Silver shelled gold nanorods for sensitive detection of cholesterol and triglycerides

We report the synthesis of bimetallic plasmonic nanostructure of silver shelled gold nanorods (Ag-Au NRs), subsequently employed for the selective detection of cholesterol (Cho) and triglycerides (TGl) utilizing Surface Enhanced Raman Spectroscopy (SERS). In this direction, the gold nanorods (Au NRs) were synthesized via seed mediated growth method followed by forming a silver shell with reduction of AgNO₃ onto Au NRs. Ag-Au NRs showed significantly augmented SERS property owing to hybridization of Localized Surface Plasmon Resonances (LSPR) of silver and gold. The enhanced plasmonic property was thus employed for biosensing. For this, two different Raman reporter molecules, 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) and 4-aminothiophenol (4ATP) were immobilized separately on Ag-Au NRs to synthesize SERS active nanoprobes, before the attachment of the bioreceptors - cholesterol oxidase (ChOx) and lipase (Lp) to form ChOx-DTNB-Ag-Au NRs and Lp-4ATP-Ag-Au NRs. These nanoprobes were then utilized for the quantification of Cho and TGl via liquid mode Raman spectroscopic study. The change in SERS spectral intensity of DTNB and 4ATP were systematically recorded in reference to the baseline sample to mark the calibration for both Cho and TGl. Additionally, interference studies considering effects of ascorbic acid, glucose, sodium and potassium ion were performed to unveil excellent selectivity of the proposed method.