DNA Detection Based on Localized Surface Plasmon Resonance Spectroscopy of Ag@Au Biocomposite Nanoparticles

Noble metal nanoparticles (NPs) have attracted much attention due to their unique physical and chemical properties such as tunable surface plasmonics, high-efficiency electrochemical sensing, and enhanced fluorescence. We produced two biosensor chips consisting of Ag@Au bimetallic nanoparticles (BNPs) on a carbon thin film by simple RF-sputtering and RF-plasmaenhanced chemical vapor co-deposition. We deposited Au NPs with average size of 4 nm (Au-1 NPs) or 11 nm (Au-2 NPs) on a sensor chip consisting of Ag NPs with mean size of 15 nm, and we investigated the effect of shell size (Au NPs) on the chemical activities of the resulting Ag@Au-1 BNPs and Ag@Au-2 BNPs. We estimated the average size and morphology of Ag@Au BNPs by scanning electron microscopy (SEM) and atomic force microscopy (AFM) images. X-ray diffraction (XRD) patterns revealed that Ag NPs and Au NPs had face-centered cubic (FCC) structure. We studied aging of the biosensor chips consisting of Ag@Au BNPs by localized surface plasmon resonance (LSPR) spectroscopy for up to 3 months. UV-visible aging of the prepared samples indicated that Ag@Au1 BNPs, which corresponded to Ag NPs covered with smaller Au NPs, were more chemically active than Ag@Au-2 BNPs. Furthermore, we evaluated changes in the LSPR absorption peaks of Ag@Au-1 BNPs and bare Ag NPs in the presence of a DNA primer decamer at fM concentrations, to find that Ag@Au-1 BNPs were more sensitive biosensor chips within a short response time as compared to bare Ag NPs.