Functionalized Graphene Oxide Composites-based Dopamine,Uric Acid And NO₂^- Electrochemical Biosensor

Graphene oxide materials have been widely used to improve the performance of electrochemical biosensors, for they have many unique properties. Over the last few decades, electrochemical biosensors for determining biomolecules have gained considerable attention because of their merits of easy operation, low cost, instant response, high sensitivity, and other advantages. According to previous studies, the introduction of graphene oxide-based materials can not only solve the problems of immobilizing effective sensitive materials and regenerating sensors, but also can further improve the electrochemical catalytic performance of electrochemical biosensors. Owing to the advantages of electrochemical biosensors and graphene oxide materials, this paper studied the fabrication of functionalized graphene oxide composites-based modified electrodes and the applications of detecting and separating small biomolecules. The main contents are as follows:?1? A home-made carbon paste electrode ?CPE? was reformed by graphene oxide ?GO?/lanthanum ?La? complexes, and a modified electrode, called GO-La/CPE, was fabricated for the selective determination of dopamine ?DA? by cyclic voltammetry ?CV? and differential pulse voltammetry ?DPV?. Moreover, several factors affecting the electrocatalytic performance of the modified sensor were investigated in this study. Owning to the combination of GO and La ions, the GO-La/CPE sensor exhibited large surface area, well selectivity and good stability in the oxidation reaction of DA. At optimal conditions, the response of the GO-La/CPE electrode for determining DA was linear in the region of 0.01-0.1 ?M and 0.1-400.0 ?M. The limit of detection was down to 0.32 nM ?S/N=3?. In addition, this modified electrode was successfully applied to the detection of DA in real urine and serum samples by using standard adding method, showing its promising application in the electroanalysis of real samples.?2? A bare glassy carbon electrode ?GCE? was reformed by carboxylated graphene oxide/lanthanum, and the modified electrode, called GO-COOLa/GCE, was fabricated for simultaneously detecting dopamine ?DA?, uric acid ?UA? and nitrite ?NO₂? by cyclic voltammetry ?CV?, differential pulse voltammetry ?DPV? and amperometry. Several factors which affected the electrocatalytic activity of the GO-COOLa/GCE electrode, such as the effect of pH, scan rate and concentration were studied. Under the synergistic catalytic effects of carboxylated graphene oxide and lanthanum ions, the GO-COOLa/GCE sensor showed rapid response, excellent selectivity and high catalytic performance toward the electrooxidation of DA, UA and NO₂^-. In optimized conditions, two linear response ranges for determining DA were obtained over ranges of 0.01-1.96×10² ?M and 1.96×10²-1.23×10³ ?M with detection limit of 0.018 ?M ?S/N=3?. And the responses of the GO-COOLa/GCE electrode for UA and NO₂^- were linear in the region of 1-1.53×10³ ?M and 1-2.75×10³ ?M with detection limits of 0.058 ?M and 0.070 ?M, respectively. Furthermore, this reformed electrode was successfully used to the detection of DA, UA and NO₂ in real urine and serum samples.