Two different behaviors in 4-ABT and 4,4′-DMAB surface enhanced Raman spectroscopy

In surface enhanced Raman scattering (SERS) community, the origin of b₂-type bands of 4-aminobenenethiol (4-ABT) has been controversial until now, and the debate has positively contributed deeper understanding of SERS enhancement mechanism. Here, I report two experimental results to support chemical enhancement mechanism regarding origin of b₂-type bands in 4-ABT SERS. At first, I compared the peak growth phenomena between 4-ABT and 4,4-dimercaptoazobenzene (4,4′-DMAB) SERS. After making that no b₂-type bands were exhibited in SERS spectra both at 4-ABT and 4,4′-DMAB sides by treating strong reductant reagent like borohydride or applying strong negative electrochemical potential, 4-ABT side shows clear b₂-type peak growth with laser irradiation, while 4,4′-DMAB side does not show any peak growth even with weak laser power, rather just shows abrupt peak appearance regardless of laser power. Secondly, amide coupling reagent was used to discriminate the property between 4-ABT and 4,4′-DMAB. When the reagent was flowed over 4-ABT and 4,4′-DMAB, of which their SERS fingerprints seem totally same because of laser irradiation, only the spectrum of 4-ABT changes after the treatment. The results verify that the amine group in 4-ABT still exists (not transformed to azo-compound), while strong b₂-type bands were exhibited, which supports that b₂-type bands in 4-ABT have no relationship with azo-compound (4,4′-DMAB).