DNA detection using nanostructured SERS substrates with Rhodamine B as Raman label

A technique is demonstrated to detect DNA hybridization at low concentrations, based on Surface-Enhanced Raman Scattering (SERS) using silicon nanostructures coated with gold–silver as substrate. Standard silicon process technologies were employed to fabricate the SERS substrates featuring nanogaps with a characteristic distance of 15 ± 10 nm. Target DNA was hybridized with cysteine-modified Peptide Nucleic Acids (PNA), which was previously fixed into the nanogaps as the capture sites. After hybridization, the introduced phosphate groups from the backbone of the target DNA showed strong affinity to an inorganic linker, Zr4+, so that resulting in the assembly substrate–PNA–DNA–Zr. Since PNA does not possess phosphate groups, the linker is avoided when there is no hybridization from the complimentary DNA. Subsequently, the assembly of substrate–PNA–DNA–Zr was incubated with a Raman label, Rhodamine B (RB). The carboxylic acid group in RB reacted with the linker Zr4+ allowing this Raman Label to be attached to the assembly substrate–PNA–DNA–Zr. The Raman peaks corresponding to RB were selected to detect the target DNA, with a detection limit of 1 × 10−12 M.