• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2010.05a
• /
• pp.811-812
• /
• 2010

• Journal of the Korean Electrochemical Society
• /
• v.13 no.1
• /
• pp.50-56
• /
• 2010

The multi-wall carbon nano-tube composite mixed with carbon paste electrode presented more sensitive and selective amperometric signals in the oxidation of glucose than general screen-printed carbon electrodes(SPCEs). Redox mediators to transport electrodes from enzyme to electrodes are very important part in the biosensor. A novel osmium redox complex was synthesized by the coordinating pyridine group containing primary amines which were electrochemically immobilized onto the MWCNT-SPCEs surface. Electrochemical studies of osmium complexes were investigated by cyclic voltammetry, chronoamperometry. The surface coverage of osmium complexes on the modified carbon nano-tube electrodes were significantly increased at 100 time (${\tau}_0=2.0\;{\times}\;10^{-9}\;mole/cm^2$) compared to that of the unmodified carbon electrodes. It's practical application of the glucose biosensor demonstrated that it shows good linear response to the glucose concentration in the range of 0-10 mM.

• Applied Chemistry for Engineering
• /
• v.32 no.3
• /
• pp.229-236
• /
• 2021

During the last two decades, metal-organic frameworks (MOFs) have been drawn attention due to their high specific surface area, porosity, and catalytic activities that allow to use in many applications such as sensor, catalysis, energy storage, etc. To synthesize MOFs hydrothermal or solvothermal method were generally used. However, these methods require high-cost equipment and long time-spend for the synthesis with multi-step process. In contrast, electrochemical synthesis has been considered as a simple and easy process under the ambient conditions. In this review, we described the mechanism of electrochemical MOFs synthesis by the number of configured electrodes system, with the recent reports of various applications.

• Journal of the Optical Society of Korea
• /
• v.10 no.3
• /
• pp.130-142
• /
• 2006

Lab-on-a-chip technology is attracting great interest because the miniaturization of reaction systems offers practical advantages over classical bench-top chemical systems. Rapid mixing of the fluids flowing through a microchannel is very important for various applications of microfluidic systems. In addition, highly sensitive on-chip detection techniques are essential for the in situ monitoring of chemical reactions because the detection volume in a channel is extremely small. Recently, a confocal surface enhanced Raman spectroscopic (SERS) technique, for the highly sensitive biological analysis in a microfluidic sensor, has been developed in our research group. Here, a highly precise quantitative measurement can be obtained if continuous flow and homogeneous mixing condition between analytes and silver nano-colloids are maintained. Recently, we also reported a new analytical method of DNA hybridization involving a PDMS microfluidic sensor using fluorescence energy transfer (FRET). This method overcomes many of the drawbacks of microarray chips, such as long hybridization times and inconvenient immobilization procedures. In this paper, our recent applications of the confocal Raman/fluorescence microscopic technology to a highly sensitive lab-on-a-chip detection will be reviewed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2010.10a
• /
• pp.537-537
• /
• 2010

High precision sensing is very important in various technologies. Especially, it is more important when it were applied to nano/micro meter level's sensing like AFM, storage, etc. And capacitive sensing is widely used method. To improve the measurement efficiency, many signal conditioners were studied and one of them was surface acoustic wave (SAW) device. SAW device is very widely used as a high frequency bandwidth filter. Due to the reflective characteristic of high frequency, the response of SAW device contains both propagative and reflective signal at the external impedance. In this paper, we used SAW device as signal conditioner of capacitive sensor. And high precision gap measurement was executed using capacitive load. Reference signal was reflective SAW response and the magnitude at the center frequency of SAW device by the change of impedance was checked. Finally, the attainable gap resolution was determined.

• Korean Journal of Materials Research
• /
• v.24 no.9
• /
• pp.451-457
• /
• 2014

We developed a high-performance methane gas sensor based on a $SnO_2$ hollow hemisphere array structure of nano-thickness. The sensor structures were fabricated by sputter deposition of Sn metal over an array of polystyrene spheres distributed on a planar substrate, followed by an oxidation process to oxidize the Sn to $SnO_2$ while removing the polystyrene template cores. The surface morphology and structural properties were examined by scanning electron microscopy. An optimization of the structure for methane sensing was also carried out. The effects of oxidation temperature, film thickness, gold doping, and morphology were examined. An impressive response of ~220% was observed for a 200 ppm concentration of $CH_4$ gas at an operating temperature of $400^{\circ}C$ for a sample fabricated by 30 sec sputtering of Sn, and oxidation at $800^{\circ}C$ for 2 hr in air. This high response was enabled by the open structure of the hemisphere array thin films.

• Journal of Sensor Science and Technology
• /
• v.23 no.6
• /
• pp.383-387
• /
• 2014

Electrically conductive polypyrrole-polyvinylpyrrolidone (PPy-PVP) nanofiber mats with a core-shell structure have been successfully fabricated by a two-step process: the formation of FeCl3-containing PVP nanofiber mat by electrospinning, and the vapor-phase polymerization (VPP) of pyrrole monomer on the mat in a sealed chamber at room temperature. Surface morphology and chemical composition of the PPy-PVP mat were characterized by SEM, EDX and FTIR analyses. The as-prepared nonwoven mat was composed of PPy-PVP nanofibers with an average diameter of 300 nm. The sheet conductivity of the nanofiber mat was measured to be approximately 0.01 S/cm by a four-point probe. We have also investigated gas-sensing properties of PPy-PVP nanofiber mat upon exposure to methanol vapor. The PPy-PVP nanofiber sensors were observed to have excellent methanol-sensing performance. The nanofiber-based core-shell nanostructure could give an opportunity to fabricate a highly sensitive and fast response sensor due to its high surfaceto-volume ratio.

• Bulletin of the Korean Chemical Society
• /
• v.32 no.6
• /
• pp.1865-1872
• /
• 2011

This study investigates the sensitivity of a gas sensor to volatile organic compounds (VOCs) at various operating temperatures and catalysts. Nano-sized powdered $WO_3$ prepared by sol-gel and chemical precipitation methods was mixed with various metal oxides. Next, transition metals (Pt, Ru, Pd, and In) were doped on the surface of the mixture. Metal-$WO_3$ thick films were prepared using the screen-printing method. The physical and chemical properties of the films were studied by SEM/EDS, XRD, and BET techniques. The measured sensitivity to VOCs is defined as the ratio ($R_a/R_g$) of resistance ($R_{air}$) of $WO_3$ film in the air to resistance ($R_{gas}$) of $WO_3$ film in a VOCs test gas. The sensitivity and selectivity of the films were tested with various VOCs such as acetaldehyde, formaldehyde, methyl alcohol, and BTEX. The thick $WO_3$ film containing 1 wt % of Ru and 5 wt % of $SnO_2$ showed the best sensitivity and selectivity to acetaldehyde gas at an operating temperature of 300 $^{\circ}C$.

• Proceedings of the KSME Conference
• /
• 2007.05a
• /
• pp.1439-1443
• /
• 2007

In this paper, vibration reduction techniques of a voice coil motor (VCM) actuator are presented for AFM imaging system. The damping coefficient of the actuator driven by VCM with a flexure hinge is quite low and it cause the about 30dB peak amplitude response at the resonance frequency. To decrease this peak response, we design and apply elliptical band-stop filters to xy and z axis VCM actuator. Frequency response of each actuator with filter is measured to verify the effect of the filters. As a sensor, capacitive sensor is used. Vibration reduction rate of the xy actuator with the filter is also measured while real AFM scanning condition. As another method, closed loop control with the capacitive sensor is applied to the xy axis actuator to add an electrical damping effect and vibration reduction rate measured. These vibration reduction rates with each method are compared. In the case of z axis actuator, the frequency response of force (gap) control loop is measured. For comparison, the frequency response using a conventional PID controller is also obtained. Finally, the AFM image of a standard grid sample is measured with the designed controller to analyze the effect in the AFM imaging.

• Korean Journal of Materials Research
• /
• v.18 no.7
• /
• pp.367-372
• /
• 2008

ZnO nanorod gas sensors were prepared by an ultrasound radiation method and their gas sensing properties were investigated for NO gas. For this procedure, 0.01, 0.005 and 0.001M of zinc nitrate hydrate [$Zn(NO_3)_2\;{\cdot}\;6H_2O$] and hexamethyleneteramine [$C_6H_{12}N_4$] aqueous solutions were prepared and then the solution was irradiated with high intensity ultrasound for 1 h. The lengths of ZnO nanorods ranged from 200 nm to 500 nm with diameters ranging from 40 nm to 80 nm. The size of the ZnO nanorods could be controlled by the concentration of solution. The sensing characteristics of these nanostructures were investigated for three kinds of sensor. The properties of the sensors were influenced by the morphology of the nanorods.