• Applied Chemistry for Engineering
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• v.9 no.1
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• pp.44-51
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• 1998

In this work, the in-situ viscoelastic characteristics of electropolymerized polypyrrole (PPy) thin film were investigated in the electrolyte solutions of $NaClO_4$, $LiClO_4$, and $KClO_4$ by using quartz crystal analyzer (QCA). One side of quartz crystal was used as a working electrode mounted in a special fabricated QCA electrochemical ceil. The resonant frequency and resonant resistance diagram (F-R diagram) was used to interpret the viscoelastic characteristics of Pby thin film and compared with AFM photograph. The resonant frequency, resonant resistance, and current were measured to analyze the redox reaction behaviors when the cyclic voltammetry was performed using AT-cut quartz crystal electrode coated with galvanostatically polymerized Ppy film. The result suggests that the Ppy film polymerized onto the crystal behaves as a rigid elastic layer at the initial stage of electropolymerization, while the film becomes a viscoelastic layer the polymerization proceeds further. At the same time, the film thickness increases and some morphological changes take place due to the penetration of electrolyte solution into the film. These phenomena take place when cyclic voltammetry was performed using different electrolyte solution compared with polymerization process.

• Proceedings of the KIEE Conference
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• 1992.07b
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• pp.757-758
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• 1992

At-cut quarts crystal has been applied as chemical vapour sensors. The responses of quartz crystal at 9 MHz coated with various lipids were determined for organic gases which showed different affinities for each lipid. The identification of odorants depending on the species of lipid used for coating is discussed in terms of the normalized resonant frequency shift pattern.

• International Journal of Oral Biology
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• v.36 no.2
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• pp.103-108
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• 2011

Measurement of estrogen concentration in bio-samples are very important for differential diagnosis of various disease or evaluation of health status. However, it is difficult to collect immediate data of estrogen concentration because they are measured by radioimmunoassay or chromatography which need time- and cost-consuming sample pre-treatment. This study was performed for development of new estrogen biosensor employing taste principles, and for evaluation of cross reactivity between various steroid hormones. Gene sequence of ligand binding domain of ${\alpha}$-human estrogen receptor (amino acid 302-553; hER-LBD) was cloned from human breast cancer cell line. The proteins of hER-LBD were produced by T7-E.coli expression system, and isolated by chromatography. hER-LBD were coated on the gold plated quartz crystal (AT-cut 9MHz), and resonance frequencies were measured by universal frequency counter. Estradiol, progesterone, testosterone, and aldosterone were used for cross reactivity of the hER-LBD. We also monitored influences of pH change in resonance frequency. The resonance frequencies of hER-LBD coated quartz crystal were decreased during increase of estrogen concentration from $15 \;{\mu}g/mL$ to $50\;{\mu}g/mL$. However, similar steroid hormones, progesterone and aldosterone, did not elicit the change in resonance frequency. Testosterone evoke weak change in resonance frequency. The new estrogen biosensor was more sensitive in pH 7.2 than in pH 7.6. These results suggest that hER-LBD coated quartz crystal biosensor is a probable estrogen biosensor.

• Proceedings of the KIEE Conference
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• 1998.07d
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• pp.1503-1505
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• 1998

Stearic acid was deposited on surface of 9[MHz], AT-cut quartz crystal microbalance as gas sensing material using Langmuir-Blodgett(LB) technique. We measured gas response between deposited LB films and organic gas for various temperature($0{\sim}80^{\circ}C$). The resonant frequency changed due to absorbance of organic gas such as methanol and butanol gas at room temperature. However, the resonant frequency not responded to methanol gas at temperature above melting point of deposited LB films.

• Journal of Sensor Science and Technology
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• v.5 no.4
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• pp.71-79
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• 1996

The mechanism of electrochemical polymerization of polypyrrole was analyzed using Q.C.A. via measuring the resonant frequency and resonant resistance of AT-cut quartz crystal, whose electrodes were fabricated with indium tin oxide by sputtering method. The quantity of polymerized polypyrrole was able to be calculated from the resonant frequency and the viscoelasticity of polypyrrole film from resonant resistance. We found that the elastic film is formed at the first stage of the polymerization, but transformed to viscoelastic film later and that this transition repeated at some point. From these results, it was confirmed that the rheological characteristics of electrochemically polymerized polypyrrole thin film can be analyzed using Q.C.A.

• Proceedings of the KIEE Conference
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• 1995.11a
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• pp.417-419
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• 1995

Polymer-coated piezoelectric crystals were applied to analyze response characteristic of organic gases. AT-cut quartz crystal with 9 MHz resonant frequency can measure mass of 1 nanogram. Flow type gas-sensing system was used in this experiment. Flow type gas-sensing system has very simple apparatus and shows very fast frequency response for injection of organic gas. We have made parameter using relaxation ratio of frequency response for organic gas. Consequently, we found that the parameter had no relation with quantity of gas injection and dipping.

• Proceedings of the KIEE Conference
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• 1992.07b
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• pp.860-863
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• 1992

In this paper, we investigate $\pi$-A isotherms of biological lipid layer such as cholesterol and phosphatidyl choline to study a gas sensor characteristics which response only to specific materials. And, we also deposit it on the surface of quartz crystal by vertical dipping method and horizontal lifting method. Then, we evaluate the deposition status of cholesterol and phosphatidyl choline LB film using AT-cut quartz crystal. We obtain the following results: (1) Cholesterol's solid surface pressure is about 20$\sim$40(dyne/cm) and limiting area is about 50${\AA}^2$/molecule. And, phosphatidyl choline's surface pressure is about 25$\sim$40(dyne/cm) and limiting area is about 20 ${\AA}^2$/molecule. (2) When LB films are deposited, the deposition ratio is coincident with the frequency shift. Therefore, we can evaluate the deposition status of LB film. (3) For cholesterol, Y type LB films are deposited up to 15 layers by vertical dipping method. (4) For phosphatidyl choline, X typo LB films are deposited to 15 layers by horizontal lifting method. But, in case of vertical dipping method, the deposition status is not good.

• Proceedings of the Korea Society for Simulation Conference
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• 2001.10a
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• pp.215-219
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• 2001

The resonators made of piezoelectric crystals such as a quartz crystal are widely used. Their frequency-temperature characteristics are of primary importance for their applications to the frequency control devices. The characteristics estimation is useful for determining their design parameters. In the present paper, several types of resonators are numerically analyzed. The numerical solutions are made using 3-D Finite Element Modeling, and the results are compared with the theoretical values whenever they are available. To demonstrate the validity of the present numerical approach, the application is made to the analysis of the plates with some well-established cutting angles. For the resonator stable with temperature change, the cutting angle is important in which the temperature coefficient of the first order is chosen to be zero. The rotated Y-cut plates in thickness-shear mode are considered. The equivalent circuit representation is often used fur describing the characteristics at the electrical terminals which enables the circuit analysis including the effect of temperature change by using the circuit simulators. The equivalent circuit parameters are obtained by fitting the admittance-frequency curve from the finite element analysis.

• Asian Pacific Journal of Cancer Prevention
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• v.15 no.21
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• pp.9375-9378
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• 2014

Background: A piezoelectric immunosensor for early cervical cancer detection was developed involving short analyis time and less invasive technique for $p16^{INK4a}$, a protein that has been linked to cervical cancer. Materials and Methods: $5{\mu}L$ of 5.0 mg/mL $p16^{INK4a}$ antibody and then supernatant from different clinical samples from West China Second University Hospital (Sichuan, China) were dripped on the center of the AT-cut crystal through a micro-injector. Absorption of the $p16^{INK4a}$ by antibody caused a shift in the resonant frequency of the immunosensor, and the resonant frequency was correlated to the amount of the $p16^{INK4a}$ in the supernatant. Results: The greater severity of lesion grading, the greater the expression level of $p16^{INK4a}$. Conclusion: Degree of cervical cancer lesion development could be determined by detected amount of $p16^{INK4a}$ in different clinical samples.

• Applied Biological Chemistry
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• v.49 no.3
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• pp.254-258
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• 2006

Vitellogenin has been known as a potent biomarker protein for the estrogenic activity in fish exposed to endocrine disruptors. In this study, a piezoelectric immunosensor making use of an anticarp vitellogenin antibody and an AT-cut quartz crystal microbalance as the biological component and transducer was prepared, followed by its application to the analysis of carp vitellogenin as follows. Antibody immobilization was conducted by chemisorption of a thiolated antibody with a heterobifunctional thiolation cross-linker, sulfosuccinimidyl 6-[3-(2-pyridyldithio)propionamido]hexanoate. The reaction buffer for the immunosensor system was optimized as 0.1 M sodium phosphate (pH 7.4). Concentration-dependent sensor responses were obtained in the vitellogenin concentrations ranging from 0.4864 to 486.4000 nM, with a linear correlation between vitellogenin concentration and frequency shift in double-logarithmic scale. The limit of detection of the immunosensor for carp vitellogenin was presumed as 0.4864 nM.