Selective cholesterol assay using peroxidase-like iron-copper Co-doped nitrogen carbon quantum dots in colorimetric and fluorometric modes.

Effective disease management and diagnosis rely on monitoring biomarkers such as cholesterol in bodily fluids. This study presents iron and copper-coordinated nitrogen-doped carbon quantum dots (FeCu@NCQDs) synthesized via a straightforward hydrothermal method, exhibiting a notable photoluminescence quantum yield of 39.09 %. With fluorescence emission at 450 nm under 330 nm excitation, FeCu@NCQDs are ideal for sensitive biosensing. A detection probe combining FeCu@NCQDs, 4-aminoantipyrine, and phenol was developed. In the presence of cholesterol oxidase-generated H₂O₂, 4-aminoantipyrine, and phenol reacted to produce a pink compound that quenches FeCu@NCQDs' fluorescence through an inner-filter effect, enabling fluorometric detection. Colorimetric detection is achieved by measuring this compound's absorbance at 515 nm. The FeCu@NCQDs' peroxidase-like activity, enhanced by Fe and Cu, facilitates this process. Under optimized conditions, the fluorometric and colorimetric methods exhibited linear detection ranges of 0.03-600 μM and 0.13-600 μM, respectively. This dual-mode system effectively detected cholesterol in serum samples with high accuracy and recovery, offering a sensitive, reliable, and economical tool for clinical diagnostics and personalized health monitoring.