Carbon dots with red emission as a fluorescent and colorimeteric dual-readout probe for the detection of chromium(vi) and cysteine and its logic gate operation.

A novel visual probe with red fluorescent carbon dots (CDs) has been facilely fabricated for the sequential detection of chromium(vi) [Cr(vi)] and cysteine (Cys) via a fluorescent and colorimetric double-mode readout assay. The as-prepared CDs exhibit not only exceedingly optical stability, but also excellent biocompatibility and biolabeling potentials. The fluorescence of the CDs can be extinguished dramatically with Cr(vi). After the addition of Cys, the fluorescence of the CDs was restored due to the complexation between Cr(vi) and Cys that leads Cr(vi) to escape from the surface of CDs. The probe displayed high selectivity and sensitivity toward Cr(vi) and Cys over other analytes with a low detection limit of 0.26 μM and 0.14 μM, respectively. Simultaneously, the color of the CDs solution was changed (red-purple-yellow) along with the fluorescence signal of the CDs, and the CDs can be used as a dual response signal sensor. Based on the above results, an "AND" logic gate for red-emitting CDs has been constructed. Moreover, to the best of our knowledge, it is the first red-emissive carbon dots for chromium(vi) and cysteine assays. The probe was extended to cellular imaging. Based on the simplicity, time-saving, and cost-effectiveness of the constructed program, this probe shows great potential in biosensing, bioimaging, and environmental monitoring.