Mercury (Hg2+) is a natural element present in foods such as fish, water and soil. Exposure
to mercury leads to severe toxic effects on the nervous, digestive, and immune
systems. Here, a novel, green, and environmentally friendly fluorescent probe decorated
with cysteine/MnO2 quantum dots (Cys@MnO2 QDs) was synthesized. This
synthesis was carried out using a simple ultrasound technique with the aid of cysteine
for fabricating Cys@MnO2 QDs to estimate Hg levels in fish and water samples. In this
morphological study, Cys@MnO2 QDs were fully characterized using high-resolution
transmission electron microscopy, zeta potential analysis, fluorescence, ultraviolet–
visible and infrared spectroscopy. The fluorescence of the synthesized Cys@MnO2
QDs was significantly quenched by gradually increasing the Hg(II) concentration. The
quenching mechanism based on the Hg–S bonds strengthened the utility of the
Cys@MnO2 QDs as a novel luminescent nanoprobe. The estimation of Hg was linear
in the concentration range 0.7–100.0 ng mL1 with a limit of quantitation equal to
0.30 ng mL1. The Cys@MnO2 QDs are fluorescent probes with various benefits such
as speed, ease of use, cost- effective, and being environmentally friendly; they are
easily applied in food manufacturing and for public health improvement.