An Ag+ soldering strategy is developed to achieve strongly coupled nanoparticle clusters for plasmonic and surface enhanced Raman scattering applications.

Achieving highly tunable and localized surface plasmon resonance up to near infrared (NIR) regions is a key target in nanoplasmonics. In particular, a self-assembly process capable of producing highly uniform and solution-processable nanomaterials with tailor-made plasmonic properties is lacking. We herein address this problem through a conjunctive use of wet Ag soldering and dry thermal sintering to produce nanodimer-derived structures with precisely engineered charge-transfer plasmon (CTP). The sintered dimers are water soluble, featuring gradually shifted CTP spanning an 800 nm wavelength range (up to NIR II). Upon silica removal, the products are grafted by DNA to offer surface functionality. This process is also adaptable to DNA-linked AuNP dimers toward plasmonic meta-materials via DNA-guided soldering and sintering.

A novel Au dimer-based colorimetric sensor is reported that consists of Au dimers to a chitosan hydrogel film. It utilizes the ultrasensitively gapdependent properties of plasmonic coupling (PC) peak shift, which is associated with the dynamical tuning of the interparticle gap of the Au dimer driven by the volume swelling of the chitosan hydrogel film. The interparticle gap and PC peak shift of the Au dimer can be precisely and extensively controlled through the pH-driven volume change of chitosan hydrogel film. This colorimetric sensor exhibits a high optical sensitivity and stability, and it works in a completely reversible manner at high pH values. Importantly, the sensitivity of the composite film can be tuned by controlling the crosslinking time of the composite film, and thus leading to a wide dynamic tuning sensitive range for different applications. This presented strategy paves a way to achieve the construction of high-quality colorimetric sensors with ultrahigh sensitivity, stability and wide dynamic tuning sensitive range.