Incorporation of Fluorescent Carbon Quantum Dots into Metal–Organic Frameworks with Peroxidase-Mimicking Activity for High-Performance Ratiometric Fluorescent Biosensing

A new ratiometric fluorescent sensor based on the bifunctional carbon quantum dots (CQDs)@metal–organic framework (MOF) nanocomposite possessing peroxidase-mimicking catalytic and luminescent characteristics was developed for hydrogen peroxide (H2O2) and cholesterol detection. The incorporation of fluorescent CQDs into the cavities of MIL-101(Fe) MOF with peroxidase-like activities endows the nanocomposite with bifunctional properties. The CQDs@MOF can oxidize o-phenylene-diamine to 2,3-diaminophenolazine by H2O2 with yellow fluorescence (556 nm). Meantime, the intrinsic fluorescence signal (455 nm) of CQDs@MOF is inhibited due to the inner filter effect. Therefore, the ratio of the fluorescent intensity is employed as the signal output to construct the H2O2 ratiometric biosensor. In addition, the cholesterol can be determined by the ratiometric sensor with high sensitivity. In addition, the total cholesterol in human serum is determined with high accuracy using our ratiometric biosensor. This ratiometric fluorescent platform based on the bifunctional CQDs@MOF provides new insights in the field of bio-sensing.