▎ 摘　　要

NOVELTY - The preparation method involves ultrasonically mixing the GO powder and L-cysteine in water. The pH value is adjusted to 8-9. A high-temperature heating reaction is performed to obtain a supernatant. The water is removed to obtain a pale yellow solid, and freeze-dried to obtain N-doped graphene quantum dot powders (N-GQDs). The N-doped graphene quantum dot powder is heated. A solution containing zinc ions is added dropwise under stirring to avoid light reaction. The precipitate is obtained by centrifugation and washed. A solution is prepared with deionized water to obtain nitrogen-zinc co-doped graphene quantum dots after freeze-drying, namely N-doped zinc graphene quantum dot powders (N,Zn-GQDs) nanocomposites. The zinc ion-containing solution includes zinc acetate, zinc sulfate, zinc chloride, zinc nitrate, zinc fluorosilicate, zinc fluoroborate and zinc gluconate. USE - Preparation method of nitrogen-zinc co-doped graphene quantum dots used in preparation of ratiometric immunosensor for detection of biomarkers in human serum samples (all claimed) applied in fields of protein detection, virus detection and detection of other biologically active substances. ADVANTAGE - The ratiometric immunosensor with photoelectric dual response is constructed and used in the detection of disease markers and achieved good results with low detection limit, based on graphene oxide and nitrogen-zinc co-doped graphene quantum dot composites. The N-GQDs synthesized nitrogen-zinc co-doped graphene quantum dots by reacting with zinc acetate, which enhances the fluorescence intensity of quantum dots, and increases the quantum yield of quantum dots to 31.5%. The method has higher selectivity and strong stability, and can be applied to the detection of various disease biomarkers. The content of disease biomarkers can be detected by analyzing the ratio of the photochemical signal and the current signal. The analysis method has the advantages of simplicity, rapidity, high sensitivity and strong practicability, which provides a broader application prospect for the development and research of biosensors. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following: (1) a nitrogen-zinc co-doped graphene quantum dot; (2) a preparation method of a ratiometric immunosensor; (3) a ratiometric immunosensor; and (4) an application of the ratiometric immunosensor in the detection of biomarkers in human serum samples. DESCRIPTION OF DRAWING(S) - The drawing shows an X-ray photoelectron spectroscopy images of N,Zn-GQDs nanocomposites.