Colorimetric aptasensors for sensitive low-density lipoprotein detection based on reduced oxide graphene@molybdenum disulfide-ferrocene nanosheets with peroxidase-like activity†

Low-density lipoprotein (LDL) is a key biomarker for cardiovascular disease (CVD) risk assessment. Monitoring LDL for the early diagnosis of CVD and its complications is an important clinical analysis tool. In this work, a novel colorimetric aptasensor for LDL detection was constructed via reduced graphene oxide@molybdenum disulfide-ferrocene-carboxylic nanosheets (rGO@MoS₂-Fc) with excellent peroxidase-like activity. On this basis, the LDL aptamer (LDLapt) immobilized on the surface of rGO@MoS₂-Fc served as a signal probe (rGO@MoS₂-Fc/LDLapt), while the unmodified LDLapt served as a capture probe. When LDL was present, it was recognized by the LDLapt and rGO@MoS₂-Fc/LDLapt to form an rGO@MoS₂-Fc/LDLapt/LDL/LDLapt sandwich-type conjugate with excellent enzymatic catalytic properties that can catalyze the generation of hydroxyl radicals (·OH) from hydrogen peroxide (H₂O₂), which in turn oxidized the colorless substrate o-phenylenediamine (OPD) to the yellow compound 2,3-diamino phenothiazine (DAP). In addition, the catalytic mechanism of the reaction was confirmed to be induced by ·OH through free radical experiments. The aptasensor had a linear range of 15.0 to 200.0 μg mL⁻¹, and a limit of detection (LOD) of 2.199 μg mL⁻¹. Overall, the assay has high selectivity, sensitivity and operability, showing broad application prospects in the clinical diagnosis of CVD.