Highly sensitive detection of glucose: A quantitative approach employing nanorods assembled plasmonic substrate

Sensitive glucose detection enables indirect blood glucose sensing through easily accessible biofluids such as saliva and sweat. In this work, silver coated gold nanorods (Au@Ag NRs) were synthesized and used to prepare plasmonic substrate for surface-enhanced Raman spectroscopy (SERS) to leverage highly sensitive detection of glucose for quantitative analysis. By synthetically manipulating of gold NRs and the outer silver shell, the size and aspect ratio of Au@Ag NRs were optimized, and the plasmon resonance wavelength was tuned to approximately the excitation wavelength. 4-Mercaptophenyl-boronic acid (4-MPBA) and 4-Cyanophenylboronic acid (4-CPBA) were used as primary and secondary receptors respectively to specifically capture glucose molecules. The distinct Raman peak at 2226cm^-1 of the cyano group in 4-CPBA was used as a signal reporter for glucose sensing. It is located in a biological silent region (1800-2800cm^-1), thus offering specific sensing of glucose, without the interference of other endogenous molecules. Our results showed that the SERS substrate was long-term stable. Glucose in urine solution with additive glucose was quantitatively and specifically determined, with the detection limit down to 10^-8M. Further experiments using urine from mild diabetes shows positive results, demonstrating the feasibility of clinical use.