Standard electrochemical data for high-quality, boron-doped diamond thin-film electrodes are presented. Films from two different sources were compared (NRL and USU) and both were highly conductive, hydrogen-terminated, and polycrystalline. The films are acid washed and hydrogen plasma treated prior to use to remove nondiamond carbon impurity phases and to hydrogen terminate the surface. The boron-doping level of the NRL film was estimated to be in the mid 1019 B/cm3 range, and the boron-doping level of the USU films was approximately 5 x 10(20) B/cm(-3) based on boron nuclear reaction analysis. The electrochemical response was evaluated using Fe-(CN)6(3-/4-), Ru(NH3)6(3+/2+), IrCl6(2-/3-), methyl viologen, dopamine, ascorbic acid, Fe(3+/2+), and chlorpromazine. Comparisons are made between the apparent heterogeneous electron-transfer rate constants, k0(app), observed at these high-quality diamond films and the rate constants reported in the literature for freshly activated glassy carbon. Ru(NH3)6(3+/2+), IrCl6(2-/3-), methyl viologen, and chlorpromazine all involve electron transfer that is insensitive to the diamond surface microstructure and chemistry with k0(app) in the 10(-2)-10(-1) cm/s range. The rate constants are mainly influenced by the electronic properites of the films. Fe(CN)6(3-/4-) undergoes electron transfer that is extremely sensitive to the surface chemistry with k0(app) in the range of 10(-2)-10(-1) cm/s at the hydrogen-terminated surface. An oxygen surface termination severely inhibits the rate of electron transfer. Fe(3+/2+) undergoes slow electron transfer at the hydrogen-terminated surface with k0(app) near 10(-5) cm/s. The rate of electron transfer at sp2 carbon electrodes is known to be mediated by surface carbonyl functionalities; however, this inner-sphere, catalytic pathway is absent on diamond due to the hydrogen termination. Dopamine, like other catechol and catecholamines, undergoes sluggish electron transfer with k0(app) between 10(-4) and 10(-5) cm/s. Converting the surface to an oxygen termination has little effect on k0(app). The slow kinetics may be related to weak adsorption of these analytes on the diamond surface. Ascorbic acid oxidation is very sensitive to the surface termination with the most negative Ep(ox) observed at the hydrogen-terminated surface. An oxygen surface termination shifts Ep(ox) positive by some 250 mV or more. An interfacial energy diagram is proposed to explain the electron transfer whereby the midgap density of states results primarily from the boron doping level and the lattice hydrogen. The films were additionally characterized by scanning electron microscopy and micro-Raman imaging spectroscopy. The cyclic voltammetric and kinetic data presented can serve as a benchmark for research groups evaluating the electrochemical properties of semimetallic (i.e., conductive), hydrogen-terminated, polycrystalline diamond.

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The electrochemistry of four redox analytes [Fe(CN) 6 Ϫ3/Ϫ4 , Ru(NH 3 ) 6 ϩ2/ϩ3 , IrCl 6 Ϫ2/Ϫ3 , and methyl viologen, MV ϩ2/ϩ/0 ] was investigated at polycrystalline, boron-doped diamond thin-film electrodes before and after anodic polarization and hydrogen plasma treatment. The as-deposited diamond surface is predominantly hydrogen terminated, and quasi-reversible cyclic voltammograms (⌬E p of 60-80 mV) were observed for all of these couples at 0.1 V/s. After anodic polarization in H 2 SO 4 , the surface atomic O/C ratio, as determined by X-ray photoelectron spectroscopy, increased from 0.02 to ca. 0.20. Concomitant with the increase in surface oxygen, the ⌬E p for Fe(CN) 6Ϫ3/Ϫ4 increased to over 200 mV, while the ⌬E p values for the other redox systems remained relatively unchanged. After acid washing and rehydrogenating the surface in a hydrogen plasma (i.e., atomic hydrogen), the ⌬E p for Fe(CN) 6Ϫ3/Ϫ4 returned to ca. 80 mV, while the ⌬E p values for the other three redox analytes remained close to the original values. The results demonstrate that electron transfer for ferri/ferrocyanide is very sensitive to the presence of surface carbon-oxygen functionalities and that the electron transfer involves a site associated with the hydrogen-terminated surface. The results also unequivocally rule out the influence of adventitious nondiamond carbon phases as the sole sites for the electron transfer.

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Thin structures of alternating magnetic and nonmagnetic layers with a total thickness of a few hundred nanometers exhibit a phenomenon known as giant magnetoresistance. The resistance of microfabricated giant magnetoresistors (GMRs) is dependent on the strength of an external magnetic field. This paper examines magnetic labeling methodologies and surface derivatization approaches based on protein-protein binding that are aimed at forming a general set of protocols to move GMR concepts into the bioanalytical arena. As such, GMRs have been used to observe and quantify the immunological interaction between surface-bound mouse IgG and alpha-mouse IgG coated on superparamagnetic particles. Results show the response of a GMR network connected together as a set of two sense GMRs and two reference GMRs in a Wheatstone bridge as a means to compensate for temperature effects. The response can be readily correlated to the amount of the magnetically labeled alpha-mouse IgG that is captured by an immobilized layer of mouse IgG, the presence of which is confirmed with X-ray photoelectron spectroscopy and atomic force microscopy. These results, along with a detailed description of the experimental testing platform, are described in terms of sensitivity, detection limits, and potential for multiplexing.