Functionalized aligned silver nanorod arrays for glucose sensing through surface enhanced Raman scattering

Glucose detection through surface enhanced Raman scattering (SERS) has recently attracted a lot of interest due to its potential as a minimally-invasive, in vivo sensing technology. However, the application of SERS to glucose detection is greatly limited because of its small Raman scattering cross-section and low affinity with bare metal surfaces. In this work, an active SERS substrate composed of nearly aligned silver nanorods with uniform distribution was fabricated using high vacuum electron beam physical vapor deposition. A monolayer of 4-mercaptophenylboronic acid (MPBA) was self-assembled on the Ag nanorod surfaces, through the covalent interaction between its thio group and the Ag surface, thus resulting in a functional SERS substrate for glucose detection. The results from X-ray photoelectron spectroscopy and Raman spectroscopy clearly indicate that MPBA was successfully functionalized on the Ag nanorod surfaces. The specific binding of glucose with the boronic acid motif in MPBA significantly affects the SERS signal of MPBA on Ag nanorods, which can be measured and correlated to glucose concentrations. Quantitative detection of glucose in a clinically relevant (0-20 mM) concentration range was successfully demonstrated. The fundamental mechanism behind this approach was also discussed, and both electromagnetic and chemical enhancement mechanisms are attributed to the enhanced SERS signals. These results provide new insights into the development of SERS-based glucose sensors using Ag nanorod arrays.