Development of cysteine-doped MnO₂ quantum dots for spectrofluorimetric estimation of copper: applications in...

Copper (Cu) plays a role in maintaining healthy nerve cells and the immune system. Osteoporosis is a high-risk factor for Cu deficiency. In the proposed research, unique green, fluorescent cysteine-doped MnO₂ quantum dots (Cys@MnO₂ QDs) were synthesized and assessed for the determination of Cu in different food and hair samples. The developed quantum dots were synthesized with the help of cysteine using a straightforward ultrasonic approach to create 3D fluorescent Cys@MnO₂ QDs. The resulting QDs' morphological and optical characteristics were carefully characterized. By adding Cu ions, the intensity of fluorescence for the produced Cys@MnO₂ QDs was found to be dramatically reduced. Additionally, the applicability of Cys@MnO₂ QDs as a new luminous nanoprobe was found to be strengthened by the quenching effect grounded on the Cu-S bonding. The concentrations of Cu²⁺ ions were estimated within the range of 0.06 to 7.00 µg mL^-1, with limit of quantitation equal to 33.33 ng mL^-1 and detection limit equal to 10.97 ng mL^-1. The Cys@MnO₂ QD technique was applied successfully for the quantification of Cu in a variety of foods, including chicken meat, turkey, and tinned fish, as well as in human hair samples. The chance that this novel technique could be a useful tool for figuring out the amount of cysteine in bio-samples is increased by the sensing system's remarkable advantages, which include being rapid, simple, and economical.