A promising on-off Chemosensor Based on Manganese(II) Complex of a Xanthene Ligand as an Easily Commercially Available Dye for the Detection of Cysteine in Biological Samples

A novel colorimetric chemosensor for naked-eye detection and determination of Mn2+ and cysteine (Cys) based on indicator displacement assay (IDA) was designed using bromo pyrogallol red (BPR). The indicator exchange occurred between BPR and Cys by the addition of Cys to the Mn(BPR) complex, which is accomplished by an immediate visible color change from purple to magenta, in EtOH/HEPES buffer 10.0 mmol L-1, pH 9.3 (1:4 v/v). The proposed method exhibits a 0.02 μmol L−1 detection limit and good linearity in the range of 0.11–2.87 μmol L−1 for cysteine amino acid. Additionally, the absorption and color change obtained in this chemosensor operate as an “IMPLICATION” logic gate considering Mn2+ and Cys as inputs. Eventually, based on such a fast, reversible, and reproducible signal, a molecular-scale sequential memory unit was designed to display “keypad lock” behavior. The developed chemosensor presented satisfactory repeatability, good precision, and successful application for the selective determination of Cys in human biological fluids. Furthermore, the method s accuracy was evaluated by comparing the results obtained from the proposed method and those from the reference method.