Thermoresponsive chiral plasmonic nanoparticles

Chiral metallic nanoparticles can exhibit novel plasmonic circular dichroism (PCD) in the ultraviolet and visible range of the electromagnetic spectrum. Here, we investigate how thermoresponsive dielectric nanoenvironments will influence such PCD responses through poly(N-isopropylacrylamide) (PNIPAM) modified chiral gold nanorods (AuNRs). We observed the temperature-dependent chiral plasmonic responses distinctly from unmodified counterparts. As for the modified systems, the PCD peaks for both l-AuNRs and d-AuNRs at 50 degrees C red shifted simultaneously with enhanced intensities compared to the results at 20 degrees C. In contrast, the unmodified l-AuNRs and d-AuNRs exhibited no peak shift with reduced intensities. Subsequent simulation and experimental studies demonstrated that the enhanced PCD was attributed to PNIPAM chain collapse causing the increase of the refractive index by expelling minute water out of the corona surrounding chiral plasmonic AuNRs. Notably, such thermoresponsive chiral plasmonic responses are reversible, general, and extendable to other types of chiral plasmonic nanoparticles.

Automated summary

This study investigates the thermoresponsive chiral plasmonic responses of PNIPAM-modified gold nanorods. The modified nanorods exhibit red shifts and enhanced intensities of plasmonic circular dichroism (PCD) peaks at 50 degrees C, while the unmodified ones show no peak shifts and reduced intensities. The enhanced PCD is attributed to the collapse of PNIPAM chains, resulting in the expulsion of water molecules surrounding the chiral plasmonic nanorods and an increase in refractive index. These thermoresponsive chiral plasmonic responses are reversible, general, and applicable to other types of chiral plasmonic nanoparticles.