the catalyst. An absorbance change of 0.005 is equivalent to a 50-ppb nonanal concentration change in the calibration curve; considering that the developed sensor variation is related to variations in the porous structure and thus the amount of loaded detection reagents, this phenomenon indicates that the sensor may potentially achieve an LOD of approximately 50 ppb if the sensor variability is controlled or suppressed. Thus, the developed sensor is potentially suitable for gas detection over a wide nonanal concentration range of between 50 ppb and 1.5 ppm.
Furthermore, we investigated the sensors at an atmospheric humidity of approximately 50%. Notably, the sensitivity of a porous glass sensor increases with increasing humidity, which is because the water layer inside the porous structure becomes more stable. (25,39) This is a positive attribute of this sensor in comparison to semiconductor sensors, which become less sensitive with increasing humidity. Variations due to humidity changes can also be corrected by in situ monitoring and subsequent sensitivity correction; for example, using automated software processes.
The selectivity of the sensor is another important aspect to consider. Exhaled breath contains aldehydes; thus, the operational sensor must be able to distinguish between nonanal and other aldehyde gases, especially C8 and C10 aliphatic aldehydes, which are similar in size to nonanal. The sensor was therefore evaluated for its sensitivity to octanal (C8H16O) and decanal (C10H20O). It was found that increasing the number of carbons in the aldehyde backbone increases the sensitivity because the molecular boiling point increases with increasing molecular weight; the sensor was therefore more sensitive to decanal than octanal. Thus, there is scope for future work to be conducted by investigating the differentiation of gases by the sensor as a function of the pore size or other parameters. An additional limitation of the developed sensor is the irreversible nature of the sensing mechanism, whereas semiconductor gas sensors can be used repeatedly.
Moreover, when considering the future application of this sensor type toward point-of-care diagnostic devices, it would be preferable that the porous glass matrix be incorporated into a metal framework that can be easily heated by a miniature heating device. LEDs and optical detectors may also enable the measurement of an adsorption change at a specified wavelength. (24,40) To enable the practical use of this sensor type, supporting device technologies will need to be developed.

Conclusions

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In this study, we used ammonia instead of sodium hydroxide as a catalyst in a porous glass gas sensor for the detection of nonanal. This prevented the deterioration in transmittance that was observed previously in sodium hydroxide-loaded sensors and was subsequently found to be caused by the formation of carbonate deposits in the sensor. In a model solution system, when ammonia was used to catalyze the aldol condensation of vanillin with nonanal, the absorbance changed in response to the presence or absence of nonanal. Because ammonia tends to volatilize, the retention performance of the developed porous glass was greater than that of the conventional porous glass, owing to the former’s higher surface acidity. A comparison of the retained amount of ammonia revealed that the developed product contained 50 times more ammonia than the conventional product. When the sensor was subsequently tested for the detection of gaseous nonanal, specific absorption changes were observed in accordance with the solution system experiments. The resulting calibration curve indicated a linear relationship between nonanal concentration and absorbance, confirming the feasibility of the sensor for quantitative detection, with the LOD found to be 0.66 ppm. Moreover, when ammonia was used as the catalyst instead of sodium hydroxide, the transmittance of the sensor chip was improved, leading to the detection of minute absorbance changes. Notably, high sensitivity may be achieved when the sensor variation is suppressed. This new porous glass sensor therefore provides a practical sensing mechanism for nonanal detection that utilizes ammonia-catalyzed aldol condensation. By utilizing the properties of the pore surfaces, we demonstrated that ammonia can be stably and homogeneously used as a catalyst in nanoscale environments. Thus, porous glass materials can be used as sensing platforms that can provide nanoscale reaction fields and catalytic activity owing to their significant surface properties. Such materials are promising candidates for sensing materials in future point-of-care diagnostic devices. Future research should focus on investigating the ability of the sensor to differentiate gases according to pore size or other properties.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.2c07622.

  • Schematic of the preparation process of the alkali-resistant porous glass; chemical structures of nonanal and vanillin; reaction scheme of the aldol condensation reaction between vanillin and nonanal (PDF)

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  • Corresponding Author
  • Authors
    • Yasushi Kii - Evaluation Division, Research and Development Group, Nippon Electric Glass Co., Ltd., 7-1, Seiran 2-chome, Otsu, Shiga 520-8639, Japan
    • Takashi Aitoku - Development Division, Research and Development Group, Nippon Electric Glass Co., Ltd., 7-1, Seiran 2-chome, Otsu, Shiga 520-8639, Japan
    • Masaru Iwao - Development Division, Research and Development Group, Nippon Electric Glass Co., Ltd., 7-1, Seiran 2-chome, Otsu, Shiga 520-8639, Japan
    • Yasuko Yamada Maruo - Department of Applied Chemistry and Environment, Faculty of Engineering, Tohoku Institute of Technology, 35-1, Yagiyama, Kasumicho, Taihakuku, Sendai 982-8577, Japan
  • Author Contributions

    M.T. conceived the project, performed the experiments, and wrote the manuscript. Y.K. significantly contributed to the TDS measurements. T.A. contributed to the porous glass synthesis. M.I. and Y.Y.M. contributed to the experiments and supervised the work. All the authors have approved the final version of the manuscript.

  • Funding

    This research did not receive any specific grants from funding agencies in the public, commercial, or not-for-profit sectors.

  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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The authors thank Noriaki Masuda of Nippon Electric Glass Co., Ltd., for his support and useful discussions regarding this study. The authors also thank Naoki Toyofuku of Nippon Electric Glass Co., Ltd., for his support in the XRD measurements. The authors also thank Yuki Sato of the Tohoku Institute of Technology for her support in the solution system and nonanal sensing tests.

Abbreviations

Click to copy section linkSection link copied!
LOD

limit of detection

PTFE

polytetrafluoroethylene

SEM

scanning electron microscopy

TDS

thermal desorption spectrometry

UV–Vis

ultraviolet–visible

VOC

volatile organic compound

XRD

X-ray diffraction

References

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This article references 40 other publications.

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    A review. Exhaled human breath anal. is a very promising field of research work having great potential for diagnosis of diseases in noninvasive way. Breath anal. has attracted huge attention in the field of medical diagnosis and disease monitoring in the last two decades. VOCs/gases (Volatile Org. Compds.) in exhaled breath bear the finger-prints of metabolic and biophys. processes going on in human body. It's a non-invasive, fast, non-hazardous, cost effective, and point of care process for disease state monitoring and environmental exposure assessment in human beings. Some VOCs/gases in exhaled breath are bio-markers of different diseases and their presence in excess amt. is indicative of un-healthiness. Breath anal. has the potential for early detection of diseases. However, it is still underused and com. device is yet not available owing to multiferrious challenges. This review is intended to provide an overview of major biomarkers (VOCs/gases) present in exhaled breath, importance of their anal. towards disease monitoring, anal. techniques involved, promising materials for breath anal. etc. Finally, related challenges and limitations along with future scope will be touched upon.
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    Volatile org. compds. (VOCs) emitted by a human body form a chem. signature capable of providing invaluable information on the physiol. status of an individual and, thereby, serving as signs of life for detecting victims after natural or man-made disasters. For this review, we created a database of potential biomarkers of human presence based on literature reports on VOCs in human breath, skin emanations, blood and urine. We estd. approx. fluxes of these VOCs from the human body, and used them to predict concns. in the vicinity of victims. We classified proposed markers in groups by potential for victim detection. The major classification discriminants were the capability of detection by portable, real-time anal. instruments and background levels of VOCs in the urban environment. We intend data summarized in this review to assist studies on the detection of humans via chem. anal. and to accelerate investigations in this area of knowledge.
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  18. 18
    Itoh, T.; Nakashima, T.; Akamatsu, T.; Izu, N.; Shin, W. Nonanal gas sensing properties of platinum, palladium, and gold-loaded tin oxide VOCs sensors. Sens. Actuators, B 2013, 187, 135– 141,  DOI: 10.1016/j.snb.2012.09.097
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    18
    Nonanal gas sensing properties of platinum, palladium, and gold-loaded tin oxide VOCs sensors
    Itoh, Toshio; Nakashima, Takaomi; Akamatsu, Takafumi; Izu, Noriya; Shin, Woosuck
    Sensors and Actuators, B: Chemical (2013), 187 (), 135-141CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)
    We have investigated the nonanal sensing properties of Pt-, Pd-, and Au-loaded SnO2 (Pt, Pd, Au/SnO2) thick films. These films show a higher response to nonanal than a non-loaded SnO2 film, can detect several tens of ppb of nonanal and exhibit fast response and recovery times. Their nonanal sensing ability is improved by pretreatments, such as annealing temp. and aging. The resistance of these films in pure air depends on the working temp., but the resistance in nonanal gas depends mainly on the film thickness. We suggest nonanal detection models for Pt, Pd, Au/SnO2 films with different film thicknesses, and det. the optimum film thickness for nonanal detection.
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  19. 19
    Daneshkhah, A.; Vij, S.; Siegel, A. P.; Agarwal, M. Polyetherimide/carbon black composite sensors demonstrate selective detection of medium-chain aldehydes including nonanal. Chem. Eng. J. 2020, 383, 123104  DOI: 10.1016/j.cej.2019.123104
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    Polyetherimide/carbon black composite sensors demonstrate selective detection of medium-chain aldehydes including nonanal
    Daneshkhah, Ali; Vij, Shitiz; Siegel, Amanda P.; Agarwal, Mangilal
    Chemical Engineering Journal (Amsterdam, Netherlands) (2020), 383 (), 123104CODEN: CMEJAJ; ISSN:1385-8947. (Elsevier B.V.)
    This study presents the synthesis, fabrication, and development of a selective polyetherimide (PEI)/carbon black (CB) sensor, engineered to detect aldehydes such as nonanal. Using a novel approach, spin coating of the PEI/CB in 1-methyl-2-pyrrolidone (NMP) was followed by a redn. of the composite through heat treating at 200°C resulting in a highly sensitive and selective film (with low hydrophilicity) for detection of nonanal. This represents a key step, as it decreased surface oxygen and increased surface amine/imine sites. XPS anal. demonstrated the engineered surface was comprised of >3.5% nitrogen (including 1.2% amines/imines) and displayed a contact angle of 80°. The sensor response to nonanal (1 ppm to 80 ppm) ranged from 0.02% to 1.9%. Fabricated sensors showed over 14 times more sensitivity to nonanal than volatiles with similar mol. wts. but different functional groups such as 2-nonanone, dodecane, and 1-octanol. This confirms the sensing film has high selectivity to aldehydes over ketones, hydrocarbons, and alcs. Importantly, the proposed sensor maintained its response to nonanal over a period of 36 days. In addn., a multifactor machine learning algorithm was developed based on principal component anal. (PCA) to detect the type and concn. of a VOC using the temporal response of the sensor. Fabrication, characterization, testing methods, and results are presented and discussed.
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  20. 20
    Jha, S. K.; Hayashi, K. Polyacrylic acid polymer and aldehydes template molecule based MIPs coated QCM sensors for detection of pattern aldehydes in body odor. Sens. Actuators, B 2015, 206, 471– 487,  DOI: 10.1016/j.snb.2014.09.102
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    20
    Polyacrylic acid polymer and aldehydes template molecule based MIPs coated QCM sensors for detection of pattern aldehydes in body odor
    Jha, Sunil K.; Hayashi, Kenshi
    Sensors and Actuators, B: Chemical (2015), 206 (), 471-487CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)
    Molecularly imprinted polymers (MIPs) have been prepd. using the polyacrylic acid (PAA) as host polymer and hexanal, heptanal, and nonanal as pattern mols. MIPs were employed as selective coating layer of quartz crystal microbalance (QCM) sensors. Hexanal, heptanal, and nonanal were opted as target chems. after gas chromatog.-mass spectrometer (GC-MS) characterization of body odor samples. Transient and static responses of four QCM sensors (three coated with MIPs and one with non-MIP) to target aldehydes in singly, binary and tertiary mixts., and water at distinct concns. have been measured. Transient responses were analyzed to compute the response time (ton), and recovery time (toff) of sensors. This result av. values of ton ≈ 5 s and toff ≈ 10 s to typical concns. of target odors. The sensitivity and baseline drift of sensors were also calcd. using their static response. The heptanal template mol. based MIP coated QCM exhibit improved sensitivity, reproducibility and faster response, than the rest two MIPs, and non-MIP coated QCMs. Static sensors response matrixes were further processed with principal component anal. (PCA) for qual. (visual) discrimination and support vector machine (SVM) classifier for quant. recognition (in %) of target aldehydes: in singly, binary and tertiary mixts. Aldehydes odor was effectively identified in principal component (PC) space. Maximum recognition rate of 89% has been achieved for three classes of binary odors, and 79% for the combination of single, binary and tertiary odor classes in 3-fold cross-validation of SVM classifier.
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  21. 21
    Wasilewski, T.; Szulczyński, B.; Wojciechowski, M.; Kamysz, W.; Gębicki, J. Determination of long-chain aldehydes using a novel quartz crystal microbalance sensor based on a biomimetic peptide. Microchem. J. 2020, 154, 104509  DOI: 10.1016/j.microc.2019.104509
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    Determination of long-chain aldehydes using a novel quartz crystal microbalance sensor based on a biomimetic peptide
    Wasilewski, Tomasz; Szulczynski, Bartosz; Wojciechowski, Marek; Kamysz, Wojciech; Gebicki, Jacek
    Microchemical Journal (2020), 154 (), 104509CODEN: MICJAN; ISSN:0026-265X. (Elsevier B.V.)
    This study presents investigation on usefulness of the peptide mimicking HarmOBP7 region as a receptor element of the piezoelec. sensor for selective anal. of long-chain aldehydes. Identification of odorant binding proteins creates new possibilities for design of peptides mimicking binding properties of their volatile compds. Exploration of OBPs and new peptide sequences capable to effectively bind volatile compds. is necessary to enhance artificial olfaction. For the development of biosensors where simple detection is crucial rather than identification of subsequent metabolic activity, the use of sub-protein components (e.g. ligand-binding regions or synthetic peptides) is still escalating. Bearing all this in mind, a segment of a peptide sequence assocd. with a specific function of HarmOBP7 (involved in binding the long-chain aldehydes) has been designed, synthesized and immobilized on a piezoelec. transducer. The results of in silico investigations were correlated with the exptl. measurements of gas substances. The correlated results confirm a high selectivity of the KLLFDSLTDLKKKMSEC-based sensor with respect to long-chain aliph. aldehydes including octanal, decanal, undecanal, nonanal and helional. Odorant mols. interact with recognition peptide with specific affinities. The results can throw a new light on the possibility of synthetic peptide application as a receptor layer in biosensors in odorants anal.
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  22. 22
    Tsujiguchi, M.; Aitoku, T.; Takase, H.; Maruo, Y. Y. Nonanal sensor fabrication using aldol condensation reaction inside alkali-resistant porous glass. IEEE Sens. J. 2021, 21, 8868– 8877,  DOI: 10.1109/JSEN.2021.3055264
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    Nonanal sensor fabrication using aldol condensation reaction inside alkali-resistant porous glass
    Tsujiguchi, Masato; Aitoku, Takashi; Takase, Hironori; Maruo, Yasuko Yamada
    IEEE Sensors Journal (2021), 21 (7), 8868-8877CODEN: ISJEAZ; ISSN:1558-1748. (Institute of Electrical and Electronics Engineers)
    Monitoring the gases released during breathing or via the skin has gained significance towards diagnosing diseases. In this study, a sensor chip capable of detecting nonanal gas, which is known to be a marker of lung cancer, was developed. The gas detection agent used was vanillin, which underwent aldol condensation with nonanal in the presence of a basic catalyst, resulting in the formation of an unsatd. aldehyde. Porous glass was used as the reaction field to carry the detection agent. Alkali-resistant porous glass was chosen because conventionalporous glasses show low durabilities under basic conditions, as they primarily consist of SiO2. Nonanal can be detected through changes in the absorption spectrum of the sensor. An accumulate-type sensor was used in this study, which exhibited a linear relationship between the degree of absorption changes at 470 nm and nonanal concn. in the 60 ppb-1.3 ppm range. Therefore, this biol. marker gas sensor is effective for the early diagnosis of diseases. The alkali-resistant porous glass sensor chip exhibited a higher degree of absorption change than the conventional porous glass sensor chip.
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    Maruo, Y. Y.; Nakamura, J.; Uchiyama, M.; Higuchi, M.; Izumi, K. Development of formaldehyde sensing element using porous glass impregnated with Schiff’s reagent. Sens. Actuators, B 2008, 129, 544– 550,  DOI: 10.1016/j.snb.2007.09.002
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    Development of formaldehyde sensing element using porous glass impregnated with Schiff's reagent
    Maruo, Yasuko Yamada; Nakamura, Jiro; Uchiyama, Masahiro; Higuchi, Masanori; Izumi, Katsuyuki
    Sensors and Actuators, B: Chemical (2008), 129 (2), 544-550CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)
    A sensor for detecting formaldehyde was developed. The sensor element was made of a porous glass impregnated with both a Schiff's reagent and an acid. The sensor element changed its color from yellow to violet after exposure to formaldehyde, and an absorption peak appeared at a wavelength of 570 or 580 nm. There was a quasilinear relationship between the 570 and 580 nm absorbance of the sensor element after exposure to formaldehyde and a logarithm of the exposed formaldehyde concn. Also, the sensor element worked as a reversible type, not as an accumulate type, and the absorbance at 570 or 580 nm of a once exposed sensor element decreased when it was exposed to a less concd. formaldehyde atm. The sensor element is reversible and suitable for the detection of a wide formaldehyde concn. range, for example from 20 ppm to 10 ppb.
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    Maruo, Y. Y.; Nakamura, J. Portable formaldehyde monitoring device using porous glass sensor and its applications in indoor air quality studies. Anal. Chim. Acta 2011, 702, 247– 253,  DOI: 10.1016/j.aca.2011.06.050
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    Portable formaldehyde monitoring device using porous glass sensor and its applications in indoor air quality studies
    Maruo, Yasuko Yamada; Nakamura, Jiro
    Analytica Chimica Acta (2011), 702 (2), 247-253CODEN: ACACAM; ISSN:0003-2670. (Elsevier B.V.)
    We have developed a portable device for formaldehyde monitoring with both high sensitivity and high temporal resoln., and carried out indoor air formaldehyde concn. anal. The absorbance difference of the sensor element was measured in the monitoring device at regular intervals of, for example, 1 h or 30 min, and the result was converted into the formaldehyde concn. This was possible because we found that the lutidine deriv. that was formed as a yellow product of the reaction between 1-phenyl-1,3-butandione and formaldehyde was stable in porous glass for at least 6 mo. We estd. the reaction rate to be 0.049 min-1 and the reaction occurred quickly enough for us to monitor hourly changes in the formaldehyde concn. The detection limit was 5 μg m-3 h. We achieved hourly formaldehyde monitoring using the developed device under several indoor conditions, and estd. the air exchange rate and formaldehyde adsorption rate, which we adopted as a new term in the mass balance equation for formaldehyde, in one office.
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    Maruo, Y. Y.; Tachibana, K.; Suzuki, Y.; Shinomi, K. Development of an analytical chip for detecting acetone using a reaction between acetone and 2,4-dinitrophenylhidrazine in a porous glass. Microchem. J. 2018, 141, 377– 381,  DOI: 10.1016/j.microc.2018.05.041
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    Development of an analytical chip for detecting acetone using a reaction between acetone and 2,4-dinitrophenylhidrazine in a porous glass
    Maruo, Yasuko Y.; Tachibana, Kenta; Suzuki, Yoshifumi; Shinomi, Kouki
    Microchemical Journal (2018), 141 (), 377-381CODEN: MICJAN; ISSN:0026-265X. (Elsevier B.V.)
    Acetone is a human biogas and is widely used in industrial manufg. Acetone can be detected in the breath of diabetic patients, and the measurement of acetone in human breath provides significant, non-invasive, diagnostic information on a patient's diabetic condition. An anal. chip for detecting acetone was developed herein. The anal. chip was composed from porous glass impregnated with 2,4-dinitrophenylhydrazine (DNPH) and hydrochloric acid. The anal. chip before exposure to acetone and the reaction product between acetone and DNPH (Acetone-DNPH) showed an absorption peak at 349 nm and 359 nm, resp. The molar absorption coeff. of Acetone-DNPH in the porous glass at 359 nm was 1.57 times larger than that of DNPH. Based on these results, the percentage of reaction ([Acetone-DNPH]t/[DNPH]0) could be calcd. using the absorbance values at 359 nm. The logarithm of the percentage of reaction was correlated with the cumulative acetone concn., which was a product of an exposed acetone concn. and an exposure time. The developed anal. chip was active in the cumulative acetone concn. range from 0.53 ppm x hour to 20 ppm x hour, and was functional in an atm. with 30%-90% relative humidity (R.H.).
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    Porter, H. H.; Emery, N. M. Treated Borosilicate Glass; US Patent 2, 106, 744, 1938.
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    Enke, D.; Janowski, F.; Schwieger, W. Porous glasses in the 21st century––a short review. Microporous Mesoporous Mater. 2003, 60, 19– 30,  DOI: 10.1016/S1387-1811(03)00329-9
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    Porous glasses in the 21st century - A short review
    Enke, D.; Janowski, F.; Schwieger, W.
    Microporous and Mesoporous Materials (2003), 60 (1-3), 19-30CODEN: MIMMFJ; ISSN:1387-1811. (Elsevier Science B.V.)
    A review. This article reviews recent studies concerning the prepn., modification, characterization, modeling and application of porous glasses on the basis of phase-sepd. alkali borosilicate glasses.
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    Yazawa, T.; Machida, F.; Kubo, N.; Jin, T. Photocatalytic activity of transparent porous glass supported TiO2. Ceram. Int. 2009, 35, 3321– 3325,  DOI: 10.1016/j.ceramint.2009.05.029
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    Photocatalytic activity of transparent porous glass supported TiO2
    Yazawa, Tetsuo; Machida, Fumiko; Kubo, Noriaki; Jin, Tetsuro
    Ceramics International (2009), 35 (8), 3321-3325CODEN: CINNDH; ISSN:0272-8842. (Elsevier Ltd.)
    A porous glass tube with a compn. of 96SiO2.4B2O3 (wt%) supported TiO2 shows high photooxidn. activity due to its transparency and large surface area. The surface area of the porous glass tube supported TiO2 is 10,000 times larger than that of conventional materials. TiO2 crystals supported are anatase type. Transparency of the porous glass tube is very important. Herein, sol-gel and chem. vapor deposition (CVD) processes were employed as TiO2 supporting processes. CVD process is more effective. For instance, an aq. methylene blue soln. with 1 ppm concn. almost thoroughly decomps. at a contact time of 300 s using porous glass tube supported TiO2 prepd. by CVD process under irradiating with 10 W low-pressure mercury lamp, on the other hand, opaque porous alumina tube supported TiO2 was only 25%. The smaller the pore size of the porous glass tube, the larger the transparency and the permeation resistance through porous glass tube. Hence, porous glass tube with ≈40 nm pore diam. is suitable from the standpoint of a practical use.
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    Sakai, G.; Matsunaga, N.; Shimanoe, K.; Yamazoe, N. Theory of gas-diffusion controlled sensitivity for thin film semiconductor gas sensor. Sens. Actuators, B 2001, 80, 125– 131,  DOI: 10.1016/S0925-4005(01)00890-5
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    Theory of gas-diffusion controlled sensitivity for thin film semiconductor gas sensor
    Sakai, Go; Matsunaga, Naoki; Shimanoe, Kengo; Yamazoe, Noboru
    Sensors and Actuators, B: Chemical (2001), 80 (2), 125-131CODEN: SABCEB; ISSN:0925-4005. (Elsevier Science B.V.)
    Influences of gas transport phenomena on the sensitivity of a thin film semiconductor gas sensor were studied theor. A diffusion equation was formulated by assuming that an inflammable gas (target gas) moves inside the film by Knudsen diffusion, while it reacts with the adsorbed oxygen following a 1st-order reaction kinetic. By solving this equation under steady-state conditions, the target gas concn. inside the film was derived as a function of depth (x) from the film surface, Knudsen diffusion coeff. (DK), rate const. (k) and film thickness (L). The gas concn. profile thus obtained allowed to est. the gas sensitivity (S) defined as the resistance ratio (Ra/Rg), under the assumption that the sheet conductance of the film at depth x is linear to the gas concn. there with a proportionality const. (sensitivity coeff.), a. The derived equation shows that S decreases sigmoidally down to unity with an increase in L k/DK. Further by assuming that the temp. dependence of rate const. (k) and sensitivity coeff. (a) follows Arrhenius type ones with resp. activation energies, it was possible to derive a general expression of S involving temp. (T). The expression shows that, when the activation energies are selected properly, the S vs. T correlation results in a volcano-shaped one, its height increasing with decreasing L. The dependence of S on L at const. T as well as on T at const. L can thus be simulated fairly well based on the equation.
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    Shim, J. G.; Lee, D. W.; Lee, J. H.; Kwak, N. S. Experimental study on capture of carbon dioxide and production of sodium bicarbonate from sodium hydroxide. Env. Eng. Res. 2016, 21, 297– 303,  DOI: 10.4491/eer.2016.042
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    Tuguldurova, P. V.; Fateev, V. A.; Malkov, S. V.; Poleshchuk, K. O.; Vodyankina, V. O. Acetaldehyde-ammonia interaction: A DFT study of reaction mechanism and product identification. J. Phys. Chem. A 2017, 121, 3136– 3141,  DOI: 10.1021/acs.jpca.7b00823
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    Acetaldehyde-Ammonia Interaction: A DFT Study of Reaction Mechanism and Product Identification
    Tuguldurova, Vera P.; Fateev, Alexander V.; Malkov, Victor S.; Poleshchuk, Oleg Kh.; Vodyankina, Olga V.
    Journal of Physical Chemistry A (2017), 121 (16), 3136-3141CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
    The product of acetaldehyde and ammonia reaction, namely, 2,4,6-trimethyl-1,3,5-hexahydrotriazine trihydrate, was synthesized and identified using a combination of exptl. (NMR spectroscopy, IR spectroscopy, m.p. detn.) and DFT-based theor. approaches. A reaction mechanism was proposed. The reaction was shown to proceed via the formation of aminoalc., imine, and geminal diamine intermediates accompanied by cyclization of these species. The calcn. results allowed us to build a potential energy surface of the acetaldehyde and ammonia interaction and det. the most energetically favorable pathway to yield acetaldehyde ammonia trimer. The reaction product was found in an energy min. (-53.5 kcal/mol).
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    Katada, N.; Niwa, M. Analysis of acidic properties of zeolitic and non-zeolitic solid acid catalysts using temperature-programmed desorption of ammonia. Catal. Surv. Asia. 2004, 8, 161– 170,  DOI: 10.1023/B:CATS.0000038534.37849.16
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    Analysis of Acidic Properties of Zeolitic and Non-Zeolitic Solid Acid Catalysts Using Temperature-Programmed Desorption of Ammonia
    Katada, Naonobu; Niwa, Miki
    Catalysis Surveys from Asia (2004), 8 (3), 161-170CODEN: CSAABF; ISSN:1571-1013. (Springer Science+Business Media, Inc.)
    A review; a method of ammonia temp.-programmed desorption (TPD) for anal. of acidic property of a solid was improved by introduction of a water vapor treatment method and development of a theory for calcn. of ammonia adsorption heat from the TPD profile. The improved method was applied to various solid acid catalysts to establish relationships between the acidic properties and catalytic performances for various acid-catalyzed reactions. Here, examples of the applications to some important acid catalysts are reviewed. The exact anal. of acidic property of Y zeolite and its change by such modifications as steaming and EDTA treatment gave a new interpretation on the generation of alkane (paraffin) cracking activity on an ultra stable Y (USY) zeolite. The surface d. and strength of acid sites on WO3/ZrO2 and SO42-/ZrO2 catalysts were detd., and their relations with catalytic activities for Friedel-Crafts type alkylation and skeletal isomerization of alkane were found.
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    Setoyama, T.; Kobayashi, M.; Kabata, Y.; Kawai, T.; Nakanishi, A. New industrial process of PTMG catalyzed by solid acid. Catal. Today 2002, 73, 29– 37,  DOI: 10.1016/S0920-5861(01)00515-6
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    New industrial process of PTMG catalyzed by solid acid
    Setoyama, Tohru; Kobayashi, Mitsuharu; Kabata, Yoshio; Kawai, Tomohiro; Nakanishi, Akio
    Catalysis Today (2002), 73 (1-2), 29-37CODEN: CATTEA; ISSN:0920-5861. (Elsevier Science B.V.)
    Polymn. of THF catalyzed by solid acid in the presence of acetic anhydride was studied. A moderate Lewis acid catalyst produces required PTME (PTMG-acetate) having adequate Mn. Zeolitic material is not suitable for this prodn. because very high mol. wt. PTME is co-produced. From this aspect, mixed oxide materials show good performance because only these have the required acidic character. Mass-transfer study suggests the importance of pore size of support and the homogeneity of active sites. They affect on the Mn and the Mw/Mn strikingly. The com. technol. has established by utilizing these results.
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    Flego, C.; Carluccio, L.; Rizzo, C.; Perego, C. Synthesis of mesoporous SiO2–ZrO2 mixed oxides by sol–gel method. Catal. Commun. 2001, 2, 43– 48,  DOI: 10.1016/S1566-7367(01)00006-1
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    Synthesis of mesoporous SiO2-ZrO2 mixed oxides by sol-gel method
    Flego, C.; Carluccio, L.; Rizzo, C.; Perego, C.
    Catalysis Communications (2001), 2 (2), 43-48CODEN: CCAOAC; ISSN:1566-7367. (Elsevier Science B.V.)
    A series of SiO2-ZrO2 mixed oxides were prepd. by sol-gel method in the presence of directing agent, with variable amts. of ZrO2 between pure silica and pure zirconia, with the aim to obtain catalytic materials suitable as solid acid catalysts. SiO2-ZrO2 mixed oxides differ from the two pure starting oxides. While SiO2 has a low OH d. without peculiar acid character, the introduction of increasing amts. of Zr increases the d. of the acid sites in the materials. Furthermore both SiO2/ZrO2 molar ratio and drying procedure are able to influence the physico-chem. characteristics (textural properties, acid sites distribution, etc.) of these mixed oxides.
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    Dickens, K. T.; Warren, S. Chemistry of the carbonyl group: A step-by-step approach to understanding organic reaction mechanisms; Willey: Iowa, 2018.
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    Zonta, G.; Anania, G.; Fabbri, B.; Gaiardo, A.; Gherardi, S.; Giberti, A.; Guidi, V.; Landini, N.; Malagù, C. Detection of colorectal cancer biomarkers in the presence of interfering gases. Sens. Actuators, B 2015, 218, 289– 295,  DOI: 10.1016/j.snb.2015.04.080
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    Detection of colorectal cancer biomarkers in the presence of interfering gases
    Zonta, G.; Anania, G.; Fabbri, B.; Gaiardo, A.; Gherardi, S.; Giberti, A.; Guidi, V.; Landini, N.; Malagu, C.
    Sensors and Actuators, B: Chemical (2015), 218 (), 289-295CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)
    Medical studies have shown that tumor growth is accompanied by protein changes that may lead to the peroxidn. of the cell membrane, with consequent emission of volatile org. compds. (VOCs). VOCs can be detected through breath or intestinal gases and are biomarkers for colorectal cancer (CRC). The anal. of VOCs represents a non-invasive and potentially inexpensive pre-screening technique. An array of chemoresistive gas sensors, based on screen-printed Metal OXide (MOX) semiconducting films, has been selected to identify gaseous compds. of oncol. interest, i.e. benzene, 1-iodo-nonane and decanal, from the main interferers that can be found in the intestine. MOX sensors are able to detect concns. down to about 10th ppb, as exptl. proven in previous works, so they can identify very slight differences in concn. among gas mixts. In this work it has been proven that the array used is able to identify tumor markers singularly and in combination with other gases both in wet and dry conditions. Moreover, the sensors chosen can discriminate target VOCs from interferers even at low concns.
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    Wang, C.; Hosomi, T.; Nagashima, K.; Takahashi, T.; Zhang, G.; Kanai, M.; Yoshida, H.; Yanagida, T. Phosphonic acid modified ZnO nanowire sensors: directing reaction pathway of volatile carbonyl compounds. ACS Appl. Mater. Interfaces 2020, 12, 44265– 44272,  DOI: 10.1021/acsami.0c10332
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    ACS Applied Materials & Interfaces (2020), 12 (39), 44265-44272CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    Surface mol. transformations on nanoscale metal oxides are inherently complex, and directing those reaction pathways is still challenging but important for designing their various applications, including mol. sensing, catalysts, and others. Here, a rational strategy to direct a reaction pathway of volatile carbonyl compds. (nonanal: biomarker) on single-cryst. ZnO nanowire surfaces via mol. modification is demonstrated. The introduction of a methylphosphonic acid modification on the ZnO nanowire surface significantly alters the surface reaction pathway of nonanal via suppressing the detrimental aldol condensation reaction. This is directed by intentionally decreasing the probability of two neighboring mol. activations on the nanowire surface. Spectrometric measurements reveal the correlation between the suppression of the aldol condensation surface reaction and the improvement in the sensor performance. This tailored surface reaction pathway effectively reduces the operating temp. from 200 to 100°C while maintaining the sensitivity. This is because the aldol condensation product ((E)-2-heptyl-2-undecenal) requires a higher temp. to desorb from the surface. Thus, the proposed facile strategy offers an interesting approach not only for the rational design of metal oxide sensors for numerous volatile carbonyl compds. but also for tailoring various surface reaction pathways on complex nanoscale metal oxides.
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    Asanuma, K.; Hino, S.; Maruo, Y. Y. Development of an analytical chip for nitrogen monoxide detection using porous glass impregnated with 2-phenyl-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl. Microchem. J. 2019, 151, 104251  DOI: 10.1016/j.microc.2019.104251
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    Asanuma, Kohgo; Hino, Shinji; Maruo, Yasuko Y.
    Microchemical Journal (2019), 151 (), 104251CODEN: MICJAN; ISSN:0026-265X. (Elsevier B.V.)
    Nitrogen monoxide (NO) is an important bio-regulatory mol. NO presence in exhaled breath is a biomarker for an airway inflammation. Thus, measuring NO in the exhaled air is considered a noninvasive method for disease screening. In this study, we developed an anal. chip made of porous glass impregnated with 2-phenyl-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl (PTIO) for NO gas detection. The anal. chip had an absorption peaks at 338 and 567 nm, which decreased when exposed to NO, whereas the absorbance at 413 nm increased with an isosbestic point at 477 nm. It was found that there is a linear relationship between the logarithmic change in the absorbance at 338 nm and 567 nm and the cumulative NO concn. Addnl., the spectrum of the anal. chip was affected by humidity. There was a linear relationship between the PTIO's molar absorption coeff. at 567 nm and the relative humidity. Therefore, the absorbance of PTIO can be cor. in order to take the effect of humidity into consideration. The working ranges of the anal. chip were between 0.15 and 3.7 ppm × h of cumulative NO concn. and at a relative humidity between 40% and 90%. We also measured NO in a small amt. of air (1.8 L to mimic the actual exhaled air vol.) and we were able to measure the NO concn. of 30 ppb for 24 h.
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    Sensors and Actuators, B: Chemical (2012), 173 (), 191-196CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)
    We have developed an NO2 sensing device with high time resoln. for application to a wide-area ubiquitous network. The NO2 sensing device employs the colorimetric reaction between NO2 and diazo-coupling reagents. We estd. the formation and decompn. rate of the azo dye in the sensor elements and found that no decompn. occurred and that the formation rate was fast enough for us to measure NO2 concn. at 10 min intervals with a detection limit of 12 ppb. We have constructed sensing terminal units contg. the NO2 sensing device, a GPS device, a compass, a switch, LEDs and a wireless terminal unit for a wide-area ubiquitous network. We successfully monitored the outdoor NO2 level at 10 min intervals using the developed terminal units mounted on a bicycle in certain areas of several cities. We also designed and implemented an application where bicycles collect geo-tagged air quality samples and post them on a map that other cyclists can use to det. their route.
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  1. Zichen Zheng, Kewei Liu, Yiwen Zhou, Kaichun Xu, Yifan Luo, Jiabao Ding, Carla Bittencourt, Marc Debliquy, Chao Zhang. Decorated‐Induced Oxygen Vacancy Engineering for Ultra‐Low Concentration Nonanal Sensing: A Case Study of La‐Decorated Bi 2 O 2 CO 3. Advanced Science 2024, 11 (43) https://doi.org/10.1002/advs.202408096
  2. Nasrin Sultana, Palash Jyoti Medhi, Neelotpal Sen Sarma. Amino acid functionalized phosphorene: an optical sensing platform for the detection of antibiotic residues in milk and a clay based electrical CO 2 sensor. Journal of Materials Chemistry C 2024, 12 (37) , 14902-14914. https://doi.org/10.1039/D4TC02035A
  3. Kohei Tada, Masato Tsujiguchi, Takumi Tominaga, Masaru Iwao, Hiroaki Sakurai, Tetsuro Jin, Yasushi Maeda. Functionalisation of alkali-resistant nanoporous glass via Au nanoparticle decoration using alkaline impregnation: catalytic activity for CO removal. RSC Advances 2024, 14 (12) , 8214-8221. https://doi.org/10.1039/D3RA07333E
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  • Abstract

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    Figure 1

    Figure 1. Illustration of a nonanal sensor chip preparation process and a subsequent nonanal sensing test.

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    Figure 2

    Figure 2. (a) Exterior photograph and (b) SEM image of an alkali-resistant porous glass sample; (c) UV–Vis transmittance spectrum of the sample; (d) pore-size distribution of the sample as determined by a nitrogen adsorption method.

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    Figure 3

    Figure 3. (a) UV–Vis absorption spectra and (b) XRD patterns of sodium hydroxide-loaded glass after several time intervals of NaOH exposure; (c) cross-sectional SEM image of the sodium hydroxide-loaded porous glass.

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    Figure 4

    Figure 4. (a) UV–Vis absorption spectra and (b) XRD patterns of ammonia-supported glass after several time intervals of ammonia exposure; (c) cross-sectional SEM image of the ammonia-loaded porous glass.

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    Figure 5

    Figure 5. Absorption spectra of solution systems before and after heating at 373 K for 1 h: (a) vanillin and ammonia mixed with ethanol, and (b) vanillin and ammonia mixed with ethanol-diluted nonanal; comparisons of the post-reaction absorbance spectra of (c) the control and nonanal-mixed ammonia-catalyzed solutions and (d) the nonanal mixed ammonia- and sodium hydroxide-catalyzed solutions.

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    Figure 6

    Figure 6. Thermal desorption spectra of ammonia released from alkali-resistant porous glass and conventional porous glass exposed to a mixed ammonia/vanillin solution.

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    Figure 7

    Figure 7. Amount of nonanal adsorbed on pristine and ammonia-loaded alkali-resistant porous glasses.

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    Figure 8

    Figure 8. Absorption spectra (300–800 nm) of the gas sensor chip before loading, after vanillin and ammonia loading, and after exposure to 1 ppm nonanal gas for 24 h followed by subsequent heating (373 K, 1 h).

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    Figure 9

    Figure 9. Photographs of (a) untreated alkali-resistant porous glass, (b) nonanal sensor chip after vanillin and ammonia loading, and nonanal sensor after exposure to (c) 0 or (d) 1 ppm nonanal with subsequent heating.

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    Figure 10

    Figure 10. Calibration curve illustrating the relationship between nonanal concentration and the change in absorbance at 420 nm.

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  • References

    This article references 40 other publications.

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      When a human being is placed for several days on a completely define diet, consisting almost entirely of small mols. that are absorbed from the stomach into the blood, intestinal flora disappear because of lack of nutrition. By this technique, the compn. of body fluids can be made const. (std. deviation about 10%) after a few days, permitting significant quant. analyses to be performed. A method of temp.-programmed gas chromatog. was developed for this purpose. It permits the quant. detn. of about 250 substances in a sample of breath, and of about 280 substances in a sample of urine vapor. The technique should be useful in the application of the principles of orthomol. medicine.
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      Objective: To review the fast-developing topic of assessment of exhaled breath components to improve the diagnosis and monitoring of respiratory and systemic diseases. Data Sources: Review of the literature available in monographs and journals. Study Selection: Articles and overviews on the broad spectrum of existing exptl. and routinely applied methods to assess different aspects of human exhaled breath anal. were selected for presentation in this review. Results: Exhaled breath constitutes more than 3,500 components, the bulk of which are volatile org. compds. in miniature quantities. Many of these characterize the functioning of the organism as a whole (systemic biomarkers), but some are related to processes taking place in the respiratory system and the airways in particular (lung biomarkers). Assessment of lung biomarkers has proven useful in airway inflammatory diseases. It involves direct measurement of gases such as nitric oxide and inflammatory indicators in exhaled breath condensate such as oxidative stress markers (eg, hydrogen peroxide and isoprostanes), nitric oxide derivs. (eg, nitrate and nitrates), arachidonic acid metabolites (eg, prostanoids, leukotrienes, and epoxides), adenosine, and cytokines. Integral approaches have also been suggested, such as exhaled breath temp. measurement and devices of the "electronic nose" type, which enable the capture of approaches have also been suggested, such as exhaled breath temp. measurement exhaled mol. fingerprints (breath prints). Tech. factors related to standardization of the different techniques need to be resolved to reach the stage of routine applicability. Conclusions: Examn. of exhaled breath has the potential to change the existing routine approaches in human medicine. The rapidly developing new anal. and computer technologies along with novel, unorthodox ideas are prerequisites for future advances in this field.
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      Sinues, M.-L. P.; Kohler, M.; Zenobi, R. Human breath analysis may support the existence of individual metabolic phenotypes. PLoS One 2013, 8, e59909  DOI: 10.1371/journal.pone.0059909
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      Human breath analysis may support the existence of individual metabolic phenotypes
      Sinues, Pablo Martinez-Lozano; Kohler, Malcolm; Zenobi, Renato
      PLoS One (2013), 8 (4), e59909CODEN: POLNCL; ISSN:1932-6203. (Public Library of Science)
      The metabolic phenotype varies widely due to external factors such as diet and gut microbiome compn., among others. Despite these temporal fluctuations, urine metabolite profiling studies have suggested that there are highly individual phenotypes that persist over extended periods of time. This hypothesis was tested by analyzing the exhaled breath of a group of subjects during nine days by mass spectrometry. Consistent with previous metabolomic studies based on urine, we conclude that individual signatures of breath compn. exist. The confirmation of the existence of stable and specific breathprints may contribute to strengthen the inclusion of breath as a biofluid of choice in metabolomic studies. In addn., the fact that the method is rapid and totally non-invasive, yet individualized profiles can be tracked, makes it an appealing approach.
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      Francesco, F. D.; Fuoco, R.; Trivella, M. G.; Ceccarini, A. Breath analysis: trends in techniques and clinical applications. Microchem. J. 2005, 79, 405– 410,  DOI: 10.1016/j.microc.2004.10.008
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      Righettoni, M.; Amann, A.; Pratsinis, S. E. Breath analysis by nanostructured metal oxides as chemo-resistive gas sensors. Mater. Today 2015, 18, 163– 171,  DOI: 10.1016/j.mattod.2014.08.017
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      Breath analysis by nanostructured metal oxides as chemo-resistive gas sensors
      Righettoni, Marco; Amann, Anton; Pratsinis, Sotiris E.
      Materials Today (Oxford, United Kingdom) (2015), 18 (3), 163-171CODEN: MTOUAN; ISSN:1369-7021. (Elsevier Ltd.)
      A review. Recently breath anal. has attracted a lot of attention for disease monitoring and clin. diagnostics as spectrometric techniques of high sophistication and novel sensing materials become available. Here advances in these technologies in connection to breath anal. are critically reviewed. A no. of breath markers or tracer compds. are summarized and related to different diseases, either for diagnostics or for monitoring. Emphasis is placed on chemo-resistive gas sensors for their low cost and portability highlighting their potential and challenges for breath anal. as they start to be used in studies involving humans.
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      Human exhaled air analytics: biomarkers of diseases
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      Biomedical Chromatography (2007), 21 (6), 553-566CODEN: BICHE2; ISSN:0269-3879. (John Wiley & Sons Ltd.)
      A review. Over the last few years, breath anal. for the routine monitoring of metabolic disorders has attracted a considerable amt. of scientific interest, esp. since breath sampling is a non-invasive technique, totally painless and agreeable to patients. The investigation of human breath samples with various anal. methods has shown a correlation between the concn. patterns of volatile org. compds. (VOCs) and the occurrence of certain diseases. It has been demonstrated that modern anal. instruments allow the detn. of many compds. found in human breath both in normal and anomalous concns. The compn. of exhaled breath in patients with, for example, lung cancer, inflammatory lung disease, hepatic or renal dysfunction and diabetes contains valuable information. Furthermore, the detection and quantification of oxidative stress, and its monitoring during surgery based on compn. of exhaled breath, have made considerable progress. This paper gives an overview of the anal. techniques used for sample collection, preconcn. and anal. of human breath compn. The diagnostic potential of different disease-marking substances in human breath for a selection of diseases and the clin. applications of breath anal. are discussed.
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      Phillips, M.; Beatty, J. D.; Cataneo, R. N.; Huston, J.; Kaplan, P. D.; Lalisang, R. I.; Lambin, P.; Lobbes, M. B. I.; Mundada, M.; Pappas, N.; Patel, U. Rapid point-of-care breath test for biomarkers of breast cancer and abnormal mammograms. PLoS One 2014, 9, e90226  DOI: 10.1371/journal.pone.0090226
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      Rapid point-of-care breath test for biomarkers of breast cancer and abnormal mammograms
      Phillips, Michael; Beatty, J. David; Cataneo, Renee N.; Huston, Jan; Kaplan, Peter D.; Lalisang, Roy I.; Lambin, Philippe; Lobbes, Marc B. I.; Mundada, Mayur; Pappas, Nadine; Patel, Urvish
      PLoS One (2014), 9 (3), e90226/1-e90226/6, 6 pp.CODEN: POLNCL; ISSN:1932-6203. (Public Library of Science)
      Background: Previous studies have reported volatile org. compds. (VOCs) in breath as biomarkers of breast cancer and abnormal mammograms, apparently resulting from increased oxidative stress and cytochrome P 450 induction. We evaluated a six-minute point-of-care breath test for VOC biomarkers in women screened for breast cancer at centers in the USA and the Netherlands. Methods: 244 women had a screening mammogram (93/37 normal/abnormal) or a breast biopsy (cancer/no cancer 35/79). A mobile point-of-care system collected and concd. breath and air VOCs for anal. with gas chromatog. and surface acoustic wave detection. Chromatograms were segmented into a time series of alveolar gradients (breath minus room air). Segmental alveolar gradients were ranked as candidate biomarkers by C-statistic value (area under curve [AUC] of receiver operating characteristic [ROC] curve). Multivariate predictive algorithms were constructed employing significant biomarkers identified with multiple Monte Carlo simulations and cross validated with a leave-one-out (LOO) procedure. Results: Performance of breath biomarker algorithms was detd. in three groups: breast cancer on biopsy vs. normal screening mammograms (81.8% sensitivity, 70.0% specificity, accuracy 79% (73% on LOO) [C-statistic value], neg. predictive value 99.9%); normal vs. abnormal screening mammograms (86.5% sensitivity, 66.7% specificity, accuracy 83%, 62% on LOO); and cancer vs. no cancer on breast biopsy (75.8% sensitivity, 74.0% specificity, accuracy 78%, 67% on LOO). Conclusions: A pilot study of a six-minute point-of-care breath test for volatile biomarkers accurately identified women with breast cancer and with abnormal mammograms. Breath testing could potentially reduce the no. of needless mammograms without loss of diagnostic sensitivity.
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      Ratiu, A. I.; Ligor, T.; Bocos-Bintintan, V.; Mayhew, A. C.; Buszewsli, B. Volatile organic compounds in exhaled breath as fingerprints of lung cancer, asthma and COPD. J. Clin. Med. 2020, 10, 32,  DOI: 10.3390/jcm10010032
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      Campanella, A.; Summa, D. S.; Tommasi, S. Exhaled breath condensate biomarkers for lung cancer. J. Breath Res. 2019, 13, 044002  DOI: 10.1088/1752-7163/ab2f9f
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      Exhaled breath condensate biomarkers for lung cancer
      Campanella, Annalisa; De Summa, Simona; Tommasi, Stefania
      Journal of Breath Research (2019), 13 (4), 044002CODEN: JBROBW; ISSN:1752-7155. (IOP Publishing Ltd.)
      A review. Lung cancer is the main cause of cancer incidence and mortality worldwide and the identification of clin. useful biomarkers for lung cancer detection at both early and metastatic stage is a pressing medical need. Although many improvements have been made in the treatment and in the early screening of this cancer, most diagnosis are made at a late stage, when a lot of genetic and epigenetic changes have occurred. A promising source of biomarkers reflective of the pathogenesis of lung cancer is exhaled breath condensate (EBC), a biol. fluid and a natural matrix of the respiratory tract. Mols. such as DNAs, RNAs, proteins, metabolites and volatile compds. are present in EBC, and their presence/absence or their variation in concns. can be used as biomarkers. The aims of this review are to briefly describe exhaled breath compn., firstly, and then to document some of the EBC candidate biomarkers for lung cancer by dividing them according to their origin (genome, transcriptome, epigenome, metabolome, proteome and microbiota) in order to demonstrate the potential use of EBC as a helpful tool in cancer diagnostics, mol. profiling, therapy monitoring and screening of high risk individuals.
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      Fuchs, P.; Loeseken, C.; Schubert, J. K.; Miekisch, W. Breath gas aldehydes as biomarkers of lung cancer. Int. J. Cancer 2010, 126, 2663– 2670,  DOI: 10.1002/ijc.24970
      11
      Breath gas aldehydes as biomarkers of lung cancer
      Fuchs, Patricia; Loeseken, Christian; Schubert, Jochen K.; Miekisch, Wolfram
      International Journal of Cancer (2010), 126 (11), 2663-2670CODEN: IJCNAW; ISSN:0020-7136. (Wiley-Liss, Inc.)
      There is exptl. evidence that volatile substances in human breath can reflect presence of neoplasm. Volatile aldehydes were detd. in exhaled breath of 12 lung cancer patients, 12 smokers and 12 healthy volunteers. Alveolar breath samples were collected under control of expired CO2. Reactive aldehydes were transformed into stable oximes by means of on-fiber-derivatization (SPME-OFD). Aldehyde concns. in the ppt and ppb level were detd. by means of gas chromatog.-mass spectrometry (GC-MS). Exhaled concns. were cor. for inspired values. Exhaled C1-C10 aldehydes could be detected in all healthy volunteers, smokers and lung cancer patients. Concns. ranged from 7 pmol/l (161 pptV) for butanal to 71 nmol/l (1582 ppbV) for formaldehyde. Highest inspired concns. were found for formaldehyde and acetaldehyde (0-55 nmol/l and 0-13 nmol/l, resp.). Acetaldehyde, propanal, butanal, heptanal and decanal concns. showed no significant differences for cancer patients, smokers and healthy volunteers. Exhaled pentanal, hexanal, octanal and nonanal concns. were significantly higher in lung cancer patients than in smokers and healthy controls (ppentanal = 0.001; phexanal = 0.006; poctanal = 0.014; pnonanal = 0.025). Sensitivity and specificity of this method were comparable to the diagnostic certitude of conventional serum markers and CT imaging. Lung cancer patients could be identified by means of exhaled pentanal, hexanal, octanal and nonanal concns. Exhaled aldehydes reflect aspects of oxidative stress and tumor-specific tissue compn. and metab. Noninvasive recognition of lung malignancies may be realized if anal. skills, biochem. knowledge and medical expertise are combined into a joint effort.
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    12. 12
      Das, S.; Pal, M. Non-invasive monitoring of human health by exhaled breath analysis: a comprehensive review. J. Electrochem. Soc. 2020, 167, 037562  DOI: 10.1149/1945-7111/ab67a6
      12
      Review on non-invasive monitoring of human health by exhaled breath analysis
      Das, Sagnik; Pal, Mrinal
      Journal of the Electrochemical Society (2020), 167 (3), 037562CODEN: JESOAN; ISSN:0013-4651. (Electrochemical Society)
      A review. Exhaled human breath anal. is a very promising field of research work having great potential for diagnosis of diseases in noninvasive way. Breath anal. has attracted huge attention in the field of medical diagnosis and disease monitoring in the last two decades. VOCs/gases (Volatile Org. Compds.) in exhaled breath bear the finger-prints of metabolic and biophys. processes going on in human body. It's a non-invasive, fast, non-hazardous, cost effective, and point of care process for disease state monitoring and environmental exposure assessment in human beings. Some VOCs/gases in exhaled breath are bio-markers of different diseases and their presence in excess amt. is indicative of un-healthiness. Breath anal. has the potential for early detection of diseases. However, it is still underused and com. device is yet not available owing to multiferrious challenges. This review is intended to provide an overview of major biomarkers (VOCs/gases) present in exhaled breath, importance of their anal. towards disease monitoring, anal. techniques involved, promising materials for breath anal. etc. Finally, related challenges and limitations along with future scope will be touched upon.
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    13. 13
      Zhou, X.; Xue, Z.; Chen, X.; Huang, C.; Bai, W.; Lu, Z.; Wang, T. Nanomaterial-based gas sensors used for breath diagnosis. J. Mater. Chem. B 2020, 8, 3231– 3248,  DOI: 10.1039/C9TB02518A
      13
      Nanomaterial-based gas sensors used for breath diagnosis
      Zhou, Xinyuan; Xue, Zhenjie; Chen, Xiangyu; Huang, Chuanhui; Bai, Wanqiao; Lu, Zhili; Wang, Tie
      Journal of Materials Chemistry B: Materials for Biology and Medicine (2020), 8 (16), 3231-3248CODEN: JMCBDV; ISSN:2050-7518. (Royal Society of Chemistry)
      A review. Gas-sensing applications commonly use nanomaterials (NMs) because of their unique physicochem. properties, including a high surface-to-vol. ratio, enormous no. of active sites, controllable morphol., and potential for miniaturization. NM-based gas sensors, as a noninvasive, real-time technique, are a promising candidate for monitoring human breath. This review focuses on NM-based gas sensors used for breath diagnosis. First we describe some representative biomarkers of diseases that are detectable in breath and requirements for breath sensors. Then we review elec., optical and mass-sensitive gas sensors in terms of these performance requirements, together with describing the detection capability of these sensors for trace concns. of biomarkers and their initial attempts to diagnose disease. Moreover, we discuss breath sensor platforms with a multivariable sensing system, wireless communication and breath sampling, essential for predictive, preventive, personalized, and participatory ("P4") medicine. Finally, we conclude with problems and challenges assocd. with the selectivity, humidity and validation of breath sensors. We hope that this article will inspire the development of high-performance gas sensors based on novel NMs.
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    14. 14
      Mochalski, P.; King, J.; Unterkofler, K.; Hinterhuber, H.; Amann, A. Emission rates of selected volatile organic compounds from skin of healthy volunteers. J. Chromatogr., B 2014, 959, 62– 70,  DOI: 10.1016/j.jchromb.2014.04.006
      14
      Emission rates of selected volatile organic compounds from skin of healthy volunteers
      Mochalski, Pawel; King, Julian; Unterkofler, Karl; Hinterhuber, Hartmann; Amann, Anton
      Journal of Chromatography B: Analytical Technologies in the Biomedical and Life Sciences (2014), 959 (), 62-70CODEN: JCBAAI; ISSN:1570-0232. (Elsevier B.V.)
      Gas chromatog. with mass spectrometric detection (GC-MS) coupled with solid phase micro-extn. as pre-concn. (SPME) was applied to identify and quantify volatile org. compds. (VOCs) emitted by human skin. A total of 64 C4-C10 compds. were quantified in skin emanation of 31 healthy volunteers. Amongst them aldehydes and hydrocarbons were the predominant chem. families with eighteen and seventeen species, resp. Apart from these, there were eight ketones, six heterocyclic compds., six terpenes, four esters, two alcs., two volatile sulfur compds., and one nitrile. The obsd. median emission rates ranged from 0.55 to 4790 fmol cm-2 min-1. Within this set of analytes three volatiles; acetone, 6-methyl-5-hepten-2-one, and acetaldehyde exhibited esp. high emission rates exceeding 100 fmol cm-2 min-1. Thirty-three volatiles were highly present in skin emanation with incidence rates over 80%. These species can be considered as potential markers of human presence, which could be used for early location of entrapped victims during Urban Search and Rescue Operations (USaR).
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    15. 15
      Haze, S.; Gozu, Y.; Nakamura, S.; Kohno, Y.; Sawano, K.; Ohta, H.; Yamazaki, K. 2-Nonenal newly found in human body odor tends to increase with aging. J. Invest. Dermatol. 2001, 116, 520– 524,  DOI: 10.1046/j.0022-202x.2001.01287.x
      15
      2-Nonenal newly found in human body odor tends to increase with aging
      Haze, Shinichiro; Gozu, Yoko; Nakamura, Shoji; Kohno, Yoshiyuki; Sawano, Kiyohito; Ohta, Hideaki; Yamazaki, Kazuo
      Journal of Investigative Dermatology (2001), 116 (4), 520-524CODEN: JIDEAE; ISSN:0022-202X. (Blackwell Science, Inc.)
      Human body odor consists of various kinds of odor components. Here, we have investigated the changes in body odor assocd. with aging. The body odor of subjects between the ages of 26 and 75 was analyzed by headspace gas chromatog./mass spectrometry. 2-Nonenal, an unsatd. aldehyde with an unpleasant greasy and grassy odor, was detected only in older subjects (40 yr or older). Furthermore, anal. of skin surface lipids revealed that ω7 unsatd. fatty acids and lipid peroxides also increased with aging and that there were pos. correlations between the amt. of 2-nonenal in body odor and the amt. of ω7 unsatd. fatty acids or lipid peroxides in skin surface lipids. 2-Nonenal was generated only when ω7 unsatd. fatty acids were degraded by degrdn. tests in which some main components of skin surface lipids were oxidatively decompd. using lipid peroxides as initiator of an oxidative chain reaction. The results indicate that 2-nonenal is generated by the oxidative degrdn. of ω7 unsatd. fatty acids, and suggest that 2-nonenal may be involved in the age-related change of body odor.
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    16. 16
      Fujisaki, M.; Endo, Y.; Fujimoto, K. Retardation of volatile aldehyde formation in the exhaust of frying oil by heating under low oxygen atmospheres. J. Am. Oil Chem. Soc. 2002, 79, 909– 914,  DOI: 10.1007/s11746-002-0578-3
      16
      Retardation of volatile aldehyde formation in the exhaust of frying oil by heating under low oxygen atmospheres
      Fujisaki, Mariko; Endo, Yasushi; Fujimoto, Kenshiro
      Journal of the American Oil Chemists' Society (2002), 79 (9), 909-914CODEN: JAOCA7; ISSN:0003-021X. (AOCS Press)
      Volatile aldehydes were generated in the exhaust of high-oleic safflower oil during heating at 180°C by spraying water into atmospheres with four levels of oxygen concns. (2, 4, 10, and 20%). These aldehydes were quant. analyzed by HPLC after the conversion to 2,4-dinitrophenyl hydrazones. Alkanals (C2 through C10), eight 2-alkenals (C3 through C10) and three 2,4-alkadienals (C7, C9, and C10) were found. These aldehyde levels were found to be pos. correlated with both the heating time and the atm. oxygen concn. The total amts. of aldehydes were the lowest in the oil heated in an atm. with 2% O2, and corresponded to 1/10 of those in the atm. with 20% O2. Acrolein was not found in oils heated in the atm. with 2% oxygen. These results suggest that frying in atmospheres with low oxygen levels can effectively decrease the generation of volatile aldehydes in the exhaust.
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    17. 17
      Mochalski, P.; Unterkofler, K.; Teschl, G.; Amann, A. Potential of volatile organic compounds as markers of entrapped humans for use in urban search-and-rescue operations. TrAC Trends Anal. Chem. 2015, 68, 88– 106,  DOI: 10.1016/j.trac.2015.02.013
      17
      Potential of volatile organic compounds as markers of entrapped humans for use in urban search-and-rescue operations
      Mochalski, Pawel; Unterkofler, Karl; Teschl, Gerald; Amann, Anton
      TrAC, Trends in Analytical Chemistry (2015), 68 (), 88-106CODEN: TTAEDJ; ISSN:0165-9936. (Elsevier B. V.)
      Volatile org. compds. (VOCs) emitted by a human body form a chem. signature capable of providing invaluable information on the physiol. status of an individual and, thereby, serving as signs of life for detecting victims after natural or man-made disasters. For this review, we created a database of potential biomarkers of human presence based on literature reports on VOCs in human breath, skin emanations, blood and urine. We estd. approx. fluxes of these VOCs from the human body, and used them to predict concns. in the vicinity of victims. We classified proposed markers in groups by potential for victim detection. The major classification discriminants were the capability of detection by portable, real-time anal. instruments and background levels of VOCs in the urban environment. We intend data summarized in this review to assist studies on the detection of humans via chem. anal. and to accelerate investigations in this area of knowledge.
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    18. 18
      Itoh, T.; Nakashima, T.; Akamatsu, T.; Izu, N.; Shin, W. Nonanal gas sensing properties of platinum, palladium, and gold-loaded tin oxide VOCs sensors. Sens. Actuators, B 2013, 187, 135– 141,  DOI: 10.1016/j.snb.2012.09.097
      18
      Nonanal gas sensing properties of platinum, palladium, and gold-loaded tin oxide VOCs sensors
      Itoh, Toshio; Nakashima, Takaomi; Akamatsu, Takafumi; Izu, Noriya; Shin, Woosuck
      Sensors and Actuators, B: Chemical (2013), 187 (), 135-141CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)
      We have investigated the nonanal sensing properties of Pt-, Pd-, and Au-loaded SnO2 (Pt, Pd, Au/SnO2) thick films. These films show a higher response to nonanal than a non-loaded SnO2 film, can detect several tens of ppb of nonanal and exhibit fast response and recovery times. Their nonanal sensing ability is improved by pretreatments, such as annealing temp. and aging. The resistance of these films in pure air depends on the working temp., but the resistance in nonanal gas depends mainly on the film thickness. We suggest nonanal detection models for Pt, Pd, Au/SnO2 films with different film thicknesses, and det. the optimum film thickness for nonanal detection.
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    19. 19
      Daneshkhah, A.; Vij, S.; Siegel, A. P.; Agarwal, M. Polyetherimide/carbon black composite sensors demonstrate selective detection of medium-chain aldehydes including nonanal. Chem. Eng. J. 2020, 383, 123104  DOI: 10.1016/j.cej.2019.123104
      19
      Polyetherimide/carbon black composite sensors demonstrate selective detection of medium-chain aldehydes including nonanal
      Daneshkhah, Ali; Vij, Shitiz; Siegel, Amanda P.; Agarwal, Mangilal
      Chemical Engineering Journal (Amsterdam, Netherlands) (2020), 383 (), 123104CODEN: CMEJAJ; ISSN:1385-8947. (Elsevier B.V.)
      This study presents the synthesis, fabrication, and development of a selective polyetherimide (PEI)/carbon black (CB) sensor, engineered to detect aldehydes such as nonanal. Using a novel approach, spin coating of the PEI/CB in 1-methyl-2-pyrrolidone (NMP) was followed by a redn. of the composite through heat treating at 200°C resulting in a highly sensitive and selective film (with low hydrophilicity) for detection of nonanal. This represents a key step, as it decreased surface oxygen and increased surface amine/imine sites. XPS anal. demonstrated the engineered surface was comprised of >3.5% nitrogen (including 1.2% amines/imines) and displayed a contact angle of 80°. The sensor response to nonanal (1 ppm to 80 ppm) ranged from 0.02% to 1.9%. Fabricated sensors showed over 14 times more sensitivity to nonanal than volatiles with similar mol. wts. but different functional groups such as 2-nonanone, dodecane, and 1-octanol. This confirms the sensing film has high selectivity to aldehydes over ketones, hydrocarbons, and alcs. Importantly, the proposed sensor maintained its response to nonanal over a period of 36 days. In addn., a multifactor machine learning algorithm was developed based on principal component anal. (PCA) to detect the type and concn. of a VOC using the temporal response of the sensor. Fabrication, characterization, testing methods, and results are presented and discussed.
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    20. 20
      Jha, S. K.; Hayashi, K. Polyacrylic acid polymer and aldehydes template molecule based MIPs coated QCM sensors for detection of pattern aldehydes in body odor. Sens. Actuators, B 2015, 206, 471– 487,  DOI: 10.1016/j.snb.2014.09.102
      20
      Polyacrylic acid polymer and aldehydes template molecule based MIPs coated QCM sensors for detection of pattern aldehydes in body odor
      Jha, Sunil K.; Hayashi, Kenshi
      Sensors and Actuators, B: Chemical (2015), 206 (), 471-487CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)
      Molecularly imprinted polymers (MIPs) have been prepd. using the polyacrylic acid (PAA) as host polymer and hexanal, heptanal, and nonanal as pattern mols. MIPs were employed as selective coating layer of quartz crystal microbalance (QCM) sensors. Hexanal, heptanal, and nonanal were opted as target chems. after gas chromatog.-mass spectrometer (GC-MS) characterization of body odor samples. Transient and static responses of four QCM sensors (three coated with MIPs and one with non-MIP) to target aldehydes in singly, binary and tertiary mixts., and water at distinct concns. have been measured. Transient responses were analyzed to compute the response time (ton), and recovery time (toff) of sensors. This result av. values of ton ≈ 5 s and toff ≈ 10 s to typical concns. of target odors. The sensitivity and baseline drift of sensors were also calcd. using their static response. The heptanal template mol. based MIP coated QCM exhibit improved sensitivity, reproducibility and faster response, than the rest two MIPs, and non-MIP coated QCMs. Static sensors response matrixes were further processed with principal component anal. (PCA) for qual. (visual) discrimination and support vector machine (SVM) classifier for quant. recognition (in %) of target aldehydes: in singly, binary and tertiary mixts. Aldehydes odor was effectively identified in principal component (PC) space. Maximum recognition rate of 89% has been achieved for three classes of binary odors, and 79% for the combination of single, binary and tertiary odor classes in 3-fold cross-validation of SVM classifier.
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    21. 21
      Wasilewski, T.; Szulczyński, B.; Wojciechowski, M.; Kamysz, W.; Gębicki, J. Determination of long-chain aldehydes using a novel quartz crystal microbalance sensor based on a biomimetic peptide. Microchem. J. 2020, 154, 104509  DOI: 10.1016/j.microc.2019.104509
      21
      Determination of long-chain aldehydes using a novel quartz crystal microbalance sensor based on a biomimetic peptide
      Wasilewski, Tomasz; Szulczynski, Bartosz; Wojciechowski, Marek; Kamysz, Wojciech; Gebicki, Jacek
      Microchemical Journal (2020), 154 (), 104509CODEN: MICJAN; ISSN:0026-265X. (Elsevier B.V.)
      This study presents investigation on usefulness of the peptide mimicking HarmOBP7 region as a receptor element of the piezoelec. sensor for selective anal. of long-chain aldehydes. Identification of odorant binding proteins creates new possibilities for design of peptides mimicking binding properties of their volatile compds. Exploration of OBPs and new peptide sequences capable to effectively bind volatile compds. is necessary to enhance artificial olfaction. For the development of biosensors where simple detection is crucial rather than identification of subsequent metabolic activity, the use of sub-protein components (e.g. ligand-binding regions or synthetic peptides) is still escalating. Bearing all this in mind, a segment of a peptide sequence assocd. with a specific function of HarmOBP7 (involved in binding the long-chain aldehydes) has been designed, synthesized and immobilized on a piezoelec. transducer. The results of in silico investigations were correlated with the exptl. measurements of gas substances. The correlated results confirm a high selectivity of the KLLFDSLTDLKKKMSEC-based sensor with respect to long-chain aliph. aldehydes including octanal, decanal, undecanal, nonanal and helional. Odorant mols. interact with recognition peptide with specific affinities. The results can throw a new light on the possibility of synthetic peptide application as a receptor layer in biosensors in odorants anal.
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    22. 22
      Tsujiguchi, M.; Aitoku, T.; Takase, H.; Maruo, Y. Y. Nonanal sensor fabrication using aldol condensation reaction inside alkali-resistant porous glass. IEEE Sens. J. 2021, 21, 8868– 8877,  DOI: 10.1109/JSEN.2021.3055264
      22
      Nonanal sensor fabrication using aldol condensation reaction inside alkali-resistant porous glass
      Tsujiguchi, Masato; Aitoku, Takashi; Takase, Hironori; Maruo, Yasuko Yamada
      IEEE Sensors Journal (2021), 21 (7), 8868-8877CODEN: ISJEAZ; ISSN:1558-1748. (Institute of Electrical and Electronics Engineers)
      Monitoring the gases released during breathing or via the skin has gained significance towards diagnosing diseases. In this study, a sensor chip capable of detecting nonanal gas, which is known to be a marker of lung cancer, was developed. The gas detection agent used was vanillin, which underwent aldol condensation with nonanal in the presence of a basic catalyst, resulting in the formation of an unsatd. aldehyde. Porous glass was used as the reaction field to carry the detection agent. Alkali-resistant porous glass was chosen because conventionalporous glasses show low durabilities under basic conditions, as they primarily consist of SiO2. Nonanal can be detected through changes in the absorption spectrum of the sensor. An accumulate-type sensor was used in this study, which exhibited a linear relationship between the degree of absorption changes at 470 nm and nonanal concn. in the 60 ppb-1.3 ppm range. Therefore, this biol. marker gas sensor is effective for the early diagnosis of diseases. The alkali-resistant porous glass sensor chip exhibited a higher degree of absorption change than the conventional porous glass sensor chip.
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    23. 23
      Maruo, Y. Y.; Nakamura, J.; Uchiyama, M.; Higuchi, M.; Izumi, K. Development of formaldehyde sensing element using porous glass impregnated with Schiff’s reagent. Sens. Actuators, B 2008, 129, 544– 550,  DOI: 10.1016/j.snb.2007.09.002
      23
      Development of formaldehyde sensing element using porous glass impregnated with Schiff's reagent
      Maruo, Yasuko Yamada; Nakamura, Jiro; Uchiyama, Masahiro; Higuchi, Masanori; Izumi, Katsuyuki
      Sensors and Actuators, B: Chemical (2008), 129 (2), 544-550CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)
      A sensor for detecting formaldehyde was developed. The sensor element was made of a porous glass impregnated with both a Schiff's reagent and an acid. The sensor element changed its color from yellow to violet after exposure to formaldehyde, and an absorption peak appeared at a wavelength of 570 or 580 nm. There was a quasilinear relationship between the 570 and 580 nm absorbance of the sensor element after exposure to formaldehyde and a logarithm of the exposed formaldehyde concn. Also, the sensor element worked as a reversible type, not as an accumulate type, and the absorbance at 570 or 580 nm of a once exposed sensor element decreased when it was exposed to a less concd. formaldehyde atm. The sensor element is reversible and suitable for the detection of a wide formaldehyde concn. range, for example from 20 ppm to 10 ppb.
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    24. 24
      Maruo, Y. Y.; Nakamura, J. Portable formaldehyde monitoring device using porous glass sensor and its applications in indoor air quality studies. Anal. Chim. Acta 2011, 702, 247– 253,  DOI: 10.1016/j.aca.2011.06.050
      24
      Portable formaldehyde monitoring device using porous glass sensor and its applications in indoor air quality studies
      Maruo, Yasuko Yamada; Nakamura, Jiro
      Analytica Chimica Acta (2011), 702 (2), 247-253CODEN: ACACAM; ISSN:0003-2670. (Elsevier B.V.)
      We have developed a portable device for formaldehyde monitoring with both high sensitivity and high temporal resoln., and carried out indoor air formaldehyde concn. anal. The absorbance difference of the sensor element was measured in the monitoring device at regular intervals of, for example, 1 h or 30 min, and the result was converted into the formaldehyde concn. This was possible because we found that the lutidine deriv. that was formed as a yellow product of the reaction between 1-phenyl-1,3-butandione and formaldehyde was stable in porous glass for at least 6 mo. We estd. the reaction rate to be 0.049 min-1 and the reaction occurred quickly enough for us to monitor hourly changes in the formaldehyde concn. The detection limit was 5 μg m-3 h. We achieved hourly formaldehyde monitoring using the developed device under several indoor conditions, and estd. the air exchange rate and formaldehyde adsorption rate, which we adopted as a new term in the mass balance equation for formaldehyde, in one office.
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    25. 25
      Maruo, Y. Y.; Tachibana, K.; Suzuki, Y.; Shinomi, K. Development of an analytical chip for detecting acetone using a reaction between acetone and 2,4-dinitrophenylhidrazine in a porous glass. Microchem. J. 2018, 141, 377– 381,  DOI: 10.1016/j.microc.2018.05.041
      25
      Development of an analytical chip for detecting acetone using a reaction between acetone and 2,4-dinitrophenylhidrazine in a porous glass
      Maruo, Yasuko Y.; Tachibana, Kenta; Suzuki, Yoshifumi; Shinomi, Kouki
      Microchemical Journal (2018), 141 (), 377-381CODEN: MICJAN; ISSN:0026-265X. (Elsevier B.V.)
      Acetone is a human biogas and is widely used in industrial manufg. Acetone can be detected in the breath of diabetic patients, and the measurement of acetone in human breath provides significant, non-invasive, diagnostic information on a patient's diabetic condition. An anal. chip for detecting acetone was developed herein. The anal. chip was composed from porous glass impregnated with 2,4-dinitrophenylhydrazine (DNPH) and hydrochloric acid. The anal. chip before exposure to acetone and the reaction product between acetone and DNPH (Acetone-DNPH) showed an absorption peak at 349 nm and 359 nm, resp. The molar absorption coeff. of Acetone-DNPH in the porous glass at 359 nm was 1.57 times larger than that of DNPH. Based on these results, the percentage of reaction ([Acetone-DNPH]t/[DNPH]0) could be calcd. using the absorbance values at 359 nm. The logarithm of the percentage of reaction was correlated with the cumulative acetone concn., which was a product of an exposed acetone concn. and an exposure time. The developed anal. chip was active in the cumulative acetone concn. range from 0.53 ppm x hour to 20 ppm x hour, and was functional in an atm. with 30%-90% relative humidity (R.H.).
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    26. 26
      Porter, H. H.; Emery, N. M. Treated Borosilicate Glass; US Patent 2, 106, 744, 1938.
      There is no corresponding record for this reference.
    27. 27
      Enke, D.; Janowski, F.; Schwieger, W. Porous glasses in the 21st century––a short review. Microporous Mesoporous Mater. 2003, 60, 19– 30,  DOI: 10.1016/S1387-1811(03)00329-9
      27
      Porous glasses in the 21st century - A short review
      Enke, D.; Janowski, F.; Schwieger, W.
      Microporous and Mesoporous Materials (2003), 60 (1-3), 19-30CODEN: MIMMFJ; ISSN:1387-1811. (Elsevier Science B.V.)
      A review. This article reviews recent studies concerning the prepn., modification, characterization, modeling and application of porous glasses on the basis of phase-sepd. alkali borosilicate glasses.
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    28. 28
      Yazawa, T.; Machida, F.; Kubo, N.; Jin, T. Photocatalytic activity of transparent porous glass supported TiO2. Ceram. Int. 2009, 35, 3321– 3325,  DOI: 10.1016/j.ceramint.2009.05.029
      28
      Photocatalytic activity of transparent porous glass supported TiO2
      Yazawa, Tetsuo; Machida, Fumiko; Kubo, Noriaki; Jin, Tetsuro
      Ceramics International (2009), 35 (8), 3321-3325CODEN: CINNDH; ISSN:0272-8842. (Elsevier Ltd.)
      A porous glass tube with a compn. of 96SiO2.4B2O3 (wt%) supported TiO2 shows high photooxidn. activity due to its transparency and large surface area. The surface area of the porous glass tube supported TiO2 is 10,000 times larger than that of conventional materials. TiO2 crystals supported are anatase type. Transparency of the porous glass tube is very important. Herein, sol-gel and chem. vapor deposition (CVD) processes were employed as TiO2 supporting processes. CVD process is more effective. For instance, an aq. methylene blue soln. with 1 ppm concn. almost thoroughly decomps. at a contact time of 300 s using porous glass tube supported TiO2 prepd. by CVD process under irradiating with 10 W low-pressure mercury lamp, on the other hand, opaque porous alumina tube supported TiO2 was only 25%. The smaller the pore size of the porous glass tube, the larger the transparency and the permeation resistance through porous glass tube. Hence, porous glass tube with ≈40 nm pore diam. is suitable from the standpoint of a practical use.
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    29. 29
      Sakai, G.; Matsunaga, N.; Shimanoe, K.; Yamazoe, N. Theory of gas-diffusion controlled sensitivity for thin film semiconductor gas sensor. Sens. Actuators, B 2001, 80, 125– 131,  DOI: 10.1016/S0925-4005(01)00890-5
      29
      Theory of gas-diffusion controlled sensitivity for thin film semiconductor gas sensor
      Sakai, Go; Matsunaga, Naoki; Shimanoe, Kengo; Yamazoe, Noboru
      Sensors and Actuators, B: Chemical (2001), 80 (2), 125-131CODEN: SABCEB; ISSN:0925-4005. (Elsevier Science B.V.)
      Influences of gas transport phenomena on the sensitivity of a thin film semiconductor gas sensor were studied theor. A diffusion equation was formulated by assuming that an inflammable gas (target gas) moves inside the film by Knudsen diffusion, while it reacts with the adsorbed oxygen following a 1st-order reaction kinetic. By solving this equation under steady-state conditions, the target gas concn. inside the film was derived as a function of depth (x) from the film surface, Knudsen diffusion coeff. (DK), rate const. (k) and film thickness (L). The gas concn. profile thus obtained allowed to est. the gas sensitivity (S) defined as the resistance ratio (Ra/Rg), under the assumption that the sheet conductance of the film at depth x is linear to the gas concn. there with a proportionality const. (sensitivity coeff.), a. The derived equation shows that S decreases sigmoidally down to unity with an increase in L k/DK. Further by assuming that the temp. dependence of rate const. (k) and sensitivity coeff. (a) follows Arrhenius type ones with resp. activation energies, it was possible to derive a general expression of S involving temp. (T). The expression shows that, when the activation energies are selected properly, the S vs. T correlation results in a volcano-shaped one, its height increasing with decreasing L. The dependence of S on L at const. T as well as on T at const. L can thus be simulated fairly well based on the equation.
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    30. 30
      Shim, J. G.; Lee, D. W.; Lee, J. H.; Kwak, N. S. Experimental study on capture of carbon dioxide and production of sodium bicarbonate from sodium hydroxide. Env. Eng. Res. 2016, 21, 297– 303,  DOI: 10.4491/eer.2016.042
      There is no corresponding record for this reference.
    31. 31
      Tuguldurova, P. V.; Fateev, V. A.; Malkov, S. V.; Poleshchuk, K. O.; Vodyankina, V. O. Acetaldehyde-ammonia interaction: A DFT study of reaction mechanism and product identification. J. Phys. Chem. A 2017, 121, 3136– 3141,  DOI: 10.1021/acs.jpca.7b00823
      31
      Acetaldehyde-Ammonia Interaction: A DFT Study of Reaction Mechanism and Product Identification
      Tuguldurova, Vera P.; Fateev, Alexander V.; Malkov, Victor S.; Poleshchuk, Oleg Kh.; Vodyankina, Olga V.
      Journal of Physical Chemistry A (2017), 121 (16), 3136-3141CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
      The product of acetaldehyde and ammonia reaction, namely, 2,4,6-trimethyl-1,3,5-hexahydrotriazine trihydrate, was synthesized and identified using a combination of exptl. (NMR spectroscopy, IR spectroscopy, m.p. detn.) and DFT-based theor. approaches. A reaction mechanism was proposed. The reaction was shown to proceed via the formation of aminoalc., imine, and geminal diamine intermediates accompanied by cyclization of these species. The calcn. results allowed us to build a potential energy surface of the acetaldehyde and ammonia interaction and det. the most energetically favorable pathway to yield acetaldehyde ammonia trimer. The reaction product was found in an energy min. (-53.5 kcal/mol).
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    32. 32
      Katada, N.; Niwa, M. Analysis of acidic properties of zeolitic and non-zeolitic solid acid catalysts using temperature-programmed desorption of ammonia. Catal. Surv. Asia. 2004, 8, 161– 170,  DOI: 10.1023/B:CATS.0000038534.37849.16
      32
      Analysis of Acidic Properties of Zeolitic and Non-Zeolitic Solid Acid Catalysts Using Temperature-Programmed Desorption of Ammonia
      Katada, Naonobu; Niwa, Miki
      Catalysis Surveys from Asia (2004), 8 (3), 161-170CODEN: CSAABF; ISSN:1571-1013. (Springer Science+Business Media, Inc.)
      A review; a method of ammonia temp.-programmed desorption (TPD) for anal. of acidic property of a solid was improved by introduction of a water vapor treatment method and development of a theory for calcn. of ammonia adsorption heat from the TPD profile. The improved method was applied to various solid acid catalysts to establish relationships between the acidic properties and catalytic performances for various acid-catalyzed reactions. Here, examples of the applications to some important acid catalysts are reviewed. The exact anal. of acidic property of Y zeolite and its change by such modifications as steaming and EDTA treatment gave a new interpretation on the generation of alkane (paraffin) cracking activity on an ultra stable Y (USY) zeolite. The surface d. and strength of acid sites on WO3/ZrO2 and SO42-/ZrO2 catalysts were detd., and their relations with catalytic activities for Friedel-Crafts type alkylation and skeletal isomerization of alkane were found.
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    33. 33
      Setoyama, T.; Kobayashi, M.; Kabata, Y.; Kawai, T.; Nakanishi, A. New industrial process of PTMG catalyzed by solid acid. Catal. Today 2002, 73, 29– 37,  DOI: 10.1016/S0920-5861(01)00515-6
      33
      New industrial process of PTMG catalyzed by solid acid
      Setoyama, Tohru; Kobayashi, Mitsuharu; Kabata, Yoshio; Kawai, Tomohiro; Nakanishi, Akio
      Catalysis Today (2002), 73 (1-2), 29-37CODEN: CATTEA; ISSN:0920-5861. (Elsevier Science B.V.)
      Polymn. of THF catalyzed by solid acid in the presence of acetic anhydride was studied. A moderate Lewis acid catalyst produces required PTME (PTMG-acetate) having adequate Mn. Zeolitic material is not suitable for this prodn. because very high mol. wt. PTME is co-produced. From this aspect, mixed oxide materials show good performance because only these have the required acidic character. Mass-transfer study suggests the importance of pore size of support and the homogeneity of active sites. They affect on the Mn and the Mw/Mn strikingly. The com. technol. has established by utilizing these results.
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    34. 34
      Flego, C.; Carluccio, L.; Rizzo, C.; Perego, C. Synthesis of mesoporous SiO2–ZrO2 mixed oxides by sol–gel method. Catal. Commun. 2001, 2, 43– 48,  DOI: 10.1016/S1566-7367(01)00006-1
      34
      Synthesis of mesoporous SiO2-ZrO2 mixed oxides by sol-gel method
      Flego, C.; Carluccio, L.; Rizzo, C.; Perego, C.
      Catalysis Communications (2001), 2 (2), 43-48CODEN: CCAOAC; ISSN:1566-7367. (Elsevier Science B.V.)
      A series of SiO2-ZrO2 mixed oxides were prepd. by sol-gel method in the presence of directing agent, with variable amts. of ZrO2 between pure silica and pure zirconia, with the aim to obtain catalytic materials suitable as solid acid catalysts. SiO2-ZrO2 mixed oxides differ from the two pure starting oxides. While SiO2 has a low OH d. without peculiar acid character, the introduction of increasing amts. of Zr increases the d. of the acid sites in the materials. Furthermore both SiO2/ZrO2 molar ratio and drying procedure are able to influence the physico-chem. characteristics (textural properties, acid sites distribution, etc.) of these mixed oxides.
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    35. 35
      Dickens, K. T.; Warren, S. Chemistry of the carbonyl group: A step-by-step approach to understanding organic reaction mechanisms; Willey: Iowa, 2018.
      There is no corresponding record for this reference.
    36. 36
      Zonta, G.; Anania, G.; Fabbri, B.; Gaiardo, A.; Gherardi, S.; Giberti, A.; Guidi, V.; Landini, N.; Malagù, C. Detection of colorectal cancer biomarkers in the presence of interfering gases. Sens. Actuators, B 2015, 218, 289– 295,  DOI: 10.1016/j.snb.2015.04.080
      36
      Detection of colorectal cancer biomarkers in the presence of interfering gases
      Zonta, G.; Anania, G.; Fabbri, B.; Gaiardo, A.; Gherardi, S.; Giberti, A.; Guidi, V.; Landini, N.; Malagu, C.
      Sensors and Actuators, B: Chemical (2015), 218 (), 289-295CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)
      Medical studies have shown that tumor growth is accompanied by protein changes that may lead to the peroxidn. of the cell membrane, with consequent emission of volatile org. compds. (VOCs). VOCs can be detected through breath or intestinal gases and are biomarkers for colorectal cancer (CRC). The anal. of VOCs represents a non-invasive and potentially inexpensive pre-screening technique. An array of chemoresistive gas sensors, based on screen-printed Metal OXide (MOX) semiconducting films, has been selected to identify gaseous compds. of oncol. interest, i.e. benzene, 1-iodo-nonane and decanal, from the main interferers that can be found in the intestine. MOX sensors are able to detect concns. down to about 10th ppb, as exptl. proven in previous works, so they can identify very slight differences in concn. among gas mixts. In this work it has been proven that the array used is able to identify tumor markers singularly and in combination with other gases both in wet and dry conditions. Moreover, the sensors chosen can discriminate target VOCs from interferers even at low concns.
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    37. 37
      Wang, C.; Hosomi, T.; Nagashima, K.; Takahashi, T.; Zhang, G.; Kanai, M.; Yoshida, H.; Yanagida, T. Phosphonic acid modified ZnO nanowire sensors: directing reaction pathway of volatile carbonyl compounds. ACS Appl. Mater. Interfaces 2020, 12, 44265– 44272,  DOI: 10.1021/acsami.0c10332
      37
      Phosphonic Acid Modified ZnO Nanowire Sensors: Directing Reaction Pathway of Volatile Carbonyl Compounds
      Wang, Chen; Hosomi, Takuro; Nagashima, Kazuki; Takahashi, Tsunaki; Zhang, Guozhu; Kanai, Masaki; Yoshida, Hideto; Yanagida, Takeshi
      ACS Applied Materials & Interfaces (2020), 12 (39), 44265-44272CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      Surface mol. transformations on nanoscale metal oxides are inherently complex, and directing those reaction pathways is still challenging but important for designing their various applications, including mol. sensing, catalysts, and others. Here, a rational strategy to direct a reaction pathway of volatile carbonyl compds. (nonanal: biomarker) on single-cryst. ZnO nanowire surfaces via mol. modification is demonstrated. The introduction of a methylphosphonic acid modification on the ZnO nanowire surface significantly alters the surface reaction pathway of nonanal via suppressing the detrimental aldol condensation reaction. This is directed by intentionally decreasing the probability of two neighboring mol. activations on the nanowire surface. Spectrometric measurements reveal the correlation between the suppression of the aldol condensation surface reaction and the improvement in the sensor performance. This tailored surface reaction pathway effectively reduces the operating temp. from 200 to 100°C while maintaining the sensitivity. This is because the aldol condensation product ((E)-2-heptyl-2-undecenal) requires a higher temp. to desorb from the surface. Thus, the proposed facile strategy offers an interesting approach not only for the rational design of metal oxide sensors for numerous volatile carbonyl compds. but also for tailoring various surface reaction pathways on complex nanoscale metal oxides.
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    38. 38
      Taleuzzaman, M. Limit of blank (LOB), limit of detection (LOD), and limit of quantification (LOQ). Org. Med. Chem. I. J. 2018, 7, 555722
      There is no corresponding record for this reference.
    39. 39
      Asanuma, K.; Hino, S.; Maruo, Y. Y. Development of an analytical chip for nitrogen monoxide detection using porous glass impregnated with 2-phenyl-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl. Microchem. J. 2019, 151, 104251  DOI: 10.1016/j.microc.2019.104251
      39
      Development of an analytical chip for nitrogen monoxide detection using porous glass impregnated with 2-phenyl-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl
      Asanuma, Kohgo; Hino, Shinji; Maruo, Yasuko Y.
      Microchemical Journal (2019), 151 (), 104251CODEN: MICJAN; ISSN:0026-265X. (Elsevier B.V.)
      Nitrogen monoxide (NO) is an important bio-regulatory mol. NO presence in exhaled breath is a biomarker for an airway inflammation. Thus, measuring NO in the exhaled air is considered a noninvasive method for disease screening. In this study, we developed an anal. chip made of porous glass impregnated with 2-phenyl-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl (PTIO) for NO gas detection. The anal. chip had an absorption peaks at 338 and 567 nm, which decreased when exposed to NO, whereas the absorbance at 413 nm increased with an isosbestic point at 477 nm. It was found that there is a linear relationship between the logarithmic change in the absorbance at 338 nm and 567 nm and the cumulative NO concn. Addnl., the spectrum of the anal. chip was affected by humidity. There was a linear relationship between the PTIO's molar absorption coeff. at 567 nm and the relative humidity. Therefore, the absorbance of PTIO can be cor. in order to take the effect of humidity into consideration. The working ranges of the anal. chip were between 0.15 and 3.7 ppm × h of cumulative NO concn. and at a relative humidity between 40% and 90%. We also measured NO in a small amt. of air (1.8 L to mimic the actual exhaled air vol.) and we were able to measure the NO concn. of 30 ppb for 24 h.
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    40. 40
      Maruo, Y. Y.; Nakamura, M.; Higashijima, Y.; Kikuya, Y.; Nakamura, M. Development of highly sensitive nitrogen dioxide monitoring device and its application to wide-area ubiquitous network. Sens. Actuators, B 2012, 173, 191– 196,  DOI: 10.1016/j.snb.2012.06.075
      40
      Development of highly sensitive nitrogen dioxide monitoring device and its application to wide-area ubiquitous network
      Maruo, Yasuko Yamada; Nakamura, Masayuki; Higashijima, Yuka; Kikuya, Yukio; Nakamura, Motonori
      Sensors and Actuators, B: Chemical (2012), 173 (), 191-196CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)
      We have developed an NO2 sensing device with high time resoln. for application to a wide-area ubiquitous network. The NO2 sensing device employs the colorimetric reaction between NO2 and diazo-coupling reagents. We estd. the formation and decompn. rate of the azo dye in the sensor elements and found that no decompn. occurred and that the formation rate was fast enough for us to measure NO2 concn. at 10 min intervals with a detection limit of 12 ppb. We have constructed sensing terminal units contg. the NO2 sensing device, a GPS device, a compass, a switch, LEDs and a wireless terminal unit for a wide-area ubiquitous network. We successfully monitored the outdoor NO2 level at 10 min intervals using the developed terminal units mounted on a bicycle in certain areas of several cities. We also designed and implemented an application where bicycles collect geo-tagged air quality samples and post them on a map that other cyclists can use to det. their route.
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  • Supporting Information

    Supporting Information

    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.2c07622.

    • Schematic of the preparation process of the alkali-resistant porous glass; chemical structures of nonanal and vanillin; reaction scheme of the aldol condensation reaction between vanillin and nonanal (PDF)


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