Cys-Functionalized MoS₂ Quantum Dots and Calcium Ion for Ratiometric Fluorescence Probes for Doxycycline

We used Cys-functionalized molybdenum disulfide quantum dots (MoS 2 QDs) and calcium ion (Ca 2+ ) for ratiometric fluorescence (FL) determination of doxycycline (DC). MoS 2 QDs were prepared by a hydrothermal method and emitted FL at 435 nm with 355 nm excitation. DC can quench the FL of MoS 2 QDs at 435 nm by static quenching and the inner filter effect. In the presence of Ca 2+, DC can coordinate with Ca 2+ to form a stable six-membered ring complex (DC/Ca 2+ ) with increased FL intensity at 510 nm. The FL ratio of F 510 / F 435 exhibited a good linear relationship with DC concentration (0.2 to 100 μM), along with a limit of detection of 23.2 nM. Moreover, the ratiometric FL assay was successfully used for DC detection in food samples with satisfactory recoveries (97.1–100.1%). The detection process can be completed in 1 min at room temperature, providing a rapid method for the assessment of DC concentrations in the food field, while demonstrating its competitiveness in detection applications. This study shows that MoS 2 QDs have great potential in constructing ratiometric fluorescent probes with good detection performance.