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In Vivo Detection of Gold−Imidazole Self-Assembly Complexes: NIR-SERS Signal Reporters

Glauco R. Souza,^†^‡ Carly S. Levin,^† Amin Hajitou,^‡ Renata Pasqualini,^‡ Wadih Arap,^‡ and J. Houston Miller*^†

Department of Chemistry, The George Washington University, Washington, D.C. 20052, and The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, Texas 77030

Anal. Chem., 2006, 78 (17), pp 6232–6237

DOI: 10.1021/ac060483a

Publication Date (Web): July 22, 2006

†

The George Washington University.

‡

The University of Texas M. D. Anderson Cancer Center.

Corresponding author. Phone: 202-994-7474. Fax: 202-994-5873. E-mail: Houston@gwu.edu.

Abstract

Here we report in vitro and in vivo detection of self-assembled Au−imidazole by using near-infrared surface-enhanced Raman scattering (NIR-SERS). In vivo, the Au−imidazole structures were administered into tumor-bearing mice and detected noninvasively. The self-assembled Au−imidazole complexes were generated by the adsorption of imidazole molecules onto Au nanoparticles (NP) and were then characterized as aqueous suspensions by using NIR-SERS, angle-dependent light scattering with fractal dimension analysis, and visible extinction spectroscopy. The structure and optical activity was sensitive to imidazole concentration and Au NP size. Specifically, the Au−imidazole assemblies formed at lower imidazole concentrations had the lowest fractal dimension (D_f = 1.2) and the largest Raman enhancement factors for the dominant NIR-SERS feature, a ring-breathing vibrational mode at 954 cm^-¹. Changes in elastic scattering intensity, fractal dimension, and surface plasmon absorption were observed with increasing imidazole concentration. The Raman enhancement factor was also found to range between 10⁶ and 10⁹ with different primary Au nanoparticle sizes. For the higher enhancement factor systems, NIR-SERS detection of Au−imidazole was performed with data acquisitions time of only 5 s. The largest enhancement was observed for the 954-cm^-¹ feature at an imidazole concentration of 1.9 μM when coupled to 54-nm-diameter Au NPs (the largest NP tested). Finally, we show the first demonstration of in vivo, noninvasive, and real-time SERS detection.

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