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Biomedical subjects

Mark A Hayes

Publications and source records attributed to Mark A Hayes.

9 recordsLinked to original sources
PubMed2006

Detection of FITC-cortisol via modulated supraparticle lighthouses.

Hormones are important bioactive compounds in blood and tissue that vary in concentration in response to stress and certain disease states. Establishing the changes in physiological hormone concentrations over time can lead to more effective diagnoses and perhaps a better understanding of the evolution of stress and disease. To monitor concentration over time, the sampling must be rapid and noninvasive; specimens such as saliva that require little effort to collect are preferred. However, more sensitive assay techniques are needed when compared to blood analysis since free hormone concentration in saliva is only a small fraction of the concentration in circulating blood. In this work, magnetic field-induced structures of paramagnetic particles are used as a solid substrate to demonstrate improved detection limits for a separation-free assay of cortisol. Once formed, the structures are subjected to a rotating magnetic field and this leads to two important features. First is the ability to utilize frequency and phase filtering (lock-in amplification) for the signal generated from surface-bound labeled species. Second is the improved mass transport of the antigen to the surface of the rotating structures. These two unique capabilities result in a quantifiable signal at a relatively low target antigen concentration. This method has been demonstrated with the detection of fluorescein isothiocyanate-labeled cortisol (FITC-cortisol) at a concentration of 300 pM.

Equipment Design↗
PubMed2006

Surface modification methods for enhanced device efficacy and function.

Currently available microfluidic devices can accomplish a variety of tasks useful in molecular biology. When moving analytical processes to a microenvironment, the properties of the device surface play a larger role in the functioning of the device. Surface modification may become necessary or advantageous for the purpose of control of the functional mechanics of the device, keeping cell components from adsorbing, attaching antibodies to the surface for detection of biological components, and attaching a functional bonding complex. Modification of the surface of microfluidic devices for the control of flow and device function, or for functionalization of the surface to tailor the device to a specific use, can be accomplished in numerous bench-top, postfabrication procedures. The use of polyelectrolyte multilayers, ultraviolet grafting of polymers, and polydimethylsiloxane/surfactant coating to control flow and mitigate adsorption is discussed. In addition, the functionalization of devices through amine termination of surfaces, and immobilization of biotin within a phosphotidylcholine bilayer is detailed.

Biotin↗
PubMed2005

Multiplexed DNA sequencing-by-synthesis.

We report a new DNA sequencing-by-synthesis method in which the sequences of DNA templates, hybridized to a surface-immobilized array of DNA primers, are determined by sensing the number of nucleotides by which the primers in each array spot are extended in sequential DNA polymerase-catalyzed nucleotide incorporation reactions, each with a single fluorescein-labeled deoxyribonucleoside triphosphate (dNTP) species. The fluorescein label is destroyed after each readout by a photostimulated reaction with diphenyliodonium chloride. A DNA polymerase with enhanced ability to incorporate, and to extend beyond, modified nucleotides is used. Self-quenching of adjacent fluorescein labels, which impedes readout of homopolymeric runs, is avoided by diluting the labeled dNTP with unlabeled reagent. Misincorporation effects have been quantified and are small; however, low-level contamination of dNTPs with other nucleotides mimics misincorporation and can produce significant false-positive signals. These impurities are removed by polymerase-catalyzed incorporation into complementary "cleaning duplexes." Here, we demonstrate the accurate sequence readout for a small array of known DNA templates, the ability to quantify homopolymeric runs, and a short sequencing example of sections of the wild-type and mutant BRCA1 gene. For a 20,000-spot array, readout rates in excess of 6000 bases per minute are projected.

Amino Acid Sequence↗
PubMed2005

Effects of deformability, uneven surface charge distributions, and multipole moments on biocolloid electrophoretic migration.

Liposomes have been widely used as cellular and bioparticle mimics due to their lipid bilayer structure and relative ease of production and manipulation. Such biocolloids are frequently characterized by capillary electrophoresis (CE), which promises a wealth of information about such properties as surface charge, composition, and rigidity. The applicability of this information is somewhat limited, however, since it is interpreted with colloidal theories that do not account for the unique properties of biocolloids. In this work, the effects of deformability, mobile surface charges, intrinsic polarizability, and uneven surface charge distributions are incorporated into colloidal theories in order to better model the electrophoretic behaviors of liposomes.

Colloids↗
PubMed2005

Analysis of human blood serum using the off-line coupling of capillary isoelectric focusing to matrix-assisted laser desorption/ionization time of flight mass spectrometry.

Off-line coupling of capillary IEF (CIEF) with matrix-assisted laser desorption/ionization mass spectrometry was utilized for the analysis of human blood serum. Serum proteins were initially separated by CIEF, and fractions of the isoelectric separation were eluted sequentially to a MALDI-TOF MS sample target. During pressure elution of the CIEF sample, voltage was maintained across the capillary system utilizing a sheath flow arrangement to minimize band broadening induced by the laminar flow field. Both pI and mass information were obtained from the complex biological sample, similar to traditional 2-DE techniques, and the platform was faster (hours versus days), more automatable, and simpler than 2-DE. The volume of raw sample present in the actual analysis was approximately 100 nL, making this technique well suited for very rare specimens. Additionally, the speed and simplicity of the technology make it an attractive technique for performing initial comparative analyses of complex samples.

Humans↗
PubMed2004

Examination of the electrophoretic behavior of liposomes.

The electromigration of liposomes is a complex process resulting in many unexpected behaviors that are difficult to address with existing theories. In this study, the electrophoretic behaviors of liposome populations under various conditions were examined through the use of capillary electrophoresis and the results compared to classical electrokinetic, colloid, and spheroid theories. To elucidate the possible effects of applied field strength, bilayer rigidity, and surface charge on these behaviors, the electrophoretic mobilities of liposome populations were monitored while varying the applied potential, ionic strength of the medium, and the surface charge and cholesterol content of the liposomes. On the basis of comparisons made to the theoretical predictions, our results suggest that liposomal deformation and field-induced polarization may occur during electrophoresis and these mechanisms help to describe many of the observed behaviors.

Cholesterol↗
PubMed2004

Modeling microflow and stirring around a microrotor in creeping flow using a quasi-steady-state analysis.

The microflow and stirring around paramagnetic particle microchains, referred to as microrotors, are modeled as a circular cylinder rotating about its radial axis at very low Reynolds number. Time scales for momentum transfer under these conditions are determined to be much smaller than those for boundary movement, hence a quasi-steady approximation can be used. The flow is derived at every instant from the case of a steady motion of a horizontally translating cylinder, with the rotation approximated to a series of differential incremental translations. A numerical simulation is used to determine the pathlines and material lines of virtual point fluid elements, which were analyzed to understand the behavior of the flow around the microrotor. The results indicate the flow to be unsteady, with chaotic advection observed in the system. The fluid motion is primarily two-dimensional, parallel to the rotational plane, with mixing limited to the immediate area around the rotating cylinder. Fluid layers, up to many cylinder diameters, in the axial direction experience the disturbance. Elliptic and star shaped pathlines, including periodic orbits, are observed depending on the fluid element's initial location. The trajectories and phase angles compare well with the experimental results, as well as with data from particle dynamics simulations. Material lines and streaklines display stretching and folding, which are indicative of the chaotic behavior and stirring characteristics of the system. The material lines have similar lengths for the same amount of rotation at different speeds, and the effect of rotational speeds appears to be primarily to change the time of mixing. The results are expected to help in the design of a particle microrotor based sensing technique.

Microfluidic Analytical Techniques↗
PubMed2002

Examination of theoretical models in external voltage control of capillary electrophoresis.

Control of electroosmosis by an external voltage in capillaries of varying geometry was examined and investigated. Controlled geometric factors included inner and outer radii, external electrode coverage area, and the method of voltage application. The behavior of the flow in response to the external voltage from earlier work and this study were compared to existing literature models. A noticeable lack of correlation between the current modeling theories and the published data is noted. In light of these results, suggestions for further areas of investigation of a description of external voltage flow control mechanism are suggested.

Journal Article↗