Dynamically Tunable Plasmonic Band for Reversible Colorimetric Sensors and Surface-Enhanced Raman Scattering Effect with Good Sensitivity and Stability

Abstract

Colorimetric sensor based on plasmonic nanoparticles (NPs) is a promising and convenient detection tool, but its reproducibility and adjustability remain a challenge because the NPs are mainly random and uncontrollable. Herein, a colorimetric sensor with good reversibility and reproducibility was prepared by embedding the two-dimension (2D) Au NP arrays on the surface of the polyacrylamide (PAAm) hydrogel film to form 2D Au NP arrays attached hydrogel composite. For this composite, with the change of the interspacing distance of Au NPs driven by swelling-shrinking behavior of the hydrogel carrier, the diffraction peaks faded away and plasmonic coupling (PC) peaks appeared, and accompanied by a series of obvious color change (iridescence ↔ violet ↔ golden yellow ↔ red), which can be correlated to the applied water content. Importantly, the composite had good reproducibility due to highly ordered array structure. Additionally, this colorimetric sensor with dynamically tunable plasmonic band can be used as a high-quality SERS substrate because the gap distance of the Au NPs can be uniformly controlled. We demonstrated that as the active gap distance decreased, the SERS signals can be significantly intensified. When the water content reached to 40%, this SERS substrate exhibited high sensitivity (10-10M for 4-aminothiophenol (4-ATP) and 10-9M for thiram) and good reproducibility (RSD < 20%) using the excitation laser of 785 nm because of small gap between two adjacent Au NPs and the highly ordered periodic structure. Such 2D Au NP arrays attached hydrogel composite could be a new strategy to obtain high-quality colorimetric sensor and dynamic SERS substrate.