An effective real-time colorimeteric sensor for sensitive and selective detection of cysteine under physiological conditions

In this contribution, a new, real-time and sensitive colorimetric sensor, di-N-methyl-N-hydroxyethylaniline squaraine (SQ), has been identified and synthesized for cysteine analysis based on its Delta A in neutral aqueous medium (pH approximate to 7.5). The proposed method was applied to analyse synthetic amino acid samples and human serum samples. The results show that the linear range of cysteine detection in aqueous medium at pH approximate to 7.5 is 10 similar to 700 nmol L(-1) with a correlation coefficient (R) of 0.9984 and a limit of detection (3 sigma, n = 20) of 3.9 nmol L(-1). The relative standard deviation (RSD) for cysteine detection was lower than 4.1% (n = 5). The proposed method possesses the advantages of simplicity, rapidity, high selectivity and sensitivity. This makes it possible, for the first time, the real-time detection of cysteine under normal physiological conditions.