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

We used Cys-functionalized molybdenum disulfidequantum dots (MoS2 QDs) and calcium ion (Ca2+) for ratiometricfluorescence (FL) determination of doxycycline (DC). MoS2 QDswere prepared by a hydrothermal method and emitted FL at 435nm with 355 nm excitation. DC can quench the FL of MoS2 QDsat 435 nm by static quenching and the inner filter effect. In thepresence of Ca2+, DC can coordinate with Ca2+ to form a stable six membered ring complex (DC/Ca2+) with increased FL intensity at510 nm. The FL ratio of F510/F435 exhibited a good linearrelationship with DC concentration (0.2 to 100 μM), along with alimit of detection of 23.2 nM. Moreover, the ratiometric FL assaywas successfully used for DC detection in food samples withsatisfactory recoveries (97.1−100.1%). The detection process canbe 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 MoS2 QDs have great potential inconstructing ratiometric fluorescent probes with good detection performance.