Seleno-BODIPY as a fluorescent sensor for differential and highly selective detection of Cysteine and Glutathione for bioimaging in HeLa cells

Abstract

Biothiols like cysteine and glutathione are involved in maintaining redox balance in living organisms and perform essential functions in pathological and physiological processes. Depending on the concentration they can be regarded as biomarkers for oxidative stress and be associated with diseases such as cancer, immune dysfunctions, among others. Herein, we report a synthetic route for a Seleno-BODIPY to act as a fluorescent probe by reaction with biological thiols in living cells. The probe presented high selectivity for biothiols between 26 analytes of biological interest. Distinct responses for Cys and GSH by colorimetric and fluorometric analysis in a turn-on fluorescent process were observed, with low detection limits (61.18 nM for Cys; 1.66 μM for GSH), ratiometric response by absorption for Cys, high fluorescence quantum yield after reaction (88.1 % for Cys and 31.8 % for GSH), high sensitivity, and fast response time for Cys. A mechanistic investigation was conducted, using N-ethylmaleimide as a thiol trapper. This strategy allowed us to conclude that the reaction between BODIPY and Cys gave an amino-BODIPY while the analogous reaction with GSH results in a thio-BODIPY with different spectral shifts, making possible the distinction and quantification of both analytes by fluorescence. Kinetic studies demonstrated that the reaction with Cys is much faster than with GSH, allowing them to be differentiated. A pH study showed that the probe behaves well at a physiological pH range (6.2–8.0). Finally, the Se-BODIPY was successfully used to detect biothiols in HeLa cells, demonstrating the sensor applicability in real systems, presenting high potential for both diagnostics and analytical (bio)chemistry areas.