Smartphone-based colorimetric determination of glucose in food samples based on the intrinsic peroxidase-like activity of nitrogen-doped carbon dots obtained from locusts

In this study, nitrogen-doped carbon dots (N-CDs) with excellent peroxidase-like activity were prepared using locust powder as the carbon source by a self-exothermic reaction. The obtained N-CDs could catalyze the oxidation of the chromogenic substrate 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2 to generate a blue oxidized product (TMBox) with a maximum absorption peak at 654 nm. The catalytic reaction conditions were optimized; furthermore, steady-state kinetic analysis indicated that N-CDs exhibited high affinity toward both TMB and H2O2, and the Michaelis-Menten constant (km) values were 0.115 mM (TMB) and 0.764 mM (H2O2). A smartphone-based colorimetric method was developed for quantitative detection. The 1/L values (L stands for lightness in HSL color space) of the TMBox solution were recorded via an iPhone application Color Analyzer. Since H2O2 is the by-product of glucose (Glu) oxidation in the presence of glucose oxidase (GOx), a simple, sensitive, and selective smartphone-based colorimetric method was developed for the determination of Glu, and the detection limit was 1.09 μM. The smartphone-based method was successfully applied to determine Glu in different food samples with recoveries in the range of 88.5–109.0 %.