New Insights into Surface-Enhanced Raman Spectroscopy Label-Free Detection of DNA on Ag°/TiO₂ Substrate

Abstract

Four DNA polybases (polyA, polyC, polyG, and polyT), modified or not with an external NH2 group, have been immobilized on an original, robust, and low-cost Ag°/TiO2 surface-enhanced Raman spectroscopy (SERS) platform. The latter was elaborated through an optimized chemically assisted photocatalytic reduction process. The label-free SERS detection of these polybases has been performed, and the analysis of SERS spectra has been supported by X-ray photoelectron spectroscopy measurements. The high-resolution and signal/noise ratio of SERS spectra enabled us to clearly index the main and secondary Raman lines of all types of studied polybases and to propose some aspects of the polybase immobilization mechanism. Regardless of polybase type and presence or absence of NH2 modification, an optimum detection is obtained for polybase concentrations lying in the 5–10 μM range, which gives rise to reproducible SERS spectra. This behavior has been interpreted in terms of distribution, orientation, and packing density of immobilized molecules.