PubMed Health⌕ Search

Biomedical subjects

Charles S Henry

Publications and source records attributed to Charles S Henry.

At least 19 recordsLinked to original sources
PubMed2006

Generation of hydrophilic poly(dimethylsiloxane) for high-performance microchip electrophoresis.

Poly(dimethylsiloxane) (PDMS) has become one of the most widely used materials for microchip capillary electrophoresis and microfluidics. The popularity of this material is the result of its low cost, simple fabrication, and rugged elastomeric properties. The hydrophobic nature of PDMS, however, limits its applicability for microchip CE, microfluidic patterning, and other nonelectrophoresis applications. The surface of PDMS can be made hydrophilic using a simple air plasma treatment; however, this property is quickly lost through hydrophobic recovery caused by diffusion of unreacted oligomer to the surface. Here, a simple approach for the generation of hydrophilic PDMS with long-term stability in air is presented. PDMS is rendered hydrophilic through a simple two-step extraction/oxidation process. First, PDMS is extracted in a series of solvents designed to remove unreacted oligomers from the bulk phase. Second, the oligomer-free PDMS is oxidized in a simple air plasma, generating a stable layer of hydrophilic SiO2. The conversion of surface-bound siloxane to SiO2 was followed with X-ray photoelectron spectroscopy. SiO2 on extracted-oxidized PDMS was stable for 7 days in air as compared to less than 3 h for native PDMS. Furthermore, the contact angle for modified PDMS was reduced to <40 degrees and remained low throughout the experiments. As a result of the decreased contact angle, capillary channels self-wet through capillary action, making the microchannels much easier to fill. Finally, the modification significantly improved the performance of the devices for microchip electrophoresis. The electroosmotic flow increased from 4.1 x 10(-4) to 6.8 x 10(-4) cm(2)/V.s for native compared to oxidized PDMS. Separation efficiencies for electrochemical detection also increased from 50 000 to 400 000 N/m for a 1.1-nL injection volume. The result of this modification is a significant improvement in the performance of PDMS for microchip electrophoresis and microfluidic applications.

Dimethylpolysiloxanes↗
PubMed2006

Analysis of anions in ambient aerosols by microchip capillary electrophoresis.

We describe a microchip capillary electrophoresis method for the analysis of nitrate and sulfate in ambient aerosols. Investigating the chemical composition of ambient aerosol particles is essential for understanding their sources and effects. Significant progress has been made towards developing mass spectrometry-based instrumentation for rapid qualitative analysis of aerosols. Alternative methods for rapid quantification of selected high abundance compounds are needed to augment the capacity for widespread routine analysis. Such methods could provide much higher temporal and spatial resolution than can be achieved currently. Inorganic anions comprise a large percentage of particulate mass, with nitrate and sulfate among the most abundant species. While ion chromatography has proven very useful for analyzing extracts of time-integrated ambient aerosol samples collected on filters and for semi-continuous, on-line particle composition measurements, there is a growing need for development of new compact, inexpensive approaches to routine on-line aerosol ion analysis for deployment in spatially dense, atmospheric measurement networks. Microchip capillary electrophoresis provides the necessary speed and portability to address this need. In this report, on-column contact conductivity detection is used with hydrodynamic injection to create a simple microchip instrument for analysis of nitrate and sulfate. On-column contact conductivity detection was achieved using a Pd decoupler placed upstream from the working electrodes. Microchips containing two Au or Pd working electrodes showed a good linear range (5-500 microM) and low limits-of-detection for sulfate and nitrate, with Au providing the lowest detection limits (1 microM) for both ions. The completed microchip system was used to analyze ambient aerosol filter samples. Nitrate and sulfate concentrations measured by the microchip matched the concentrations measured by ion chromatography.

Journal Article↗
PubMed2006

Screening for physical stability of a Pseudomonas amylase using self-interaction chromatography.

Formulation development is an integral step in the successful commercialization of protein-based products in both the biotechnology and pharmaceutical industries. As the number of these protein formulations increases, so does the need for innovative approaches to characterize physical and chemical product stability. In this study, the osmotic second virial coefficient (B) of a commercial amylase was evaluated by self-interaction chromatography (SIC) as an innovative approach to characterize physical protein stability. B was measured as a function of pH and several common formulation additives (cosolvents), including sodium chloride, sucrose, and sorbitol. Cosolvent- and pH-induced physical stabilization of amylase is discussed in terms of positive shifts in B. Liquid chromatographic measurements of total soluble amylase and enzymatic activity measurements correlated qualitatively with trends in B except near the pI of amylase, where physical stability was minimal.

Amylases↗
PubMed2006

Second virial coefficient determination of a therapeutic peptide by self-interaction chromatography.

Self-interaction of macromolecules has been shown to play an important role in a number of physical processes, including crystallization, solubility, viscosity, and aggregation. Peptide self-interaction is not as well studied as for larger proteins, but should play an equally important role. The osmotic second virial coefficient, B, can be used to quantify peptide and protein self-interaction. B values are typically measured using static light scattering (SLS). Peptides, however, do not scatter enough light to allow such measurements. This study describes the first use of self-interaction chromatography (SIC) for the measurement of peptide B values because SIC does not have the molecular size limitations of SLS. In the present work, SIC was used to measure B for enfuvirtide, a 36-amino acid therapeutic peptide, as a function of salt concentration, salt type, and pH. B was found to correlate strongly with solubility and apparent molecular weight. In general, the solubility of enfuvirtide increases with pH from 6 to 10 and decreases as the salt concentration increases from 0 to 0.5M for three different salts. The effect of peptide concentration on B was also investigated and shown to have a significant effect, but only at high concentrations (>80 mg/mL).

Chromatography↗
PubMed2006

Effect of buffer species on the thermally induced aggregation of interferon-tau.

It is now becoming apparent that a common pathway of protein aggregation involves the unimolecular structural rearrangement from the native state to a slightly expanded aggregation-competent species. It is the goal of this study to understand the aggregation and the effects of buffer on the stability of IFN-tau. In this study, the thermally-induced aggregation of interferon-tau (IFN-tau) is described. By monitoring the aggregation rate in the presence of increasing amounts of sucrose, the relative change in surface area (Deltas) for conversion to the aggregation-competent state can be determined. Under conditions of pH 7 and in 20 mM buffer, the protein displays different aggregation rates depending on the nature of the buffer species. The protein aggregates mostly quickly in phosphate buffer, slower in the presence of Tris and slowest in the presence of histidine. The largest value for Deltas occurs for the histidine-containing samples, where aggregation proceeds via a slightly expanded aggregation competent state with a surface area increase of 7.6%. Furthermore, it appears that histidine binds to the native state of IFN-tau, thereby stabilizing the native state and retarding aggregation. Measurement of the second virial coefficient, B(22), for different formulations indicates that inclusion of histidine has only a small effect on repulsion between protein molecules, suggesting that colloidal stabilization is not the dominant mechanism for stabilization of IFN-tau. This study represents the first detailed biophysical study of specific buffer-induced stabilization, resulting in shifting the equilibrium towards the native state and away form the expanded aggregation-competent species.

Animals↗
PubMed2006

Microchip capillary electrophoresis: an introduction.

Microchip capillary electrophoresis emerged in the early 1990s as an interesting and novel approach to the high-speed separation of biological compounds, including DNA and proteins. Since the early development in this area, growth in the research field has exploded and now includes chemists and engineers focused on developing new and better microchips, as well as biologists and biochemists who have begun to apply this exciting and still relatively new methodology to real-world problems. This chapter seeks to outline the historical development of microchip, the key elements of microchip capillary electrophoresis, and finally some of the important applications being developed that utilize microchip capillary electrophoresis.

DNA↗
PubMed2006

Micro-molding for poly(dimethylsiloxane) microchips.

In the present chapter, some basic definitions about the photolithography process are explained and then the standard preparation of the silicon wafer, the fabrication of the mold, and the preparation and assembly of poly(dimethylsiloxane) (PDMS)-based microchips are discussed. The purpose of this chapter is to describe the most used techniques for preparation of PDMS microchips. A list of tips is included in order to provide a troubleshooting guide for the most common difficulties found during the fabrication process. Some recent alternative approaches to microfabrication are also discussed.

Dimethylpolysiloxanes↗
PubMed2006

Polyelectrolyte coatings for microchip capillary electrophoresis.

In chip-based electrophoretic analysis of biomolecules, chemical modification of the microchannel is widely employed to reduce or eliminate the analyte-wall interactions and alter electroosmotic flow (EOF) in the microchannel. A stable polyelectrolyte multilayer coating is one common way to regulate or eliminate EOF and prevent analyte adsorption for the rapid, efficient separation of biomolecules within microchannels. A wide variety of polyelectrolytes have been used as coatings. This chapter deals with how to coat microchips with polyelectrolytes and the expected results using polybrene and dextran sulfate as models. The technique presented here is generally applicable to any polyelectrolyte.

Dimethylpolysiloxanes↗
PubMed2005

Second virial coefficient studies of cosolvent-induced protein self-interaction.

Protein self-interaction is important in protein crystal growth, solubilization, and aggregation, both in vitro and in vivo, as with protein misfolding diseases, such as Alzheimer's. Although second virial coefficient studies can supply invaluable quantitative information, their emergence as a systematic approach to evaluating protein self-interaction has been slowed by the limitations of traditional measurement methods, such as static light scattering. Comparatively, self-interaction chromatography is an inexpensive, high-throughput method of evaluating the osmotic second virial coefficient (B) of proteins in solution. In this work, we used self-interaction chromatography to measure B of lysozyme in the presence of various cosolvents, including sucrose, trehalose, mannitol, glycine, arginine, and combinations of arginine and glutamic acid and arginine and sucrose in an effort to develop a better fundamental understanding of protein self-interaction in complex cosolvent systems. All of these cosolvents, alone or in combination, increased B, indicating a reduction in intermolecular attraction. However, the magnitude of cosolvent-induced changes in B was found to be largely dependent on the ability to control long-range electrostatic repulsion. To the best of our knowledge, this work represents the most comprehensive virial coefficient study to date focusing on complex cosolvent-induced effects on the self-interaction of lysozyme.

Algorithms↗
PubMed2005

Analysis of natural flavonoids by microchip-micellar electrokinetic chromatography with pulsed amperometric detection.

Catechins (catechin and other derivatives) are naturally occurring flavonoids present in a number of plants and foods. They are also part of numerous nutraceutical formulations because they are believed to have antioxidant, cancer chemo-preventative, anti-inflammatory and antimicrobial properties. The determination of catechins has traditionally been performed by HPLC. However, this methodology is both time and sample intensive and generates large amounts of organic solvent waste. In the current report, an application of MEKC using a PDMS microchip is presented for the analysis of catechins. The system uses pulsed amperometric detection for direct analysis of important naturally occurring catechins. The effect of pH, surfactant concentration, detection potential and signal stability were analyzed. Linear relationships were found between the concentration and peak current, with good stability and limits of detection of 8 [micro sign]M for catechin, epigallocatechin gallate and epicatechin, and 14 [micro sign]M for epicatechin gallate. Optimum conditions were applied to the detection of selected catechins in a commercially available green tea extract nutraceutical and the results were compared to HPLC analysis. The analysis using microchip micellar electrokinetic chromatography and pulsed amperometric detection was completed in 4.5 min, 10 times faster than the HPLC analysis.

Catechin↗
PubMed2005

Determination of levoglucosan from smoke samples using microchip capillary electrophoresis with pulsed amperometric detection.

Separation and detection of native anhydrous carbohydrates derived from the combustion of biomass using an electrophoretic microchip with pulsed amperometric detection (PAD) is described. Levoglucosan represents the largest single component of the water extractable organics in smoke particles and can be used to trace forest fires or discriminate urban air pollution sources. Detection of levoglucosan and other sugar anhydrides in both source and ambient aerosol samples is typically performed by gas chromatographic (GC) separation with mass spectrometric (MS) detection. This method is cost, time, and labor intensive, typically involving a multistep solvent extraction, chemical derivatization, and finally analysis by GC/MS. However, it provides a rich wealth of chemical information as the result of the combination of a separation method and MS and exhibits good sensitivity. In contrast, microchip capillary electrophoresis offers the possibility of performing simpler, less expensive, and faster analysis. In addition, integrated devices can be fabricated and incorporated with an aerosol collection system to perform semicontinuous, onsite analysis. In the present report, the effect of the separation potential, buffer pH and composition, injection time, and pulsed amperometric detection parameters were studied in an effort to optimize both the separation and detection of anhydrous sugars. Using the optimized conditions, the analysis can be performed in less than a minute, with detection limits ranging from 22 fmol (16.7 microM) for levoglucosan to 336 fmol (258.7 microM) for galactosan. To demonstrate the capabilities of the device, a comparison was made between GC/MS and microchip electrophoresis using an aerosol source sample generated in a wood-burning chamber. A second example utilizing an ambient aerosol sample illustrates a matrix interference necessitating additional method development for application to samples not dominated by wood smoke.

Aerosols↗
PubMed2005

Comparison of surfactants for dynamic surface modification of poly(dimethylsiloxane) microchips.

In the present report, the use of negatively charged surfactants as modifiers of the background electrolyte is reported using poly(dimethylsiloxane) (PDMS) microchips. In particular, the use of anionic surfactants, such as sodium dodecyl sulfate, phosphatidic acid, and deoxycholate, was studied. When surfactants were present in the run buffer, an increase in the electroosmotic flow (EOF) was observed. Two additional effects were also observed: (i) stabilization of the run-to-run EOF, (ii) an improvement in the electrochemical response for several biomolecules. In order to characterize the analysis conditions, the effects of different surfactant, electrolyte, and pH were studied. EOF measurements were performed using either the current monitoring method or by detection of a neutral molecule. The first adsorption/desorption kinetics studies are also reported for different surfactants onto PDMS. The separation of biologically important analytes (glucose, penicillin, phenol, and homovanillic acid) was improved decreasing the analysis time from 200 to 125 s. However, no significant changes in the number of theoretical plates were observed.

Adsorption↗
PubMed2005

Simplified current decoupler for microchip capillary electrophoresis with electrochemical and pulsed amperometric detection.

There is a need to develop broadly applicable, highly sensitive detection methods for microchip CE that do not require analyte derivatization. LIF is highly sensitive but typically requires analyte derivatization. Electrochemistry provides an alternative method for direct analyte detection; however, in its most common form, direct current (DC) amperometry, it is limited to a small number of easily oxidizable or reducible analytes. Pulsed amperometric detection (PAD) is an alternative waveform that can increase the number of electrochemically detectable analytes. Increasing sensitivity for electrochemical detection (EC) and PAD requires the isolation of detection current (nA) from the separation current (muA) in a process generally referred to as current decoupling. Here, we present the development of a simple integrated decoupler to improve sensitivity and its coupling with PAD. A Pd microwire is used as the cathode for decoupling and a second Au or Pt wire is used as the working electrode for either EC or PAD. The electrode system is easy to make, requiring no clean-room facilities or specialized metallization systems. Sensitive detection of a wide range of analytes is shown to be possible using this system. Using this system we were able to achieve detection limits as low as 5 nM for dopamine, 74 nM for glutathione, and 100 nM for glucose.

Cysteine↗
PubMed2005

Colloidal behavior of proteins: effects of the second virial coefficient on solubility, crystallization and aggregation of proteins in aqueous solution.

There has been an increasing awareness that proteins, like other biopolymers, are large enough to exhibit colloidal behavior in aqueous solution. Net attractive or repulsive forces have been found to govern important physical properties, such as solubility and aggregation. The extent of intermolecular interactions, usually expressed in terms of the osmotic second virial coefficient, B, is most often measured using static light scattering. More recently, self-interaction chromatography (SIC) has emerged as a method for rapid determination of B in actual formulations, as it uses much less protein and has higher throughput. This review will summarize the relationship of B to crystallization, solubility, and aggregation of proteins in aqueous solution. Moreover, the capability of SIC to obtain B values in a rapid and reproducible fashion will be described in detail. Finally, the use of miniaturized devices to measure B is presented.

Chromatography↗
PubMed2004

Direct detection of renal function markers using microchip CE with pulsed electrochemical detection.

Creatinine, creatine, and uric acid are three important compounds that are measured in a variety of clinical assays, most notably for renal function. Traditional clinical assays for these compounds have focused on the use of enzymes or chemical reactions. Electrophoretic microchips have the potential to integrate separation power of capillary electrophoresis with devices that are small, portable, and have the speed of conventional sensors. The development of a microchip CE system for the direct detection of creatinine, creatine, and uric acid is presented. The device uses pulsed amperometric detection (PAD) to detect the nitrogen-containing compounds as well as the easily oxidizable uric acid. Baseline separation of creatinine, creatine and uric acid was achieved using 30 mM borate buffer (pH = 9.4) in less than 200 s. Linear calibration curves were obtained with limits of detection of 80 microM, 250 microM and 270 microM for creatinine, creatine and uric acid respectively. An optimization of the separation conditions and a comparison of PAD with other amperometric detection modes is also shown. Finally, analysis of a real urine sample is presented with validation of creatinine concentrations using a clinical assay kit based on the Jaffé reaction.

Biomarkers↗
PubMed2004

Simple and sensitive electrode design for microchip electrophoresis/electrochemistry.

A simple and sensitive electrode design for microchip capillary electrophoresis/electrochemistry (CE-EC) is presented. The system employs metal microwires as the working electrodes for electrochemical detection. Two general approaches for integration of electrodes in microchip CE-EC are commonly used, end-channel and microfabrication. The end-channel approach allows electrode cleaning and the use of chemically modified electrodes; however, the designs generally lack portability and the ability to incorporate multiple electrodes. Microfabrication allows the incorporation of multiple electrodes on-chip and is easily made portable; however, it requires the use of expensive metallization and clean room facilities, and integration of more than one electrode material is challenging. The reported approach aligns a solid metal microwire through the separation channel allowing integration of multiple electrodes and the use of different electrode materials without sacrificing the portability. A detection limit of 100 nM for dopamine was achieved without the use of a decoupler as a result of a higher collection efficiency with the new design.

Journal Article↗
PubMed2004

Spectrum of hypertensive emergencies in pregnancy.

Hypertension in pregnancy represents a spectrum of clinical entities, including pregnancy-induced hypertension (PIH), preeclampsia, eclampsia, and hemolysis, elevated liver enzyme levels, low platelet count syndrome. Although hypertension is a common denominator in this group of disorders, the pathogenesis, clinical features, and clinical course of these disorders is variable and somewhat distinct. Therapy must be tailored to the clinical entity and the patient. The incidence and prevalence of preeclampsia and eclampsia is decreasing worldwide. This decrease partly may be caused by the improved treatment of PIH and improved obstetrical services.

Antihypertensive Agents↗