Manganese(II)-doped carbon dots as effective oxidase mimics for sensitive colorimetric determination of ascorbic acid

A colorimetric assay is presented for the determination of ascorbic acid (AA). Manganese(II) doped carbon dots (Mn-CDs) were prepared by a convenient hydrothermal route and are shown to possess oxidase-like catalytic ability. They catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by dissolved oxygen to form a blue colored product (oxTMB). AA can reduce blue oxTMB to colorless TMB. The fading of the blue color (measured at 652 nm) can be applied for quantifying AA in the 50 to 2500 nM concentration range and with a 9 nM detection limit. The method was successfully used for the quantitation of AA in real samples. Schematic representation of a colorimetric assay platform for the sensitive detection of ascorbic acid (AA) in view of inhibitory effect of AA on the 3,3′,5,5′-tetramethylbenzidine (TMB) oxidation, benefitting from excellent oxidase-like catalytic activity of manganese(II) doped carbon dots (Mn-CDs).