Dong-Yun Lee

A Power-Control Scheme With Constant Switching Frequency in Class-D Inverter for Induction-Heating Jar Application

In this paper, a simple power-control scheme for a constant-frequency class-D inverter with variable duty cycle at constant frequency is proposed. It is more suitable and acceptable for high-frequency induction-heating (IH) jar applications. The proposed control scheme has the advantages of not only wide power-regulation range but also ease of output-power control. In addition, it can achieve stable and efficient zero-voltage switching in the whole load range. The control principles of the proposed method are described in detail, and the validity is verified through the simulated and experimental results on the 42.8-kHz insulated gate bipolar transistor for an IH rated on 1.6 kW with constant-frequency variable power

DNA as a support for glucose oxidase immobilization at prussian blue-modified glassy carbon electrode in biosensor preparation

An amperometric glucose biosensor has been developed using DNA as a matrix of Glucose oxidase (GOx) at Prussian-blue (PB)-modified glassy carbon (GC) electrode. GC electrode was chemically modified by the PB. GOx was immobilized together with DNA at the working area of the PB-modified electrode by placing a drop of the mixture of DNA and GOx. The response of the biosensor for glucose was evaluated amperometrically. Upon immobilization of glucose oxidase with DNA, the biosensor showed rapid response toward the glucose. On the other hand, no significant response was obtained in the absence of DNA. Experimental conditions influencing the biosensor performance were optimized and assessed. This biosensor offered an excellent electrochemical response for glucose concentration in micro mol level with high sensitivity and selectivity and short response time. The levels of the relative standard deviation (RSDs), (<4%) for the entire analyses reflected a highly reproducible sensor performance. Through the use of optimized conditions, a linear relationship between current and glucose concentration was obtained up to 4 x 10(-4) M. In addition, this biosensor showed high reproducibility and stability.

Electrochemical Detection of Self-Assembled Viologen Modified Electrode as Mediator of Glucose Sensor

An amperometric glucose biosensor has been developed using viologen derivatives as a charge transfer mediator between a glucose oxidase (GOD) and a gold electrode. A highly stable selfassembled monolayer (SAM) of thiol-based viologen was immobilized onto the gold electrode of a quartz crystal microbalance (QCM) and GOD was immobilized onto the viologen modified electrode. This biosensor response to glucose was evaluated amperometrically in the potential of -300 ㎷. Upon immobilization of the glucose oxidase onto the viologen modified electrode, the biosensor showed rapid response towards glucose. Experimental conditions influencing the biosensor performance, such as pH potential, were optimized and assessed. This biosensor offered excellent electrochemical responses for glucose concentration below μ mol level with high sensitivity and selectivity and short response time. The levels of the RSDs (＜ 5 %) for the entire analyses reflected the highly reproducible sensor performance. A linear calibration range between the current and the glucose concentration was obtained up to 4.5 × 10 -4 M. The detection limit was determined to be 3.0 ×10 -6 M.

Influence of anions on electrochemical redox reactions and electrical properties using a viologen derivative

Self-assembled monolayers of alkane derivatives with sulfur-containing head groups on gold substrates have been widely examined recently, since the binding between S atoms and the Au surface is strong. Viologen derivatives have been extensively investigated because of their well-known electrochemical behavior, including behavior as the electron acceptors for the electric charge delivery mediation of devices. Self-assembled viologen monolayers were prepared on the gold surface of a quartz crystal microbalance (QCM) that has been used as a nanogram order mass detector. The self-assembly of viologen derivatives has been determined by the resonant frequency shift of a QCM using a quartz crystal analyzer (QCA). Well-defined peaks were observed at nearly equal charges during the redox reaction in cyclic voltammetry (CV). The electrochemical behavior of self-assembled viologen monolayers has been measured by the electrochemical QCM (EQCM) method. We also used scanning tunneling microscopy (STM) to manipulate the surface on a nanometer scale to form nano-structures and measured current–voltage (I–V) characteristics using scanning tunneling spectroscopy (STS).

Electrochemical properties of heme-protein in lauric acid films and its application as a biosensor

In this research, the enhancement of electron-transfer activity of hemoglobin (Hb) in lauric acid film was investigated for the first time. This type of composite film was made on a glassy carbon electrode by a casting method. Cyclic voltammetric result of the modified electrode displays a well-defined redox peak, which was attributed to the direct electrochemical response of Hb. Our results illustrate that Hb exchange electrons directly with electrode and exhibits the characteristics of peroxidase. When we use this modified electrode as a biosensor, it gives excellent performance in the electrocatalytic reduction of hydrogen peroxide (H2O2). The parameters such as pH and applied potential of the biosensor influencing in H2O2 detection were optimized carefully. Through the optimal conditions, the proposed biosensor shows the linear range for H2O2 determination was from 1×10−5 to 1.25×10−4 mol L−1 with a detection limit of 1×10−7 mol L−1. The biosensor retained more than 90% of the initial response after 14 d.

Evaluation of anticancer effect using quartz crystal microbalance and micro CCD camera

We have developed a monitoring system for evaluating the effect of anticancer agent, such as cisplatin and 5-fluorouracil (5-FU). The system mainly consisted of a quartz crystal microbalance (QCM) and a micro CCD camera that can function in a CO2 incubator. As the behavior on the resonance frequency (F) — resonance resistance (R) diagram shows the viscoelastic change on the surface of the QCM, the effect of the anticancer agent was evaluated with the F-R diagram and the micro CCD camera, in comparison with the results in the case of general culturing (no anticancer agent injection). During general culturing, the resonance frequency decreased and the resonance resistance increased. This means that the mass loading of a viscous material occurred. Observing with the micro CCD camera, the cells were spread, divided, and the number of the cells increased. On the other hand, when the anticancer agent was injected to the cancer cells, the resonance frequency and the resonance resistance increased gradually. This means the decrement of the mass effect and the increment of the viscosity on the QCM. By observation with the micro CCD camera, the number of the cells did not change. The cells shrinked and changed the shape flat to round by loosing the cell activity.

Brewster angle microscopic study of mixed lipid-protein monolayer at air-water interface and its electrochemical properties

This study investigated the lipid-protein LB Fdm formation with Brewster angle microscope. Our experimental results show that Hb molecule can enter the lipid layer and stands for long time. This kind of lipid-Hb film is very useful for designing sensitive biosensors.

Study on the Electron Transfer Properties of Self-Assembled Viologen Monolayers Using QCA

ABSTRACT The self-assembled monolayers of alkane derivatives with sulfur containing head groups on gold substrates have been widely examined recently, since the binding between S atoms and Au surface is strong. We could know it was formed monolayer onto QCM surface by self-assembly from resonant frequency shift using QCA. The measured frequency shift for V8SH was about 351 Hz. From this value, the adsorption mass was about 375 ng. The EQCM measurements revealed the anions transfer during reduction and oxidation, respectively. From the EQCM data, the well-defined shape peaks were nearly equal charges by cyclic voltammetry.

A STUDY ON THE SURFACE CHARACTERISTIC OF THE VIOLOGEN SELF-ASSEMBLED MONOLAYERS USING QCA AND STM

Viologen has been extensively investigated in the paper because their well-behaved electro-chemistry has led to their use in a variety of thesises, including the electron acceptor for the electric charge delivery mediation of the devices. The self-assembled monolayers of alkane derivatives with sulfur containing head groups on gold substrates have been widely examined recently, since the binding between S atoms and Au surface is strong. We could know it was formed monolayer onto quartz crystal microbalance (QCM) surface by self-assembly method from resonant frequency shift using quartz crystal analyzer (QCA). The measured frequency shift were about 408 Hz by VC8SH. From this value, we calculated that the mass adsorbed VC8SH were about 432 ng. The EQCM measurements revealed that anions exit and enter the viologen monolayer during reduction and oxidation, respectively. We also use the scanning tunneling microscopy (STM) for manipulating the surface on a nanometer scale to form nanostructures.