Gold nanoparticle decorated Au-Ag alloy tubes: A bifunctional substrate for label-free and in situ surface-enhanced Raman scattering based reaction monitoring

Abstract

A quantitative monitoring of a heterogeneously catalyzed reaction based on surface-enhanced Raman scattering (SERS) requires fabrication of a bifunctional substrate with exposed SERS and catalytic sites. Fabrication of such dual-functional substrates is challenging, owing to the different size limits of metal nanoparticles set by both SERS and catalysis. Larger-sized nanoparticles are suitable for SERS, whereas catalysis requires smaller particles, hence, the integration of both features into a single nanostructured material can be demanding. In this study, we report access to simple fabrication of a bifunctional nanostructure based on gold nanoparticle decorated Au-Ag tubes (Au@Au-AgTs) having both SERS and catalytic features. A facile approach using polymer linkages facilitated the immobilization of catalytically active gold nanoparticles on Au-AgTs. The decoration process involves a simple mixing of polyethylenimine capped gold nanoparticles with Au-Ag alloy tubes, and requires no harsh conditions or complex synthetic procedures. The synergistic effect of gold and silver metals enabled a sensitive SERS performance of Au@Au-AgTs, and the small gold nanoparticles functioned as active catalytic sites. Using the catalytic conversion of 4-nitrothiophenol to 4-aminothiophenol as a model reaction, the Au@Au-AgTs exhibited the ability to function as an active catalytic and SERS-responsive platform in quantifying the reaction kinetics.