Quantitative SERS by electromagnetic enhancement normalization with carbon nanotube as an internal standard

Quantitative surface-enhanced Raman scattering (SERS) in practical applications still remain unresolved, mainly due to low reproducibility relying on the quality of the SERS substrates. In this paper, a carbon nanotube and Ag nanoparticles composite (CNT/AgNPs) is reported, and the carbon nanotube is as an internal standard for the calibration of SERS intensity of analyte molecules. The quantification of analyte molecules rhodamine 6G (R6G) is demonstrated in an aqueous solution with the concentration of 10-9 to 10-7 M. Raman mapping is used to investigate the stability of SERS spectra in a large scanning area, and the corresponding relative standard deviation (RSD) is calculated. SERS mapping reveals that the uniformity of Raman enhancement is improved through the build-in calibration with 2D Raman peak of CNT. Meanwhile, CNT/AgNPs samples are used to detect N2 in natural air, indicating that such self-calibration method can improve the reliability of the SERS analysis.