Recent research demonstrates that SERS substrate modifies analyte Raman signal through two competitive mechanisms: SERS enhancement and substrate inner filter effect, not SERS enhancement alone as commonly believed.  Using combination of time-resolved Raman spectroscopy and solvent internal reference method, reported herein is quantitative determination of SERS EFs of mercaptobenzimidazole (MBI), a model organothiol adsorbed onto AuNPs and AgNPs.  The peak MBI SERS EF depends only on the types and sizes of nanoparticles, but not on other experimental conditions we explored (analyte and AuNP concentrations, and the type and concentrations of the electrolytic aggregation agents (KF, KCl, KBr, and K2SO4)).  The experimental peak SERS EFs of MBI on AuNPs and AgNPs with sizes of 30 and 50 nm can be fully explained with electromagnetic mechanism alone.   This result, in combination of our recent finding that a series of highly structurally organothiols have similar SERS EFs, argue strongly against the possibility of strong chemical enhancement (>10 times, for example) for organothiol adsorbed onto colloidal AuNP and AgNP.

Robust and reproducible quantification of SERS enhancement factors using combination of time-resolved Raman spectroscopy and solvent internal reference

245th National Meeting (2013)

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