Single molecule detection of 4-dimethylaminoazobenzene by surface-enhanced Raman spectroscopy

4-Dimethylaminoazobenzene (DAB) is anticipated to be a human carcinogen based on sufficient evidence of carcinogenicity in experimental animals. The trace detection of DAB is of great significance in environmental protection and safe life of the people. To test the availability of DAB trace detection using surface-enhanced Raman scattering (SERS), the SERS spectra of DAB single molecules adsorbed on the silver particle aggregates in colloid were investigated. The phenomena of blinking, spectral diffusion, and intensity fluctuations of the vibrational lines in the SERS spectra were observed. Statistical analysis of spectral intensity fluctuations indicates a multimodal distribution of some specific Raman bands, which are consistent with the identification of single molecule detection. Our results demonstrated that SERS can be applied to the trace detection of DAB molecules and other azo dyes.