Research On Uric Acid Biosensor Based On Gold Nanoarticles/Graphene Nanocomposites

Uric acid is a metabolic end product from purine derivatives in human bodies.Normally, the concentration of uric acid in serum keeps constant because of the balance of production and excretion. However, excessive uric acid can cause serious disease, such as gout. The deposition of uric acid in joint may lead to the turgidity and pain. Therefore, fast and reliable determination of uric acid in biological fluids is urgently required for diagnosis and treatment of uric acid-related diesease. Current development in nano-material and nano-technology shows that nano-material is a promising choice for fabricating biosensors. The biosensors based on nano-materials have the characteristics such as high sensitivity, good selectivity, low detection limits and fast electron transfer kinetics, which can meet the request of the determination of uric acid. In this thesis, we prepared the Au NPs/graphene nanocomposites by using nitrogen-doped graphene and graphene oxide as stabilizer, respectively. The Au NPs/graphene nanocomposites show many characteristics such as large surface area,good conductivity and high activity, and were used for developing the enzymatic and nonenzymatic uric acid biosensors. The studies included:（1） The uric acid biosensor based on Au NPs/graphene/uricase nanocompositesGraphene and gold nanoparticles（Au NPs） have many characteristics such as high conductivity, large surface-to-volume ratio and good biocompatibility. Moreover,Au NPs can bind the antibodies, enzymes and proteins through the Au-S interaction.Therefore, we prepared nitrogen-doped graphene aerogel by the hydrothermal method.Au NPs was then deposited on the surface of nitrogen-doped graphene by using Na BH4-reduction method to obtain Au NPs/graphene nanocomposites. Finally, uricase was immobilized on the surface of the nanocomposites through the Au-S interaction.The electrochemical properties of Au NPs/graphene/uricase nanocomposites were investigated by electrochemical impedance spectroscopy and cyclic voltammetry.Cyclic voltammetry showed that the introduction of uric acic results in a well-defined anodic peak at 0.9 V and the peak current increases linearly with the uric acid concentration in the range of 20 μM to 800 μM, indicating that the Au NPs/graphene/uricase nanocomposites could be used as enzyme-based uric acid biosensor. The sensitivity and the detection limit of this proposed biosensor is 2.89 ×10^-5A/m M and 10 μM, respectively.（2） The nonenzymatic uric acid biosensor based on Au NPs/graphene multilayersGraphene oxide absorbed with HAu Cl₄ was assembled on to the ITO by layer-by-layer technique. Then Na BH₄ was applied to reduce the HAu Cl₄ to Au NPs to obtain the nonenzymatic uric acid biosensor. The biosensor performance was investigated by the cyclic voltammetry and chronoamperometry. The nonenzymatic uric acid biosensor based on Au NPs/graphene multilayers showed several advantages,such as a wide linear range from 5 μM to 1200 μM, high sensitivity of 1.563 × 10^-4A/m M, and low detection limit of 0.1 μM（S/N = 3）. Moreover, the biosensor has good selectivity, excellent reproducibility and stability.