Cary J. Miller

Microporous aluminum oxide films at electrodes part II. studies of electron transport in the Al2O3 matrix derivatized by adsorption of poly(4-vinylpyridine)

Abstract Porous aluminum oxide films are used as matrices for immobilization of electroactive reagents at electrodes. Aluminum oxide of highly regular porosity is produced by electrooxidation of aluminum substrates in polyprotic acid electrolytes. Its porosity consists of densely packed cylindrical pores perpendicular to the oxide film and penetrating its entire thickness. Depending on the applied voltage of the preparatory electrolysis, the average pore diameter of the oxide film can be varied in the range of ca. 10 nm to 200 nm. After separation of the Al 2 O 3 film from the aluminum substrate and the appropriate chemical tratment, the oxide films are overcoated with gold in vacuum in order to prepare porous aluminum oxide coated gold electrodes. The porosity of the Al 2 O 3 films ranges from 38% to 55% as assessed by rotating disk voltametry and transmission electron microscopy. Adsorption fo poly(4-vinylpyridine) along the pores of the oxide film results in binding of iron hexacyanide ions from acid media. The rate of electron transport along the pores of the oxide film was studied by a transient method, chronocoulometry and by a steady state technique, rotating disk voltammetry. Due to the heterogeneous nature of the electrode films in which electroactive ions are simultaneously present in the polymer phase and the aqueous phase of the oxide pores, the electron transport involves charge diffusion in both phases coupled by rapid electron and mass exchange equilibria. A new and generally applicable method of chronocoulometric data analysis was developed which allowed calculation of the diffusion coefficient of electron transport in the polymer phase, D p . This data analysis method parallels that developed by Anson et al. for steady-state conditions (J. Phys. Chem., 87 (1983) 214). Both techniques gave a D p value of ca. 1.0 × 10 −8 cm 2 /s.

Antibody-antigen exchange equilibria in a field of an external force: design of reagentless biosensors.

This correspondence presents a new strategy for detecting biological molecules that relies on competitive exchange interactions of an analyte with two-component molecular tethers attaching superparamagnetic microspheres (4 microm in diameter) to a sensor surface. The individual tethers consist of an antibody-antigen complex and are designed to selectively detect antigenic proteins in a sensitive reagentless fashion. In order to impart a driving force to the otherwise free energy neutral antibody-antigen exchange equilibrium, a small mechanical force of approximately 10 pN was applied to stretch the antibody-antigen tethers using a massively parallel magnetic tweezers device. The experimental work was carried out with human cardiac troponin I. This serum heart attack marker was used as an example of analytes of credible relevance to biomedical diagnostics. The initial results illustrate the functioning of a cardiotroponin sensor and offer a preliminary estimate of its sensitivity of 16 pM.

Antibody-Antigen Equilibria in a Field of Magnetic Forces: Design of Reagentless Biosensors

This project concerns a new strategy of detecting biological molecules that relies on competitive exchange interactions of an analyte with two-component molecular tethers attaching superparamagnetic microspheres (4 micron in diameter) to a sensor surface. The individual tethers consist of either double stranded DNA or antibody-antigen complex and are designed to selectively detect either specific ssDNA or antigenic proteins, respectively, in sensitive reagentless fashion. Performance of sensors was investigated using human cardiac troponin I, a serum heart attack marker, as an example of analytes of credible relevance to biomedical diagnostics.