Construction of Homochiral Covalent Organic Frameworks as Enantioselective Probes for Homogeneous Photoelectrochemical-Red–Green–Blue Dual-Mode Selective Sensing of <scp>d</scp> -Cysteine

Abstract

Cysteine (Cys) serves as a fundamental building block for protein synthesis and drug development. Due to that l -Cys plays a crucial role in neurological function and cellular detoxification, whereas d -Cys exhibits notable cytotoxicity and health risks, and the rapid and selective assay of d -Cys in l -Cys-related pharmaceuticals is critically important. Here, a multifunctional chiral recognition probe was synthesized to achieve photoelectrochemical (PEC) and red–green–blue (RGB) colorimetric dual-mode selective detection of d -Cys in the presence of l -Cys. Through thiol-ene click chemistry, a d -Cys modified covalent organic framework ( d -COF) was synthesized with abundant chiral recognition sites. Driven by homochiral interactions, d -COF exhibits a significantly stronger adsorption affinity for d -Cys than l -Cys. The adsorbed Cys acts as an electron donor to enhance the photocurrent of d -COF, yielding a high chiral recognition efficiency of Δ I D /Δ I L = 12.0 in PEC mode. Furthermore, the strongly adsorbed d -Cys protonates the imine bonds in d -COF via its carboxyl and thiol groups, inducing a distinct color change from dark yellow to red, whereas l -Cys adsorption causes negligible color change due to the weak interaction between d -COF and l -Cys. Thus, based on the obvious difference in photocurrent and color changes of d -COF adsorbed with d -Cys and l -Cys, selective detection of d -Cys through PEC-RGB dual-mode sensing platform is achieved in the presence of l -Cys. This work demonstrates a PEC-RGB dual-mode sensing platform for selective detection of d -Cys and a generalizable strategy that can be extended to other chiral substance assays by changing the chiral selector, showing promising potential in chiral drug identification and biomedical detection.

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