Broadband surface‐enhanced coherent anti‐Stokes Raman spectroscopy with high spectral resolution

Abstract

Both the surface‐enhanced Raman spectroscopy (SERS) and coherent anti‐Stokes Raman spectroscopy (CARS) are widely used methods in the bio‐sensing field for improving the intensity of Raman scattering process. By combining the mechanisms of CARS (coherence and nonlinear process) and SERS (plasmon resonance), a multiplicative enhancement can be achieved through surface‐enhanced CARS (SECARS). Besides sensitivity, high specificity with wide spectral bandwidth is also preferred for bio‐sensing techniques but not well developed in SECARS setups reported in the literature. In this work, a broadband SECARS setup with high sensitivity and high spectral resolution is presented. Rhodamine 6G dye molecules and several biomolecules are used as the model system to benchmark the functionality of the SECARS system in terms of its sensitivity, the lowest detectable concentration, and the spectral resolution. Our setup rendered single‐molecule sensitivity with spectral resolution of <35 cm −1 . More than 10 2 times stronger signal‐to‐noise ratio compared with that of SERS is observed with the detection limit being 10 −9 m . Different from the SECARS systems in the literature, our setup employs a unique graphene‐Au pyramids hybrid platform. The graphene in this structure provides additional SERS enhancement and a bio‐compatible surface. This powerful technique could be instrumental in furthering the understanding of various chemical and biological processes. Copyright © 2017 John Wiley & Sons, Ltd.