Amplification of SERS “hot spots” by silica clustering in a silver-nanoparticle/nanocrystalline-cellulose sensor applied in malachite green detection

Add time:07/21/2019    Source:sciencedirect.com

Nanocrystalline cellulose (NCC) was used as a dual reducing- and stabilizing agent in the production of silver nanoparticles (AgNPs), and addition of Stӧber silica (SiO2) provided an efficient support. The silica was prepared by a sol-gel method, the added NCC confined the AgNPs and added stability. The formed AgNPs/SiO2/NCC nanocomposite was evaluated as a substrate for surface-enhanced Raman scattering (SERS) of the fungicide and pesticide malachite green (MG) and the results were compared with the corresponding silica-free AgNPs/NCC material. A UV–vis peak for AgNPs/SiO2/NCC was broad with a shoulder at 490 nm, which we ascribe to the phenomena of plasmonic nanoparticle clustering. TEM micrographs showed that the plasmonic nanoparticles were monodispersed with a mean diameter of 19.5 nm in AgNPs/NCC while they aggregated into clusters on SiO2 in AgNPs/SiO2/NCC resulting in approximately 20 nm increase in mean diameter of the SiO2. The SERS performance of the composite material was evaluated by using MG as a probe and showed AgNPs/SiO2/NCC as a superior sensory substrate due to the silica clustering which is directly related to an increased formation “hot spot” zones leading to a significant amplification of SERS signals observed as higher intensities of Raman peaks of MG. SERS substrate of silver nanoclusters with net negative surface charge detected MG. The improved “hot spot” signal detection led to high sensitivity with a limit of detection (LOD) of 0.9 nM while AgNPs/NCC showed LOD of 5.2 nM, based on a signal to background ratio of 3:1. This result underscores the huge but under-appreciated contribution of SERS “hot spots” as AgNPs assembled into clusters in contrast to monodispersed AgNPs in the absence of SiO2.

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