• Journal of Sensor Science and Technology
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• v.10 no.4
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• pp.239-249
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• 2001

LAPS is a device which is dependent on the bias potential between a pH sensitivity and alternating photocurrent. We implemented the multichannel LAPS device and the detection system which was able to effectively measure the sensor's output by a synchronized detection circuit and multiple methods. The implemented LAPS was structured the multiple sensing sites for analyzing a various components simultaneously. And the system included a time-division method using one pre-amplifier being able to detect the multichannel pH concentration preserving a high S/N ratio and a control part. System hardware consists of a pre-amplifier, digital unit and sensor unit, and software consists of a system program and PC program. As results, we verified the successful operations of system including an implemented pre-amplifier and signal processing units.

• Journal of Sensor Science and Technology
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• v.10 no.6
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• pp.317-327
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• 2001

In this paper, we proposed a new detection method of pH image to effectively measure a 2-dimensional pH distribution of test materials by irradiating an frequency modulated light to LAPS using a reticle. It could measure simultaneously signals in one line by applying a modulated light having difference frequency for each pixel using a frequency modulating reticle, and calculating an amplitude with respect to a frequency component by the light source. To experiment the proposed method, we designed and implemented a reticle considering of a LAPS's characteristic, and reconstructed an image by frequency analysis using the implemented reticle and test pattern image. As a result, we verified that the proposed method using the reticle was able to detect 30 times faster for a $30{\times}30$ pixels pH image having a PSNR of 22-24 [dB] than conventional method.

• Journal of Sensor Science and Technology
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• v.10 no.4
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• pp.266-272
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• 2001

A coil-type capacitive sensor on which the deterioration of the car engine oil can be in situ measured, has been developed. The sensor was designed to get over 10 pF at the limited space on the drain hole of the oil pan. The design factors for stable capacitance measurement such as coil diameter and winding condition, materials and configuration of the coil former, and shielding method, etc., were known by both computer simulation and experimental investigations. The dielectric properties measured by several sensors for an used sample oil were consisted within 0.25%. The sensor installed on the car having severe vibration, temperature and humidity fluctuation, even electromagnetic noise, has shown very distinguishable results.

• Journal of Sensor Science and Technology
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• v.1 no.1
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• pp.5-12
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• 1992

We have fabricated a-Si:H multilayer for contact-type linear image sensor by means of RF glow discharge decomposition method. The ITO/i-a-Si:H/Al structure has relatively high dark current due to indium diffusion and carrier injection from both electrodes, resulting in low photocurrent to dark current. To suppress the dark current and to enhance interface electric field between ITO and i-a-Si:H film we have fabricated ITO/insulator/i-a-S:H/p-a-S:H/Al multilayer film with blocking structure. The photocurrent of ITO/$SiO_{2}(300{\AA})$/i-a-Si:H/p-a-Si:H($1500{\AA}$)/Al multilayer sensor with 5V bias voltage became saturated at about 20nA under $20{\mu}W/cm^{2}$ light intensity, while the dark current was less than 0.1nA. To increase the light generation efficiency we have adopted ITO/$SiO_{x}N_{y}(300{\AA})$/i-a-Si:H/p-a-Si:H($1500{\AA}$)/Al structure, showing photocurrent of 30nA and dark current of 0.08nA with 5V bias voltage. Also the spectral photosensitivity of the multilayer was enhanced for short wavelength visible region of 560nm, compared with that of the a-Si:H monolayer of 630nm. And its photoresponse time was about 0.3msec with the film homogeneity of 5% deviation.

• Journal of Sensor Science and Technology
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• v.23 no.3
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• pp.211-215
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• 2014

The Pt-, Ni- and Cr-decorated tubular $SnO_2$ nanofibers for gas sensors were prepared by the electrospinning of polyvinylpyrrolidone (PVP) nanofibers containing Pt, Ni, and Cr precursors, the sputtering of $SnO_2$ on the electrospun PVP nanofibers, and the removal of sacrificial PVP parts by heat treatment at $600^{\circ}C$ for 2 h. Pt-decorated tubular $SnO_2$ nanofibers showed high response ($R_a/R_g=210.5$, $R_g$: resistance in gas, $R_a$: resistance in air) to 5 ppm $C_2H_5OH$ at $350^{\circ}C$ with negligible cross-responses to other interference gases (5 ppm trimethylamine, $NH_3$, HCHO, p-xylene, toluene and benzene). Cr-decorated tubular $SnO_2$nanofibers showed the selective detection of p-xylene at $400^{\circ}C$. In contrast, no significant selectivity to a specific gas was found in Ni-decorated tubular $SnO_2$ nanofibers. The selective and sensitive detection of gases using Pt-decorated and Cr-decorated tubular $SnO_2$ nanofibers were discussed in relation to the catalytic promotion of gas sensing reaction.

• Journal of Sensor Science and Technology
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• v.4 no.4
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• pp.55-61
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• 1995

A new ISFET array chip, based on detection of the threshold voltages of ISFETs by using an adjustable input, was designed. The chip includes 240 pH-ISFETs and circuitry such as comparators, a decoder and register. The chip has increased reliability, improved accuracy, digital output capability and the possibility of multi sensor implementation. To fabricate the chip, an extended CMOS process was devised and implemented.

• Bulletin of the Korean Chemical Society
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• v.32 no.12
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• pp.4377-4381
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• 2011

In this study, real-time and label-free methods for monitoring the enzymatic reaction of urease, which releases ammonia through the hydrolysis of urea in an aqueous solution, were developed using a liquid crystal (LC)-based pH sensor. Nematic liquid crystal 4-cyano-4'-pentylbiphenyl (5CB), doped with 4'-pentyl-biphenyl-4-carboxylic acid (PBA), exhibited a shift in optical appearance from bright to dark when it was in contact with ammonia generated from the enzymatic reaction between urease and urea. This optical change was attributed to the anchoring transitions of LCs caused by hydrophobic interactions between the tails of deprotonted PBA ($PBA^-$) molecules and the LCs at the aqueous/LC interface. This novel technique holds great promise for the sensitive detection of urease along with its substrates and inhibitors.

• Proceedings of the Korean Society of Dyers and Finishers Conference
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• 2000.04a
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• pp.150-151
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• 2000

Some chromophores that can undergo a pronouncend colour change when acted upon an extenal agency, such as light, heat, pH, or chemical agents, have many potential applicationa as functional dyes. They may be used as indicators, optical sensors, biochemical probes, optical and thermal recording materials. The results will investigate donor-acceptor chromophores which have the potential for such colour change processes. In particular, cross-conjugated donor-acceptor chormophores, analogous to indigo and squarylium-type chromophores, will be examined for pH sensitizing and for their oxidation-reduction colour change behaviour.

• Journal of Sensor Science and Technology
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• v.22 no.3
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• pp.233-237
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• 2013

We fabricated electrolyte-insulator-semiconductor (EIS) devices using a solution process and measured the sensing properties of EIS devices according to the thicknesses of sensing membrane. For high pH sensitivity and better stability properties, we used $SiO_2/HfO_x$ (OH) layer as a sensing membrane. In this work, $HfO_x$ sensing membranes were deposited on 5 nm thick $SiO_2$ buffer layer by spin coater with thicknesses of 15, 31, 42, 55 nm, respectively. As a result, we founded that the thickness of $HfO_x$ sensing membrane affects to sensitivity and chemical stability of EIS device. Especially, the EIS device with 42 nm thick $HfO_x$ membrane showed superior sensing ability in terms of pH-sensitivity, linearity, hysteresis voltage and drift rate characteristics than the other devices. In conclusion, we confirmed that it is possible to improve the sensing ability and the chemical stability properties using optimized thickness of sensing membrane and proper annealing process.

• Journal of Sensor Science and Technology
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• v.20 no.6
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• pp.400-405
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• 2011

This study introduced the development of a strip type disposable enzyme-linked immunosensor platform for the detection of IgG. Strips of the strip sensor were fabricated by using commercial nitrocellulose filter membranes and a housing holder for the strips was manufactured by using a standard injection molding process for a plastic material. An IgG-urease conjugate was prepared and used for the competitive immune-binding with sample IgG. From the enzymatic reaction between the conjugated urease and urea added, ammonia was generated and caused a localized alkaline pH change on the immobilized antibody band which was coated onto the sensor strips. This pH increase subsequently caused a color change of the antibody band in the presence of a pH indicator, phenol red. Used in conjunction with a competitive immunoassay format, the intensity of the color produced is directly linked with the concentration of target analyte, IgG, and specific measurement of IgG in a lateral flow immunoassay format was achieved over the range 100 ppb to 2000 ppb IgG.