In vivo detection of gold-imidazole self-assembly complexes: NIR-SERS signal reporters

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 intensify, 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.