Triggering blue–red transition response in polydiacetylene vesicles: an electrochemical surface plasmon resonance method

Abstract

Electrochemical surface plasmon resonance (E-SPR) was used to investigate whether the chromic properties of a polydiacetylene (PDA) vesicle films, adsorbed onto an ultra-thin gold electrode, could be triggered by applied potential. This approach constitutes a preliminary model for a novel approach to the use of a triggered chromic transition, as an indicator of biorecognition headgroup binding in these materials. A PDA chromic blue–red transition was identified in E-SPR against the background Δε_e and Δε_m. The latter resulted in a ca. 100 mDeg V⁻¹ shift in the SPR minimum, in the presence of PDA, with the PDA shielding changes in ε_e. Electrochemical charge transfer processes in the pre-oxide/oxide anodic region with adsorbed oxygen and hydroxide, involving a change in Au redox state (Au⁰/Au⁺) were visible in the SPR, due to a change in the gold layer thickness and gold oxide layer. However, the cathodic processes, not involving a change in the Au redox state or a increase/decrease in the surface layer dielectric, did not cause a change in the SPR. Based on this, dramatic changes in the optical properties of the adsorbed PDA film could be triggered at an applied cathodic potential, and were identified using SPR. These correlated with a pH-induced chromic transition. Both protonation and ion binding, linked with headgroup environment, were implicated in causing structural transitions in the adsorbed vesicle layer that may also be linked with their bulk optical properties.