Sensitive detection of alkyne-terminated hydrophobic drug by surface-enhanced stimulated Raman scattering in cetyltrimethylammonium bromide-coated gold nanorod suspensions

We demonstrate the sensitive detection of alkyne-terminated ethinylestradiol (EE2) in a cetyltrimethylammonium bromide (CTAB)-coated gold nanorod (AuNR) suspension by surface-enhanced stimulated Raman scattering (SRS). Since alkynes show a distinct Raman peak at the silent wavenumber region, EE2 can be detected by obtaining the alkyne-specific SRS signals. Here we find the CTAB coating uniformly adsorbs the hydrophobic EE2 and enables it to exist in the plasmonic hotspot of AuNRs without the alkyne binding to AuNR surfaces. As a result, ensemble-averaged plasmonic enhancement using a CTAB-coated AuNR suspension improved the detection limit for SRS signals from EE2 by one order of magnitude.