Coating Fe 3 O 4 quantum dots with glutamic acid to achieve enhanced catalysis for facile and sensitive detection of chromium(VI) in water.

A universal green synthesis approach for Glu-Fe 3 O 4 quantum dots (QDs) with ultrasmall size (∼3.3 nm) and enhanced catalysis was demonstrated using glutamic acid (Glu) as a dopant. Abundant carboxylic groups and amino groups on the surfaces with a zeta potential of -6.28 mV resulted in greatly improved environmental stability. The Glu-Fe 3 O 4 QDs exhibited oxidoreductase-like catalytic activity. The steady-state kinetic assays indicated that the QDs had a high binding affinity for the substrate TMB. A facile and sensitive colorimetric platform was developed using the Glu-Fe 3 O 4 QDs for the detection of Cr(VI) in naturally sourced water and waste water, which showed a detection limit of 31.02 nM, much lower than the maximum Cr(VI) level permitted in drinking water by the World Health Organization (WHO) and the industrial water threshold. This universal green synthesis approach and the unique catalytic activity of Fe 3 O 4 QDs open a new horizon in materials chemistry and the development of colorimetric biosensors for environmental protection and public health.