We have used single-walled carbon nanotube transistors to measure changes in the chemical potential of a solution due to redox-active transition-metal complexes. The interaction of the molecules with a gold electrolyte-gate wire changes the electrostatic potential sensed by the nanotube, which in turn shifts the gate-voltage dependence of the nanotube conductance. As predicted by the Nernst equation, this shift depends logarithmically on the ratio of oxidized to reduced molecules.

Biological systems have a tendency to adsorb nonspecifically onto a solid substrate, thus reducing the efficacy of the interface being used in biorecognition. This nonspecific adsorption is a common problem in the development of biosensors as it typically reduces the efficacy of the sensor platform. In this manuscript we report the synthesis of an oligo(ethylene glycol) (OEG) containing ATRP (atom transfer radical polymerization) thiol initiator and demonstrate the role of this initiator in preventing nonspecific adsorption of IgG antibodies on chemically functionalized gold electrode surfaces using cyclic voltammetry. A new synthetic route for the synthesis of the new ATRP thiol initiator in high yields has been reported. Surface initiated poly(acrylic acid) brushes grown off the gold surface with modified OEG containing and conventional ATRP thiol initiators were chemically modified with 2,4-dinitrophenyl (DNP) groups. Amperometric studies were carried out on gold electrodes modified with DNP-PAA brushes using DNP-specific and nonspecific IgG antibodies. The cyclic voltammograms of an osmium redox mediator recorded over time suggest that the chemical modification of the gold electrodes with DNP-PAA brushes using the OEG-containing ATRP initiator is much more effective in preventing nonspecific adsorption of antibodies than polymer brushes grown from the conventional initiator. Finally, we confirmed these results with the quartz crystal microbalance (QCM) technique by quantitatively evaluating the adsorption of nonspecific IgG antibodies on DNP-PAA functionalized QCM surfaces. The use of this modified ATRP thiol initiator to chemically functionalize macro/microelectrode surfaces will help develop reproducible, reliable, and robust electrochemical biosensors with minimized nonspecific adsorption.

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