A simple, rapid, and highly sensitive bioelectrochemical immunoassay method based on magnetic beads (MBs) and disposable screen-printed electrodes (SPE) has been developed to detect polychlorinated biphenyls (PCBs). The principle of this bioassay is based on a direct competitive enzyme-linked immunosorbent assay using PCB-antibody-coated MBs and horseradish peroxidase (HRP)-labeled PCB (HRP-PCB). A magnetic process platform was used to mix and shake the samples during the immunoreactions and to separate free and unbound reagents after the liquid-phase competitive immunoreactions among PCB-antibody-coated MBs, PCB analyte, and HRP-PCB. After a complete immunoassay, the HRP tracers attached to MBs were transferred to a substrate solution containing o-aminophenol and hydrogen peroxide for electrochemical detection. The different parameters, including the amount of HRP-PCB conjugates, immunoreaction time, and the concentration of substrate that governs the analytical performance of the immunoassay have been studied in detail and optimized. The detection limit of 10 gmL(-1) was obtained under optimum experimental conditions. The performance of this bioelectrochemical immunoassay was successfully evaluated with untreated river water spiked with PCBs, and the results were validated by commercial PCB enzyme-linked immunosorbent assay kit, indicating that this convenient and sensitive technique offers great promise for decentralized environmental application and trace PCBs monitoring.
[Show abstract][Hide abstract] ABSTRACT: The derivation of atomistic potential parameters, based on electronic structure calculations, for modeling electron and hole polarons in titania polymorphs is presented. The potential model is a polarizable version of the Matsui and Akaogi model (Matsui, M.; Akaogi, M. Mol. Simul. 1991, 6, 239) that makes use of a shell model to account for the polarizability of oxygen ions. The −1 and +1 formal charges of the electron and hole polarons, respectively, are modeled by delocalizing the polaron’s charge over a titanium or oxygen ion, respectively, and its first nearest-neighbors. The charge distributions and the oxygen polarizability were fitted to the reorganization energies of a series of electron and hole polaron transfers in rutile and anatase obtained from electronic structure calculations at zero Kelvin and validated against lattice deformation due to both types of polaron. Good agreement was achieved for both properties. In addition, the potential model yields an accurate representation of a range of bulk properties of several TiO2 polymorphs as well as Ti2O3. The model thus derived enables us to consider systems large enough to investigate how the charge transfer properties at titania surfaces and interfaces differ from those in the bulk. For example, reorganization energies and free energies of charge transfer were computed as a function of depth below vacuum-terminated rutile (110) and anatase (001) surfaces using a mapping approach first introduced by Warshel (Warshel, A. J. Phys. Chem. 1982, 86, 2218). These calculations indicate that deviations from bulk values at the surface are substantial but limited to the first couple of surface atomic layers and that polarons are generally repelled from the surface. Moreover, attractive subsurface sites may be found as is predicted for hole polarons at the rutile (110) surface. Finally, several charge transfers from under-coordinated surface sites were found to be in the so-called Marcus inverted-region.
The Journal of Physical Chemistry C 04/2008; 112(20). DOI:10.1021/jp8007865 · 4.77 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper presents a novel microfluidic system for rapid label-free detection of endothelial progenitor cells (EPCs) from small volumes of white blood cells samples, to obtain a bedside cardiovascular diagnostic solution. The system was built on a single 1 cm(2) microelectrode array silicon chip, integrated with negative dielectrophoresis for cell trapping, surface immunochemistry for selective cell capture, and fluidics for cell washing and impedance detection. The level of circulating EPC level in blood is a biomarker of clinical interest, linked to the assessment of risk factors in cardiovascular diseases which are a major global concern. Rare EPCs are usually detected through in vitro culture or flow cytometry, which are too time-consuming to bring timely reports in acute diseases. Although microfluidics approaches have enabled reduced processing time and enhanced portability, their sensitivity and processing volumes are still inadequate for rare cell detection at a bedside setting. Using small highly sensitive microelectrodes, our novel integrated system achieved the detection of 720 EPCs in a small 12 microl sample of 72,000 peripheral blood mononuclear cells (PBMC), i.e. equivalent to a concentration of EPCs of 0.1% of 100 microl blood. This demonstrated that clinically significant level of EPCs (<0.5% of PBMC) could be detected for the first time on a detection system at bedside set-up, showing great potential in applications for point-of-care diagnosis.
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