Biomedical subjects

Chong H Ahn

Publications and source records attributed to Chong H Ahn.

13 recordsLinked to original sources

PubMed2006

Flexible biosensors on spirally rolled micro tube for cardiovascular in vivo monitoring.

New flexible biosensors on a spirally rolled micro tube have been designed, fabricated and characterized for microcatheter-based cardiovascular in vivo monitoring. With this new microfabrication method, sensors, wires and circuits can be fabricated first on the flexible polymer substrate (Kapton film) and then rolled spirally to make micro tubes with different diameters. This approach provides a unique method for mounting multiple sensors on both the inside and outside the tube. So, the new spirally rolled polymer tube flexibly conceives physical, biomedical and physiological microsensors, elevating most problems arisen from wiring and assembling of microsensors in conventional microcatheters. As a demonstration vehicle, we fabricated glucose biosensors on the 25 microm thick Kapton film first, then the film was spirally rolled to make a polymer micro tube with the glucose sensors on the inside wall of the tube. To verify the performance of the spirally rolled glucose biosensor, we characterized it both in a planar unrolled and rolled conditions and compared their performances. The spirally rolled glucose sensors showed good performance in the typical glucose concentration range in human blood from 60 mg/dL to 120 mg/dL with different rolled diameters at different working temperature.

Biosensing Techniques↗

PubMed2006

A disposable on-chip phosphate sensor with planar cobalt microelectrodes on polymer substrate.

Disposable microsensors on polymer substrates consisting of fully integrated on-chip planar cobalt (Co) microelectrodes, Ag/AgCl reference electrodes, and microfluidic channels have been designed, fabricated, and characterized for phosphate concentration measurement in aqueous solution. The planar Co microelectrode shows phosphate-selective potential response over the range from 10(-5) to 10(-2)M in acidic medium (pH 5.0) for both inorganic (KH(2)PO(4)) and organic (adenosine 5'-triphosphate (ATP) and adenosine 5'-diphosphates (ADP)) phosphate compounds. This microfabricated sensor also demonstrates significant reproducibility with a small repeated sensing deviation (i.e. relative standard deviation (R.S.D.)<1%) on a single chip and a small chip-to-chip deviation (i.e. R.S.D.<2.5%). Specifically, while keeping the high selectivity, sensitivity, and stability of a conventional bulk Co-wire electrode, the proposed phosphate sensor yields advantages such as ease of use, cost effectiveness, reduced analyte consumption, and ease of integrating into disposable polymer lab-on-a-chip devices. The capability to sense both inorganic and organic phosphate compounds makes this sensor applicable in diverse areas such as environmental monitoring, soil extract analysis, and clinical diagnostics.

Biosensing Techniques↗

PubMed2006

Disposable integrated microfluidic biochip for blood typing by plastic microinjection moulding.

Blood typing is the most important test for both transfusion recipients and blood donors. In this paper, a low cost disposable blood typing integrated microfluidic biochip has been designed, fabricated and characterized. In the biochip, flow splitting microchannels, chaotic micromixers, reaction microchambers and detection microfilters are fully integrated. The loaded sample blood can be divided by 2 or 4 equal volumes through the flow splitting microchannel so that one can perform 2 or 4 blood agglutination tests in parallel. For the purpose of obtaining efficient reaction of agglutinogens on red blood cells (RBCs) and agglutinins in serum, we incorporated a serpentine laminating micromixer into the biochip, which combines two chaotic mixing mechanisms of splitting/recombination and chaotic advection. Relatively large area reaction microchambers were also introduced for the sake of keeping the mixture of the sample blood and serum during the reaction time before filtering. The gradually decreasing multi-step detection microfilters were designed in order to effectively filter the reacted agglutinated RBCs, which show the corresponding blood group. To achieve the cost-effectiveness of the microfluidic biochip for disposability, the biochip was realized by the microinjection moulding of COC (cyclic olefin copolymer) and thermal bonding of two injection moulded COC substrates in mass production with a total fabrication time of less than 20 min. Mould inserts of the biochip for the microinjection moulding were fabricated by SU-8 photolithography and the subsequent nickel electroplating process. Human blood groups of A, B and AB have been successfully determined with the naked eye, with 3 microl of the whole sample bloods, by means of the fabricated biochip within 3 min.

Blood Grouping and Crossmatching↗

PubMed2005

A serpentine laminating micromixer combining splitting/recombination and advection.

Mixing enhancement has drawn great attention from designers of micromixers, since the flow in a microchannel is usually characterized by a low Reynolds number (Re) which makes the mixing quite a difficult task to accomplish. In this paper, a novel integrated efficient micromixer named serpentine laminating micromixer (SLM) has been designed, simulated, fabricated and fully characterized. In the SLM, a high level of efficient mixing can be achieved by combining two general chaotic mixing mechanisms: splitting/recombination and chaotic advection. The splitting and recombination (in other terms, lamination) mechanism is obtained by the successive arrangement of "F"-shape mixing units in two layers. The advection is induced by the overall three-dimensional serpentine path of the microchannel. The SLM was realized by SU-8 photolithography, nickel electroplating, injection molding and thermal bonding. Mixing performance of the SLM was fully characterized numerically and experimentally. The numerical mixing simulations show that the advection acts favorably to realize the ideal vertical lamination of fluid flow. The mixing experiments based on an average mixing color intensity change of phenolphthalein show a high level of mixing performance was obtained with the SLM. Numerical and experimental results confirm that efficient mixing is successfully achieved from the SLM over the wide range of Re. Due to the simple and mass producible geometry of the efficient micromixer, SLM proposed in this study, the SLM can be easily applied to integrated microfluidic systems, such as micro-total-analysis-systems or lab-on-a-chip systems.

Journal Article↗

PubMed2005

Electrochemical determination of reversible redox species at interdigitated array micro/nanoelectrodes using charge injection method.

In this work, the interdigitated array microelectrodes/nanoelectrodes (approximately 0.2 mm2 surface area) have been fabricated and characterized using the charge injection method for the electrochemical determination of reversible redox species. Using p-aminophenol as the redox species, approximately 4 x 10(-7) M and 6 x 10(-9) M detection limits on the species concentration ar respectively achieved with the microelectrodes and the nanoelectrodes.

Aminophenols↗

PubMed2004

On-chip generated mercury microelectrode for heavy metal ion detection.

In this paper, the on-chip generated mercury microelectrode for heavy metal ion detection has been presented. A mercury droplet (approximately 150 microm in diameter) is on-chip generated to form a microelectrode through the mercury microfluidics control. The mercury microelectrode is used to electrochemically detect the heavy metal ions. The sample solutions with different concentration of heavy metal ions (Pb(2+) and Cd(2+)) have been successfully detected on the mercury droplet microelectrode using the square wave stripping voltammetry.

Journal Article↗

PubMed2004

A new dynamic electrochemical transduction mechanism for interdigitated array microelectrodes.

A dynamic electrochemical transduction mechanism for interdigitated array microelectrodes using an electrical charge pumping method is presented in this paper. In this dynamic transduction mechanism, a charged external capacitor is used as the charge supplier for the electrochemical reaction of the reversible redox species at the interdigitated array electrodes. The charges stored in the capacitor are consumed as the electrochemical reaction current, which causes the capacitor potential decay. The theoretical analysis has shown that the species concentration has a decisive effect on the capacitor potential decay, and therefore the characteristics of the capacitor potential decay are recorded and analyzed to evaluate the concentration of redox species. The new transduction mechanism has the advantages of achieving high sensitivity with small sensor area and simplifying the measurement instrumentation. As a demonstration device, interdigitated array microelectrodes (approximately 0.2 mm(2) electrode surface area) have been fabricated and successfully characterized using p-aminophenol as the redox species under this dynamic mechanism. The detection limit of p-aminophenol was calculated to be approximately 4 x 10(-7) M for the sensor with the new dynamic transduction mechanism.

Aminophenols↗

PubMed2004

Autostereoscopic three-dimensional display based on a micromirror array.

A novel approach for three-dimensional (3-D) display systems implemented with a micromirror array was proposed, designed, realized, and tested. The major advantages of this approach include the following: (1) micromirrors are reflective and hence achromatic (panchromatic), (2) a wide variety of displays can be used as image sources, and (3) time multiplexing can be introduced on top of space multiplexing to optimize the viewing zone arrangements. A two-view (left and right) 3-D autostereoscopic display system was first constructed. Left- and right-eye views in the forms of both still and motion 3-D scenes were displayed, and viewers were able to fuse the stereo information. A multiview (two left and two right) 3-D autostereoscopic display system was then simulated.

Journal Article↗

PubMed2004

A novel in-plane passive microfluidic mixer with modified Tesla structures.

An innovative in-plane passive micromixer using modified Tesla structures, which are used as passive valves, has been designed, simulated, fabricated and successfully characterized in this paper. Simulation and experimental results of the developed novel micromixer have shown excellent mixing performance over a wide range of flow conditions in the micro scale. The micromixer realized in this work has achieved even better mixing performance at a higher flow rate, and its pressure drop is less than 10 KPa at the flow rate of 100 microl min(-1). This micromixer shows characteristics similar to Taylor dispersion, with contributions from both diffusion and convection. The mixer has a diffusion domain region at low flow rate, but it moves to a convection domain region at high flow rate. Due to the simple in-plane structure of the novel micromixer explored in this work, the mixer can be easily realized and integrated with on-chip microfluidic devices and micro total analysis systems (micro-TAS).

Journal Article↗

PubMed2003

A functional on-chip pressure generator using solid chemical propellant for disposable lab-on-a-chip.

This paper presents a functional on-chip pressure generator that utilizes chemical energy from a solid chemical propellant to perform fluidic delivery in applications of plastic-based disposable biochips or lab-on-a-chip systems. In this functional on-chip pressure generator, azobis-isobutyronitrile (AIBN) as the solid chemical propellant is deposited on a microheater using a screen-printing technique, which can heat the AIBN at 70 degrees C to produce nitrogen gas. The output pressure of nitrogen gas, generated from the solid chemical propellant, is adjustable to a desired pressure by controlling the input power of the heater. Using this chemical energy source, the generated pressure depends on the deposited amount of the solid chemical propellant and the temperature of the microheater. Experimental measurements show that this functional on-chip pressure generator can achieve around 3 000 Pa pressure when 189 mJ of energy is applied to heat the 100 microg of AIBN. This pressure can drive 50 nl of water through a microfluidic channel of 70 mm and cross-sectional area of 100 microm x 50 microm. Due to its compact size, ease of fabrication and integration, high reliability (no moving parts), biologically inert gas output along with functionality of gas generation, this pressure generator will be an excellent pressure source for handling the fluids of disposable lab-on-a-chip, biochemical analysis systems or drug delivery systems.

Aerosol Propellants↗

PubMed2003

Determination of endogenous extracellular signal-regulated protein kinase by microchip capillary electrophoresis.

The application of microchip capillary electrophoresis (CE) to the assay of extracellular signal-regulated protein kinase (ERK) is presented. In this assay, ERK catalyzes the transfer of gamma-phosphate from adenosine 5(')-triphosphate to the threonine residue of a fluorescently labeled nonapeptide (APRTPGGRR), and the phosphorylated and nonphosphorylated peptides were detected by fluorescence. The phosphorylated and nonphosphorylated peptides and the internal standard were separated within 20s, and the increase in magnitude of the phosphorylated peptide peak was monitored to assess ERK activity. ERK reactions were prepared off-chip and analyzed on a single-lane glass microchip fabricated by standard methods. It was demonstrated that microchip CE could be used to measure endogenous amounts of ERK by spiking known concentrations of recombinant ERK2 into the lysates of serum-starved human umbilical vein endothelial cells (HUVEC) and recovering between 90 and 100% for all samples. Endogenous ERK activity was determined by microchip where HUVEC were stimulated with 500pM vascular endothelial growth factor (VEGF) at different times before cell lysis. The results showed a transient VEGF-mediated ERK activation that peaked at 10min, which was consistent with previous reports using conventional techniques. The microchip assay provided a rapid, accurate, and precise alternative to conventional methods of determining endogenous ERK activity.

Cells, Cultured↗

PubMed2002

Fixed-volume metering microdispenser module.

In this work, we present a novel fixed-volume metering microdispenser module using the sPROMs (structurally programmable microfluidic systems) technology. We have designed, simulated, fabricated and characterized an array of microdispensers with volumes ranging from 50 nL [nanoliter] to 150 nL. We have characterized several key components of the microdispenser, such as passive microvalves and the air-driven liquid column splitting process, using extensive simulations. The fabricated devices show extremely good accuracy (99.2%) and repeatability characteristics. We also present a simple technique for unloading the sub-microL [microliter] volumes from the microfluidic chip for measurement purposes. The dispensers realized in this work have immediate applications as a key ingredient of the lab-on-a-chip device.

Journal Article↗

PubMed2001

An integrated microfluidic biochemical detection system for protein analysis with magnetic bead-based sampling capabilities.

This paper presents the development and characterization of an integrated microfluidic biochemical detection system for fast and low-volume immunoassays using magnetic beads, which are used as both immobilization surfaces and bio-molecule carriers. Microfluidic components have been developed and integrated to construct a microfluidic biochemical detection system. Magnetic bead-based immunoassay, as a typical example of biochemical detection and analysis, has been successfully performed on the integrated microfluidic biochemical analysis system that includes a surface-mounted biofilter and electrochemical sensor on a glass microfluidic motherboard. Total time required for an immunoassay was less than 20 min including sample incubation time, and sample volume wasted was less than 50 microl during five repeated assays. Fast and low-volume biochemical analysis has been successfully achieved with the developed biofilter and immunosensor, which is integrated to the microfluidic system. Such a magnetic bead-based biochemical detection system, described in this paper, can be applied to protein analysis systems.

Electrochemistry↗