Sensing Performance For Acidic Small Molecules Based On Copper Germanate Nanowires And Polyaniline Composite Electrodes

It is of important significance to detect acidic small molecules with biological effect in the area of environmental protection,food safety and human health.Great interest has been devoted to the electrochemical sensors owing to high sensitivity,simple operation process,easy miniaturization and multi-functionlization.In the paper,novel electrochemical sensing technology has been developed for three kinds of acidic molecules including L-cysteine(L-Cys),tartaric acid(TA)and benzoic acid(BA).Copper germanate nanowires(CGONWs)modified glassy carbon electrode(GCE)and polyaniline/CGONWs[PAn/CGONWs)modified GCE are prepared,and the electrochemical behaviors and sensing performance of L-Cys,TA and BA at the electrodes have been analyzed in detail.Main results are listed as follows:1.CGONWs have been prepared by a simple hydrothermal deposition process using Ge dioxide as the Ge source and Cu sheets as the deposition substrate and optimal hydrothermal deposition parameters are determined.CGONWs with orthorhombic phase are obtained from the Cu sheet substrate at 250 0C for 12 h.The length of the nanowires is several dozens of micrometers and the diameter is 30-150 nm.Formation and growth of the CGONWs can be explained according to the solid state nucleation and crystalline growth process.PAn/CGONWs-W%composite(W refers to the mass percentage of PAn in the composite)with various PAn content has been prepared using PAn and CGONWs as the raw materials by hydrothermal process.In these composites,sphere-shaped PAn particles with the diameter of 100-300 nm are attached on the surface of the CGONWs.Both of CGONWs and PAn/CGONWs can attach to the GCE surface firmly forming the film with the thickness of about 2 ?m.2.The CGONWs electrode shows good catalytic performance to the oxidation and reduction reaction of L-Cys,TA and BA.The three molecules present low oxidation overpotential at the electrodes with two oxidation peaks at 0.3?0.0 V[vs SCE)in neutral condition.There is a linear relationship between the scan rate and the intensity of the anodic peaks,while the pH of the electrolytes has similar effect on the electrochemical behaviors of L-Cys,TA and BA.All of the three molecules possess carboxyl functional groups and can react with the Ge-containing sites and Cu ions at the surface of the CGONWs.A plausible mechanism for surface electrochemical reaction of the three molecules,which is coupled with proton transfer process is thus proposed based on the adsorption of the reactants at two active sites of CGONWs.3.In neutral condition,PAn has no catalytic activity toward electrochemical reaction of L-Cys,TA and BA.The oxidation and reduction mechanism at the PAn/CGONWs electrode is similar to that at the CGONWs electrode.However,PAn can obviously improve the electro-catalytic activity of PAn/CGONWs electrode.Therefore,the current intensity of the oxidation peak is increased obviously.The results show that the higher of PAn mass percentage in the compsoites,the lower of interface electron transfer resistance of the PAn/CGONWs electrode.PAn can also affect the diffusion and adsorption process of L-Cys,TA and BA at the interface of the electrode.High PAn mass percentage is adverse to adsorption of the reactants.Therefore,there is an optimal PAn mass percentage in the composite electrodes.4.CGONWs electrode shows good electrochemical sensing performance for L-Cys,TA and BA under ambient temperature and atmosphere.The detection limit,linear detection range and sensitivity in 0.1 M KCl solution are 0.9 ?M,0.001-2 mM and 75.7?AmM-1 for the detection of L-Cys;7.7 ?M,0.01-2 mM and 44.2 ?AmM-1 for the detection of TA;and 0.91 ?M,0.001-2 mM and 69.9 ?AmM-1 for the detection of BA.5.PAn/CGONWs electrode exhibits better sensing performance than CGONWs electrode under same conditions.Among PAn/CGONWs-10%,PAn/CGONWs-20%,PAn/CGONWs-40%and PAn/CGONWs-60%electrodes,PAn/CGONWs-40%electrode has the best sensing performance.The detection limit,linear detection range and sensitivity are 0.23 ?M,0.0005-2 mM and 271.47 ?AmM-1 for the detection of L-Cys;while the corresponding values are 1.4 ?M,0.005-2 mM and 42.0 ?AmM-1 for the detection of TA and 0.28 ?M,0.001-2 mM and 118.8 ?AmM-1 for the detection of BA.The prepared CGONWs and PAn/CGONWs electrodes show good stability and reproducibility for the electrochemical sensing performance.The results show that the CGONWs and PAn/CGONWs have great application potential in the electrochemical detection of acidic small molecules.