Multifunctional iron carbon dots with multi-enzyme activity: Enabling dual-mode fluorescence-colorimetric detection of Hg2+

The excellent optical properties, enzyme-mimicking activities and unique surface functional groups of carbon dots (CDs) offer promising potential for fluorescent/colourimetric dual-mode detection of Hg 2+ . This paper reports the preparation of yellow-green fluorescent carbon dots (Fe-CDs) with outstanding peroxidase (POD) and superoxide dismutase (SOD) activities via a one-step hydrothermal method, achieving a quantum yield of 20.6%. Kinetic analysis revealed that the Michaelis constants ( K m ) of the Fe-CDs’ POD-like activity for OPD and H 2 O 2 were 0.15 mM and 2.36 mM, respectively. Furthermore, Fe-CDs demonstrated SOD-like activity, with half-maximal inhibitory concentration (IC 50 ) values of 0.1 mg/mL for O 2 •− and 4 μg/mL for DPPH radicals. Fe-CDs were also capable of reacting with ABTS radical cations (ABTS •+ ), generating a purple product with a characteristic absorption peak at 540 nm. Based on the inhibitory effect of Hg 2+ on the enzymatic activity of Fe-CDs—which reduces the formation of ABTS •+ , thereby restoring fluorescence intensity and causing the fading of the solution's colour—a dual-channel fluorescent/colourimetric detection platform was developed. This study not only achieved the synthesis of CDs with multi-enzyme activities but also established a selective detection method.