• Proceedings of the Korean Society Of Semiconductor Equipment Technology
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• 2004.10a
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• pp.49-63
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• 2004

• Journal of Environmental Science International
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• v.29 no.8
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• pp.801-808
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• 2020

In this study, an effective fluorescence pH sensor based on conjugated polyelectrolyte micelles (CPMs) was devised for detecting extremely acidic conditions. An amphiphilic coumarin derivative (CC12-N), a building block, was prepared, into which an ionizable amino group, aryl amine, was incorporated as a potential hydrophilic moiety. This monomer displays self-assembled micelle formation in extremely acidic pH ranges, giving a hydrophobic π-extended conjugated system at the inner part and hydrophilic functionality at the periphery, resulting in efficient fluorescence intensity enhancement. This new micelle-based fluorescence provides an efficient sensing platform for detecting very low pH values in the presence of competing substances.

• Textile Coloration and Finishing
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• v.16 no.1
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• pp.53-58
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• 2004

The preparation of responsive fibers from acrylic fibers is studied. Various responsive fibers, such as fibers which change their color on exposure to light or with change in temperature, have been developed and are used commercially However, the responsive material in these fibers are not the fiber itself but chemicals in microcapsules attached to the fibers by finishing, and few fibers exhibit responsive properties by itself. The partial hydrolysis of polyacrylonitrile fibers to obtain pH responsive fibers is presented in this paper. Partial hydrolysis was effected by control of the concentration of the sodium hydroxide used in the hydrolysis, hydrolysis temperature and time. The degree of hydrolysis was evaluated by nitrogen content of the hydrolyzed fibers and their response, change in length, to aqueous solutions of varying pH was studied by continually changing the pH. Significant changes in lengths with pH were observed and the gel transition behavior varied with the conditions of hydrolysis. The hysteresis of the length change was also studied to evaluate the possibilities of using hydrolyzed acrylic fibers as pH sensors.

• Journal of Sensor Science and Technology
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• v.30 no.5
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• pp.326-330
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• 2021

Reactions between gold (Au) surface plasmon resonance (SPR) chips and bovine serum albumin (BSA) dissolved in solutions of different pH were investigated. The charge on the BSA depends on the pH of the solution in which it is dissolved. Thus, dissolving BSA in different pH solutions resulted in different charges of BSA. Among the BSA dissolved in solutions with pH 4.01, 7.4, and 10.01, the SPR response was the highest for BSA dissolved in the solution of pH 4.01. To eliminate the response variation owing to the difference in the refractive indices of the solutions, phosphate buffered saline (PBS) was injected into the system after the reaction of BSA with the Au SPR chip had happened. In this case too, the BSA dissolved in the solution with pH 4.01 exhibited the highest response. This may be attributed to the non-uniform distribution of ionic patches on the BSA, which can induce electrostatic attraction to the surface even though BSA has a positive charge at pH 4.01, and the absolute values of the net charge of BSA at pH 4.01 and 7.4 were very close.

• Journal of Sensor Science and Technology
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• v.9 no.2
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• pp.106-112
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• 2000

A FET-type reference electrode(REFET) is an effective method to eliminate typical problems with ISFET(ion sensitive field-effect transistor) such as drift, temperature, light-dependence and miniaturization of reference electrode. However, it is difficult to make the highly reliable REFET with excellent long-term stability and reproducibility. In this paper, an ion-blocking membrane was applied to the REFET for the PET-type electrolyte sensors(pH, pNa-ISFET). The fabricated REFET indicated the stable sensitivity (55.4 mV/pH, 53.5 mV/decade) and good linearity in the pH and pNa measurement. In the measurement, ISFET/Pt/REFET configuration showed excellent stability and reproducibility.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.434.2-434.2
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• 2014

We observe enhanced pH response of solution-gated field-effect transistors (SG-FET) having 1D-2D hybrid channel of vertical grown ZnO nanorods grown on CVD graphene (Gr). In recent years, SG-FET based on Gr has received a lot of attention for biochemical sensing applications, because Gr has outstanding properties such as high sensitivity, low detection limit, label-free electrical detection, and so on. However, low-defect CVD Gr has hardly pH responsive due to lack of hydroxyl group on Gr surface. On the other hand, ZnO, consists of stable wurtzite structure, has attracted much interest due to its unique properties and wide range of applications in optoelectronics, biosensors, medical sciences, etc. Especially, ZnO were easily grown as vertical nanorods by hydrothermal method and ZnO nanostructures have higher sensitivity to environments than planar structures due to plentiful hydroxyl group on their surface. We prepared for ZnO nanorods vertically grown on CVD Gr (ZnO nanorods/Gr hybrid channel) and to fabricate SG-FET subsequently. We have analyzed hybrid channel FETs showing transfer characteristics similar to that of pristine Gr FETs and charge neutrality point (CNP) shifts along proton concentration in solution, which can determine pH level of solution. Hybrid channel SG-FET sensors led to increase in pH sensitivity up to 500%, compared to pristine Gr SG-FET sensors. We confirmed plentiful hydroxyl groups on ZnO nanorod surface interact with protons in solution, which causes shifts of CNP. The morphology and electrical characteristics of hybrid channel SG-FET were characterized by FE-SEM and semiconductor parameter analyzer, respectively. Sensitivity and sensing mechanism of ZnO nanorods/Gr hybrid channel FET will be discussed in detail.

• Journal of Sensor Science and Technology
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• v.21 no.4
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• pp.256-262
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• 2012

Hyaluronic acid(HA) hydrogels were synthesized by immersing HA microbeads in phosphate buffered saline solutions having different pH levels to assess the effect of pH on the swelling ratio of HA hydrogels for smart drug delivery systems. No beads were formed when the HA solution(below pH 9) was crosslinked with divinyl sulfone(DVS) because DVS is a basic solution. The variation regarding the size of the microbead was not significant, suggesting that the bead size is not a function of pH(10 ~ 14). However, the pore size of the microbeads decreased with increasing pH from 10 to 14, leading to the surface smoothness and dense network as a result of higher crosslinking. The swelling ratio of hydrogels increased when the pH rose from 2(acidic) to 6(neutral). Afterwards, it decreased with further increasing pH(basic). The lower swelling ratio may be due to the lack of ionization of the carboxyl groups. On the other hand, a higher swelling ratio is likely due to the increased electrostatic repulsions between negatively charged carboxyl groups on different chains. Experimental results suggested that pH-responsive HA hydrogels can be applicable to the controlled drug delivery systems.

• Journal of Sensor Science and Technology
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• v.31 no.5
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• pp.337-342
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• 2022

Hydrogen (H₂) gas is widely preferred for use as a renewable energy source owing to its characteristics such as environmental friendliness and a high energy density. However, H₂ can easily reverse or explode due to minor external factors. Therefore, H₂ gas monitoring is crucial, especially when the H₂ concentration is close to the lower explosive limit. In this study, metal oxide materials and their p-n heterojunctions were synthesized by a hydrothermal-assisted dip-coating method. The synthesized thin films were used as sensing materials for H₂ gas. When the H₂ concentration was varied, all metal oxide materials exhibited different gas sensitivities. The performance of the metal oxide gas sensor was analyzed to identify parameters that could improve the performance, such as the choice of the metal oxide material, effect of the p-n heterojunctions, and operating temperature conditions of the gas sensor. The experimental results demonstrated that a CuO/ZnO gas sensor with a p-n heterojunction exhibited a high sensitivity and fast response time (134.9% and 8 s, respectively) to 5% H₂ gas at an operating temperature of 300℃.

• Journal of Sensor Science and Technology
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• v.13 no.3
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• pp.213-217
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• 2004

The general method to find a H. pylori in the stomach is the rapid urease test but it is only used to decide the infection with H. pylori. In this study, it is tried to develope fiber-optic pH sensor which can be used with gastroscop to quantify H. pylori. To measure the degree of infection with H. pylori, the color change of phenol red according to the degree of pH is measured by optical fibers with different light sources and the optimum distance from a sample to the end of sensor tip is decided by measuring the maximum reflectivity from a sample. Also the sensitivity study is carried out to decide the optimum light source which has sensitive change of reflectivity to the change of pH. It is expected that the fiber-optic pH sensor which measures the degree of infection with H. pylori exactly can be developed.

• Journal of Sensor Science and Technology
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• v.21 no.3
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• pp.186-191
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• 2012

In this paper, we present a pH measurement method that uses a microcantilever-array-based biosensor system. It is composed of microcantilever array, liquid cell, micro syringe pump, laser diode array, position sensitive detector, data acquisition device, and data processing software. Four microcantilevers are functionalized with pH-sensitive MHA(mercaptohexadecanoic acid) as a probe, while three microcantilevers are functionalized with HDT(hexadecane thiol) as reference. We prepare PBS(phosphate buffered saline) solutions of different pH and inject them into the liquid cell with a predefined volumetric speed at regular time intervals. The functionalized mircocantilevers in the liquid cell deflect as a self-assembled monolayer on the microcantilever binds with probe molecules in the solution. The difference in deflection between the MHA-covered probe microcantilever and the HDT-covered reference microcantilever was used to compensate for thermal drift. The deflection difference clearly increases with increasing pH in the solution. It was shown that when the pH values of the PBS solutions are high, there were large variations in the deflection of microcantilevers, whereas there were small variations for low pH value. The experimental results show that the microcantilever array functionalized with MHA and HDT can detect pH value with good repeatability.