Size-Based Norfentanyl Detection with SWCNT@UiO-MOF Composites

Single-walled carbon nanotube (SWCNT)@metal–organic framework (MOF) field-effect transistor (FET) sensors generate a signal through analytes restricting ion diffusion around the SWCNT surface. Four composites made up of SWCNTs and UiO-66, UiO-66-NH2, UiO-67, and UiO-67-CH3 were synthesized to explore the detection of norfentanyl (NF) using SWCNT@MOF FET sensors with different pore sizes. Liquid-gated FET devices of SWCNT@UiO-67 showed the highest sensing response toward NF, whereas SWCNT@UiO-66 and SWCNT@UiO-66-NH2 devices showed no sensitivity improvement compared to bare SWCNT. Comparing SWCNT@UiO-67 and SWCNT@UiO-67-CH3 indicated that the sensing response is modulated by not only the size-matching between NF and MOF channel but also NF diffusion within the MOF channel. Additionally, other drug metabolites, including norhydrocodone (NH), benzoylecgonine (BZ), and normorphine (NM) were tested with the SWCNT@UiO-67 sensor. The sensor was not responding toward NH and or BZ but a similar sensing result toward NM because NM has a similar size to NF. The SWCNT@MOF FET sensor can avoid interference from bigger molecules but sensor arrays with different pore sizes and chemistries are needed to improve the specificity.


Characterization
Transmission Electron Microscopy (TEM).FEI Morgagni was used for taking TEM images.

Scanning Electron Microscopy (SEM)
. SEM images were taken on a Zeiss Sigma 500 VP analytical FE-SWM equipment.
Powder X-ray Diffraction (PXRD).PXRD was conducted with Bruker D8 XRD system equipped with LynxEye detector.Samples were prepared by drop-casting on glass slides.2θ angles between 3.5° and 50° were measured at 0.02° interval with a rate of 0.3 seconds/point.The X-ray source was Cu Kα held at 40 kV and 40 μA.
Gas adsorption isotherms were collected on a Micromeritics 3-flex gas adsorption analyzer.Approximately 20 mg of each sample was added into a pre-weighed sample analysis tube that had been evacuated and backfilled with N2 before massing.The samples were degassed at 423 K under vacuum for 24 hours until the pressure change rate was no more than 3.5 mTorr/min.A liquid N2 bath was used for the N2 adsorption experiments at 77 K. UHP grade N2 adsorbate (99.999 %) was used in this study.

Experimental details
Synthesis of 2-methyl-biphenyl-4,4'-dicarboxylic acid (MeBPDC).MeBPDC was synthesized according to literature conditions. 1 Synthesis of SWCNT@UiO-66.To a 20 mL scintillation vial, 12.18 mL DMF, 3.73 mg terephthalic acid, 0.40 mL acetic acid and 0.32 mL SWCNT suspension (0.5 mg/mL) were added.The mixture was sonicated for 1 minute before 1.10 mL Zr oxide-cluster solution was added.The mixture was kept at room temperature under stirring for 20 hours before the composites were recovered using centrifugation.Composites were washed with DMF and ethanol three times and were stored in ethanol.
Synthesis of SWCNT@UiO-66-NH2.To a 20 mL scintillation vial, 12.18 mL DMF, 4.07 mg 2aminoterephthalic acid, 0.40 mL acetic acid and 0.32 mL SWCNT suspension (0.5 mg/mL) were added.The mixture was sonicated for 1 minute before 1.10 mL Zr oxide-cluster solution was added.The mixture was kept at room temperature under stirring for 20 hours before the composites were recovered using centrifugation.Composites were washed with DMF and ethanol three times and were stored in ethanol.
Synthesis of SWCNT@UiO-67.To a 20 mL scintillation vial, 12.75 mL DMF and 24.23 mg biphenyl-4,4'-dicarboxylic acid (BPDC) was added.The solution was heated at 150°C in an oil bath to dissolve BPDC.After cooling the solution to room temperature, 23.30 mg ZrCl4, 1.75 mL acetic acid and 0.50 mL SWCNT suspension (0.5 mg/mL) was added.The solution was sonicated for 1 minute and then kept in a 120°C oil bath for 5 hours under stirring.The yield composites were recovered using centrifugation and were washed with DMF and ethanol three times.Composites were stored in ethanol.
Synthesis of SWCNT@UiO-67-CH3.To a 20 mL scintillation vial, 9.74 mL DMF, 0.50 mL acetic acid and 9.32 mg ZrCl4 were added.The solution was sonicated for 1 minute and then kept in a 100°C oil bath for 10 minutes.The transparent solution was then cooled to room temperature and 10.24 mg MeBPDC and 0.26 mL SWCNT suspension (0.5 mg/mL) were added.The mixture was kept in a 100°C oil bath for 20 hours under stirring.The composites were recovered using centrifugation and were washed with DMF and ethanol three times.Composites were stored in ethanol.

Figure S1 .
Figure S1.SEM image of the interdigitated electrode device.The dimension of the electrode area is 300 μm x 200 μm.Distance between each electrode finger is 6 μm.

Figure S5 .
Figure S5.Optimized molecular structures of drug metabolites (NF, NM, NH, BZ) and their corresponding molecular dimensions.Molecular size is determined as the distance between the two farthest atoms within each molecule.

Figure S8 .
Figure S8.New and aged SWCNT@UiO-67 FET sensor responses toward norfentanyl.Error bars are device-to-device variance.Number of devices (n) is presented for each device type.