Biomedical subjects

A Manz

Publications and source records attributed to A Manz.

At least 19 recordsLinked to original sources

PubMed2001

Shah convolution differentiation Fourier transform for rear analysis in microchip capillary electrophoresis.

This paper first reports the application of Shah convolution differentiation Fourier transform for rear analysis. Rear analysis eliminates the need to create a well-defined and reproducible sample plug, thus making the operation simpler. The number of solution reservoirs, for microchip capillary electrophoresis (CE), could be reduced from the usual four to three. Sample bias in CE could be avoided too. The separation channel was first filled with the fluorescent sample solution, and subsequently flushed out with the buffer. The rear of each analyte zone gives rise to its flight of sigmoid-shaped steps in the time-domain. The time-domain detector signal was first differentiated and then Fourier transform was performed. The Fourier transform results were represented in the form of a magnitude plot. It is proposed that this would be as equally applicable to other separation techniques (e.g., chromatography) and detection methods (e.g., absorption).

Electrophoresis, Capillary↗

PubMed2001

A wireless electrochemiluminescence detector applied to direct and indirect detection for electrophoresis on a microfabricated glass device.

A novel electrochemiluminescence (ECL) detector is presented in this article. The detector is applied for micellar electrokinetic chromatographic separation of dichlorotris(2,2'-bipyridyl)ruthenium(II) hydrate [Ru-(bpy)] and dichlorotris(1,10-phenanthroline)ruthenium-(II) hydrate [Ru(phen)] on a microfabricated glass device. It consists of a microfabricated "U"-shape floating platinum electrode placed across the separation channel. The legs of the U function respectively as working and counter electrode. The required potential difference for the ECL reaction is generated at the Pt electrode by the electric field available in the separation channel during electrophoretic separation. Initial experiments demonstrate a micellar electrokinetic separation and direct ECL detection of 10(-16) mol of Ru(phen) (10(-6) M) and 4.5 x 10(-16) mol of Ru(bpy) (5 x 10(-6) M). Also, preliminary results show the indirect detection of three amino acids. The high voltage at the location of detection does not interfere with the electrochemistry.

Journal Article↗

PubMed2001

Narrow sample channel injectors for capillary electrophoresis on microchips.

In microchip CE, sample injection is generally achieved through cross, double-tee, or tee injector structures. In these reported approaches, channel width and depth are uniform at the injection intersection. Here, we present cross and tee injectors having narrow sample channels. Using a cross injector with reduced sample channel width, resolution, column efficiency, and sensitivity are remarkably improved. Furthermore, no leakage control is required in both injection and separation phases, making the microchip CE system more user-friendly. Good resolution can also be obtained using tee injectors with narrow sample channels, which would otherwise be impossible using conventional tee injectors. Using the narrow sample channel tee injector instead of conventional cross and double-tee injectors, the number of reservoirs in multiplexed systems can be reduced to N + 2 (N, the number of paralleled CE systems), the real theoretical limit. The virtues of the novel injectors were demonstrated with poly(dimethylsiloxane)-glass chips incorporating eight parallel CE channels.

Journal Article↗

PubMed2001

Velocity measurement of particles flowing in a microfluidic chip using Shah convolution Fourier transform detection.

A noninvasive radiative technique, based on Shah convolution Fourier transform detection, for velocity measurement of particles in fluid flows in a microfluidic chip, is presented. It boasts a simpler instrumental setup and optical alignment than existing measurement methods and a wide dynamic range of velocities measurable. A glass-PDMS microchip with a layer of patterned Cr to provide multiple detection windows which are 40 microns wide and 70 microns apart is employed. The velocities of fluorescent microspheres, which were electrokinetically driven in the channel of the microfluidic chip, were determined. The effects of increasing the number of detection windows and sampling period were investigated. This technique could have wide applications, ranging from the determination of the velocity of particles in pressure-driven flow to the measurement of electrophoretic mobilities of single biological cells.

Algorithms↗

PubMed2001

Shah convolution Fourier transform detection: multiple-sample injection technique.

For the direct measurement of electrophoretic mobility, multiple-point (Shah function) detected, time-domain detector signals were converted into frequency-domain plots by means of Fourier transformation. Multiple sample plugs (up to a maximum of three) were introduced into the separation channel and the resultant time-domain signals were then Fourier-transformed. The multiple-sample injection technique has been successfully demonstrated for a one-component system and a separation. Though the number of fluorescing zones flowing through the illuminated length of the channel is greater than the number of analytes in the solution, Shah convolution Fourier transform detection (SCOFT) is able to identify the number of fluorescent species in the solution based on their migration velocities. The height of the fundamental peak increases as the number of injected sample plugs is increased. More importantly, the signal-to-noise ratio (S/N) is found to be proportional to the number of injected sample plugs. With these findings, the multiple-sample injection technique certainly has got many potential applications in trace analysis. The technique would be equally applicable to other separation techniques (e.g., high-performance liquid chromatography) and detection methods (e.g., absorption, refractive index).

Electrophoresis↗

PubMed2001

Microfabricated devices for fluid mixing and their application for chemical synthesis.

Over the last few decades, the processes of miniaturization, integration, and automation have revolutionized the world of science and industry. Within a chemical reaction process the unit operations, mixing, heating, and cooling, can be regarded as key steps. In microreactors, enhanced heat and mass transport, due to small characteristic dimensions together with large surface to volume ratios, are expected to open up a whole range of new possibilities. Increase in reaction yield, reduction of reaction time as well as byproduct formation, inherent process safety, and even completely new process routes are some of the advantages associated with microTAS (micro Total Analysis Systems) or microSYNTAS (micro SYNthesis Total Analysis Systems). This article aims to describe the development of microfabricated devices for fluid mixing, so-called micromixers, and their application for chemical synthesis.

Journal Article↗

PubMed2001

Synchronized cyclic capillary electrophoresis using channels arranged in a triangle and low voltages.

Synchronized cyclic capillary electrophoresis (SCCE) makes use of a closed loop separation channel by which the same sample can be separated during many cycles. This enables the repeated use of the same voltage for separations such that a high total voltage, and thus high efficiency, is obtained for the synchronized components. This can be accomplished by using any type of polygon geometry for the separation channel; and calculations of the available field and number of connections needed for polygons from 3 to 5 sides are presented. Triangular designs have the advantage of using the lowest number of wells. Such designs are described, with two additional features compared to that of earlier work: 1. voltage connections that are much shallower than the separation channel, to reduce losses and dispersion at the intersections; and 2. corners that are narrower than the separation channels to reduce dispersion in the turns. Experimental data is presented for the separation of a mixture of amino acids, and for a DNA separation in a polymeric sieving matrix. The DNA separation is most sensitive to the corner dispersion problem, which reduces the observed efficiency for that separation.

Amino Acids↗

PubMed2001

[Home transfer of 2,3,7,8-tetrachlorodibenzo-p-dioxin and beta-hexachlorocyclohexane?].

Persons living together with workers who have been exposed to dioxins, furans or hexachlorocyclohexane, accumulate increased concentrations of these molecules in the blood and in fatty tissue, in comparison with normal people. This result is based on an investigation of 14 workers and their female partners. The workers had been contaminated with high concentrations of 2,3,7,8-TCDD and moderate concentrations of beta-HCH, respectively, in contrast with their female partners who had never been exposed to these poisons. Nevertheless, the female partners accumulated a significant amount of these molecules, corresponding to 10% of the concentrations of their male partners. The origin of this correlation is still unknown. As a working hypothesis, we discuss the possibility of molecular transfer by clothing and underwear. The clinical consequences of these findings are still unclear. Further observations are needed.

Adult↗

PubMed2000

Integrated potentiometric detector for use in chip-based flow cells

A new kind of potentiometric chip sensor for ion-selective electrodes (ISE) based on a solvent polymeric membrane is described. The chip sensor is designed to trap the organic cocktail inside the chip and to permit sample solution to flow past the membrane. The design allows the sensor to overcome technical problems of ruggedness and would therefore be ideal for industrial processes. The sensor performance for a Ba2+-ISE membrane based on a Vogtle ionophore showed electrochemical behavior similar to that observed in conventional electrodes and microelectrode arrangements.

Journal Article↗

PubMed2000

A dc microplasma on a chip employed as an optical emission detector for gas chromatography

A micromachined plasma chip is coupled to a conventional gas chromatograph to investigate its performance as an optical emission detector. The device employs a 180-nL plasma chamber in which an atmospheric pressure dc glow discharge is generated in helium. Applied power is 9 mW (770 V, 12 microA) and helium flow rate 320 nL s(-1). A number of carbon-containing compounds are detected in the column effluent by recording the emission at 519 nm. For hexane, the detector has a linear dynamic range of over two decades and a minimum detectability of 10(-12) g s(-1) (800 ppb). The detector signal shows a marked peak broadening and tailing when compared with the signal of a flame ionization detector. This is mainly attributed to dead volumes and chromatographic processes introduced by the connecting tubing and the chip glass channels. The device was operated for more than 24 h without a significant change in performance. Operation is stable and instrumental requirements are simple. Future use of the detector chip in conventional gas chromatography or as an integrated detector in on-chip gas chromatography is discussed.

Journal Article↗

PubMed2000

Indirect fluorescence detection of phenolic compounds by capillary electrophoresis on a glass device.

A micromachined capillary electrophoresis system has been fabricated on a glass device for the separation and indirect fluorescence detection of phenols. Using this device two phenols viz., 2,4-dichlorophenol and pentachlorophenol, were separated within 12 s compared to under 19 min on a conventional capillary electrophoresis system using direct ultraviolet detection. The precision of the glass device ranged from 12.7%-16.7% compared to 0.42%-4.9% for the conventional system. Both systems showed good linearity in the concentration range of 0.8-6.38 mM for the glass device and 5-130 microM for the conventional system. The relationship between temperature and high voltage with baseline drift was also investigated. These results provide a foundation for the development of a miniaturised chemical analysis system for the on-line analysis of phenols in water.

Journal Article↗

PubMed2000

Lack of inhibition: a motivational deficit in children with attention deficit/hyperactivity disorder and children with traumatic brain injury.

Recent research has demonstrated that both brain-injured children and children with attention deficit/hyperactivity disorder (ADHD) suffer from response inhibition deficits. To investigate whether these deficits can be influenced by motivational factors, the stop-signal task was performed with and without reward contingencies for successful inhibition. Three groups of children between 8 and 12 years of age, participated in the study: 31 children with ADHD, 37 with traumatic brain injuries (TBI), and 26 normal controls. Results indicated that, although all groups showed comparable learning effects, reward contingencies had different effects on the groups. Whereas the performance of children with ADHD under reward contingencies were brought up to the performance level of normal controls, rewards were found less effective at improving response inhibition in children with TBI. The results further support a motivational/energetic explanation of the inhibitory deficit in children with ADHD, and of a primary response inhibition deficit due to structural brain damage in children with TBI.

Analysis of Variance↗

PubMed2000

Inhibitory control in children with traumatic brain injury (TBI) and children with attention deficit/hyperactivity disorder (ADHD).

The behavioural and cognitive sequelae of traumatic brain injury (TBI) have features in common with attention deficit/hyperactivity disorder (ADHD), best characterized by deficits in response inhibition.The performance was, therefore, examined of 27 children with TBI, 31 children with developmental ADHD, and 26 matched controls aged 8-12, on two inhibition tasks: the Stop-Signal Task and a Delayed-Response-Task. Children with TBI and children with ADHD showed a pervasive deficit in their inhibitory control processes with respect to inhibition of both pre-potent and on-going responses. In addition, children with TBI were found to suffer from a general slowing of their information processing, which was not correlated with the inhibition deficit. TBI children with and without a secondary ADHD differed only tendentially in their Mean Go-Reaction time in the stop-task. However, subdividing TBI children according to actigraph data into hypo-, hyper- and normokinetic subgroups revealed that the hyperactive TBI children had inhibitory deficit patterns that were similar to children with developmental ADHD. It is concluded that slowing of information processing speed seems to be a general consequence of TBI in childhood, whereas slowing of the stop-processes or inhibitory deficits, specifically, are associated with post-injury hypo- or hyperactivity.

Attention Deficit Disorder with Hyperactivity↗

PubMed1999

[Splenic rupture as a complication of ventilation in the prone position and pneumococcal sepsis as a late complication].

We are reporting the case of a female patient who had to undergo splenectomy after she suffered splenic rupture as a result from "kinetic therapy" during the treatment for pulmonary failure secondary to sepsis. Four years later the patient was again admitted with a clinical picture consistent with sepsis. Two blood cultures were positive for pneumococci confirming the diagnosis of pneumococcal sepsis. This paper discusses the potential risks of kinetic therapy in patients with ARDS. After splenectomy there is increased risk of infection with certain bacteria, funghi, viruses and protozoa. The most common bacterial pathogen is pneumococcus. A polyvalent vaccine is available for prophylaxis. Although penicillin G is still commonly used as an antibiotic therapy for pneumococcal infection, increased resistance of pathogens to penicillin must be anticipated. Alternative antibiotic regimens are demonstrated.

Female↗

PubMed1999

[Significance of the label "risk duplication" in occupational medicine expert opinion and redefinition of occupational diseases].

Referring to scientifically well-founded epidemiological statistical parameters for characterising probabilities of causal relationships, a critical assessment is given of the use of the parameter 'doubling risk' in research and expert evidence in occupational medicine. When assessing single cases, the attainment of this frequency level can serve as an appropriate additional argument for assuming a corresponding relationship; but even if lower frequency levels are attained, such a relationship cannot be excluded. In addition to the statistical data, any conspicuous features from the occupational history and from the course of the disease must be included in the analysis. In the investigation of causal relationships, the exclusive consideration of research results with enhanced frequencies dose to the doubling risk value would imply an illegitimate neglect of existing important information and would thus possibly lead to a misjudgement of the real situation. In the author's opinion, this would also result in set-backs both in legislation concerning occupational diseases and in the realm of labour protection.

Germany↗

PubMed1998

Chemical amplification: continuous-flow PCR on a chip.

A micromachined chemical amplifier was successfully used to perform the polymerase chain reaction (PCR) in continuous flow at high speed. The device is analogous to an electronic amplifier and relies on the movement of sample through thermostated temperature zones on a glass microchip. Input and output of material (DNA) is continuous, and amplification is independent of input concentration. A 20-cycle PCR amplification of a 176-base pair fragment from the DNA gyrase gene of Neisseria gonorrhoeae was performed at various flow rates, resulting in total reaction times of 90 seconds to 18.7 minutes.

DNA Topoisomerases, Type II↗

PubMed1998

Immunologic findings in workers formerly exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin and its congeners.

One hundred ninety-two workers in a German pesticide factory who were exposed to polychlorinated dibenzodioxins and -furans (PCDD/PCDF) were investigated for former and present diseases and laboratory changes of the immune system. Moreover, in a subgroup of 29 highly exposed and 28 control persons, proliferation studies were performed. In addition to assays such as blood count, immunoglobulins, serum electrophoresis, monoclonal bands, surface markers, autoantibodies, and lymphocyte proliferation, two new methods, the rise of tetanus antibody concentration after vaccination and the in vitro resistance of lymphocytes to chromate, were used to diagnose the morphologic and functional state of the immune system. There was no stringent correlation of actual PCDD/PCDF concentrations with the occurrence of infections or with one of the immune parameters. In addition, outcomes of the tetanus vaccination and the chromate resistance test were not correlated with PCDD/PCDF. However, the chromate resistance of lymphocytes stimulated by phytohemagglutinin of highly exposed persons was significantly lower than that for the control group. These findings indicate that the function of lymphocytes can be stressed and possibly impaired by high exposure to PCDD/PCDF.

Adult↗

PubMed1998

Immune cell functions in industrial workers after exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin: dissociation of antigen-specific T-cell responses in cultures of diluted whole blood and of isolated peripheral blood mononuclear cells.

A comparative analysis was performed of the phenotype and function of peripheral blood leukocytes of two age-matched cohorts of industrial workers in chemical plants, one of which was exposed occupationally to high concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Median actual TCDD burdens were 116 ng/kg and 4 ng/kg, respectively. The phenotype analysis of peripheral blood mononuclear cells (PBMC) revealed no significant differences in the proportions of CD3, CD4, or CD8+ T lymphocytes, of CD16+ natural killer cells, and of CD19+ B lymphocytes. However, in PBMC of the TCDD-exposed workers; the proportion of CD8+ memory T cells (CD45R0+) was significantly higher, and that of lymphocytes with naive phenotype (CD45RA+) was significantly lower than in PBMC of the control group. Polyclonal and antigen-specific T-cell activation was assessed in parallel in isolated PBMC as well as in diluted whole blood cultures. In both culture systems the polyclonally stimulated cytokine release did not differ significantly between the two cohorts; however, we found a significantly reduced interferon gamma release in diluted whole blood cultures but not in isolated PBMC cultures of the TCDD-exposed cohort when we performed an antigen-specific T-cell stimulation with tetanus-toxoid. Therefore, we propose that exposure of individuals to high doses of TCDD can partially impair in the "blood milieu" those T-cell/monocyte interactions that are essential for antigen-specific T-cell responses, whereas isolated PBMC of the same donors appear functionally less affected.

Adult↗