▎ 摘　　要

NOVELTY - Preparing electrochemical sensor based on graphene quantum dot modified polydopamine-nano titanium dioxide comprises e.g. (1) weighing 1.5-2.5 g citric acid in a container, placing the container at a temperature of 190-210 degrees C to enable the citric acid to begin to melt, then changing the color of the liquid from colorless to light yellow, finally turning to orange color, and indicating the generation of graphene quantum dot (GQD) solution; and (2) using 20-30 ml absolute ethanol, sequentially adding 0.8-1.2 ml n-butanol, 0.8-1.2 ml polyethylene glycol, 0.35-0.40 ml hydrofluoric acid, 0.8-1.2 ml ethylene glycol, and 0.5-0.6 ml deionized water, stirring for 10-20 minutes to prepare solution A; using 2.5-3.5 ml tetrabutyl titanate, adding 8-12 ml absolute ethanol, and stirring for 10-20 minutes to prepare a solution B; and injecting the solution B into solution A at the injection speed of 3.5-4.5 ml/hour, vigorously stirring solution, and preparing graphene quantum dots-titanium dioxide. USE - The method is useful for preparing electrochemical sensor based on graphene quantum dot modified polydopamine-nano titanium dioxide. ADVANTAGE - The method: can enhance the electrochemical response signal and can sensitively detect the fibroin protein. DETAILED DESCRIPTION - Preparing electrochemical sensor based on graphene quantum dot modified polydopamine-nano titanium dioxide comprises (1) weighing 1.5-2.5 g citric acid in a container, placing the container at a temperature of 190-210 degrees C to enable the citric acid to begin to melt, then changing the color of the liquid from colorless to light yellow, finally turning to orange color, and indicating the generation of the graphene quantum dot (GQD) solution; (2) using 20-30 ml absolute ethanol, sequentially adding 0.8-1.2 ml n-butanol, 0.8-1.2 ml polyethylene glycol, 0.35-0.40 ml hydrofluoric acid, 0.8-1.2 ml ethylene glycol, and 0.5-0.6 ml deionized water, stirring for 10-20 minutes, and preparing the solution A; using 2.5-3.5 ml tetrabutyl titanate, adding 8-12 ml absolute ethanol, and stirring for 10-20 minutes to prepare a solution B; and injecting the solution B into solution A at the injection speed of 3.5-4.5 ml/hour, while vigorously stirring the solution A, continuously stirring for 2-4 hours after the injection is finished; stirring the solution at 140-160 degrees C for 3-4 hours, until the reaction is finished, respectively centrifugal washing using de-ionized water, n-butanol and anhydrous ethanol, drying the product obtained by washing, after grinding and calcining, to obtain the nano-titanium dioxide; (3) adding 15.5-16 g sodium salicylate to 8-12 mol/L GQD, adding water to constant volume to 35-45 ml, stirring for 25-35 minutes, and preparing 8-12 mol/l GQD-containing sodium hydroxide solution; then using 15- 15.2 mg titanium dioxide, adding GQD-containing sodium hydroxide solution, stirring for 25-35 minutes, and reacting at 130-150 degrees C for 6-10 hours, after the reaction is completed, performing centrifugal cleaning with 4-6 wt.% hydrochloric acid solution and deionized water respectively, removing the surface water by centrifugal washing with water and ethanol, and dispersing the obtained product in a mixed solution of anhydrous ethanol and n-butanol in a volume ratio of 2.5-3.5:1, and carrying out crystallization and shaping 150-170 degrees C to obtain the GQDs-titanium dioxide, (4) adding 80-120 mg dopamine hydrochloride to a mixed solution of 80-120 ml tris-hydrochloric acid buffer solution and 30-70 ml isopropanol, and the reaction is protected from light at room temperature for 20-30 hours, then washing with water many times, dispersing the product into 4-6 ml ultrapure water to obtain the polydopamine nanospheres (PDANS) dispersion; diluting 0.8-1.2 ml PDANS dispersion into 4-6 ml ultrapure water, and adding 500-700 mg trisodium citrate, and 18-22 ml 0.015-0.035 mol/l silver nitrate solution in sequence under stirring, introducing in nitrogen gas to remove oxygen, and stirring and reacting for 2.5-4.5 hours under dark conditions; after the reaction is completed, centrifuging the product and washing with ultrapure water for many times, vacuum drying to obtain preparing polydopamine nanospheres loaded with silver nanoparticles (PDANS-Ag); (5) adding 13.4-17.4 mg mercaptoethylamine and 85.8-105.8 mg 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) to 20 ml GQD solution obtained in step (1), and shaking and reacting at room temperature for 20-30 hours, dialyzing the reacted solution for 1-3 days, and preparing thiolated GQD solution; (6) mixing 1-3 ml thiolated GQD solution with 1-3 ml PDANS-Ag solution with a concentration of 1.8-2.2 mg/ml, shaking at room temperature for 10-14 hours, and centrifuging to obtain PDANS-Ag/GQD; (7) polishing the working glassy carbon electrode on the chamois with nano-grade alumina and deionized water; then immersing in absolute ethanol for ultrasonic cleaning, and finally cleaning with deionized water; (8) adding 2-4 mu l PDANS-Ag/GQD solution with 8-12 mu g/l prepared on the electrode surface, washing with phosphate-buffered saline buffer after drying, continue to add 2-4 mu l 8-12 mu g/l prepared GQDs-TiO2 solution on the electrode surface, and then drying to prepare electrode; and (9) washing and drying the electrode, adding 18-22 mu l 0.04-0.06 M aqueous solution of 3-hydroxypropionic acid to the electrode surface after drying, incubating for 0.5-1.5 hours to form a saturated 3-hydroxypropionic acid monolayer, then using phosphate-buffered saline buffer solution thoroughly cleaning, electrode modified with 3-hydroxypropionic acid, incubating in 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride buffer containing 0.04-0.06 M 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide/0.02-0.04 M N-hydroxysuccinimide for 0.5-1.5 hours, converting the terminal carboxy group of 3-hydroxypropionic acid into active N-hydroxysuccinimide ester; taking 4-6 mu l 8-12 mu g/ml silk fibroin antibody solution and applied dropwise to the surface of the electrode, drying at room temperature, and washing the unfixed antibody with phosphate-buffered saline buffer to obtain the antibody-modified electrode, then, blocking with bovine serum albumin (BSA) solution for 20-40 minutes to block the non-specific binding sites that may exist on the electrode surface, after removing, washing with phosphate-buffered saline buffer and air-drying to obtain the electrochemical sensor based on graphene quantum dot modified polydopamine-nano titanium dioxide.