Biomedical subjects

Chang Auck Choi

Publications and source records attributed to Chang Auck Choi.

3 recordsLinked to original sources

PubMed2004

An independent, temperature-controllable microelectrode array.

Rapid, localized temperature control and negligible power consumption are key requisites for realizing effective parallel and sequential processing in the miniaturized, integrated biomedical microdevices where temperature-dependent biochemical reactions and fluid flow occur. In this study, an independent, temperature-controllable microelectrode array, with excellent temperature control rates and minimal power consumption, has been developed using microelectromechanical systems technology. The microfabricated array consists of Pt microelectrodes (100-microm diameter), with n-doped polysilicon microheaters (1.4-k Omega resistance), and vacuum-sealed cavities of depth 6.2 microm and diameter 200 microm. The thermal characteristics of each microelectrode were evaluated electrochemically through surface temperature measurements. The large heater power coefficient (2.1 +/- 0.1 degrees C mW(-1)) and the short heating and cooling times (less than 0.2 s for T(0.95)) are consequences of the vacuum-sealed cavities, which facilitate good thermal isolation and low thermal mass. The temperature of each microelectrode is independently controlled by a dedicated microheater, without thermally influencing the adjacent microelectrodes significantly.

Journal Article↗

PubMed2003

An iridium oxide reference electrode for use in microfabricated biosensors and biochips.

In this paper we argue for the use of iridium oxide (IrO(x)) electrodes as quasi-reference electrodes in microfabricated biosensors and biochips that operate in buffered solutions. The simple microfabrication of these electrodes consists of a one-step electrodeposition of IrO(x) onto a microfabricated platinum (Pt) electrode. The IrO(x) electrode potential was found to vary less than 20 mV over 9 days after stabilization for 1 day in a phosphate-buffered saline (PBS) solution; this behavior of the electrode potential was found to be easily reproduced. Moreover, the electrode potential was found to vary by less than 15 mV in the initial hour of its use; this behavior of the electrode potential was also found to be reproducible. The performance of a microfabricated glucose sensor employing an IrO(x) reference electrode is characterized in this paper in order to evaluate the usefulness of this new IrO(x) electrode as a quasi-reference electrode. The glucose sensor consists of a recessed microfabricated Pt electrode array, an electrodeposited IrO(x) film, an inner layer composed of an electropolymerized poly(m-phenylenediamine)/glucose oxidase (PMPD/GOx) film, and an outer or protective layer composed of Teflon and polyurethane (PU) films. The response of this sensor was found to be equivalent to the response of the same sensor employing a commercial Ag/AgCl reference electrode. These results show that a microfabricated IrO(x) electrode can be used as a quasi-reference electrode in microfabricated biosensors and biochips operating in buffered solutions.

Biosensing Techniques↗

PubMed2002

Glucose sensor using a microfabricated electrode and electropolymerized bilayer films.

A new type miniaturized glucose sensor with good selectivity and stable current response has been developed. The structure consists of a recessed rectangular microfabricated platinum electrode, inner layer of two electropolymerized nonconducting films, and outer bilayer of poly(tetrafluoroethylene) (Teflon) and polyurethane (PU) films. Glucose oxidase (GOx) is entrapped during the electropolymerization of a poly(m-phenylenediamine) (PMPD) film in an acetate buffer (AB) solution, on which a highly interference-resistive PMPD film is deposited in a phosphate buffered saline (PBS) solution. The second PMPD film causes no significant decrease in accessibility of glucose to GOx. The inner layer maintains less than 1% permeability to acetaminophen for 12 days. The fairly adhesive outer layer allows stable current response. Due to high permeability, the information about enzyme activity can be obtained without serious error in spite of outer layer intervening between enzymes and solution. The apparent Michaelis-Menten constant and the maximum steady-state current density were 24 mM and 80 microA cm(-2), respectively.

Acetaminophen↗