SECM study of the effect of dispersing agents in the preparation of carbon

SOLEDAD BOLLO, NANCY F. FERREYRA, SILVIA A. MISCORIA AND GUSTAVO A. RIVAS

Canadá

Congreso; 58th Annual Meeting of the International Society of Electrochemistry.; 2007

In the last years different approaches have been conducted to improve the performance of electrochemical biosensors. In this sense, carbon nanotubes (CNTs) have largely contributed to the success of new electrochemical biosensors due to their exceptional electronic properties, electric conductivity and catalytic effects. The dispersion of CNTs in different media followed by the immobilization at solid surfaces is an interesting approach to prepare electrochemical sensors. For that reason, dispersions of CNT in acidic solutions, organic solvents and polymeric matrix have been successfully applied in electroanalysis for the determinations of diverse aalytes1-3. The aim of this work was to apply SECM technique to study the effect of different agents used to disperse CNTs on the topography and electron transfer properties of glassy carbon electrodes (GCE) modified with the resulting dispersions. Three dispersing agents, dimethylformamide, Nafion and chitosan, were selected and SECM feedback mode was used to image each modified surface with ferrocene methanol in phosphate buffer pH 7.4 as redox mediator. The results show that GCE modified with CNTs dispersed in DMF presents a homogeneous conductive surface and positiveapproach curves were always obtained. On the other hand, CNTs dispersed in Nafion and CHIT generates less homogeneous surfaces. The images showed very conductive spots, indicating an irregular distribution of CNTs on the GCE surface. When Nafion was used as dispersing agent three different behaviours were obtained with the approach experiments:(a) positive approach curves, which represent regions with high (reversible) heterogeneous ET rate constants, (b) negative approach curves indicating the presence of insulating areas, probably due to the absence of CNT and (c) regions with a mixed behaviour, indicating finite electron transfer regions. The effect of dispersing agent and CNTs concentrations were also evaluated.The knowledge of the electron transfer properties of GCE modified with different dispersions of CNTs will largely contribute to the rational design of new platforms for the development of electrochemical sensors.1-3. The aim of this work was to apply SECM technique to study the effect of different agents used to disperse CNTs on the topography and electron transfer properties of glassy carbon electrodes (GCE) modified with the resulting dispersions. Three dispersing agents, dimethylformamide, Nafion and chitosan, were selected and SECM feedback mode was used to image each modified surface with ferrocene methanol in phosphate buffer pH 7.4 as redox mediator. The results show that GCE modified with CNTs dispersed in DMF presents a homogeneous conductive surface and positiveapproach curves were always obtained. On the other hand, CNTs dispersed in Nafion and CHIT generates less homogeneous surfaces. The images showed very conductive spots, indicating an irregular distribution of CNTs on the GCE surface. When Nafion was used as dispersing agent three different behaviours were obtained with the approach experiments:(a) positive approach curves, which represent regions with high (reversible) heterogeneous ET rate constants, (b) negative approach curves indicating the presence of insulating areas, probably due to the absence of CNT and (c) regions with a mixed behaviour, indicating finite electron transfer regions. The effect of dispersing agent and CNTs concentrations were also evaluated.The knowledge of the electron transfer properties of GCE modified with different dispersions of CNTs will largely contribute to the rational design of new platforms for the development of electrochemical sensors.