1. Chemical and polymer engineering group, Yazd University, Yazd, Iran 2. Nanostructure coating institute, Yazd PayameNoor University, Yazd, Iran 3. Chemical and polymer engineering group, Yazd University, Yazd, Iran
H2o2 is an essential marker for age-related diseases such as alzheimer, cardiovascular disorders and cancer. electrochemical sensors have been developed to detect hydrogen peroxide due to high sensitivity and selectivity and low cost. over the last years, the researches focused on graphene nanostructures owing to specific surface area. agglomeration of graphene sheets during drying reduces the surface area for electrochemical reactions. 3-d graphene foams (gf) with porous structures were introduced with high porosity and huge surface area. therefore, 3-d foams with different structures were produced in this research and were used for the fabrication of non-enzymatic biosensing electrodes for h2o2 detection. electrochemical properties of such electrodes with different foam structures were investigate
2.1. graphene foam
go was prepared by modified hummers method gf was prepared by hydrothermal method. 12 ml go suspension in 1:1 water: ethanol (gf1) and in water (gf2) was poured in autoclave and maintained at 180 °c for 12 hr. the produced aerogels were freeze dried at -80 °c for 18 hr.
2.2. electrode preparation
ag paste on glass was used as substrate for all electrodes. a 3-electrode system consists of a platinum wire as counter electrode, gf on ag paste as working electrode and calomel reference electrode was used
the porous structures of gf1 and gf2 were characterized by scanning electron microscopy (sem). fig. 1 shows highly porous structures of gf1 and gf2. gf2 has more uniform porosity and larger pore size than gf1. solidifying water immediately after zero point resulted to drying graphene aerogel on the uniform solid iced structure in freeze dryer. also, water expansion approximately about 9 % in the temperatures lower than 4 °c led in bigger pores. due to ethanol freezing at much lower point, drying the aerogel was performed with less uniformity and smaller pores.
fig.1- porous structures of gf1 (left) and gf2 (right).
3.1. electrochemical behavior
electrochemical properties of gf electrodes were evaluated by cyclic voltammetry (cv) in n2-saturated 0.1 m pbs solution. a cathodic peak is shown in fig. 2 at 0.07 v for ag based electrode related to the reduction of ag paste. porous structures in gfs led to the shift of cathodic peak to lower potential. much higher current density was measured for gf electrodes due to huge surface area and high electron mobility on porous graphene structure. cathodic current for gfs were 10 times more than the ones obtained for conventionally gc electrodes.
in order to study h2o2 detection, cv was carried out in different concentration of h2o2 (fig. 2). addition h2o2 to buffer resulted to increasing cathodic peak current in all electrodes. the electrodes are capable of detecting h2o2 at different concentrations with high current density especially for gfs. higher surface area and charge transfer of gfs help more electrochemical reactions on the electrode surfaces.
fig. 2- cv diagrams for ag-based and gfs electrodes in 0.1 m pbs with different concentration of h2o2
Simple non-enzymatic biosensors were produced by 3-d porous graphene foams for h2o2 detection. taking advantage of high electro-catalytic activity of ag based electrode, in addition to high conductivity and huge surface area of gf, much higher cathodic current in detection of h2o2 was obtained.