An ultrasensitive chemosensor based on Pb(II) complex of a xanthene ligand as an easily commercially available dye for the detection of cysteine in biological samples

In this study, an ultra-sensitive colorimetric chemosensor was designed and built for the identification and determination of Pb²⁺ and cysteine (Cys) by optical color variation based on indicator displacement evaluation (IDA) using xanthine, bromopyrogallol red (BPR) dye. Label exchange between BPR and Cys occurred when Cys was added to the lead(II) complex (BPR), resulting in a clear and immediate color variation from red to purple in a DMSO/MES buffer (10.0 mmol/L, pH 5.5 (1:4 v/v)). The suggested method shows a detection limit of 5.0 nmol/L and a good linear range of 0.04–4.71 μmol/L for cysteine. Moreover, based on the produced absorbance and color variation, this chemosensor is suggested as an “IMPLICATION” logic gate discussing Pb²⁺ and cysteine as input. As an application in molecular devices, based on such a fast and repeatable signal, a molecular-scale sequential memory unit has been designed to exhibit “keypad lock” behavior. The expanded receptor provides satisfactory reproducibility, good precision, and is used for selective determination of Cys in human blood plasma and urine. In addition, the procedure's precision was compared with the results of the suggested procedure with the HPLC method.