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Cellulose nanocrystals directed in-situ assembly of Au@Ag nanostructures with multifunctional activities

Bio-template-directed synthesis of shell-engineered plasmonic nano-assemblies has attracted extensive research interest due to their profound opto-electronic properties. Herein, we report TEMPO-oxidized cellulose nanocrystals (TCNC) as a promising bio-template for the in-situ preparation and assembly of Aucore-Agshell nanoparticles (Au@Ag NPs) having excellent colloidal stability with tunable optical and catalytic properties. By modulating Ag shell thickness, TCNC promoted the assembly of Au@Ag nanostructures and resulted in abundant plasmonic hotspots. Thereby as-formed TCNC payloads could enhance its solid-state SERS activity in detecting malachite green and methylene blue concentration down to 10 fM and 100 fM, respectively. The finite element modelling (FEM) studies further supported the observed results, revealing the enhanced electric field concentrates at the junction of two adjacent TCNC-Au@Ag NPs as the origin of augmentation in the SERS signals. Further, TCNC-Au@Ag NPs assemblies showed superior catalytic activity towards 4-nitrophenol reduction with a rate constant of 32.33 × 10−3 s−1.