A visual and reversible nanoprobe for rapid and on-site determination of hexavalent chromium and lysine based on dual-emission carbon quantum dots coupled with smartphone

A straightforward, largely instrument-free, smartphone-based analytical strategy for hexavalent chromium and lysine (Lys) on-site detection via exploitation of dual-emission carbon quantum dots (DECQDs) has been demonstrated. DECQDs show dual-emission peaks at 439 and 630 nm with the excitation at 375 nm. As a dual-mode detection probe, the fluorescence and ultraviolet adsorption spectra of DECQDs vary with hexavalent chromium concentrations. Most importantly, Lys can restore the fluorescence of the hexavalent chromium added DECQD nanoprobe and change the color of the probe under natural light. At the same time, based on the participation of smartphones, the prepared DECQD probes favor the establishment of visual smart sensors that can also be used for the in-situ detection of targets. The on-site quantitative analysis exhibited a linear range of 5.3-320 mu M with a detection limit of 1.6 mu M towards Cr(VI) and the differentiation of Lys variation froml to 75 mM with a detection limit of 0.3 mM. The probe has been applied for the first time to enable vision-based colorimetric in complex samples such as water, milk and egg. The recoveries of Cr(VI) and Lys in real samples were between 90 and 104%, and the relative standard deviation (RSD) was as low as 0.4%. This work offers new perspectives for fundamental understanding and new design of functional luminescent materials that are applicable for food-safety and rapid and intelligent inspection.

Automated summary

A straightforward smartphone-based analytical strategy for on-site detection of hexavalent chromium and lysine has been demonstrated using dual-emission carbon quantum dots (DECQDs). The DECQDs show dual-emission peaks and can be used as dual-mode detection probes. The strategy, combined with smartphone technology, allows for visual smart sensors that can be used for in-situ detection of targets. The strategy has shown good performance in the quantification of hexavalent chromium and lysine in complex samples and offers new perspectives for food safety and rapid inspection.