High-Sensitive Assay of Nucleic Acid Using Tetrahedral DNA Probes and DNA Concatamers with a Surface-Enhanced Raman Scattering/Surface Plasmon Resonance Dual-Mode Biosensor Based on a Silver Nanorod-Covered Silver Nanohole Array

A novel surface-enhanced Raman scattering/surface plasmon resonance (SERS/SPR) dual-mode biosensor prepared on a silver nanorod-covered silver nanohole (Ag NR-NH) array by surface modification of tetrahedral DNA probes is proposed for highly sensitive detecting nucleic acids by a special signal amplification strategy of DNA supersandwich. The Ag NR-NH with a large area and uniformly arrayed nanostructure possesses excellent anisotropic extraordinary optical transmission and strong localized surface plasmon resonance, which lead to sensitive SPR response to the change of a local refractive index and strong localized electric fields for excellent SERS activity. To obtain high sensitivity and specificity, smart tetrahedral DNA probes are immobilized onto the Ag NR-NH array and the DNA supersandwich sensing strategy, including the signal amplification of DNA concatamers, is used. About 10 times signal enhancement for SPR and 4 times for SERS are achieved by this sensing strategy. In the detection of the target DNA in the human serum, the two sensing modes have complementary performances, i.e., the limit of detection for the SPR array is high (0.51 pM), while for SERS, it is low (0.77 fM), but the specificity for SPR is much higher than that of SERS. This improves the robustness of the DNA sensors, and subsequent recovery tests also confirm good reliability of the biosensor. The proposed SERS/SPR dual-mode biosensor has a great potential for high performance and reliable detection of trace disease-related nucleic acid biomarkers in the serum and is a powerful sensing platform for early-stage disease diagnosis.