Two-in-One Dual-Channel Boronic Ester Block Copolymer for the Colorimetric Detection of Cysteine and Glucose at Neutral pH

Developing a chemosensor to recognize more than one biologically important molecule from a single polymeric entity is essential. In this study, a block copolymer probe [PPBA-b-PDMA (P1)] of (2-phenylboronic esters-1,3-dioxane-5-ethyl) methyl acrylate (PBA) and N,N′-dimethylacrylamide (DMA) was synthesized by reversible addition–fragmentation chain transfer polymerization using a cysteine-detectable aldehyde-functionalized azobenzene chain transfer agent. P1 was self-assembled in water to form micelles at neutral pH. The colorimetric detection was not observed upon adding cysteine to the micellar solution since water-soluble cysteine could not reach the aldehyde group of the azo receptor hidden in the micelles' center. However, with the introduction of glucose, micelles became swollen since the PPBA block changed its behavior to hydrophilic by transforming a boronic ester to boronic acid. Thus, the azo receptor became exposed to cysteine, leading to the colorimetric detection of cysteine. Glucose detection was also demonstrated by titrating P1 solution with glucose at a fixed amount of cysteine. Therefore, a unique platform with a dual-detection capacity of cysteine and glucose is proposed.