Biomedical subjects

Michael C Granger

Publications and source records attributed to Michael C Granger.

5 recordsLinked to original sources

PubMed2005

Giant magnetoresistive sensors and superparamagnetic nanoparticles: a chip-scale detection strategy for immunosorbent assays.

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.

Animals↗

PubMed2005

Study and application of a controlled-potential electrochemistry-electrospray emitter for electrospray mass spectrometry.

This paper discusses continued studies and new analytical applications of a recently developed three-electrode controlled-potential electrochemical cell incorporated into an electrospray ion source (Van Berkel, G. J.; Asano, K. G.; Granger, M. C. Anal. Chem. 2004, 76, 1493-1499.). This cell contains a porous flow-through working electrode (i.e., the emitter electrode) with high surface area and auxiliary electrodes with small total surface area that are incorporated into the emitter electrode circuit to control the electrochemical reactions of analytes in the electrospray emitter. The current at the working and auxiliary electrodes, and current at the grounding points upstream and downstream of the emitter in the electrospray circuit, were recorded in this study, along with the respective mass spectra of model compound reserpine, under various operating conditions to better understand the electrochemical and electrospray operation of this emitter cell. In addition to the ability to control analyte oxidation in positive ion mode (or reduction in negative ion mode) in the electrospray emitter, this emitter cell system was shown to provide the ability to efficiently reduce analytes in positive ion mode and oxidize analytes in negative ion mode. This was demonstrated by the reduction of methylene blue in positive ion mode and oxidation of 3,4-dihydroxybenzoic acid in negative ion mode. Also, the ability to control electrochemical reactions via potential control was used to selectively ionize (oxidize) analytes with different standard electrochemical potentials within mixtures to different charge states to overcome overlapping molecular ion isotopic clusters. The analytical benefit of this ability was illustrated using a mixture of nickel and cobalt octaethylporphyrin.

Cobalt↗

PubMed2004

Controlling analyte electrochemistry in an electrospray ion source with a three-electrode emitter cell.

The inherent electrochemistry occurring at the emitter electrode of an electrospray ion source was effectively controlled by incorporating a three-electrode controlled-potential electrochemical cell into the controlled-current electrospray emitter circuit. Two different basic cell designs were investigated to accomplish this control, namely, a planar flow-by working electrode and a porous flow-through working electrode design, each operated with a potentiostat floated at the electrospray high voltage. Control of the analyte electrochemistry was tested using the indole alkaloid reserpine, which is often used to test the specifications of electrospray mass spectrometry instrumentation. Reserpine was relatively easy to oxidize (E(p) = 0.73 V vs Ag/AgCl) in the acidic electrospray medium (acetonitrile/water 1:1 v/v, 5.0 mM ammonium acetate, 0.75 vol % acetic acid) and was oxidized when the conventional electrospray emitter was used at low solution flow rate. With the proper cell auxiliary electrode configuration and adjustment of the working electrode potential, it was found that reserpine oxidation could be "turned off" at flow rates as low as 2.5 microL/min as well as at flow rates as high as 30-40 microL/min. Just as important, it was also possible to "turn on" essentially 100% oxidation of reserpine in this flow rate range. The area of the auxiliary electrode along with flow rate, which affect mass transport of analytes to this electrode, were found to be critical in controlling the electrochemical reactions in the emitter cell. Such control over analyte electrochemical reactions in the emitter has been difficult or impossible to achieve with a conventional electrospray emitter. This control is paramount in obtaining experimental results free from electrochemically generated artifacts of the analyte or in exploiting electrochemical reactions involving the analyte to analytical advantage.

Electrochemistry↗

PubMed2004

Efficient analyte oxidation in an electrospray ion source using a porous flow-through electrode emitter.

This article describes the components, operation, and use of a porous flow-through electrode emitter in an electrospray ion source. This emitter electrode geometry provided enhanced mass transport to the electrode surface to exploit the inherent electrochemistry of the electrospray process for efficient analyte oxidation at flow rates up to 800 microL/min. An upstream current loop in the electrospray source circuit, formed by a grounded contact to solution upstream of the emitter electrode, was utilized to increase the magnitude of the total current at the emitter electrode to overcome current limits to efficient oxidation. The resistance in this upstream current loop was altered to control the current and "dial-in" the extent of analyte oxidation, and thus, the abundance and nature of the oxidized analyte ions observed in the mass spectrum. The oxidation of reserpine to form a variety of products by multiple electron transfer reactions and oxidation of the ferroceneboronate derivative of pinacol to form the ES active radical cation were used to study and to illustrate the performance of this new emitter electrode design. Flow injection, continuous infusion, and on-line HPLC experiments were performed.

Borates↗

PubMed2004

Metabolomic applications of electrochemistry/mass spectrometry.

Analytical techniques used for multivariate analysis of endogenous metabolites in biological systems (e.g., metabolomics, metabonomics) must be capable of accurately and selectively monitoring many known and unknown molecules that span a diverse chemical spectrum and over extremely large dynamic concentration ranges. Mass spectrometric (MS) and electrochemical array (EC-Array) detection have been widely used for multi-component analysis with applicability to low-level (fmol) metabolites. Described here are practical considerations and results obtained with the combined use of EC-Array and MS for HPLC-based multivariate metabolomic analysis. Data presented include the study of changes in rat urinary metabolite profiles associated with xenobiotic toxin exposure analyzed by HPLC using water:acetonitrile binary gradient conditions and post-column flow splitting between EC-Array and MS detectors. Results show complementary quantitative and qualitative analysis and the ability to differentiate sample groups consistent with xenobiotic-induced histopathological changes. The potential applicability of this hyphenated technique for biomarker elucidation through measurement of redox active compounds that are commonly associated with disease pathology and xenobiotic toxicity is discussed. The use of EC reactor cells in series with MS is also presented as a means of producing likely metabolites to facilitate structural elucidation and confirmation.

Animals↗