Core–Gap–Shell Nanoparticles@Polyaniline with Tunable Plasmonic Chiroptical Activities by pH and Electric Potential Dual Modulation

Abstract

The emerging concept of tunable plasmonic chirality is mostly observed as a reconfigurable behavior or a feature of complex chiral plasmonic assemblies. For discrete colloidal particles, it is challenging to achieve reversible tunability or a transient response with regard to chiroptical activities, particularly in the visible or near-infrared region. Herein, we demonstrate a stimulus-responsive system based on chiral molecule–achiral plasmonic nanoparticles coated with polyaniline (PANI) as a variable dielectric layer, in which l-/d-cysteine molecules are introduced between the gold core and the shell as a static chiral source, allowing the chiral transfer effect to be greatly amplified by the hotspot gap of sub-monomolecular thickness. By taking advantage of the responsive properties to either pH or the electric potential dual stimuli of PANI, which also provides a stable and real-time switchable dielectric environment for the whole system, dynamic tuning of the plasmon and its induced chiroptical activities of core–gap–shell nanoparticles@PANI were precisely obtained. This well-defined design provides an open platform for flexible and rational tailoring of plasmonic cores, chiral molecules, and variable dielectrics to chiroptical needs, which is important for realizing applications in chemical sensing, chiral nanocatalysis, enantioselective separations, and novel optical devices.

Chiral Au Nanorods: Synthesis, Chirality Origin, and Applications

“…In fact, chiroptical activities of dc-Au NRs are not only contributed by the near-field electromagnetic field within the nanogap or nanocavity but also due to the twisted structural effect . Following that, several groups have extended the dc-Au NRs with other functionalities by coating semiconductors or sensitive polymers . Wang and co-workers produced a complex alloy of 3M dc-AuCuAu NRs through three-steps of seed-mediated approaches.…”

“…Copyright 2016, American Chemical Society. (e) Schematic illustrations of dielectric sensing of chiral plasmonic sensors . Panel (e) image was reproduced with permission from ref .…”

“…(e) Schematic illustrations of dielectric sensing of chiral plasmonic sensors . Panel (e) image was reproduced with permission from ref . Copyright 2022 American Chemical Society.…”

“…Similar to the modulation of pH response, the state of PANI changed from the emeraldine salt to leucoemeraldine base when the potential decreased from 0.4 V to −0.3 V, leading to the TSPR-CD being redshifted from 602 to 616 nm (Figure 6e). 162 Chiral mesoporous silica (CMS) materials show chiroptical activities, and they are synthesized in the presence of chiral surfactants, which can be used as enantioselective molecular sieve. 103,129,195,196 The PCD peaks in the visible and NIR region show a good mirror due to the strong coupling of chiral surfactants and SPR of gold NRs.…”

“…161 Following that, several groups have extended the dc-Au NRs with other functionalities by coating semiconductors or sensitive polymers. 162 Wang and coworkers produced a complex alloy of 3M dc-AuCuAu NRs through three-steps of seed-mediated approaches. Initially, AuCu heterodimers were fabricated when Au NRs were used as primary seeds in the absence of chiral stimuli.…”