SECM characterization of self assembled multilayers of gold nanoparticles, polietilenimine and DNA. Kinetic evaluation of ferrocene methanol oxidation.

N. F. FERREYRA, S. BOLLO, G. A. RIVAS

Banff, Canadá

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

ISE

Nanoparticles-DNA nanostructured films are currently under intense investigation because of their potential application in the development of biosensors, the goal is the combination of the recognition capability of DNA with the particular properties of the nanoparticles. DNA and gold nanoparticles (gNP) can be immobilized electrostatically in multilayered structures with polyelectrolytes of opposite charge. Depending on the polyelectrolyte nature, the nanoparticles morphology as well as the self-assembling conditions the final properties of the film can be modified. SECM is a versatile technique to study these nanostructures making possible imaging different substrate with about micrometer resolution. It can also be used to make a distinction of regions of different conductivity or electrochemical activity with high spatial resolution. In thiswork we ap p ly SECM to s tudy o f self assembled multilayers of gNP, the polycation polyethileneimine (PEI) and DNA. Gold electrodes were modified with a negatively charged thiol followed by the alternative adsorption of PEI/gNP/PEI/DNA. The SECM feedback mode was selected to image the modified surfaces using as redox mediator ferrocene methanol. A 10µm carbon fiber electrode, was approximated to an unmodified part of a gold electrode until the current was 1.25 times i∞ (i∞ is the diffusion current obtained when the tip is far from surface). The tip was then used to obtain images of each modification (Figure 1). Furthermore a series of approach curves were conducted to study the electrochemical activity and to determine the standard rate constant, k0 of each modified electrode. The results shown that thiol, PEI and DNA are adsorbed uniformly on the gold surface producing a decrease of k0 (table 1). The adsorption of gNp produce an increase of k0 reaching the value corresponding to the bare gold electrode∞ (i∞ is the diffusion current obtained when the tip is far from surface). The tip was then used to obtain images of each modification (Figure 1). Furthermore a series of approach curves were conducted to study the electrochemical activity and to determine the standard rate constant, k0 of each modified electrode. The results shown that thiol, PEI and DNA are adsorbed uniformly on the gold surface producing a decrease of k0 (table 1). The adsorption of gNp produce an increase of k0 reaching the value corresponding to the bare gold electrode