▎ 摘　　要

NOVELTY - A graphene/carbon nanofiber composite material is prepared by dissolving polyacrylonitrile powder in dimethylformamide solution, heating and stirring, taking into syringe, fixing syringe on syringe pump, and electrostatic spinning; placing polyacrylonitrile fiber into blast drying box, heating, stabilizing, placing stabilized polyacrylonitrile fiber into center of tubular furnace, heating, heat preserving, and cooling to obtain carbon nanofiber; cutting into sheet, immersing in ethanol solution to remove oil stain, washing using distilled water, immersing with mixed solution containing ammonium persulfate and concentrated sulfuric acid, stirring for coarsening, washing with distilled water, immersing in tin(II) chloride solution, stirring, washing with distilled water, immersing in lead(II) chloride solution, stirring to activate, and washing with distilled water; and immersing in chemical nickel plating solution. USE - Method for preparing graphene/carbon nanofiber composite material used as working electrode in electrochemical biosensor to detect levodopa (claimed). ADVANTAGE - The product solves levodopa low detection sensitivity and high detection limit. DETAILED DESCRIPTION - A graphene/carbon nanofiber composite material is prepared by: (A) dissolving 1 g polyacrylonitrile powder in 10 mL dimethylformamide solution, heating and stirring at 80-150 degrees C for 1-2 hours to obtain static spinning solution, taking 10-20 mL solution into syringe, fixing syringe on syringe pump, and electrostatic spinning at voltage of 10-20 kV, solution flow speed of 1-3 mL/hour and collecting distance of 10-15 cm; (B) placing polyacrylonitrile fiber into blast drying box, heating at 300-400 degrees C at speed of 1-2 degrees C/minute, stabilizing for 1-2 hours, placing stabilized polyacrylonitrile fiber into center of tubular furnace, heating under argon gas protection to 800-1000 degrees C from room temperature at speed of 5-10 degrees C/minute and argon gas flow rate of 300-500 sccm, heat preserving at 800-1000 degrees C for 60-100 minutes, and cooling to room temperature along with furnace to obtain carbon nanofiber; (C) cutting into sheet with area of 1-3 cm2, immersing in ethanol solution at 60-80 degrees C for 30-60 minutes to remove oil stain, washing using distilled water, immersing with mixed solution containing ammonium persulfate and concentrated sulfuric acid, stirring for coarsening for 15-30 minutes, washing with distilled water, immersing in tin(II) chloride solution, stirring for 3-10 minutes, washing with distilled water, immersing in lead(II) chloride solution, stirring to activate for 3-10 minutes, and washing with distilled water; (D) immersing in 25-30 g/L nickel(II) sulfate hexahydrate, 30-35 g/L sodium phosphinate monohydrate, 30-35 g/L sodium citrate hydrate and 70-75 g/L ammonium chloride chemical nickel plating solution, chemical nickel plating under alkaline conditions, adjusting pH value using ammonia NH3 and water to 8-10, processing at 50-70 degrees C for 30-50 minutes, and freeze-drying; and (E) placing in quartz tube type furnace center, heating under argon gas and hydrogen gas protection from room temperature to 800-1000 degrees C at speed of 10-20 degrees C, argon gas flow rate of 480-500 sccm and hydrogen flow rate of 180-200 sccm, keeping temperature at 800-1000 degrees C for 10-20 minutes, introducing methane gas into tubular furnace at 800-1000 degrees C for 20-30 minutes at speed of 10-20 sccm, cooling to room temperature, and immersing in 3-5 mol/L hydrochloric acid for 1-2 hours to remove nickel.