Colorimetric Pressure Sensing by Plasmonic Decoupling of Silver Nanoparticles Confined within Polymeric Nanoshells.

Employing a plasmonic decoupling mechanism, we report the design of a colorimetric pressure sensor that can respond to applied pressure with instant color changes. The sensor consists of a thin film of stacked uniform resorcinol-formaldehyde nanoshells with their inner surfaces functionalized with silver nanoparticles. Upon compression, the flexible polymer nanoshells expand laterally, inducing plasmonic decoupling between neighboring silver nanoparticles and a subsequent blue-shift. The initial color of the sensor is determined by the extent of plasmonic coupling, which can be controlled by tuning the interparticle distance through a seeded growth process. The sensing range can be conveniently customized by controlling the polymer shell thickness or incorporating hybrid nanoshells into various polymer matrices. The new colorimetric pressure sensors are easy to fabricate and highly versatile, allow for convenient tuning of the sensing range, and feature significant color shifts, holding great promise for a wide range of practical applications.

Reversible Modulation of Plasmonic Coupling of Gold Nanoparticles Confined within Swellable Polymer Colloidal Spheres.

Dynamic optical modulation in response to stimuli provides exciting opportunities for designing novel sensing, actuating, and authentication devices. Here, we demonstrate that the reversible swelling and deswelling of crosslinked polymer colloidal spheres in response to pH and temperature changes can be utilized to drive the assembly and disassembly of the embedded gold nanoparticles (AuNPs), inducing their plasmonic coupling and decoupling and, correspondingly, color changes. The multi-responsive colloids are created by depositing a monolayer of AuNPs on the surface of resorcinol-formaldehyde (RF) nanospheres, then overcoating them with an additional RF layer, followed by a seeded growth process to enlarge the AuNPs and reduce their interparticle separation to induce significant plasmonic coupling. This configuration facilitates dynamic modulation of plasmonic coupling through the reversible swelling/deswelling of the polymer spheres in response to pH and temperature changes. The rapid and repeatable transitions between coupled and decoupled plasmonic states of AuNPs enable reversible color switching when the polymer spheres are in colloidal form or embedded in hydrogel substrates. Furthermore, leveraging the photothermal effect and stimuli-responsive plasmonic coupling of the embedded AuNPs enables the construction of hybrid hydrogel films featuring switchable anticounterfeiting patterns, showcasing the versatility and potential of this multi-stimuli-responsive plasmonic system.

Synthesis, Optical Properties, and Applications of Luminescent Benzothiazole: Base Promoted Intramolecular C-S Bond Formation.

A novel base-catalyzed method for the synthesis of luminescent benzothiazole derivatives had been developed under metal-free conditions via C-S bond formation, which provided an efficient, convenient, and mild alternative method for constructing substituted benzothiazoles. As-prepared benzothiazole derivatives thus produced emissions in solution with quantum yield up to 85%. In addition, they still exhibited fairly strong fluorescence in the solid state. Furthermore, the compounds were used as a facile "On-Off" fluorescence probe to create handy test strips for detecting NaClO by naked eyes.