Fabrication Of High-density Graphene Electrochemical Sensing Material And Its Application

Graphene is a type of two-dimensional crystals with honeycomb structure which was resulted from the tightly arranging of sp2 hybridized carbon atoms, and they have unique electrical, optical, thermal, mechanical and chemical properties. However, they were prone to accumulate and return to the state of graphite due to the strong π-π effect and van der Waals forces between the graphene sheets, resulting in the loss of some performance. Gelation is an effective way to overcome these problems, but now we can only obtain the ultra-light graphene aerogel with the prior technology. The ultra-light characteristic would lead to the poor electronic conductivity and mechanical strength, which was mainly attributed to the thin layer and the brittle skeleton structure of the graphen, which greatly limited its wide application in many fields. We designed a new multiple method to prepare high-density graphene aerogel, and successfully applied to the electrochemical sensor.Ultrasonic dispersing graphite oxide in deionized water to form graphene oxide dispersion, L-ascorbic acid was added to promote the reduction of graphene oxide, a part of reduced graphene oxide self-assembled to form graphene hydrogel, and then the graphene aerogels were obtained by the freeze drying.; then punctured at the top of the aerogel from top to bottom with the needle to open the closed pores inside the aerogel. The aerogel was transferred to another vial, whose internal space was exactly consistent with the external dimensions of the aerogel. Graphene oxide dispersion was imported from the vertical holes, the second graphene oxide gels were obtained by the above mentioned method; Multiple high density graphene gel were prepared by repeating the above operation, and finally the multiple high density graphene aerogel was obtained by high temperature calcination in Ar/H2 atmosphere. The studies showed that the new graphene net was formed in situ in the old graphene net, with the increase of the number of the graphite oxide gel, the graphene conduction network became denser. Therefore, multiple graphene aerogel had a higher density, faster electron conductivity and stronger mechanical strength compared with conventional graphene aerogel. More interestingly, the electrochemical behavior of multiple graphene aerogel can be effectively controlled by changing the number of graphene oxide gelation.The "Star" gold nanoparticles were synthesized by seed growth method, and then the multiple high density graphene aerogel/gold nanostar complex was prepared by the combination of gold nanoparticles with high density graphene aerogel. This composite was modified on the surface of glassy carbon electrode to obtain the electrochemical sensor, which was applied to the electrochemical detection of phenols and dopamine. The electron transfer rate reached 15.3296 ± 0.13 s-1 in 1 mM solution of potassium ferricyanide, the cyclic voltammetry(CV) and differential pulse voltammetry(DPV) were employed to assay catechol and hydroquinone with a linear range of 1×10-9 ~ 9×10-5 M for catechol and 1.0×10-9 ~ 9×10-5 M for hydroquinone and a detection limit of 4.3×10-10 M and 2.1×10-10 M(S/N = 3) respectively. The system was also used to the detection of dopamine chemical sensors with a linear range from 8×10-7 to 3×10-4 M and a detection limit of 2.7×10-7 M(S/N = 3) and recoveries between 96.8% ~ 103.2%.The linear polyethylene imine(2% ~ 3%) was introduced into the graphene oxide dispersion, the high density nitrogen-doped graphene aerogel was prepared by the multiple gelation method. The results showed that nitrogen-doping improved the hydrophilicity of the material, and the contact angle decreased from 103.2° to 73.0°. We developed a glucose biosensor using the multiple nitrogen-doped graphene aerogel and gold nanoparticles as the sensing material and glucose oxidase as recognition element. The system was applied to the determination of glucose with a linear range of 1.0×10-5 ~ 1.0×10-3 M and a detection limit of 3.3×10-6 M. The method had good sensitivity, stability and reproducibility, and was successfully applied to the analysis of trace glucose in blood samples.