Alginate Gel-Mediated Photochemical Growth of Mono- and Bimetallic Gold and Silver Nanoclusters and Their Application to Surface-Enhanced Raman Scattering

摘要

Polysaccharide alginate gel beads have been used as a template for photochemical growth of monometallic and bimetallic Au and Ag manoclusters. The gel served both as a reductant under photoirradiation and as a stabilizer. Fourier transform infrared (FTIR) analysis indicated that the secondary hydroxyl function reduced the Au(m) and Ag(I) to their metallic state with the concomitant oxidation of the hydroxyl function to carbonyl group. X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), energy-dispersive X-ray spectrometry (EDX) analyses were used to characterize nanoparticle structure, size, and morphology. The effectiveness of this alginate gel-stabilized nanoparticles as substrate toward surface-enhanced Raman scattering (SERS) detection was evaluated by use of two probes, 2-aminothiophenol and 1,10-phenanthroline. Intensity of SERS signals was a function of analyte adsorption as evidenced from UV-visible absorption spectroscopy. Among all the substrates, alginate-stabilized Au has been found to be the best for SERS detection. The enhancement factors are in the range of 104 and the detection limits are in the subpicogram level.