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Biomedical subjects

M A Burns

Publications and source records attributed to M A Burns.

17 recordsLinked to original sources
PubMed1998

An integrated nanoliter DNA analysis device.

A device was developed that uses microfabricated fluidic channels, heaters, temperature sensors, and fluorescence detectors to analyze nanoliter-size DNA samples. The device is capable of measuring aqueous reagent and DNA-containing solutions, mixing the solutions together, amplifying or digesting the DNA to form discrete products, and separating and detecting those products. No external lenses, heaters, or mechanical pumps are necessary for complete sample processing and analysis. Because all of the components are made using conventional photolithographic production techniques, they operate as a single closed system. The components have the potential for assembly into complex, low-power, integrated analysis systems at low unit cost. The availability of portable, reliable instruments may facilitate the use of DNA analysis in applications such as rapid medical diagnostics and point-of-use agricultural testing.

Costs and Cost Analysis↗
PubMed1998

Isotachophoretic separations on a microchip. Normal Raman spectroscopy detection.

Isotachophoretic separations of the herbicides paraquat and diquat are performed in a glass microchip etched channel and monitored on-chip by normal Raman spectroscopy. The 40-micron-wide and 75-micron-deep separation channels are chemically etched in a serpentine design to 21-cm total length. A 120-micron-thick glass cover slip is used to seal the channels. Separation field strengths up to 380 V/cm are used. The microchip is directly coupled to a Raman microprobe. No interfacing is required. Raman spectra are generated with a 2-W, 532-nm NdY-VO4 laser and collected at 8-cm-1 resolution with a holographic transmissive spectrograph and a cryogenically cooled CCD. Data acquisition is at 2-5 spectra/s. Raman isotachopherograms of the pesticides at starting concentrations as low as 2.3 x 10(-7) M (60 ppb paraquat/80 ppb diquat) are presented.

Diquat↗
PubMed1998

Electrophoretic separations using sweeping fields.

Sweeping-field electrophoresis is investigated as a method for increasing the resolution of low-voltage slab gel separations. In this technique a low direct current (DC) voltage is time multiplexed to an array of periodically spaced electrodes placed along the length of the slab in a manner that follows the band migration. Because the electrode spacing is smaller than the slab length, a larger field is generated, yielding an improved separation. The effect of the nonuniform electric field on band distortion is studied in some detail. Experimental band distortion results showed good agreement with theoretical predictions in a macroscopic sweeping-field electrophoresis system. Both analytical and numerical results show that band distortion can be effectively minimized when an appropriate sweep rate is selected for a narrow band range. Using this scheme we have achieved the same number of theoretical plates as a DC-driven system with one third of the drive voltage.

Electrophoresis, Agar Gel↗
PubMed1996

Microfabricated structures for integrated DNA analysis.

Photolithographic micromachining of silicon is a candidate technology for the construction of high-throughput DNA analysis devices. However, the development of complex silicon microfabricated systems has been hindered in part by the lack of a simple, versatile pumping method for integrating individual components. Here we describe a surface-tension-based pump able to move discrete nanoliter drops through enclosed channels using only local heating. This thermocapillary pump can accurately mix, measure, and divide drops by simple electronic control. In addition, we have constructed thermal-cycling chambers, gel electrophoresis channels, and radiolabeled DNA detectors that are compatible with the fabrication of thermocapillary pump channels. Since all of the components are made by conventional photolithographic techniques, they can be assembled into more complex integrated systems. The combination of pump and components into self-contained miniaturized devices may provide significant improvements in DNA analysis speed, portability, and cost. The potential of microfabricated systems lies in the low unit cost of silicon-based construction and in the efficient sample handling afforded by component integration.

Automation↗
PubMed1995

Solute focusing techniques for bioseparations.

The growth of industrial biotechnology has had a major impact on the research and development of both analytical and preparative focusing techniques. Pioneering methods such as isoelectric focusing are being modified to overcome the limitations of batch mode operation, scale up difficulties, high power requirement, and excessive heat generation. present advances in focusing techniques have been made by either overcoming the limitations of standard techniques or by investigating new focusing systems. Here we review the background and history of isoelectric focusing and discuss several new focusing techniques including recycle isoelectric (RIEF), counteracting chromatographic electrophoresis (CACE), and countercurrent gradient chromatography (CGC).

Chromatography↗
PubMed1994

Selective increase in lipid peroxidation in the inferior temporal cortex in Alzheimer's disease.

The concentration of a product of lipid peroxidation (malondialdehyde) was determined in six areas of neocortex of 8 subjects with Alzheimer's disease and 8 control subjects. Malondialdehyde concentration was significantly increased by incubation with iron and ascorbate in all samples. Both basal and iron/ascorbate-stimulated malondialdehyde concentration were higher in the inferior temporal cortex of Alzheimer subjects than corresponding controls; other regions were unaffected. Basal concentrations of malondialdehyde correlated with age in both the inferior parietal lobule and the sensory/motor cortex.

Aged↗
PubMed1994

Similar effects of glycine, zinc and an oxidizing agent on [3H]dizocilpine binding to the N-methyl-D-aspartate receptor in neocortical tissue from suicide victims and controls.

This study used [3H]dizocilpine (MK-801) binding to the N-methyl-D-aspartate (NMDA) receptor to examine glycine, redox and zinc modulatory sites in membranes derived from the frontal and parietal cortex of control subjects (n = 8) and suicide victims (n = 6). [3H]dizocilpine binding in the presence of glutamate and glutamate plus glycine was similar in control and suicide subjects. The sulphydryl redox site was assessed using the oxidizing agent 5,5'-dithio-bis (2-nitrobenzoic acid), which inhibited binding in a dose-dependent fashion. Both redox and zinc sites were unaffected in the frontal and parietal cortex of suicide victims. These data indicate that the NMDA receptor and its glycine, redox and zinc subsites are preserved in the neocortex of suicide victims.

Adult↗
PubMed1994

Preservation of redox, polyamine, and glycine modulatory domains of the N-methyl-D-aspartate receptor in Alzheimer's disease.

This study used [3H]dizocilpine ([3H]MK-801) binding to the N-methyl-D-aspartate (NMDA) receptor to examine redox, polyamine, and glycine modulatory sites in membranes derived from the superior frontal and the superior temporal cortex of patients with Alzheimer's disease. In control subjects the competitive polyamine site antagonist arcaine inhibited [3H]dizocilpine binding in a dose-dependent fashion and this curve was shifted to the right by the addition of 50 microM spermidine. Arcaine inhibition of binding was more potent in the temporal cortex than in the frontal cortex, in both the absence and presence of 50 microM spermidine. In Alzheimer's disease, arcaine inhibition of [3H]dizocilpine binding (in both the absence and the presence of spermidine) was not different from control in either of the two brain areas examined. The sulfhydryl redox site of the NMDA receptor was assessed using the oxidizing agent 5,5'-dithio-bis(2-nitrobenzoic acid), which inhibited binding in a dose-dependent fashion. This inhibition was similar in patients with Alzheimer's disease and control subjects. Glycine-stimulated [3H]dizocilpine binding was also unaffected in patients with Alzheimer's disease. However, in the temporal cortex there was a significant age-associated decline in [3H]dizocilpine binding in the presence of 100 microM glutamate (Rs = -0.71) and 100 microM glutamate plus 30 microM glycine (Rs = -0.90). There was also an age-related increase in arcaine IC50 (which reflects an age-related decrease in arcaine affinity) in the frontal cortex, determined both in the absence (Rs = 0.83) and the presence (Rs = 0.79) of spermidine. These data indicate that the NMDA receptor and its modulatory redox, polyamine, and glycine subsites are intact in patients with Alzheimer's disease and that the modulatory activity of polyamine and glycine sites decline with aging.

Aged↗
PubMed1993

Metacarpophalangeal pattern profile analysis in Williams syndrome.

Many patients with Williams syndrome (WS) are not diagnosed until they are old enough to demonstrate the characteristic personality and facial changes. A number of these changes are quite subtle and none of them is present in all affected individuals. The cause of WS remains obscure and consequently, there are no cytogenetic, biochemical, or molecular studies to help in the diagnosis of patients in whom the diagnosis is uncertain. We have generated a mean WS metacarpophalangeal pattern profile (MCPP) on 21 clinically diagnosed individuals with WS. This mean syndrome profile shows that WS hands are smaller than average age-matched control hands and that the distal phalanx of the thumb is disproportionately large with respect to the rest of the hand. A mathematical model, which effectively discriminates WS patients from unaffected control individuals, was developed using discriminant analysis of the MCPP data. Of the 21 WS patients classified by this method, only 2 were misclassified as "normal." Similarly, 2 of the 24 control individuals were misclassified as "WS," yielding an over-all successful classification rate of 91%.

Abnormalities, Multiple↗
PubMed1991

Motion artifact simulating aortic dissection on CT.

We recently imaged two patients clinically suspected of having aortic dissection whose contrast-enhanced CT examinations, obtained on a new scanner with a 1-sec scanning time, showed findings suggesting an ascending aortic dissection. The subsequent clinical course and evaluation implied that the CT findings were predominantly artifactual. We identified identical artifacts in 18% of 50 consecutive contrast-enhanced CT examinations performed for a variety of indications on the same scanner. The double-lumen artifact, simulating an intimal flap, occurs in the proximal ascending aorta and is limited to one or two contiguous transaxial images. The artifact was not detected on two other CT units. We believe the artifact arises from motion of the aortic wall and the surrounding pericardial recesses during image acquisition.

Adult↗
PubMed1989

Hypersensitivity to mitomycin C cell-killing in Roberts syndrome fibroblasts with, but not without, the heterochromatin abnormality.

Roberts syndrome (RS) is a rare genetic disorder, characterized clinically by severe pre- and post-natal growth retardation and symmetric limb reduction deformities. Some patients with RS have a distinctive abnormality of the constitutive heterochromatin (the RS effect) which has been described as a premature separation of the paracentromeric and nucleolar organizing regions of the chromosomes and the distal portion of the long arm of the Y chromosome (German, 1979). These patients [denoted RS(+)] are clinically indistinguishable from the RS(-) patients who lack the cytogenetic marker for Roberts syndrome. Recently, a mutant in Drosophila has been described which has both heterochromatin undercondensation and hypersensitivity to mutagen treatment (Gatti et al., 1983). The authors suggested that the uncondensed heterochromatin may be more accessible to damage by mutagens. Thus, the present study was an investigation of the mutagen sensitivity in Roberts syndrome, to determine whether there is a similar relationship between abnormal heterochromatin structure and mutagen sensitivity. Plating efficiency experiments were performed with RS(+) fibroblasts, RS(-) fibroblasts, RS heterozygous fibroblasts and a large assortment of appropriate control cells. The RS fibroblasts with the heterochromatin abnormality were consistently more sensitive (based on D10 values) to mitomycin C treatment than were any of the other cell strains tested, including RS(-) cells. These results support the hypothesis that mitomycin C sensitivity and abnormal heterochromatin structure in Roberts syndrome are related.

Abnormalities, Multiple↗
PubMed1985

Factors associated with positive direct antiglobulin tests in pretransfusion patients: a case-control study.

During routine pretransfusion testing, the presence of IgG on patient red cells is suggested by a positive autocontrol and confirmed by a positive direct antiglobulin test (DAT) using monospecific anti-IgG sera. Most IgG on patient red cells detected in this manner are of unknown etiology. We recently showed an association between elevated serum globulin levels and positive DAT with unreactive eluate in patients with acquired immunodeficiency syndrome (AIDS). In the present study, we wished to determine whether elevated serum globulin levels contribute to some of the positive DAT encountered in pretransfusion testing of patients without AIDS. 76 patients with positive DAT were compared with 90 controls without IgG detected on their red cells during pretransfusion testing. The rate of elevated serum globulin levels was 75% in positive DAT cases versus 29% in controls (p less than 0.001); the odds ratio was 7.6. Elevated blood urea nitrogen levels occurred in 42% of cases versus 19% of controls (p less than 0.025); the odds ratio was 3.1. Cases and controls were not significantly different with regard to age, sex, race, quinidine usage, or hyperalimentation. Elevated serum globulin and blood urea nitrogen levels are significantly associated with a positive DAT with unreactive eluate in pretransfusion patients.

Adolescent↗