▎ 摘　　要

NOVELTY - Nanocomplex comprises nitrogen and sulfur co-doped graphene quantum dots (N,S-GQDs) and cobalt oxyhydroxide with fluorescence quenching function. USE - The nanocomplex is useful for detecting ascorbic acid content in cells and zebrafish using fluorescent probe, and bioimaging (all claimed). ADVANTAGE - The probe has simple preparation method, good biological compatibility and stable optical properties, is high sensitivity, and provides a new idea for designing fluorescent nanoprobes and theoretical basis for the application of fluorescent nano-material in organisms. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for: preparing the nanocomplex, comprising: (i) mixing citric acid and L-cysteine, heating and reacting, dissolving liquid in ultra-pure water, dialyzing the solution, and freeze-drying to obtain N, S-GQDs solid powder; (ii) uniformly mixing sodium hydroxide solution and cobalt chloride solution, adding (in dropwise) sodium hypochlorite solution into the mixed solution, stirring until there is no brown substance is regenerated in the solution, ultrasonically processing the obtained brown suspension, adding into a centrifuge and centrifuging to obtain cobalt oxyhydroxide nanosheet, and washing the obtained nanosheet using purified water for 2-3 times; and (iii) adding N, S-GQDs solution into cobalt oxyhydroxide nanosheet prepared in step (ii), mixing and diluting using purified water, ultrasonicating the mixed solution to obtain N, S-GQDs-cobalt oxyhydroxide nanocomplex solution, and freeze-drying the obtained nano-complex solution to obtain N,S-GQDs/ cobalt oxyhydroxide nanocomplex solid powder. detecting ascorbic acid (AA) content, comprising: (ai) dissolving N,S-GQDs/ cobalt oxyhydroxide nanocomplex solid powder in buffer solution to obtain detection liquid, mixing the detection liquid with AA standard solution of different concentrations, measuring fluorescence intensity (F) of the detection liquid before adding AA and fluorescence intensity (F) of the detection system under different AA concentration, calculating relative fluorescence intensity 1/(F-F), taking AA concentration (1/C) as horizontal coordinate, relative fluorescence intensity 1/(F-F) as longitudinal coordinate, determining the relationship of AA concentration and relative fluorescence recovery intensity, and drawing the standard curve; (aii) mixing the detection liquid and AA sample with unknown concentration, and recording the fluorescence intensity; and (aiii) obtaining the content of AA in the test sample from the standard curve.000 detecting ascorbic acid AA in cell using fluorescent probe, comprising: (bi) incubating the cells in a culture box with culture medium until the cells reach the logarithmic phase; (bii) inoculating the cell in 96-well plate for incubation, discarding the culture solution, and incubating cells using different concentration of N,S-GQDs/cobalt oxyhydroxide nanocomplex; (biii) discarding supernatant, adding (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) solution to each well and continuously incubating the cells; (biv) adding dimethyl sulfoxide (DMSO) and shaking, recording the absorbance value of each well by an enzyme labelling instrument, and measuring the cytotoxicity of N,S-GQDs/cobalt oxyhydroxide nanocomplex; (bv) inoculating the cell on a laser confocal vessel, and incubating for cell imaging; (bvi) incubating first group of cells in culture medium as control group, incubating second group of cells with N,S-GQDs/cobalt oxyhydroxide nanocomplex culture medium, and incubating the third group of cells with N,S-GQDs/cobalt oxyhydroxide nanocomplex culture medium, then adding AA to the dish for continuous incubation; and (bvii) discarding the culture solution of all the three groups of cells, washing using phosphate buffered saline solution, then fixing using paraformaldehyde, and recording fluorescent image using a laser confocal microscope. detecting ascorbic acid (AA) in zebrafish using fluorescent probe and N,S-GQDs/cobalt oxyhydroxide nanocomplex, comprising: (ci) incubating the fertilized egg of zebra fish, washing thrice using culture liquid, screening well-developed embryos using an optical microscope, and uniformly distributing embryos in two 6-well plates; (cii) incubating zebra fish embryos in the first 6-well plate containing different concentration of N,S-GQDs/cobalt oxyhydroxide nanocomplex, observing the survival number of zebra fish, and calculating the survival rate; (ciii) incubating zebra fish embryos in the first 6-well plate containing different concentration of N,S-GQDs/cobalt oxyhydroxide nanocomplex, observing the body type of zebrafish, and calculating the distortion rate; and (civ) dividing zebra fish into three groups, incubating the first group of zebra fish embryo in only culture solution, and using as a control group, incubating the second group of zebra fish embryos with culture solution containing N,S-GQDs/cobalt oxyhydroxide nanocomplex, incubating third group of zebra fish embryos with culture solution containing N,S-GQDs/cobalt oxyhydroxide nanocomplex, then incubating with culture solution containing different amount of AA, and washing the pore plate using distilled water and recording the fluorescence image of the three groups of zebra fish embryo using the laser confocal microscope.