Multiplexed SERS detection of DNA targets in a sandwich-hybridization assay using SERS-encoded core–shell nanospheres

In this study, a class of surface enhanced Raman spectroscopy (SERS) encoded core–shell nanospheres was synthesized as nano-SERS-tags for detecting specific DNA targets based on the sandwich hybridization assays. These core–shell nanospheres were synthesized by first depositing a layer of Ag-NPs (nanoparticles) onto the poly(styrene-co-acrylic acid) core and then the formation of a layer of uniform silica as the outer shell. The Ag-NPs served as SERS substrates with Raman active molecular probes adsorbed onto the Ag-NPs as indicative SERS molecular barcodes, and the silica coating shell was used for protecting the Ag-NPs and the Raman molecules from the exterior chemical and biological interference. The silica surfaces of nano-SERS-tags were further conjugated with probe DNA (pDNA) (nano-SERS-probes). The detection of single-stranded oligonucleotide (ssDNA) targets was successfully accomplished using the nano-SERS-probes in a chip-based sandwich hybridization assay in a mixed ssDNA target solution. The as-prepared nano-SERS-probes exhibited high chemical stability during the laser SERS experiments and the results were reproducible after a long-term storage. At least four different tags (a four “color” system) were quantitatively differentiated when simultaneously applied in the assays, indicating an excellent multiplexing potential of the method. Therefore, the as-prepared nano-SERS-probes are suitable for high specific detection of biomolecules with high sensitivity and remarkable multiplexing capability associated with the SERS method.