Surface-enhanced Raman-scattering biosensor on nanoparticle island substrates for DNA detection

Summary form only given. This work presents a systematic study of the surface-enhanced Raman-scattering (SERS) properties of nanoparticle island substrates (NIS) and their application for oligonucleotide target detection. Using NIS that are structurally well characterized by atomic force microscopy (AFM) and UV-VIS extinction spectrum, it demonstrates the correlation of nanostructure of substrates and extinction maximum (¿_max) of substrates fabricated on different conditions, i.e. thickness of metal Ag. To effectively implement SERS on NIS and find out optimal condition for DNA detection, the relationship between extinction maximum (¿_max) and SERS enhancement factor (EF) was explored in detail. In fact, this work demonstrates high S/N ratio SERS spectra can be achieved for NIS with ¿_max within a spectrum window (~60 nm) consisting by the excitation wavelength (514 nm) and the scattered Raman wavelength, and highest EF measured is about 4 × 10⁸ with thickness of Ag being 50 A. Detection of oligonucleotide target has been performed with a sandwich assay scheme. In this scheme a layer of thiol modified receptor oligonucleotide was assembled on NIS and 3´ of oligonucleotide probe has been labeled with a Raman-active dye. Furthermore, We compared the detection performance of strategies using probe oligonucleotide with or without gold nanoparticles (Au-NPs, 20 nm) capped on 5´. The experimental results reveal that the DNA detection implemented with NIS can provide high sensitivity, and both dynamic range and diction limit can be amplified with the aid of Au-NPs on 5´ of probes. The current detection limits of NIS with and without Au-NPs are 0.4 femtomolar and 1 nanomolar respectively.