High-Precision Fluorescence Platform for Point-of-Care Measurements of Low-Density Lipoprotein Based on Nitrogen, Sulfur-Doped Graphene Quantum Dots and Ferric Tetroxide @ Reduced Graphene Oxide

Effective detection of biomarkers related to atherosclerosis (AS) is of great importance in clinic. High concentration of low-density lipoprotein (LDL) is one of the most dangerous factors leading to AS, which can be used as a target for diagnosis of AS. In this paper, a fluorescence platform for high-precision detection of LDL was constructed with ferric tetroxide @ reduced graphene oxide (Fe 3 O 4 @rGO) nanosheets as fluorescence quencher and low-density lipoprotein aptamer (Apt) labeled with nitrogen, sulfur-doped graphene quantum dots (N,S-GQDs-Apt) as fluorescence donor. Owing to the physical adsorption and van der Waals forces between Fe 3 O 4 @rGO nanosheets and the Apt, the N,S-GQDs-Apt was close to Fe 3 O 4 @rGO nanosheets, resulting in fluorescence resonance energy transfer (FRET), and the fluorescence of N,S-GQDs-Apt was quenched. In the presence of LDL, LDL bound to Apt leads to N,S-GQDs detachment from Fe 3 O 4 @rGO nanosheets and suppresses the FRET, resulting in the recovery of fluorescence of N,S-GQDs. Under the optimum conditions, the fluorescence recovery is logarithmic linear with the concentration of LDL in the range of 0.1 ~ 10.0 μg mL −1 , with R 2 of 0.9922 and the detection limit of 0.015 ng mL −1 (s/n = 3). In the experiment using actual human serum, the recovery is high from 91 to 117%. This platform can be used for the diagnosis of early AS and provide reference for the detection of other markers.