A colorimetric indicator-displacement assay for cysteine sensing based on a molecule-exchange mechanism

In this study, we developed an ingenious yet effective strategy for cysteine detection. The colorimetric cysteine assay is established through an indicator displacement process, where Cu 2+ and pyrocatechol violet (PV) was employed as receptor and indicator, respectively. Proof-of-concept trials demonstrated that the stronger binding affinity of Cu 2+ receptor toward cysteine than PV indicator endowed our colorimetric sensor with high selectivity and excellent sensitivity as well as with a lower detection limit (4.60   μM and 120   µM, S/N =3) by UV–visible spectroscopy and the naked eye as the signal readout, respectively. More importantly, the proposed molecule-exchange process in the indicator displacement process could be successfully used to the fabrication of a colorimetric INHIBIT logic gate and even converted into a facile naked eye analysis through paper-based analytical devices for conveniently and reliably detecting cysteine (CySH) in practical applications.