Biomedical subjects

Miklós Gratzl

Publications and source records attributed to Miklós Gratzl.

7 recordsLinked to original sources

PubMed2006

Micro-miniature autonomous optical sensor array for monitoring ions and metabolites 1: design, fabrication, and data analysis.

A micro-miniature array of sensing capsules for optical monitoring of pH, potassium and glucose is described. Optode technology translates the respective ionic levels into variable colors of ionophore/dye/polymeric liquid micro-beads stuffed into individual capsules. Glucose is monitored indirectly, by coupling through glucose oxidase (GOX) immobilized in cellulose acetate phthalate (CAP) based microscopic beads that are stuffed into another microcapsule together with pH sensitive optical microscopic beads. The electrolyte and glucose sensing capsules are embedded in a transparent cellulose acetate bar 300-500 microm wide and 2-2.5 mm long called the sliver sensor that includes also a white capsule made of micro-beads without dye for optical reference. By adding further capsules custom combinations of analytes can be monitored in biomedical and non-biological contexts. In this work, as an example, design, fabrication and testing of a sliver sensor that could be developed for in vivo use are described.

Biosensing Techniques↗

PubMed2006

Micro-miniature autonomous optical sensor array for monitoring ions and metabolites 2: color responses to pH, K+ and glucose.

In Part 1 of this series (Anal. Sci., 2006, 22, 383), design, fabrication, and optical data acquisition of an array of tiny color changing capsules embedded in a cellulose acetate bar, called the "sliver sensor", have been described. Capsule colors are read by a CCD camera and translated into blue, red and green Kubelka-Munk variables for quantitative analysis. The respective concentrations are determined using prior calibration. The approach may be adapted to different non-biological analytical problems, as well as in vitro and in vivo applications. To demonstrate this adaptability to potential in vivo use as an example, sensitivity for each target ion was tuned to cover the respective interstitial levels by varying the relative amount of ionophore used in the corresponding microscopic beads. After optimizing the ratio of glucose oxidase (GOX)-containing beads relative to the coupled pH sensing beads and their composition, reversible color response to glucose was obtained in the entire clinically relevant glucose concentration range (10 to 600 mg/dL, 0.55 to 33 mM). Decoupling of pH and glucose sensing from possible variations in interstitial sodium level and buffer capacity is currently being optimized for future in vivo use. In vitro and non-biological applications are also being explored.

Biosensing Techniques↗

PubMed2005

Deconvolution of concentration recordings at live cell preparations via shape error optimization.

In many fields of science and engineering including several areas in analytical chemistry, deconvolution needs to be performed on measured data to extract meaningful information. This situation arises when a variable of interest has to be indirectly estimated from a measurable quantity that depends on this variable in some known manner. This dependence, called the "forward problem", has to be computationally undone to obtain the information sought from the experimental results. Solving this "inverse problem" requires deconvolution whenever the forward problem involves convolution. Despite its ubiquitous importance, however, performance of the methodologies used for deconvolution remains often unsatisfactory. An example is in bioanalytical applications where microsensing at live preparations is performed to obtain information on biological transport. It is in this context that a novel approach to solve inverse problems, shape error optimization, is proposed and tested in this work. The experimental paradigm addressed is in the area of multidrug resistance (MDR) in cancer that gives rise to passive and active drug efflux from cells. Doxorubicin (DOX) concentration is monitored with a carbon fiber microelectrode in vitro at close proximity to a monolayer of cells expressing MDR. The measured local concentration is the result of convolution of cellular efflux with the impulse response of diffusion in the extracellular medium. Hence, estimating DOX efflux, which is the biologically meaningful information, leads to a deconvolution problem. Performance of deconvolution via shape error optimization is compared with that of two conventional techniques: discrete Fourier transform and square error optimization. The results obtained are also applicable to other areas of science and engineering where deconvolution is commonly used for processing experimental data.

Algorithms↗

PubMed2005

Hydrodynamic electrochemistry in 20 microL drops in the rotating sample system.

The Rotating Sample System (RSS) has been conceived in the authors' laboratory as a convection platform for microliter-sized solution volumes. Convection is achieved by rotating a small drop of sample on a stationary substrate by humidified gas jets directed tangentially at the drop base with the working electrode and a liquid junction embedded in it. Simplicity and portability of the device, and substrates complete with microfabricated electrode and junction made potentially disposable, are further competitive advantages with respect to competing, conventional analytical systems. In this work the RSS' performance with variation of system parameters such as the position and size of gas jets used for sample rotation, and position of the working electrode in the substrate are studied. Trace levels of Pb could be detected with this system and is reported here.

Electrochemistry↗

PubMed2003

Optical detection in microscopic domains. 3. Confocal analysis of fluorescent amphiphilic molecules.

This series of papers demonstrates the feasibility of novel optical methodologies for microchemistry and analysis in aqueous samples of nano-, pico-, and femtoliter in volume. Not a conventional glass cuvette, but water-immiscible organic liquid, is used as the container for microscopic sample droplets in this approach. In part 1, absorption spectra of excellent quality were obtained and used for analysis from samples as small as a few tens of a micrometer in diameter. In part 2, an inert fluorescence marker as an internal standard was employed for indirectly detecting absorbing but nonfluorescent reagents in microsamples, employing inner filter effects. In this part 3, a third modality, confocal fluorescence microscopy, is added to the techniques being examined. A clearly visible emission ring emanating from an amphiphilic molecule, doxorubicin, at the sample boundary is demonstrated for the first time in "optically sliced" microdroplets. Relative intensity of this ring with respect to sample bulk can be used to study adsorption phenomena at liquid-liquid interfaces with proper calibrations for bulk and boundary. Quantitative separation of these two domains, a precondition to such calibrations, is also discussed.

Absorption↗

PubMed2003

Hydrodynamic micromanipulation of individual cells onto patterned attachment sites on biomicroelectromechanical system chips.

We report on a simple methodology to move selected single live cells to a desired location on a flat substrate, such as a patterned biomicroelectromechanical system chip. A macroscopic syringe-and-tube-based hydrodynamic manipulation system is used to achieve controlled cell navigation onto hydrophilic sites for cell attachment. Centimeter-per-second flow velocities generated by the system get downgraded to micrometers-per-second flow at the height of settled cells as a result of viscous flow in the medium. By pushing/pulling two syringes that produce two orthogonal flows, fine manipulation in any horizontal direction is feasible. After attachment of the desired cell(s) onto the selected hydrophilic site, all other unwanted cells are washed away from the surrounding hydrophobic surface with faster flow. This simple methodology is applicable for rapid cell pattern formation with high precision.

Animals↗

PubMed2003

A microscopic, continuous, optical monitor for interstitial electrolytes and glucose.

Ions, such as hydrogen (pH), sodium, or potassium, as well as metabolites, such as glucose or lactate, diffuse easily between blood in the capillaries and the interstitial fluid (ISF) residing between cells, and tissues. This work represents a synthesis of several unique concepts to achieve accurate, continuous, in vivo monitoring of critical ions and glucose in the ISF under the human skin. Ionic levels are monitored using optode technology that translates the respective concentrations into variable colors of ionophore/dye/polymeric liquid membranes. Glucose is monitored indirectly, by coupling through immobilized glucose oxidase with pH, that is then detected using a similar color scheme. The monitor consists of a tiny plastic bar ("sliver sensor"), 100-300 microns wide and 1-15 mm long, placed just under the skin, with optical spots or stripes for each analyte as well as blanks for calibration. The colors are read and translated into concentration values by a watchlike device placed above the skin. Direct optical coupling between the in vivo sensing bar and the ex vivo detector device requires negligible power, and eliminates the need for wires or optical fibers crossing the skin. The microminiature sliver penetrates the skin easily and painlessly, so that the user could insert it him- or herself. No risk of track infection exists. We are reporting here on the first successful in vitro tests of this approach.

Animals↗