Ultrasensitive surface‐enhanced Raman spectroscopy detection of explosive molecules with multibranched silver nanostructures

Abstract

AbstractMultibranched silver nanostructures (AgNSts) have attracted much attention as promising candidates for surface‐enhanced Raman spectroscopy (SERS) due to their unique plasmonic properties. We have chemically synthesized silver nanodendrites (AgNDs) and silver stars (AgSs) and investigated their SERS performance for trace‐level molecule detection. High enhancement factor (EF) ~1010 and attomolar detection limits were obtained with multibranched nanostructure‐based SERS substrates for methylene blue, thiram, and phosmet. The confinement of the local fields at the sharp tips and in the intrabranch and interbranch nanogaps of AgNDs offer highly dense three‐dimensional (3D) SERS “hot spots” and large signal enhancements of ~109. Further, the as‐prepared AgND‐based substrates were utilized for the ultrasensitive identification of explosive molecules 2,4‐DNT, PNBA, and PA with limit‐of‐detection (LOD) down to ~5.3 × 10−16, 2.9 × 10−16, and 3.8 × 10−12 M concentrations, respectively. The spectral modifications and appearance of new SERS peaks in the low wavenumber region indicate the metal–molecule complex formation and confirm the contribution of the chemical enhancement mechanism. The narrow spectral widths of Raman peaks allow the highly selective multiplexed detection of explosive molecules from the two‐component (2‐plex) mixture of dyes with different concentrations. Further, the density functional theory (DFT)‐based Raman spectrum calculations of the molecules exhibit a reasonably good correspondence with the experimental results. Therefore, the molecularly specific and distinguishably sharp Raman features enable the ultrasensitive and multiplexed detection of analytes molecules with our AgNSt‐based SERS substrates.