Direct Determination of Redox Statuses in Biological Thiols and Disulfides with Noncovalent Interactions of Poly(ionic liquid)s.

Abstract

The three most important redox couples, including cysteine (Cys)/cystine (Cyss), homocysteine (Hcys)/homocystine (Hcyss) and reduced glutathione (GSH)/glutathione disulfide (GSSG), are closely associated with human aging and many diseases. Thus, it is highly important to determine their redox statuses at the following two levels: ⅰ) the redox identity in different thiols/disulfides and ⅱ) the redox ratio in a mixture of a specific couple. Herein, by using one single AIE-doped photonic-structured poly(ionic liquid) sphere as a virtual sensor array (AIE, aggregation-induced emission), we firstly realize the direct determination of the redox status without a reducing pre-treatment of disulfides, which will greatly promote the development of high-throughput and simple procedures. The pattern-recognition method uses the multiple noncovalent interactions of imidazolium-based poly(ionic liquid)s (PILs) with these redox species to produce differential responses in both the photonic crystal and fluorescence dual channels. On the one hand, a single sphere enables the direct and simultaneous discrimination of the redox identities of Cys, Cyss, Hcys, Hcyss, GSH and GSSG under the interference of other five commonly occurring thiols. On the other hand, this sphere also allows for not only the direct quantification of the GSH/GSSG ratios without previously determining the individual concentrations of GSH and GSSG, but also the accurate prediction of the ratios in unknown redox samples. To further demonstrate the real-life applications, redox mixtures in a real biological context are differentiated. Additionally, quantum calculations further confirm the interactions between the imidazolium-based PILs and these redox species.