B,N-carbon dots-based ratiometric fluorescent and colorimetric dual-readout sensor for H₂O₂ and H₂O₂-involved metabolites detection using ZnFe₂O₄ magnetic microspheres as peroxidase mimics

In this work, a two-dimensional optical sensing platform for H₂O₂, glucose, and uric acid (UA) detection is developed, which integrates the advantages of colorimetric and ratiometric fluorescent techniques. ZnFe₂O₄ magnetic microspheres with an intrinsic peroxidase-like activity are synthesized to catalyze the oxidation of ophenylenediamine in the presence of H₂O₂, producing a typical yellow substance (oxOPD) with an absorption peak at 420 nm. The oxOPD can significantly quench the fluorescence of boron and nitrogen co-doped CDs (B,N-CDs) at 430 nm through the inner filter effect and generate a new fluorescence emission peak at 556 nm. Thus, the fluorescence intensity ratio (I₅₅₆/I₄₃₀) can be utilized for quantitative analysis of the concentrations of H₂O₂ and H₂O₂-involved metabolites (glucose and UA). The colorimetric "naked-eye" readout based on the color change of solution can also be established to determine H₂O₂, glucose, and UA levels. The detection limit based on colorimetric sensing for H₂O₂, glucose, and UA are 0.09, 0.9, and 0.9 μM, respectively, and 0.1, 8, and 1 μM using ratiometric fluorescent sensing. Furthermore, this strategy can detect glucose and UA in human serum with satisfactory results, and provide potential applications in the detection of metabolites related to H₂O₂ release.