Surface Enhanced Raman Scattering
Since its discovery more than 30 years ago, the surface enhanced Raman scattering (SERS) has been recognized as a high sensitive detection technique for chemical and biological sensing and medical diagnostics. However, the practical application of the remarkable analytical sensitivity of SERS has not been widely accepted as a viable diagnostic technique due to the difficulty in preparing robust and reproducible substrates of the correct surface morphology that provide maximum SERS enhancements. Recently, we demonstrate that the aligned silver nanorod (AgNR) array substrates engineered by the oblique angle deposition method are capable of providing extremely high SERS enhancement factors (>10^8). The substrates are large area, uniform, reproducible, and compatible with general microfabrication process. The enhancement factor depends strongly on the length of the Ag nanorods, the substrate coating, the polarization of the excitation light, as well as the incident angle. With the optimized AgNR SERS substrates, we also show that SERS is able to detect trace amount of virus, bacteria, microRNAs, or other chemical and biological molecules, and distinguish different viruses/bacteria and virus/bacteria strains, suggesting that this technology can be applied to detect genetically modified viruses that may be agents of bioterrorism. The substrate can be tailored into multi-well chip for high throughput screening of chemical/biological specimen, integrated into fiber tip for portable sensing, incorporated into fluid cells or microfluidic devices for in situ real-time monitoring dynamic process, or fabricated onto a flexible substrate for tracking and identification. By combining this unique SERS substrate with handheld Raman system, it can become a more practice sensor system for battle field application and portable device for public safety monitoring and security screening. With the help of independence component analysis and chromatography technique, the AgNR chip can also be used to identify and differentiate components in a mixture. All these development has demonstrated that AgNR SERS substrates could play an important role for practical sensing applications in future defense and security.
Suggested references for SERS and AgNR based SERS
A recommend review on SERS is "A Review on Surface-Enhanced Raman Scattering," in Biosensors by Roberto Pilot et al. in 2019.
A review book chapter for AgNR: Justin L. Abell, Jeremy D. Driskell, Ralph A. Tripp, and Yiping Zhao, "Current progress on surface-enhanced Raman scattering chemical/biological sensing," in "Functional Nanoparticles for Bioanalysis, Nanomedicine, and Bioelectronic Devices Volume 2" edited by Maria Hepel and Chuan-Jian Zhong, ACS Symposium Series, Vol. 1113 (American Chemical Society Publication, 2012) Chap. 10, pp. 235–272.