Biomedical subjects

Michael J Sepaniak

Publications and source records attributed to Michael J Sepaniak.

8 recordsLinked to original sources

PubMed2007

Facile hyphenation of gas chromatography and a microcantilever array sensor for enhanced selectivity.

The very simple coupling of a standard, packed-column gas chromatograph with a microcantilever array (MCA) is demonstrated for enhanced selectivity and potential analyte identification in the analysis of volatile organic compounds (VOCs). The cantilevers in MCAs are differentially coated on one side with responsive phases (RPs) and produce bending responses of the cantilevers due to analyte-induced surface stresses. Generally, individual components are difficult to elucidate when introduced to MCA systems as mixtures, although pattern recognition techniques are helpful in identifying single components, binary mixtures, or composite responses of distinct mixtures (e.g., fragrances). In the present work, simple test VOC mixtures composed of acetone, ethanol, and trichloroethylene (TCE) in pentane and methanol and acetonitrile in pentane are first separated using a standard gas chromatograph and then introduced into a MCA flow cell. Significant amounts of response diversity to the analytes in the mixtures are demonstrated across the RP-coated cantilevers of the array. Principal component analysis is used to demonstrate that only three components of a four-component VOC mixture could be identified without mixture separation. Calibration studies are performed, demonstrating a good linear response over 2 orders of magnitude for each component in the primary study mixture. Studies of operational parameters including column temperature, column flow rate, and array cell temperature are conducted. Reproducibility studies of VOC peak areas and peak heights are also carried out showing RSDs of less than 4 and 3%, respectively, for intra-assay studies. Of practical significance is the facile manner by which the hyphenation of a mature separation technique and the burgeoning sensing approach is accomplished, and the potential to use pattern recognition techniques with MCAs as a new type of detector for chromatography with analyte-identifying capabilities.

Acetone↗

PubMed2006

Magnetically-assisted transport evanescent field fluoroimmunoassay.

The immunoassay, based on specific recognition of an antigen by its antibody, has garnered widespread use in clinical analysis as well as application in such areas as food industry and environmental monitoring. Fluoroimmunoassays (FIAs) are especially attractive due to the inherent sensitivity of fluorescence spectroscopy and the availability of a wide range of commercial antibodies and fluorescent labels. In current form, however, FIAs can be cumbersome, multistep procedures and often lack versatility when there is interest in measuring many different target antigens. This report is proof of a concept paper introducing a new FIA approach, Magnetically-Assisted Transport Evanescent Field Fluoroimmunoassays (MATEFFs), which seeks to preserve the advantages of current approaches to FIAs while attempting to address some of the drawbacks. MATEFFs utilize magnetic microspheres as solid supports for the fluoroimmunoassay with direct detection of bound analyte within the sample mixture effected by selectively driving the functionalized beads to a prism surface using an external magnet. An evanescent wave is generated by total internal reflection of a laser beam at the optical interface between the prism and sample and serves to excite the fluorescent species magnetically delivered into the localized field. This technique eliminates wash steps without compromising sensitivity, all the while minimizing interference from fluorescing species present in the sample matrix. Preliminary optimization studies assessing the impact of background interfering agents, incident angle, magnetic field direction, laser power density via focusing, and bead concentration on MATEFFs performance characteristics are discussed herein along with a detailed description of the experimental platform. Utilizing a model sandwich assay system with biotinylated anti-IgG as the capture antibody, rabbit IgG as the antigen, and anti-IgG-R-phycoerythrin as the reporter antibody, we demonstrate a linear dynamic range of 3 orders of magnitude, physiologically relevant detection limits of low nanograms per milliliter, and RSD values of less than 5%.

Fluoroimmunoassay↗

PubMed2006

Adsorption behavior of the (+/-)-Tröger's base enantiomers in the phase system of a silica-based packing coated with amylose tri(3,5-dimethyl carbamate) and 2-propanol and molecular modeling interpretation.

The binary adsorption isotherms of the enantiomers of Tröger's base in the phase system made of Chiral Technologies ChiralPak AD [a silica-based packing coated with amylose tri(3,5-dimethyl carbamate)] as the chiral stationary phase (CSP) and 2-propanol as the mobile phase were measured by the perturbation method. The more retained enantiomer exhibits a S-shaped adsorption isotherm with a clear inflection point, the concentration of the less retained enantiomer having practically no competitive influence on this isotherm: In the entire range of concentrations studied, dq2/dC1 approximately 0. By contrast, the less retained enantiomer has a Langmuir adsorption isotherm when pure. At constant mobile phase concentrations, however, its equilibrium concentration in the adsorbed phase increases with increasing concentration of the more retained enantiomer and dq1/dC2 > 0. This cooperative adsorption behavior, opposed to the classical competitive behavior, is exceedingly rare but was clearly demonstrated in this case. Two adsorption isotherm equations that account for these physical observations were derived. They are based on the formation of an adsorbed multi-layer, as suggested by the isotherm data. The excellent agreement between the experimental overloaded elution profiles of binary mixtures and the profiles calculated with the equilibrium-dispersive model validates this binary isotherm model. The adsorption energies calculated by molecular mechanics (MM) and by molecular dynamics (MD) indicate that the chiral recognition arising from the different interactions between the functional groups of the CSP and the molecules of the Tröger's base enantiomers are mainly driven by their Van der Waals interactions. The MD data suggest that the interactions of the (-)-Tröger's base with the CSP are more favored by 8+/-(5) kJ/mol than those of (+)-Tröger's base. This difference seems to be a contributing factor to the increased retention of the - enantiomer on this chromatographic system. The modeling of the data also indicates that both enantiomers can form high stoichiometry complexes while binding onto the stationary phase, in agreement with the results of the equilibrium isotherm studies.

2-Propanol↗

PubMed2005

Characterization of ligand-functionalized microcantilevers for metal ion sensing.

A sensor for metal cations is demonstrated using single and binary mixtures of different thiolated ligands as self-assembled monolayers (SAMs) functionalized on silicon microcantilevers (MCs) with gold nanostructured surfaces. Binding of charged metal ions to the active surface of a cantilever induces an apparent surface stress, thereby causing static bending of the MC that is detected in this work by a beam-bending technique. A MC response mechanism based on changes in surface charge is discussed. The monodentated ligands arranged as SAMs on the MC surface are not expected to fully satisfy the coordination sphere of the detected metals. This leads to lower binding constants than would be expected for chelating ligands, but reversible responses. The modest binding constants are compensated in terms of the magnitudes of responses by the inherent higher sensitivity of the nanostructured approach as opposed to more traditional smooth surface MCs. Response characteristics are optimized in terms of SAM formation time, concentration of ligand solution, and pH of working buffer solution. Limits of detection for the tested mono-, di-, and trivalent metal ions are in low to submicromolar range. The results indicated that shapes and magnitudes of response profiles are characteristics of the metal ions and type of SAM. The response factors for a given SAM with the tested metal ions, or for a given metal with the tested SAMs, varied by roughly 1 order of magnitude. While the observed selectivity is not large, it is anticipated that sufficient ionic recognition contrast is available for selective metal ion identification when differentially functionalized arrays of MCs (different ligands on different cantilevers in the array) are used in conjunction with pattern recognition techniques.

Biosensing Techniques↗

PubMed2004

Evaluation of newly synthesized and commercially available charged cyclomaltooligosaccharides (cyclodextrins) for capillary electrokinetic chromatography.

A highly new charged cyclodextrin (CD) derivatives, (6-O-carboxymethyl-2,3-di-O-methyl)cyclomaltoheptaoses (CDM-beta-CDs), was synthesized and characterized as anionic reagents for capillary electrophoresis (CE) in an electrokinetic chromatography mode of separation. Substitution with dimethyl groups at the secondary hydroxyl sites of the CD is aimed at influencing the magnitude and selectivity of analyte-CD interactions, while substitution by carboxymethyl groups at the primary hydroxyl sites provides for high charge and electrophoretic mobility. Full regioselective methylation at the secondary hydroxyl sites was achieved in this work, while substitution at the primary hydroxyl sites generated a mixture of multiply charged products. The separation performance of CDM-beta-CD was evaluated using a variety of analyte mixtures. The results obtained from commercially available negatively charged cyclodextrins, heptakis(2,3-di-O-methyl-6-O-sulfo)cyclomaltoheptaose (HDMS-beta-CD) and O-(carboxymethyl)cyclomaltoheptaose (CM-beta-CD) with an average degree of substitution one (DS 1), were compared to CDM-beta-CD using a sample composed of eight positional isomers of dihydroxynaphthalene. Four hydroxylated polychlorobiphenyl derivatives, a group of chiral and isomeric catchecins, and chiral binaphthyl compounds were also separated with CDM-beta-CD. The effect of adding neutral beta-cyclodextrin (beta-CD) into the running buffer containing charged cyclodextrins was investigated and provided evidence of significant inter-CD interactions. Under certain running buffer conditions, the charged cyclodextrins also appear to adsorb to the capillary walls to various degrees.

Anions↗

PubMed2004

Metal-polymer nanocomposites for integrated microfluidic separations and surface enhanced Raman spectroscopic detection.

The widespread development of microfluidics (microfluidics) has allowed the extension of efficient separations, fluid handling, and hyphenation with many detection modes to a small, portable, highly controllable physico-chemical platform. Surface enhanced Raman spectroscopy (SERS) offers the powerful advantage of obtaining vibrational spectroscopic information about analytes in an aqueous matrix with negligible background. The mating of electrophoretic separations with vibrational spectroscopy on a microfluidic device will allow the chromatographic efficiency of capillary electrophoresis (CE) with the unequivocal analyte "fingerprinting" capability of detailed structural information. By utilizing SERS as a means of detection, this work promises to yield redress for the hindrances of electrophoretic separations, including uncertainty in analyte band identification due to changing migration times as well as compromised detection sensitivity for non-fluorescent analytes. Our work represents the first steps toward developing CE-SERS on a microfluidic platform with a region of novel metal-pliable polymer nanocomposite SERS substrate fabricated directly into the device. The device fabrication material has been extensively employed by the microfluidics community for over five years. SERS detection can be achieved in real time or after the separations, with on-column laser-induced fluorescence employed as a secondary detection mode used for confirmation of efficiencies and band locations.

Journal Article↗

PubMed2003

Studies of the optical properties of metal-pliable polymer composite materials.

Polymer-nano-metallic-particle composites have demonstrated technological potential due to their unique optical and electrical properties. Herein, we report on composites prepared via physical vapor deposition of silver metal onto pliable poly(dimethylsiloxane) (PDMS) polymer. Rapid Ag diffusion and nano-metallic-particle formation in a phase-separated surface layer of the PDMS creates unique sub-surface-based composites whose properties vary based on rate of deposition and average Ag thickness. Additionally, nanometallic-particle spacing can be altered with fair reproducibility and reversibility by physically manipulating the Ag-PDMS composite. The optical properties of the materials are studied by visible wavelength optical extinction spectrometry and surface-enhanced Raman scattering (SERS), including studies performed during physical manipulation. Direct current (DC) conductivity measurements were made during Ag deposition to study percolation conditions for the materials. Depth-profiling was performed by X-ray photoelectron spectrometry. Sample Raman spectral data collected with the composite as a SERS substrate are included. A practical technological characteristic of these composite materials arises from their potential to be molded into functional devices.

Coated Materials, Biocompatible↗

PubMed2002

Nanostructured microcantilevers with functionalized cyclodextrin receptor phases: self-assembled monolayers and vapor-deposited films.

It is shown that the performance of microcantilver-based chemical sensors in a liquid environment is affected by altering cantilever surface morphology and receptor phase type and thickness. Self-assembled monolayers of thiolated beta-cyclodextrin (HM-beta-CD) and thin films of vapor-deposited heptakis (2,3-O-diacetyl-6-O-tertbutyl-dimethylsilyl)-beta-cyclodextrin (HDATB-beta-CD) were studied on smooth and nanostructured (dealloyed) gold-coated microcantilever surfaces. The dealloyed surface contains nanometer-sized features that enhance the transduction of molecular recognition events into cantilever response, as well as increase film stability for thicker films. Improvements in the limits of detection of the compound 2,3-dihydroxynaphthalene as great as 2 orders of magnitude have been achieved by manipulating surface morphology and film thickness. The observed response factors for the analytes studied varied from 0.02-604 nm/ppm, as determined by cantilever deflection. In general, calibration plots for the analytes were linear up to several hundred nanometers in cantilever deflections.

Journal Article↗