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.
Infectious diseases, such as influenza, present a prominent global problem including the constant threat of pandemics that initiate in avian or other species and then pass to humans. We report a new sensor that can be specifically functionalized to detect antibodies associated with a wide range of infectious diseases in multiple species. This biosensor is based on electrochemical detection of hydrogen peroxide generated through the intrinsic catalytic activity of all antibodies: the antibody catalyzed water oxidation pathway (ACWOP). Our platform includes a polymer brush-modified surface where specific antibodies bind to conjugated haptens with high affinity and specificity. Hydrogen peroxide provides an electrochemical signal that is mediated by Resorufin/Amplex Red. We characterize the biosensor platform, using model anti-DNP antibodies, with the ultimate goal of designing a versatile device that is inexpensive, portable, reliable, and fast. We demonstrate detection of antibodies at concentrations that fall well within clinically relevant levels.
While the high energy density of methanol makes it a promising fuel for low-temperature fuel cells, the lack of an oxidation catalyst with sufficiently fast kinetics limits the commercial implementation of these fuel cells. The numerous adsorption and charge-transfer steps associated with complete methanol oxidation make metal alloys likely candidates for superior catalysts. Combinatorial searches employing metal thin-film libraries are well suited for methanol-oxidation catalyst studies, and we have developed experimental techniques to strengthen the evaluation of such libraries in a high-throughput regime. In particular, we employ catalyst pretreatment methods and linear sweep voltammetry with a ferrocene redox couple to determine the area and thus the specific activity of kinetically stable alloy catalysts. Particular attention is given to the relevance of the assessment to fuel cell operating conditions. These methods, combined with established techniques, provide both a rapid semiquantitative map of methanol-oxidation activity and enable a detailed quantitative analysis of the most active compositions. The efficacy of these techniques is demonstrated through the evaluation of Pt–Zn continuous composition-spread thin-films of varying thickness. The detailed characterization of the thin films is presented and discussed in the context of the electrochemical analysis.
Sputter codeposition of platinum and tantalum is used to generate catalyst libraries of Pt1−x Ta x with 0.05< x <0.9. Extensive characterization of the libraries by high-energy X-ray diffraction reveals the presence of several ordered intermetallic phases as a function of composition and deposition conditions. Assessment of the activity toward the oxidation of methanol and formic acid is achieved through a fluorescence-based parallel screening, followed by detailed testing of the most promising catalysts. Correlations among the electrochemical results, the inferred phase fields and X-ray photoelectron spectroscopy characterization provide an understanding of the catalytically active surface and highlight the utility of composition spread thin films in catalyst research. The observations suggest that the interaction between Pt and Ta suboxides is important and enhances the catalytic activity of Pt.
Although platinum and platinum-based intermetallic alloys have been extensively studied as catalysts for proton exchange membrane fuel cells, platinum-based nitride catalysts have been relatively unexplored. We report the synthesis and characterization of a platinum-based nitride, Pt2Mo3N, using a composition spread thin-film deposition technique. The Pt2Mo3N thin film was generated by codeposition of platinum and molybdenum and subsequent heat treatment in an ammonia flow at 800 °C for 6 h. The thin film was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and electrochemical tests, including the assessment of catalytic activity toward the oxidation of methanol and formic acid and the reduction of oxygen. The nitride film was smooth and contained single-phase, nearly stoichiometric Pt2Mo3N. Cyclic voltammograms of Pt2Mo3N in 0.1 M H2SO4 demonstrated electrochemical stability far greater than that of a PtMo alloy with the same Pt:Mo ratio, indicating that the formation of the nitride phase enhances electrochemical stability. The ternary nitride exhibited oxidation currents in formic acid and methanol solutions above approximately 0.0 and 0.4 V vs an Ag/AgCl reference electrode, respectively. These are above the expected equilibrium oxidation potentials of approximately −0.2 V. The onset potential for oxygen reduction was estimated to be ∼0.2 V vs Ag/AgCl, well below the equilibrium value of 1.0 V.
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