Quantitative analysis of multiplex-components and double stranded DNA by wide-range surface-enhanced Raman spectroscopy based on ordered Ag/Si nanowire arrays
Quantitative analysis by metal-nanoparticle surfaces enhanced Raman spectroscopy (SERS) systems is usually associated with complicated complementary techniques, such as microfluidics, internal standards and multivariate analysis, due to the poor signal reproducibility originating from narrow inter-particle nanogaps as hot spots. In this work, we report on direct and quantitative multiplex detection on a SERS substrate made of an ordered silver film-coated silicon nanowire (Ag/SiNW) array. Compared with the nanogap-based SERS substrate, the Ag/SiNWs are hexagonally packed with an inter-wire distance of 150 nm, and the whole surface of the silver film functions as an active site with a wide-ranging enhancing field, which make the substrates capable of detecting multiplex components and large molecules with much improved spot-to-spot reproducibility over the substrate. Quantitative measurements of a single component yields a coefficient of determination (R2) of over 0.99, while univariate calibration of two interfering components yield an R2 above 0.96. Significantly, univariate calibration of double stranded DNA yields an R2 of 0.994. The excellent reproducibility of our SERS substrate highly simplifies quantitative multiplex detection and thus exhibits great potential for practical sensing applications, especially for multiplex detection as well as for the detection of large bio-molecules.