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Many studies have been conducted on the use of nano field-effect transistor (nanoFET) sensors for the detection of biological species. However, the practical application of nanoFET-based biosensors is difficult because their operating principle has not been clarified. Most existing studies focused on ion concentration and pH level in a solution, the Debye length (the physical distance at which charged particles affect the electric field), and the surface potential of the gate electrode of the nanoFET device. In this study, we verified the operating principle of the nanoFET biosensor with an extended gate electrode and established an equivalent circuit. We experimented using a solution with different pH levels to demonstrate the operating principle of the sensor. Additionally, we analyzed the responses of the device based on the material of the extended gate electrode, the effects of the reference electrode, and the connection configuration of the electrodes. We derived an equivalent circuit to explain how the nanoFET sensor works. The analysis results show that the operating principle of measuring pH or biomolecules depends on the change of the polar capacitor in the liquid-electrode interface on the surface of the sensing electrode. The roles of the reference and extended gate electrodes were clearly explained in this paper. The results of this research will improve the understanding of the operating principle of nanoFET-based biosensors and accelerate the studies for practical biosensor applications of nanoFET devices. [ABSTRACT FROM AUTHOR]

We report a dramatic improvement in the detection sensitivity of electrochemical immunosensors through the use of a magnetic nanoparticle for immunoassay reactions and an ITO working electrode for measurement of the electrochemical enzymatic reaction signals. In general, electrochemical sensors developed for immunoassay require the immobilization of capture antibodies on the surface of the working electrode. Under these circumstances, the working electrode comes into direct contact with various biological samples, and unwanted non-specific binding inevitably interferes with the detection signal. Moreover, chemical surface treatment of the working electrode to immobilize capture antibodies degrades the quality of the electrochemical signals during target determination. Here, we address these issues by immobilizing capture antibodies on the surface of magnetic nanoparticles and separating the surface for measurement of electrochemical signals from the immune reactions. By avoiding direct contact with biological materials, the surface of the working electrode could not be contaminated and could be maintained clean. We also provide experimental evidence that these novel immunoassay platforms benefit from a reduction in the noise signal. Indeed, the signal-to-noise ratio, an essential characteristic of quantitative detection, could be improved by approximately 11.8-fold compared with the electrochemical immunoassay of conventional surface modification approach, while retaining an excellent coefficient of variation (≤ 18%). The method was applied to the practical immunosensing for matrix met-alloproteinase-9 (MMP-9), the bladder cancer marker in the urine, and exhibited excellent performance. [ABSTRACT FROM AUTHOR]

We developed a nano field-effect transistor (nanoFET) sensor for detecting ions in the air. Air ions can be measured using a commercial ion counter; however, it is large and expensive equipment, requires airflow to be through a cylinder type electrode or the plate electrode. NanoFET sensor is suitable for monitoring the ion generator module in home appliances like air purification. A nanoFET sensor can continuously measure the ion balance to monitor the performance of the ion generators which do static electricity elimination in electronics manufacturing lines. In this study, we developed a semiconductor sensor that can measure the ion balance in the air. The sensor is a nanoFET device with an extended gate electrode. The polarity of the ions adsorbed on the extended gate electrode is measured, and consequently, the ion imbalance is quantitatively estimated. The developed device enables reset with a switch connected to the extended gate. The sensor reads out with a current to voltage converting operational amplifier, a reset switch, and a microprocessor. We expect that the developed nanoFET sensor is practically applied to monitor the malfunction of ion generators in the air cleaner and in the static electricity elimination in electronics manufacturing lines. [ABSTRACT FROM AUTHOR]

In vitro diagnostic technologies, used to evaluate disease status at the point-of-care (POC), are of urgent importance to improve diagnostic capabilities in bladder cancer. However, currently available approaches have a limitation because of their lack of detection for early-staged cancer. Herein, we developed an electrochemical immunosensor for the POC diagnosis of bladder cancer in which the enzyme alkaline phosphatase (ALP) and its metabolite, ascorbic acid 2-phosphate (AAP), are employed as the electrochemical label and redox signaling unit. The indium tin oxide (ITO) electrode exhibits no redox activity toward the AAP substrate, whereas its metabolic add of ascorbic acid (AA) produces strong oxidation current under the voltammetric measurement. The ITO electrode and the ALP enzyme are revealed as an excellent combination for the development of the electrochemical immunosensors in both direct- and sandwich-type immunoassay approach. Determination of apolipoprotein-A4 and metallopeptidase-9, two representative bladder cancer markers, were used to evaluate our approach, and excellent quantification with standard deviation 10 % was achieved. Overall, our results showed that our method offers an opportunity for the development of a variety of new forms of portable POC diagnostic devices with low cost and excellent performance. [ABSTRACT FROM AUTHOR]