University of North Florida
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Stuart Chalk, Ph.D.
Department of Chemistry
University of North Florida
Phone: 1-904-620-1938
Fax: 1-904-620-3535
Email: schalk@unf.edu
Website: @unf

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Lab on a Chip

  • Publisher: Royal Society of Chemistry
  • FAD Code: LABC
  • CODEN: LCAHAM
  • ISSN: 1473-0197
  • Abbreviation: Lab on a Chip
  • DOI Prefix: 10.1039
  • Language: English
  • Comments: Fulltext from 2001 V1

Citations 7

"Containerless Reaction Monitoring In Ionic Liquids By Means Of Raman Microspectroscopy"
Lab on a Chip 2007 Volume 7, Issue 1 Pages 126-132
Mercedes López-Pastor, Ana Domínguez-Vidal, María José Ayora-Cañada, Thomas Laurell, Miguel Valcárcel and Bernhard Lendl

Abstract: Reaction monitoring by Raman microspectroscopy in levitated room temperature ionic liquid (RTIL) droplets is reported. Due to their non-volatility, RTIL droplets are well-suited to act as wall-less microreactors. The droplets were produced by a piezoelectric flow-through microdispenser connected to an automated flow injection system and were levitated by an acoustic trap. Taking advantage of the flow system versatility, the sequence of reagents was easily changed to study a model organic reaction: the Knoevenagel condensation. The reaction was followed by Raman microspectrometry and the obtained spectra were analyzed using multivariate curve resolution to retrieve the concentration profiles and pure spectra of reactants, intermediates and products involved in the reaction. In addition, information about solvation interactions was obtained by monitoring the desolvation process taking place when a volatile co-solvent evaporated from the droplet. © The Royal Society of Chemistry.

"A Microfluidic Chip Based Sequential Injection System With Trapped Droplet Liquid-liquid Extraction And Chemiluminescence Detection"
Lab on a Chip 2006 Volume 6, Issue 10 Pages 1387-1389
Hong Shen, Qun Fang and Zhao-Lun Fang

Abstract: A microfluidic chip-based sequential injection system with trapped droplet liquid-liquid extraction pre-concentration and chemiluminescence detection was developed for achieving high sensitivity with low reagent and sample consumption. The microfabricated glass lab-chip had a 35 mm long extraction channel, with 134 shrunken opening rectangular recesses (L 100 ?m x W 50 ?m x D 25 ?m) arrayed within a 1 mm length on both sides of the middle section of the channel. Ketonic peroxyoxalate ester solution was filled in the recesses forming organic droplets, and keeping the aqueous sample solution flowing continuously in the extraction channel; analytes were transferred from the aqueous phase into the droplets through molecular diffusion. After liquid-liquid extraction pre-concentration, catalyst and hydrogen peroxide solutions were introduced into the channel, and mixed with analytes and peroxyoxalate ester to emit chemiluminescence light. The performance of the system was tested using butyl rhodamine B, yielding a precision of 4% RSD (n = 5) and a detection limit of 10^-9 M. Within a 17 min analytical cycle, the consumptions of sample and peroxyoxalate solutions were 2.7 µL and 160 nL, respectively. © The Royal Society of Chemistry.

"High-efficiency Electrokinetic Micromixing Through Symmetric Sequential Injection And Expansion"
Lab on a Chip 2006 Volume 6, Issue 8 Pages 1033-1039
Jeffrey T. Coleman, Jonathan McKechnie and David Sinton

Abstract: Rapid electric field switching is an established microfluidic mixing strategy for electrokinetic flows. Many such microfluidic mixers are variations on the T- or Y-form channel geometry. In these configurations, rapid switching of the electric field can greatly improve initial mixing over that achieved with static-field mixing. Due to a fundamental lack of symmetry, however, these strategies produce lingering cross-channel concentration gradients which delay complete mixing of the fluid stream. In this paper, a field switching microfluidic mixing strategy which utilizes a symmetric sequential injection geometry with an expansion chamber to achieve high efficiency microfluidic mixing is demonstrated experimentally. A three-inlet injector sequentially interlaces two dissimilar incoming solutions. Downstream of the injector, the sequence enters an expansion chamber resulting in a dramatic (two orders of magnitude) decrease in Peclet number and rapid axial diffusive mixing. The outlet concentration may be accurately varied over the full spectrum by tuning the duty cycle of the field switching waveform. The chips are designed with input from a previous numerical study, manufactured in poly(dimethylsiloxane) using soft-lithography based microfabrication, and tested using fluorescence microscopy. In the context of on-chip chemical processing for analytical operations, the demonstrated mixing strategy has several features: high mixing efficiency (99%), compact axial length (2.3 mm), steady outflow velocity, and readily variable outlet concentration (0.15 < c* < 0.95). © The Royal Society of Chemistry 2006.

"Electroosmotic Flow Analysis Of A Branched U-turn Nanofluidic Device"
Lab on a Chip 2005 Volume 5, Issue 10 Pages 1067-1074
Gea O. F. Parikesit, Anton P. Markesteijn, Vladimir G. Kutchoukov, Oana Piciu, Andre Bossche, Jerry Westerweel, Yuval Garini and Ian T. Young

Abstract: In this paper, we present the analysis of electroosmotic flow in a branched U-turn nanofluidic device, which we developed for detection and sorting of single molecules. The device, where the channel depth is only 150 nm, is designed to optically detect fluorescence from a volume as small as 270 attolitres (al) with a common wide-field fluorescent setup. We use distilled water as the liquid, in which we dilute 110 nm fluorescent beads employed as tracer-particles. Quantitative imaging is used to characterize the pathlines and velocity distribution of the electroosmotic flow in the device. Due to the device's complex geometry, the electroosmotic flow cannot be solved analytically. Therefore we use numerical flow simulation to model our device. Our results show that the deviation between measured and simulated data can be explained by the measured Brownian motion of the tracer-particles, which was not incorporated in the simulation. © The Royal Society of Chemistry 2005.

"Microfluidic Biosensing Systems Part II. Monitoring The Dynamic Production Of Glucose And Ethanol From Microchip-immobilised Yeast Cells Using Enzymatic Chemiluminescent -biosensors"
Lab on a Chip 2004 Volume 4, Issue 5 Pages 488-494
Richard Davidsson, Bj&ouml;rn Johansson, Volkmar Passoth, Martin Bengtsson, Thomas Laurell and Jenny Emn&eacute;us

Abstract: A microfluidic flow injection (?FIA) system was employed for handling and monitoring of cell-released products from living cells immobilized on silicon microchips. The dynamic release of glucose and ethanol produced from sucrose by immobilized Saccharomyces cerevisiae cells was determined using microchip biosensors (?-biosensors) with either co-immobilized glucose oxidase-horseradish peroxidase (GOX-HRP), or alcohol oxidase-horseradish peroxidase (AOX-HRP). catalysing a series of reactions ending up with chemiluminescence (CL) generated from HRP-catalyzed oxidation of luminol in presence of p-iodophenol (PIP). The yeast cells were attached by first treating them with polyethylenimine (PEI) followed by adsorption to the microchip surface. The cell loss during assaying was evaluated qualitatively using scanning electron microscopy (SEM), showing that no cells were lost after 35 min liquid handling of the cell chip at 10 µL min-1. The enzymes were immobilized on microchips via PEI-treatment followed by glutaraldehyde (GA) activation. The GOX-HRP ?-biosensors could be used during five days without any noticeable decrease in response, while the AOX-HRP ?-biosensors showed continuously decreasing activity, but could still be used employing calibration correction. The glucose and ethanol released from the immobilized yeast chips were quantitatively monitored, by varying the incubation time with sucrose, showing the possibilities and advantages of using a microfluidic system set-up for cell-based assays.

"Microfluidic Biosensing Systems Part I. Development And Optimisation Of Enzymatic Chemiluminescent -biosensors Based On Silicon Microchips"
Lab on a Chip 2004 Volume 4, Issue 5 Pages 481-487
Richard Davidsson, Fr&eacute;d&eacute;ric Genin, Martin Bengtsson, Thomas Laurell and Jenny Emn&eacute;us

Abstract: Chemiluminescent (CL) enzyme-based flow-through microchip biosensors (?-biosensors) for detection of glucose and ethanol were developed for the purpose of monitoring real-time production and release of glucose and ethanol from microchip immobilized yeast cells. Part I of this study focuses on the development and optimization of the ?-biosensors in a microfluidic sequential injection analysis (?SIA) system. Glucose oxidase (GOX) or alcohol oxidase (AOX) was co-immobilized with horseradish peroxidase (HRP) on porous silicon flow through microchips. The hydrogen peroxide produced from oxidation of the corresponding analyte (glucose or ethanol) took part in the chemiluminescent (CL) oxidation of luminol catalyzed by HRP enhanced by addition of p-iodophenol (PIP). All steps in the ?SIA system, including control of syringe pump, multiposition valve (MPV) and data readout, were computer controlled. The influence of flow rate and luminol- and PIP concentration were investigated using a 23-factor experiment using the GOX-HRP sensor. It was found that all estimated single factors and the highest order of interaction were significant. The optimum was found at 250 ?M luminol and 150 ?M PIP at a flow rate of 18 µL min-1, the latter as a compromise between signal intensity and analysis time. Using the optimized system settings one sample was processed within 5 min. Two different immobilization chemistries were investigated for both ?-biosensors based on 3-aminopropyltriethoxsilane (APTS)- or polyethylenimine (PEI) functionalisation followed by glutaraldehyde (GA) activation. GOX-HRP ?-biosensors responded linear in a log-log format within the range 10^-1000 ?M glucose. Both had an operational stability of at least 8 days, but the PEI-GOX-HRP sensor was more sensitive. The AOX-HRP ?-biosensors responded linear (log-log) in the range between 1 and 10 mM ethanol, but the PEI-AOX-HRP sensor was in general more sensitive. Both sensors had an operational stability of at least 8 h, but with a half-life of 2-3 days.

"Rapid Fabrication Of Microfluidic Devices In Poly(dimethylsiloxane) By Photocopying"
Lab on a Chip 2001 Volume 1, Issue 1 Pages 7-9
Aimin Tan, Kenneth Rodgers, John P. Murrihy, Cian O'Mathuna and Jeremy D. Glennon

Abstract: A very simple and fast method for the fabrication of poly(dimethylsiloxane) (PDMS) microfluidic devices is introduced. By using a photocopying machine to make a master on transparency instead of using lithographic equipment and photoresist, the fabrication process is greatly simplified and speeded up, requiring less than 1.5 h from design to device. Through SEM characterization, any µ-channel network with a width greater than 50 µm and a depth in the range of 8-14 µm can be made by this method. After sealing to a Pyrex glass plate with micromachined platinum electrodes, a microfluidic device was made and the device was tested in FIA mode with on-chip conductometric detection without using either high voltage or other pumping methods.
Victoria Pure Blue Water Conductometry Microfluidic