Evaluation of a dialysis probe for continuous sampling in fermentors and in complex media

A dialysis probe is described for continuous sampling from complex solutions, such as fermentation broth, milk or waste water, to yield samples suitable for liquid chromatography, flow injection analysis, enzyme calorimetry, etc. The analyte is transferred to a flow stream separated from the sample by a dialysis membrane that is protected from fouling by a strong tangential flow of the sample solution. This flow is accomplished by placing a magnetic stirring bar close to the membrane surface. The device is constructed of materials permitting the probe to be steam-sterilized when mounted inside a fermentor.     

Monitoring of troponin release from cardiomyocytes during exposure to toxic substances using surface plasmon resonance biosensing

Troponin T (TnT) is a useful biomarker for studying drug-induced toxicity effects on cardiac cells. We describe how a surface plasmon resonance (SPR) biosensor was applied to monitor the release of TnT from active HL-1 cardiomyocytes in vitro when exposed to cardiotoxic substances. Two monoclonal human TnT antibodies were compared in the SPR immunosensor to analyse the TnT release. The detection limit of TnT was determined to be 30 ng/ml in a direct assay set-up and to be 10 ng/ml in a sandwich assay format. Exposure of the cardiomyocytes to doxorubicin, troglitazone, quinidine and cobalt chloride for periods of 6 and 24 h gave significant SPR responses, whereas substances with low toxicity showed insignificant effects (ascorbic acid, methotrexate). The SPR results were verified with a validated immunochemiluminescence method which showed a correlation of r ² = 0.790.     

Improving the Sensitivity of a Quartz Crystal Microbalance for Biosensing by Using Porous Gold

 A quartz crystal microbalance can be used as a biosensor if biological receptor molecules (ligands) are attached to the crystal. To improve the sensitivity, the surface area of the gold electrodes on the crystal was increased by rendering the electrodes porous. This increased the response up to a factor of 3. A protein model system with human anti-myoglobin as ligand and sheep skeletal myoglobin at different concentrations as analyte was used. The quartz crystal was mounted in a flow-cell, where immobilisation, binding and regeneration of the surface were carried out. The kinetics of the model system was monitored under various experimental conditions. Received February 2, 2000. Revision June 30, 2000.     

In-situ ethanol probe based on sample dilution in a double-membrane system

An in-situ probe suitable for monitoring ethanol in fermentors or other bioreactors is described. It is constructed with an ethanol-permeable double membrane covering a solid-state tin(IV) oxide sensor for gas detection. A stream of nitrogen is passed between the two membranes in order to dilute the ethanol vapour from the fermentor that has passed through the first membrane, before it reaches the second membrane covering the detector. A 100-fold dilution was obtained at a flow rate of 30 ml min^?1 of the diluent gas. The delay time was less than 5 min to obtain 80% of maximum response.     

Enzyme thermistors for process monitoring and control

In today’s biotechnology there is an increasing demand for appropriate analytical systems for process control. At present the most widely used control systems are based on measurements of pH, pO₂, and pCO₂. Such systems do not allow the direct measurement of substrates and products. To overcome this drawback sensors such as enzyme thermistors and enzyme electrodes have been designed and their development into industrial useful sensors for monitoring and controlling is the subject of active research.     

A new strategy for respiration compensation, applied toward 3D free-breathing cardiac MRI

In thorax and abdomen imaging, image quality may be affected by breathing motion. Cardiac MR images are typically obtained while the patient holds his or her breath, to avoid respiration-related artifacts. Although useful, breath-holding imposes constraints on scan duration, which in turn limits the achievable resolution and SNR. Longer scan times would be required to improve image quality, and effective strategies are needed to compensate for respiratory motion. A novel approach at respiratory compensation, targeted toward 3D free-breathing cardiac MRI, is presented here. The method aims at suppressing the negative effects of respiratory-induced cardiac motion while capturing the heart's beating motion. The method is designed so that the acquired data can be reconstructed in two different ways: First, a time series of images is reconstructed to quantify and correct for respiratory motion. Then, the corrected data are reconstructed a final time into a cardiac-phase series of images to capture the heart's beating motion. The method was implemented, and initial results are presented. A cardiac-phase series of 3D images, covering the entire heart, was obtained for two free-breathing volunteers. The present method may prove especially useful in situations where breath-holding is not an option, for example, for very sick, mentally impaired or infant patients.     

Determination of fructose using immobilized glucose isomerase in an on-line analyzer

The determination of fructose using a continuous analyzer based on analyte conversion in enzyme reactors followed by amperometric oxygen measurement is described. Two experimental setups were compared, allowing determinations in the ranges 0–180 and 0–25 mM fructose. In the former, fructose was continuously dialyzed versus a buffer stream conducting fructose to an enzyme reactor. This reactor contained two immobilized enzyme preparations, one with immobiized glucose isomerase (E.C. 5.3.1.5) that isomerized fructose to glucose and another that subsequently oxidized the former glucose by immobilized glucose oxidase (E.C. 1.1.3.4) with the consumption of dissolved oxygen. In the latter set-up, fructose was first isomerized in a glucose isomerase reactor, then glucose was continuously dialyzed and oxidized by glucose oxidase as above. This set-up was run in continuous operation for 1000 measurement cycles with a total decrease in response less than 15%.     

Magnetic resonance imaging by synergistic diffusion-diffraction patterns

Inferring on the geometry of an object from its frequency spectrum is highly appealing since the object could then be imaged noninvasively or from a distance (as famously put by Kac, "can one hear the shape of a drum?"). In nuclear magnetic resonance of porous systems, the shape of the drum is represented by the pore density function that bears all the information on the collective pore microstructure. So far, conventional magnetic resonance imaging (MRI) could only detect the pore autocorrelation function, which inherently obscures fine details on the pore structure. Here, for the first time, we report on a unique imaging mechanism arising from synergistic diffusion-diffractions that directly yields the pore density function. This mechanism offers substantially higher spatial resolution compared to conventional MRI while retaining all fine details on the collective pore morphology. Thus, using these unique synergistic diffusion-diffractions, the "shape of the drum" can be inferred.     

The word problem for one-relation monoids: a survey

This survey is intended to provide an overview of one of the oldest and most celebrated open problems in combinatorial algebra: the word problem for one-relation monoids. We provide a history of the problem starting in 1914, and give a detailed overview of the proofs of central results, especially those due to Adian and his student Oganesian. After showing how to reduce the problem to the left cancellative case, the second half of the survey focuses on various methods for solving partial cases in this family. We finish with some modern and very recent results pertaining to this problem, including a link to the Collatz conjecture. Along the way, we emphasise and address a number of incorrect and inaccurate statements that have appeared in the literature over the years. We also fill a gap in the proof of a theorem linking special inverse monoids to one-relation monoids, and slightly strengthen the statement of this theorem.