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In this research, we have realized an electrical double layer (EDL) gated high electron mobility transistor (HEMT) as DNA sensor. The sensing area on the gate electrode which is separated from the transistor channel is immobilized with probe DNA to capture target DNA from physiological salt environment. The detection limit of the sensor can be as low as 1 fM with very high sensitivity. The specificity of the DNA sensor is also demonstrated by controlling the hybridization temperature. By choosing the hybridization temperature slightly lower than the melting temperature of the well-matched sequence, the binding ratio can be controlled between the fully-matched and mismatched one. The sensor has demonstrated specificity, with the ability to achieve single base mismatch resolution. The sensor has the potential for rapid DNA sensing applications in cells, biomarkers and viruses.

This study reports the development of an efficient and sensitive method to directly sense microRNA (miRNA) in high ionic strength solutions with the use of electrical double layer (EDL) gated AlGaN/GaN high electron mobility transistor (HEMT). This FET structure uses a complementary DNA probe functionalized gate electrode which is separated from the transistor channel. In this research, we focus on the detection of miRNA samples, miR-126, miR-208a and miR-21 which are biomarkers of cardiovascular diseases (CVD). The sensor has a dynamic range that is comparable to the clinically relevant concentration range with a detection limit as low as 1 fM. Selectivity of the sensor is demonstrated by evaluating sensor response at fully complementary and slightly mismatched sequences. The miniaturized sensor can be used in point of care or homecare diagnostics for rapid miRNA detection to evaluate CVDs at an early stage.

In here, we have devised a portable biosensor system to detect protein-based biomarkers from a single drop of whole blood, in 5 minutes, without any additional sample pre-processing or extra reagents. The sensing methodology is based on electrical double layer (EDL) gated field effect transistor (FET) biosensor, in which an array of gold electrodes designed as extended gate structures, transduce immunological interaction of target protein to readable electrical signal. High electric field modulation of transistor drain current enables very high sensitivity, selectivity and wide dynamic range, in whole blood. Single drop of blood is dropped on the device and blood cells are gravitationally separated from blood plasma during 5 mins of incubation period, by rotating the device orientation to face downwards. A portable sensor measurement unit is designed to record the electrical characteristics of the sensor and display the test results in interfaced personal computer. We have demonstrated the detection of cardiac troponin I (cTnI) and brain natriuretic peptide (BNP) in 1X PBS and whole blood samples. The sensor methodology has been developed to considerably reduce cost and assay complexity, with minimal user protocols. This whole blood assay can be performed at the convenience of homes, offices and hospitals, by anyone without prior training, in 5 minutes.

This study reports the fabrication and characterization of electrical double layer gated AlGaN/GaN High electron mobility (HEMT) biosensor array to capture, detect and count circulating tumor cells (CTCs) of colorectal cancer (CRC). GaN HEMT chips were assembled into a sensor array on a thermo-curable polymer substrate in a simple and robust packaging process. The array had multiple aptamer immobilized sensing sites and was highly sensitive and selective with up to single cell resolution. The present method can detect cells in their native electrolyte composition, in a very short time with extremely low cost compared to the conventional circulating tumor cell assays. The effect of cellular binding in different test environments was further studied and reported. The electrical response of the sensor was discovered to be relevant to the transmembrane potential of the cell. This whole cell sensor array has the potential to be used as a point-of-care diagnostic tool in varied applications such as detection of rare cells, pathogens and studying the dynamics of cellular interactions.

In this study, a new type of field-effect transistor (FET)-based biosensor is demonstrated to be able to overcome the problem of severe charge-screening effect caused by high ionic strength in solution and detect proteins in physiological environment. Antibody or aptamer-immobilized AlGaN/GaN high electron mobility transistors (HEMTs) are used to directly detect proteins, including HIV-1 RT, CEA, NT-proBNP and CRP, in 1X PBS (with 1%BSA) or human sera. The samples do not need any dilution or washing process to reduce the ionic strength. The sensor shows high sensitivity and the detection takes only 5 minutes. The designs of the sensor, the methodology of the measurement, and the working mechanism of the sensor are discussed and investigated. A theoretical model is proposed based on the finding of the experiments. This sensor is promising for point-of-care, home healthcare, and mobile diagnostic device.

Diseases that are the leading causes of mortality worldwide such as cardiovascular diseases (CVD), cancer and infectious diseases can be better managed and cured with early and prompt diagnosis and prognosis. Molecular biomarkers in whole blood (blood serum proteins) have predictive, diagnostic and prognostic capacity and semiconductor based electronic biosensors can be used to deliver reliable and affordable point-of-care disease monitoring. GaN High Electron Mobility Transistor (HEMT) based sensors have previously been used in a variety of applications such as ion, gas and biomolecule sensing. However, the limitations of FET biosensors set by the charge screening effect in high ionic strength solutions required additional sample processing steps, making them practically unusable in terms of point-of-care testing. With a novel biosensing technique enabling direct detection of target proteins in high salt concentration medium using GaN HEMT and innovative biosensor packaging methodology, a portable biosensor system has been designed and fabricated which can provide quantitative blood biomarker analysis in 5 minutes with less than 5 µl sample. Antibody or aptamer functionalized reference gate electrode and transistor channel form an electrical double layer (EDL) FET structure that can detect binding of target proteins with very high sensitivity. The sensing and packaging techniques have been specifically optimized to meet the requirements and convenience of a mobile diagnostic system that can be used by anyone, at all times. HEMT chip is fabricated in a 4-5 mask process: mesa isolation, ohmic metal deposition and annealing, interconnect metal deposition and device passivation. A simple and robust two step epoxy based planar HEMT chip packaging allows for easy integration with commercially available reader sockets, much like the micro-SD card. A single step surface functionalization strategy is followed for immobilizing receptors which allows for high sensitivity with a wide dynamic range of detection. Pulsed gate voltage modulates the channel conductivity which behaves as a function of the charge distribution within the EDL structure. Thus, without complex sample pre-treatments and extremely low sampling requirements, quantitative detection of protein biomarkers can be achieved. The structural design of EDL FET brings the potential to investigate the binding events that were previously undetectable in traditional FET based biosensors. Results from testing purified proteins and clinical serum samples elucidate the potential of the sensing technique to overcome the charge screening effect and offer sensing beyond Debye length in physiological salt environment, with high sensitivity and ultra-low detection limit. This diagnostic technique can be applied to all types of FET based sensors that uses immunological reactions to detect the target. Owing to standard semiconductor fabrication processes and minimal or no sampling requirements, the portable sensing system can be affordable and accessible to all. Enabled with cloud management, this diagnostic system houses the potential to be a pioneering IoT biosensor. Figure 1

In this study, non-faradaic current was measured in time domain and investigated on a DNA-immobilized electrode in concentrated salt environment for biosensor applications. The electric current was measured for 50 μs once the pulse voltage of 0.5 V was applied to the electrode. Immobilization of double-stranded DNA (dsDNA) caused the electric current increased, compared to the electrode without any immobilization. Doxorubicin, ranging from 1 pM to 1 nM, intercalated the dsDNA and caused different relaxation of the electric currents. The characteristics of electric current for different surface modification on the electrode was compared and successfully explained with the ion concentration, ion mobility, and the electric field in solution. Instead of the impedance measurement, which usually extracts parasitic parameters for biosensor applications, this study directly explains the relevance between the electric current and the behavior of molecules in solution, with the proposed model. This method can be applied to any affinity type of biosensors. The three indexes, including the current level, the total charge, and the relaxation time can be directly used as signals for detection, which is much simpler compared to other existing techniques. © The Author(s) 2016. Published by ECS. This is an open access article distributed under the terms of the Creative Commons

Detection of disease biomarkers from whole blood is very important in disease prevention and management. However, new generation assays like point-of-care or mobile diagnostics face a myriad of challenges in detecting proteins from whole blood. In this research, we have designed, fabricated, and characterized a portable biomedical sensor for the detection of cardiac troponin I (cTnI) directly from whole blood, without sample pretreatments. The sensing methodology is based on an extended gate electrical double layer (EDL) gated field effect transistor (FET) biosensor that can offer very high sensitivity, a wide dynamic range, and high selectivity to target analyte. The sensing methodology is not impeded by electrostatic screening and can be applied to all types of FET sensors. A portable biomedical system is designed to carry out the diagnostic assay in a very simple and rapid manner, that allows the user to screen for target protein from a single drop of blood, in 5 min. This biomedical sensor can be used in hospitals and homes alike, for early detection of cTnI which is a clinical marker for acute myocardial infarction. This sensing methodology could potentially revolutionize the modern health care industry.

Lung cancer is the leading cause of cancer deaths in the world, among both men and women. It claims more lives each year than do colon, prostate, ovarian and breast cancers combined. Currently, diagnosis of lung cancer in stages I and II is very difficult and hence prognosis is delayed, leading to increased mortality rate. Carcinoembryonic antigen (CEA), is a common cancer biomarker and the expression of CEA above 5 ng/mL is suggestive of the presence of cancer. In this study, we utilize immunology, which is antibody/antigen reaction, with the combination of High Electron Mobility Transistor (HEMT) as the transducer, to develop a biosensor for detecting lung cancer biomarkers, electronically, as opposed to traditional ELISA techniques. HEMTs have already been demonstrated in gas, ion and biomolecule sensing purpose. When analytes accumulate on the gate area, the net charge on the HEMT surface changes. This electrical detection technique is simple, fast, and convenient. The detecting signal from the gate is amplified through the drain-source current, making the sensor very sensitive. Figure 1 (a) and (b) show the schematic of AlGaN/GaN HEMT and the top-view of the device. To create a high quality HEMT device, a 3 μm-thick undoped GaN buffer layer and a 150 Å-thick undoped Al0.25Ga0.75N layer were deposited by metal-organic chemical vapor deposition (MOCVD) on the substrate. Mesa isolation was formed by Inductively Coupled Plasma (ICP) etching system for 28 seconds. Ti, Al, Ni and Au were deposited by Electron Beam Evaporation and were annealed at 850 °C for 45 seconds under N2 flowing to form ohmic contacts. Passivation was provided by encapsulating the device with photoresist, with only the gate region open for antibody immobilization using photolithography. After sensor fabrication, surface functionalization is carried out by thiol binding on gold. We mixed bi-functional thio-carboxylate with the CEA antibody and let the antibody bind with the carboxyl functional group by EDC-sulfo NHS coupling reaction. Then the device is incubated in this solution for 12 hours at 4 ºC. BSA is used for surface blocking and as a protein dilution buffer. For the sensor measurement, source-drain bias is fixed at 0.5 V and the current change induced by binding of CEA was measured by applying a 0.5 V gate voltage. Figure 1 (c) shows the total charge accumulated for various concentrations of CEA. This can be used as an index to quantify the amount of CEA present in sample as it can distinguish various protein concentrations even in the physiological blood/serum concentration (1x PBS). The change in total charge with varying concentration of CEA can thus represent sensor calibration curve. Comparing to the conventional methods, the electronic detection of CEA using HEMT has the advantages of high sensitivity and low response time. We believe this method has the potential to further the research in the field of electronic biosensors. Figure 1

As AIDS caused by (human immunodeficiency virus type 1) has now spread to every country in the world. Statistics show that approximately 40 million people are currently living with HIV infection, and an estimated 35 million have died from this disease since the beginning of the epidemic. In this study, we use DNA-immobilized AlGaN/GaN high electron mobility transistors (HEMTs) for detecting low concentration of HIV-1 RT protein (1 fM) binding with DNA electronically, showing that this technique is promising for biosensor applications. Figure 1 (a) and (b) show the schematic of RT immobilized HEMT and the top-view of the device respectively. The HEMT structure consisted of a 3 μm-thick GaN buffer, 150 Å-thick undoped Al0.25Ga0.75N and 10 Å-thick undoped GaN cap layer. Mesa isolation was formed by Inductively Coupled Plasma (ICP) etching system for 28 seconds. Ti, Al, Ni and Au were deposited by Electron Beam Evaporation and were annealed at 850 °C for 45 seconds under N2 flowing to form ohmic contacts. The source and drain of HEMT were isolated by photoresist except the gate metal region. The DNA was immobilized on the gate region for 24 hours followed by surface blocking with bovine serum albumin (BSA). The HIV-1 RT protein solutions were then added on the sensing region of the sensor, and then waited for 30 minute for binding. After HIV-1 RT protein binding with DNA, the sensor was washed with 1X PBS to remove the unbound HIV-1 RT protein. 1X PBS was added on the sensor for electrical measurements. The sensor was measured by applying a dc bias of drain-source voltage (Vds) at 0.5V first, and then the gate voltage (Vg) was applied 0.5 V on the gate electrode. The drain current (Id) of the transistor was recoded in real-time when the drain-source voltage and the gate voltage were applied. The total charge was calculated by integrating the drain currents with the increasing time. Due to calculation of the total charges, any tiny difference in drain currents resulted from different HIV-1 RT protein concentrations may cause a significantly huge difference in the total charges. The total charge counted at a certain time for various concentrations of HIV-1 RT protein is shown in figure 2. It is obviously seen that the difference in total charges among different surface modification. Higher HIV-1 RT protein concentrations, including 1fM, 10fM, 100fM and 1pM were tested and caused more accumulated charges. Therefore, the change in total charge with varying concentration of HIV-1 RT protein can represent sensor calibration curve. The detection limit was then determined to be 1fM for HIV-1 RT protein measurement. The high sensitivity and the low detection limit of the sensor resulted from the charge accumulation and the less screening effect during the dynamic change of the drain current. In the detection, only a small amount of sensing materials is required and a short detection time is taken. The developed system has a great potential to measure an extremely low concentration of different proteins for biomedical applications. Figure 1

In this study, conductive polyaniline (PANI) was coated on Si3N4/Si substrates and reacted with hydroxyl radicals created by mixing ferrous ions and hydrogen peroxide in a buffer solution, as known as the Fenton reaction. The hydroxyl radicals reacted with PANI, resulting in the decreased conductivity of PANI. The reduction in the conductivity of PANI was found to be proportional to the concentration of hydroxyl radicals in the buffer solution. The concentration of hydroxyl radicals was calibrated by comparing the fluorescence intensities of the Amplex ultrared molecules oxidized by radicals and hydrogen peroxide via the catalysis of horseradish peroxidase (HRP), respectively. The conductivity change of the PANI shows a linear relationship to the concentration of hydroxyl radicals, ranging from 0.2 μM to 0.8 μM. The conductivity of PANI does not respond to either ferrous ions or hydrogen peroxide alone. Only when both ferrous ions and hydrogen peroxide are present in the solution, the conductivity of PANI decreases, indicating that the conductivity change of PANI is attributed to the existence of hydroxyl radicals. The simple process for the sensor fabrication allows the sensor to be cost-effective and disposable. This electronic sensor can detect one of the most important reactive oxygen species (ROS), the hydroxyl radical, and therefore is promising for studying oxidative stress.

Pt/GaN Schottky diodes were fabricated for detecting hydrogen sulfide at 200°C. Ga-face GaN was grown on c-plane sapphire substrate by a metal-organic chemical vapor deposition (MOCVD) system. Hydrogen sulfide was mixed with nitrogen and detected from 0.1~10 ppm with the Pt/GaN Schottky diodes. Hydrogen sulfide caused the current increase in both forward and reversed bias of the Schottky diode. Real-time detection of the hydrogen sulfide was conducted at a forward bias 1.18 V in nitrogen ambient. The sensors show good linear dependence of the current change at forward bias versus the H2S gas concentration. The sensitivity in the two ranges from 0.1~1 ppm and 1~10 ppm of hydrogen sulfide, are 14.62 and 5.844 μA/ppm, respectively. The detection limit of the sensor is around 0.2 ppm of hydrogen sulfide at the forward bias at 200°C. The results show that the Pt/GaN Schottky diodes are promising for low cost and high sensitivity hydrogen sulfide detection.

Continued risk assessment by evaluating cardiac biomarkers in healthy and unhealthy individuals can lower the mortality rate of cardiovascular diseases (CVDs). In this research, we have developed a hand-held biosensor system to rapidly screen for brain natriuretic peptide (BNP) from a single drop of whole blood. The sensor methodology is based on extended gate design of electrical double layer (EDL) field effect transistor (FET), that can directly detect BNP in whole blood, without extensive sample pre-treatments, thereby eliminating the limitations of charge screening in high ionic strength solutions. A simple sensor array chip is fabricated to integrate with the MOSFET sensor system. Sensing characteristics are elucidated using purified BNP samples in 1 × PBS (with 4% BSA), spiked BNP samples in whole blood and clinical whole blood samples. The blood cells can be gravitationally separated without the use of any external actuation. The sensor exhibits very high sensitivity over wide dynamic range of detection. The sensing characteristics are not adversely affected by the presence of background proteins or blood cells, even without gravitational blood cell separation. Thus, the biosensor system can allow users to perform rapid whole blood diagnostics with minimal user protocols, in 5 min. The features of high sensitivity, cost-effectiveness and convenience of usage empower this technology to revolutionize the mobile diagnostics and healthcare industry.

FET devices are extensively used for sensors, including gas sensors and biosensors. In contrast to traditional resistive devices, FET has transconductance gain, which can significantly improve the S/N ratio. Recently, more applications in biosensors combine microfluidic channels and FET system. In FET-based biosensors, the wafer manufacturing process always requires a lot of cost, and it is used for metal lines as interconnects. Miniaturized chip plays a key role in reducing the manufacturing cost. However, simultaneously integrating the sensor and microfluidic channels on one chip is challenging. In this study, a novel and robust packaging method has been developed, to effectively reduce the size of the sensor chip and thereby the cost. 1 mm × 1mm FET sensor chip has been fabricated and embedded in epoxy. Photolithography and metal deposition were done followed by lift-off process for metal interconnect. The FET-embedded chip was passivated and covered by the microfluidic channel made of PMMA.

DNA is usually composed of several nucleotide and form as a spring shape with good elasticity. It has been observed that DNA can be extended by external forces, such as magnetic or electric fields from literature. Through the changes of electric field, DNA can be deformed by electrical force. DNA can be compressed or stretched like a spring and store energy. When the applied forces disappear, the stored energy is released and DNA switch back to the original shape, leading to the capacitive current induced by the DNA motions. The capacitive current is recorded before the DNA fully relaxed. In this study, dsDNA was intercalated with different concentrations of Doxorubicin, causing different relation of DNA motion, and further leading to different capacitive current level. Doxorubicin is one of the commonly used drugs for cancer therapy, and it is only intercalate between G-C base pairs in dsDNA. In this study, it can be developed as a new type of biosensors and also facilitate the fundamental understanding of the dsDNA characteristics. Figure 1(a) shows the schematic of device. The devices grew 3000 Å-thick SiNx on silicon wafer for dielectric layer, and plated 1000 Å-thick Au for electrodes. The sequence of the single strand DNA (ssDNA) and the Cy3 dye- attached complimentary DNA (Cy3-cDNA) are shown as 5'- thiol-TTT GCT TTT TCG TCG TTT GCT TTT CGT TTT- thiol- 3' and 5'-(Cy3)-AAA ACG AAA AGC AAA CGA CGA AAA AGC AAA-3', respectively. The Cy3-dsDNA solution was prepared by mixing and preparing 5 μM ssDNA, 5 μM Cy3-cDNA and 5 mM TCEP together in a 30 mM phosphate buffer solution (pH=8), followed by being heated to 90 ºC lasting for 2 minutes. The heated DNA solution was then gradually cooled down to room temperature to allow the hybridization of dsDNA. The hybridized dsDNA solution was then dropped on the gold substrate and waited for 36 hours in 25 ºC. Figure 1(b) shows the schematic of different pulse width. The bias applied for measuring the capacitive current was 0.5 V. Figure 2 shows the capacitive current of dsDNA sample measured in different pulse widths. In short pulse (pulse width < 1 ms) width measurement, the capacitive current was recorded before the DNA fully relaxed. In long pulse width measurement (pulse width > 10 ms), the capacitive current was measured after dsDNA fully relaxed. Figure 3 shows the capacitive current measured when different concentration of Doxorubicin intercalating into dsDNA in 500 μs pulse width. As dsDNA molecule intercalated by higher concentration of Doxorubicin, the capacitive current was decreased with higher concentration of Doxorubicin. In summary, different pulse widths affect the types of energy stored in dsDNA. And the stored energy is further manifested in different capacitive current. The relation between the stored energy and the capacitive current can be further confirmed by comparing with the sorter pulse widths measurement in the future. This work was partially supported by National Science Council grant (101-2221-E-007-102-MY3) and by the research grant (101N7047E1) at National Tsing Hua University.

AlGaN/GaN high electron mobility transistors (HEMTs) were used to sense the binding between double stranded DNA (dsDNA) and the severe acute respiratory syndrome coronavirus (SARS-CoV) nucleocapsid protein (N protein). The sensing signals were the drain current change of the HEMTs induced by the protein–dsDNA binding. Binding-site models using surface coverage ratios were utilized to analyze the signals from the HEMT-based sensors to extract the dissociation constants and predict the number of binding sites. Two dissociation constants, K D 1 = 0.0955 nM, K D 2 = 51.23 nM, were obtained by fitting the experimental results into the two-binding-site model. The result shows that this technique is more competitive than isotope-labeling electrophoretic mobility shift assay (EMSA). We demonstrated that AlGaN/GaN HEMTs were highly potential in constructing a semiconductor-based-sensor binding assay to extract the dissociation constants of nucleotide–protein interaction.

As acquired immunodeficiency syndrome (AIDS) caused by HIV-1 (human immunodeficiency virus type 1) has been in the top 10 leading causes of death for recent years, there have been many promising treatment discovered. One of the treatments is by taking non-nucleoside reverse transcriptase inhibitors (NNRTI) to suppress the activity of the HIV-1. The binding affinity of NNRTI to the reverse transcriptase (RT) of HIV-1 is an important factor determining the efficiency of the drug performance. The HIV-1 RT immobilized AlGaN/GaN high electron mobility transistors (HEMTs) were used to find the dissociation constant of NNRTIs. Comparing to conventional drug analyzing, HEMTs assisting experiments are much faster in processing time and lower cost.

Antibody-immobilized AlGaN/GaN high electron mobility transistors (HEMTs) were used for detecting peptides and revealing the number of binding sites of the antibody and the dissociation constants. Two binding sites were found on this antibody for the peptide and the dissociation constants of the antibody-peptide complex were extracted from a two-binding-site model. The estimated dissociation constants are consistent with the detection limit of the sensor showing the important role of the dissociation constants in the performance of the sensors. The results demonstrate that the AlGaN/GaN HEMTs cannot only be used for biosensors, but also can be used for the biological affinity study.

Antibody-immobilized AlGaN/GaN high electron mobility transistors (HEMTs) were used to detect a short peptide consisting of 20 amino acids. One-binding-site model and two-binding-site model were used for the analysis of the electrical signals, revealing the number of binding sites on an antibody and the dissociation constants between the antibody and the short peptide. In the binding-site models, the surface coverage ratio of the short peptide on the sensor surface is relevant to the electrical signals resulted from the peptide–antibody binding on the HEMTs. Two binding sites on an antibody were observed and two dissociation constants, 4.404×10−11 M and 1.596×10−9 M, were extracted from the binding-site model through the analysis of the surface coverage ratio of the short peptide on the sensor surface. We have also shown that the conventional method to extract the dissociation constant from the linear regression of curve-fitting with Langmuir isotherm equation may lead to an incorrect information if the receptor has more than one binding site for the ligand. The limit of detection (LOD) of the sensor observed in the experimental result (∼10 pM of the short peptide) is very close to the LOD (around 2.7–3.4 pM) predicted from the value of the smallest dissociation constants. The sensitivity of the sensor is not only dependent on the transistors, but also highly relies on the affinity of the ligand-receptor pair. The results demonstrate that the AlGaN/GaN HEMTs cannot only be used for biosensors, but also for the biological affinity study., Highlights ► AlGaN/GaN high electron mobility transistors detected a short peptide. ► Antibody immobilized on transistors bind the peptide to form a complex. ► Binding affinity of the complex was studied using binding-site models. ► Dissociation constants and the number of binding sites were revealed.

Water droplets were either pushed or pulled with an ultra-violet (UV) light on vertically aligned ZnO nanorods. Steric acid-immobilized ZnO nanorods grown on quartz substrates exhibit a hydrophobic surface possessing high contact angles between water droplets and the substrates. Exposure of UV onto droplets on ZnO NRs led to reduction of contact angles and resulted the internal circulating flows inside the droplets. Droplets located at different sites under the spot of the UV light created different magnitudes of contact angle changes and the internal circulating flows which allowed us to push the droplets away or pull the droplets toward the centre of the UV spot.

This paper presents a comparative study of three multi-function three-phase inverters, which include three-phase three-wire full-bridge (FB) inverter, three-phase four-wire half-bridge (HB) inverter and neutral-point-clamped (NPC) inverter. Each inverter is controlled by the division-summation (D-Σ) digital control and the control law for each inverter is derived in short. The comparison among these inverters is based on the criteria of common-mode voltage (CMV) issue for a PV system, component stress/count, efficiency, application and control complexity. Moreover, operation in both grid-connection and rectification modes are considered in the comparison. Experimental results measured from the inverters are included for performance evaluation.

Fibrinogen found in blood plasma is an important protein biomarker for potentially fatal diseases such as cardiovascular diseases. This study focuses on the development of an assay to detect plasmatic fibrinogen using electrical double layer gated AlGaN/GaN high electron mobility transistor biosensors without complex sample pre-treatment methods used in the traditional assays. The test results in buffer solution and clinical plasma samples show high sensitivity, specificity, and dynamic range. The sensor exhibits an ultra-low detection limit of 0.5 g/l and a detection range of 0.5–4.5 g/l in 1× PBS with 1% BSA. The concentration dependent sensor signal in human serum samples demonstrates the specificity to fibrinogen in a highly dense matrix of background proteins. The sensor does not require complicated automation, and quantitative results are obtained in 5 min with

In this research, the electrical double layer HEMT device is used to serve as the DNA biosensor. In this experiment, we try to use the DNA sequence of miRNA-126, which serve as a novel biomarkers of cardiovascular disease (CVD), to test the ability of the novel DNA sensors. Debye length has been a haunted problem among all the field effect transistor (FET) biosensor for years. As the Debye length is extremely low in high ionic strength solutions, the traditional FET may not be direct detect the biomolecular. The novel HEMT sensors using AlGaN/GaN can performs high sensitivity and great specificity in DNA sequences testing. The sensitivity can be down to the 1fM and the specificity measurement can separate the signals between two DNA sequences with two mismatch differences. Furthermore, the mechanism of the sensor structure has also been studied. Since the structure of the device has the separation between source drain channel and gate electrode, the comparison with different electrode area and gap distance has been done as well. With repeating electrical measurement confirming, the reusability can also be seen after the 95℃ dehybridization process. With the Gibbs free energy of the specific sequences, we can also predict the equilibrium reaction constant and the binding ratio of probe DNA with the target DNA. The comparison between the thermal dynamics with the experiment consequence has been demonstrated too. Figure 1

The supplementary zones surround an ordinary Fresnel Zone Plate (FZP) are used to improve the optical resolution at focus. Based on the Fresnel-Kirchhoff diffraction formula, an optimization model is used to design the supplementary zones-included FZP (SZFZP). The model will be examined by comparing the simulations with the measurements in visible region. Then, this model is used to design the SZFZP for extreme ultraviolet (EUV) light. The ability to fabricate the FZP for applications in EUV light will be demonstrated. In addition, the simulated performance of the SZFZP in EUV region will be shown in this paper.

In this study, we fabricate an ultra-sensitive hydrogen peroxide sensor by using horseradish peroxidase (HRP)-immobilized conducting polymer, polyaniline (PANI). With the proposed detection mechanism, hydrogen peroxide first oxidizes HRP, which then oxidizes polyaniline, thus resulting in decreased conductivity of the polyaniline thin film. The reduced HRP can be further oxidized by hydrogen peroxide and the cycle of the oxidation/reduction would continue until all hydrogen peroxide are reacted, leading to the high sensitivity of the sensor due to the signal contributed from all hydrogen peroxide molecule. The detection limit of this sensor is only 0.7 nM. The detectable concentration of H2O2 is from 0.7 nM to 1 μM. Beyond 1 μM, the sensor gradually saturates and some H2O2 remains, indicating the inhibition of HRP activity at high concentration of H2O2. There is no response to hydrogen peroxide once the PANI is standalone without HRP immobilized, showing the enzymatic reaction is required in the process of hydrogen peroxide detection. The simple process for the sensor fabrication allows the sensor to be cost-effective and disposable. This electronic hydrogen peroxide sensor is promising in applications for low concentration hydrogen peroxide detections, such as the reactive oxygen species (ROS) in oxidative stress studies.

FET devices are extensively used for sensors, including gas sensors and biosensors. In contrast to traditional resistive devices, FET has transconductance gain, which can significantly improve the S/N ratio. Recently, more and more applications in biosensors combine microfluidic channels and the FET system. In FET-based biosensors, the wafer manufacturing process always requires a lot of cost, and most of the chip area is used for metal lines as interconnect. Miniaturized chip plays a key role in reducing the manufacturing cost. However, simultaneously integrating the sensor chip and microfluidic channels on one chip is challenging. In this study, a novel and robust packaging method has been developed, to effectively reduce the size of the sensor chip and thereby the cost. 1 mm x 1 mm FET sensor chip has been fabricated and embedded in epoxy. Photolithography and metal deposition were done followed by lift-off process for metal interconnect. The FET-embedded chip was passivated and covered by the microfluidic channel made of PDMS. Figure 1 shows the schematic of the system and the final package size is 1cm x 1cm. Electrical measurement is also proceeded with liquid sample to confirm the usability. Figure 1

Cardiovascular disease (CVD) is one of the major causes to claim millions of lives all across the globe every year. While the chances of CVD increase with age, it can also occur in any age group of people, both male and female. Despite all efforts and tremendous accomplishments in the precaution and treatment of CVD, its detection at an early stage is still a big challenge for scientists in this present modern world. Here, NT-pro BNP plays a crucial role in acute congestive heart failure since it is biologically inactive, binds better with its receptors and has a longer half-life than any other, making it an ideal biomarker. The detection method is based upon the ligand-receptor interaction, also called as immunoassay, which can be successfully detected with the use of High Electron Mobility Transistors (HEMTs). With its unique characteristic features like good electrical property, chemical stability, biocompatibility, thermal stability and low power consumption HEMT sensors also have been used in several other applications like ion-sensing, pH sensing, gas sensing, etc. Therefore, the detection method becomes simple, fast, convenient and cost effective. AlGaN/ GaN are the most promising candidates for HEMT sensor materials. A thin film of undoped Al0.25Ga0.75N layer (150 Å) is deposited onto the surface of 3 μm-thick undoped GaN buffer layer, which in turn is deposited on the top of Silicon substrate by metal-organic chemical vapor deposition (MOCVD) process. Using mesa ICP etching, active device area is formed. Then four different metals of various thicknesses, i.e. Ti, Al, Ni and Au, are deposited to make an ohmic contact and is annealed at an elevated temperature of 850ºC. Later, the third mask helps in making the final metal layer and the gate electrode used for immobilizing the receptor. Finally, the fourth mask lets us open some portion of the gate and the transistor region to allow liquid to cross through. The next step to sensor fabrication and device gate opening is making the surface ready for immobilization of receptor, or so called surface functionalization. The antibody disulfide bridges between the heavy chains are cleaved in the presence of mercaptoethylamine (MEA) and EDTA whereas the disulfide bridges between the heavy chain and the light chain remains unaffected. This leaves behind a number of disulfide bonds which can be bound onto gold surface easily because of the strong interactions between the native thiol group and the gold surface. Finally, the sensor measurement is performed with Agilent B1530 parameter analyzer. The figure 1 (c) represents the detection of NT- pro BNP at various concentrations. The graph shows the total charge accumulated against various concentrations of target proteins prepared in physiological environment (1X PBS). From the experiment performed, it can be observed that there is an increase in the change of charge with increase in the concentration of target proteins, which confirms the immobilization of antibody and ultimately the detection of target proteins. Moreover, the calibration curve for the sensor can be drawn by plotting change in the total charge against the concentrations with repeated testing of the device. Therefore, this method of detection is cheap, robust and time efficient making it also ideal for multi-sensor array and point-of-care diagnostics. Figure 1

Electric double layer was proved to modulate the channel of field-effect transistors, which is called electric-double-layer transistors (EDLTs) and have been reported previously. One of the unique property of the electric double layer is the much higher capacitance compared to that of silicon dioxide or other high dielectric constant materials. EDLTs are attractive not only because of its high capacitance, but also because of its other properties in solution, which is very different from conventional dielectric materials. In this study, we investigate the EDLTs using AlGaN/GaN HEMTs, with different designs of the devices and in solutions with different ionic strength. We find out that the channel conductivity is relevant to these parameters and the EDLT model becomes different from conventional FETs. By using the electric-double-layer AlGaN/GaN high electron mobility transistors, we successfully detect several proteins in physiological environment (1xPBS) with high ionic strength and in serum as well. Our devices and methods do not suffer from the charge screening effect, which is usually a critical issue for conventional FET-based biosensors. Direct detection of proteins in serum without any dilution or washing process can largely simplify the use of the FET-based biosensors for point-of-care or homecare. The results reveal future possible applications of the EDLTs.

Water droplets were either pushed or pulled with an UV light on the surface of vertically aligned and superhydrophobic ZnO nanorods (NRs). The contact angle of the droplets reduce to a lower value due to the absorption of UV by ZnO NRs and a circulating current was observed inside the droplet. The droplets were either pushed away from or pulled toward to the center of the UV light depending on the locations of the droplets to the UV light. It is obvious that in the pushing mode, the circulating current dominate the direction of the movement of the droplets, while in the pulling mode, the contact angle change dominate the direction of the droplet movement

In this study, we used antibody-immobilized AlGaN/GaN high electron mobility transistors (HEMTs) for detecting a short peptide, and revealing the number of binding sites of the antibody for the peptide and the dissociation constants of the antibody-peptide complex. In our case, two binding sites were found on the ferritin heavy chain (FHC) antibody and the dissociation constants of the antibody-peptide complex were 2.723×10−11M and 6.994×10−9M for the two binding sites, respectively. The estimated dissociation constants are consistent within the reasonable range of the IGg antibody-antigen complexes binding constants. It also reveals the limit of detection is not only decided by the performance of the transistors but also the dissociation constant of the detected molecules. To our knowledge, it is the first time that AlGaN/GaN HEMTs using on the study of protein-peptide binding affinity. The results show that AlGaN/GaN HEMTs can not only be used as biosensors, but also a good tool and platform for analytical chemistry with numerous advantages since they are label-free, low-cost, biocompatible, stable in high temperature, real-time detection. Compared with other methods and techniques investigating the binding and kinetics of biological molecules, we do demonstrate AlGaN/GaN HEMTs have great potential to compete with conventional or proposed methods.

In this article, we used AlGaN/GaN high electron mobility transistors (HEMTs) to construct the first label-free semiconductor-sensor-based binding assay to our knowledge. Our results suggested that the nucleotide-c terminal domain of SARS coronavirus (SARS-CoV) nucleocapsid protein interaction is a two-step binding event with two dissociation constants (Kd 1 = 0.052 nM, and Kd 2 = 51.24nM) extracted by using the modified two-binding-site Langmuir isotherm equation proposed here. We found that there were at least two protein binding sites on the specific 41-base SARS-CoV double-stranded DNA (dsDNA) genome (29,580–29621) conjugated with a 20-mer poly-dT tail. This result presented a high binding affinity is comparable with the antibody-antigen reaction, and suggested this designed dsDNA could be treated as an aptamer for SARS-CoV N protein capture.

The supplementary zones surrounding an ordinary Fresnel zone plate (FZP) are utilized to improve the optical resolution at focus. Based on the Fresnel–Kirchhoff diffraction formula, an optimization model is used to design the supplementary zones-surrounded FZP (SZFZP). We justified this optimization model by comparing the numerical simulations and experimental measurements in the visible light region. As expected, the comparison shows a good fit between the simulation and measurement. Mostly, both results showed that the optical resolution and the focal intensity in the visible light region are improved by applying the optimized SZFZP. Afterwards, this model is used to design the SZFZP for applications in extreme ultraviolet (EUV) light. At this point, we demonstrated the ability to fabricate the optimized SZFZP in the EUV region. In addition, we simulated the focusing properties for the designed SZFZP. Consequently, the numerical results for EUV light focused by the designed SZFZP exhibited better performances in optical resolution and intensity.

Biomolecules such as DNA immobilized on metal electrodes and non-Faradaic current was measured in buffered solution. The metal-biomolecules-liquid-metal structure can be regarded as a liquid type of capacitor. The measurement of the capacitive current, which is affected by the ions, biomolecules, and liquid in the solutions. It is interesting to investigate the charging and discharging process in time domain, which brings important information of the dynamic behavior of the whole system. In this study, double-stranded DNA (dsDNA) was immobilized on gold electrodes and the capacitive current was measured in buffer solution with a pulse stimulus. Different relation time constants were revealed for various surface modifications. The transient current of the sensor was measured in de-ionized water and in 30 mM TE buffer before dsDNA immobilized metal electrode, and in 30 mM TE buffer after dsDNA immobilized on the metal electrode, followed by different concentrations of HIV-1 RT protein, ranging from 1 aM to 100fM. This technique shows ultra-high sensitivity of the protein detection (1 aM), indicating that this technique is promising for biosensor applications. Figure 1 shows the schematic of device for capacitive current measurements.

Hydrogen sulfide is a colorless, flammable and highly toxic gas with the characteristic foul odor of rotten eggs, often results from the bacterial breakdown of organic matters. Because of its toxicity, many personal safety gas detectors are set to alarm at 10ppm[i]. A number of sensors based on Schottky diode have been investigated as gas sensors since 1980s. In 2011, Professor Liu studied a Pt/AlGaN/GaN Schottky diode, which can exhibit ammonia detection limit lower than 35ppm NH3/air[ii]. There are also many papers research in H2S sensing with Schottky diode or metal oxide, most of their detection limit is higher than 10 ppm, expect one sensor made by thin film of CuO-SnO2, which can reach to 0.02ppm[iii]. The sensor studied in this paper contains four layers, which is showed in Figure 1 in detail. The Ohmic contact was formed by lift-off of e-beam evaporated Ti(200 Å)/Al(800Å)/ Ni(400Å)/Au(1000Å) and annealed at 850°C for 42 s under a flowing N2 ambient in a Premtek / ARTs 150. 100Å of Pt was deposited by e-beam evaporation to form Schottky contact as well as used as catalytic metal. Figure 2 shows three sets of Pt/GaN Schottky diode in different size and the size for the whole device is about 2×2mm. As the result of experiment, all of these three diodes are sensitive to H2S. Figure 3 shows real-time detection of 0.7ppm H2S in air. Figure 4 shows the relation between current change and concentration of H2S from 0.1-1ppm. All of the devices are tested in 200℃ and applied with 0.5ms width 1.5V pulse every second. With this Pt/GaN Schottky diode we can detect H2S down to 0.05pp. [i] Agency for Toxic Substances and Disease Registry (July 2006)."Toxicological Profile For Hydrogen Sulfide". p. 154. Retrieved 2012-06-20. [ii] T. Y. Chen, H. I. Chen, Y. J. Liu, C. C. Huang, C. S. Hsu, C. F. Chang, and W. C. Liu, “Ammonia sensing properties of a Pt/AlGaN/GaN Schottky diode,” IEEE Trans. Electron Devices, vol. 58, no. 5, pp. 1541–1547, May 2011. [iii] Jun Tamaki , Kengo Shimanoe, Yoshihiro Yamada, Yoshifumi Yamamoto, Morio Miura, and Noboru Yamazoe,” Dilute Hydrogen Sulfide Sensing Properties of Copper Oxide-Tin Oxide Thin Film Prepared by Low-Pressure Evaporation” Solid State Sensors and Actuators, 1997 International Conference Figure 1

In this study, a cost-effective and highly sensitive cholesterol microsensor, which is consisted of cholesterol oxidase (ChOx), horseradish peroxidase (HRP), and polyaniline (PANI), was developed based on the enzyme-induced conductivity change of PANI with fast response. Hydrogen peroxide is produced via the reaction between cholesterol and ChOx, which was immobilized in a dialysis membrane. The produced hydrogen peroxide can oxidize HRP, which can be reduced by oxidizing PANI, thus resulting in decreased conductivity of the polyaniline thin film. The reduced HRP can be oxidized again by hydrogen peroxide and the cycle of the oxidation/reduction continues until all hydrogen peroxide are reacted, leading to the high sensitivity of the sensor due to the signal contributed from all hydrogen peroxide molecules. Cholesterol was detected near the physiological concentrations ranging from 100 mg/dl to 400 mg/dl with the cholesterol microsensors. The results show linear relation between cholesterol concentration and the conductivity change of the PANI. The microsensor showed no response to cholesterol when the PANI was standalone without cholesterol oxidase immobilized, indicating that the enzymatic reaction is required for cholesterol detection. The simple process of the sensor fabrication allows the sensor to be cost-effective and disposable usage. This electronic cholesterol microsensor is promising for point-of-caremore » health monitoring in cholesterol level with low cost and fast response.« less

Hydrogen peroxide is a metabolic by-product and a kind of stable reactive oxygen species (ROS). When the ROS levels increase, it may causes several harmful effects of ROS on the cell structure, such as damage of DNA and protein oxidation, and this is known as oxidative stress. The oxidative stress is also the important clinical indicators of cause of aging, Alzheimer disease, and kidney diseases. Now the common test method of oxidative stress is Enzyme-linked immunosorbent assay (ELISA). ELISA needs color giving dyes, complicated preparation of sample, and optical system, so it is very expensive and inconvenient. In our study, we present a high sensitivity hydrogen peroxide sensor with ultra-low detection limit. The sensor can directly test the sample and only need very small amount of sample. And because of the simple structural design and fabrication, the sensor can be used as a cheap, efficient, and portable sensor system. In the future, the novel hydrogen peroxide sensor has various applications in studying oxidative stress and detecting reactive oxygen species for cells. Furthermore, we can combine the PANI sensor with different enzymes to fabricate other highly sensitive sensors to detect diverse materials, such as glucose, lactic acid and cholesterin. In our study, the PANI layer and gold electrodes were deposited on silicon nitride substrate, and the PANI was applied to fabricate a thin film between two electrodes. Then the PANI layer was sultonated by propane sultone and modified with HRP. During the measurement, the sensor was operated at 100mV and different concentrations of hydrogen peroxide citrate buffer solutions (pH=5.4) were dropped on it. The current change was measured when the hydrogen peroxide reacted with the HRP Immobilized PANI thin film. We tested the hydrogen peroxide solution from 0.1 nm to 1mM. The HRP-modified resistive sensors based on n-alkylated polyaniline(PANI) detect hydrogen peroxide in solution with very high sensitivity, ultra-low limit, and short response time. The sensitivity is higher than that of other sensing methods, such as electrochemical sensors or transistor sensors. The detection limit of PANI sensor is 0.7 nM (Figure 1. a, b). It is three orders smaller than that of other common methods with detection limit around 1 μM. To the best of our knowledge, it is the lowest detection limit that has ever been reported. And We combine the hydrogen peroxide sensor with glucose oxidase to build up the glucose sensor. In summary, the hydrogen peroxide sensor can provide a more exact hydrogen peroxide concentration and quick detection. The simple process for the sensor fabrication also allows the sensor to be cheap, disposable and combinable with other sensors to build up sensing system. This work was partially supported by National Science Council grant (No.99B20495A & 101-2221-E-007-102-MY3) and by the research grant (100N2049E1) at National Tsing Hua University.

Paper is an important material in our daily lives. Paper is cheap, environmentally friendly, light, flexible and widespread all over the world. Paper-based sensors are attractive because they are cheap, portable, accessible everywhere, and easily destroyed after being used. Paper-based sensors have been widely used in food safety control, clinical test, and environmental detection. The fiber structure in paper, which can act like a tunnel for microfluidic liquid transport, plays an important role in paper-based sensors by providing a platform for chemical reaction of analytes. However, conventional paper-based biosensors, which usually involve colorimetry, has the limitation in sensitivity and detection limit. Besides, the quantitative analysis of optical signals usually requires expensive optical detection system. In sharp contrast, most electronic sensors can be fabricated in very low cost and display with a simple device. In our study, we present a novel idea, which turns regular paper into conductive by combining paper and conducting polymer together. By integrating this conducting paper with different sensor technologies, various sensors can be achieved with high sensitivity and accuracy, which can be attributed to the great biocompatibility of the conducting paper. Only small amount of sample is required for testing with these sensors. Because of the simple structural design and fabrication, the conducting paper can be fabricated as a cheap, efficient, and portable electronic biosensor. Previous research has shown the HRP-modified n-alkylated polyaniline (PANI) can detect hydrogen peroxide in buffer solution with a very high sensitivity, ultra-low detection limit, and very short response time. During fabrication, the PANI thin film may sometime suffer from cracks after baking the PANI layer on the silicon nitride substrate due to different thermal expansion coefficients between PANI and silicon nitride. By using a filter paper as the substitute for hard substrate, the mechanical stress of PANI after baking can be largely reduced. Figure 1 shows the schematic of the conducting paper. Propane sultone was doped in PANI. The PANI solution was then dropped on the filter paper and silver electrode is then coated on the back of the paper to contact with the PANI, extending to the front side, making it easy for probing. The current was measured from 0-1V. Figure 2 shows the current-voltage characteristics of the conducting paper. Figure 3(a) shows that the PANI layer is tightly merged with the filter paper Figure 3(b) shows the surface morphology of PANI on the paper. In summary, the conducting paper made of PANi can not only achieve electronic paper-based devices, but can also realized electronic paper-based biosensors which can provide better sensitivity and lower cost, compared to the conventional paper-based sensors. Combining it with different technologies and enzymes, it can be used to detect several kinds of analytes. The portability and flexibility of conducting paper also make it more convenient to use. Because the fabrication process is quite simple and cheap, it can be widely promoted commercially in the future. This work was partially supported by National Science Council grant (No.99B20495A & 101-2221-E-007-102-MY3) and by the research grant (100N2049E1) at National Tsing Hua University.

Hydrogen peroxide attracts a great interest due to its important role in food, pharmaceutical, and clinical applications. Hydrogen peroxide is also a by-product in many enzyme catalytic reactions, such as glucose oxidase, lactate oxidase, cholesterol oxidase, alcohol oxidase, urate oxidase, aldehyde oxidase, and oxalate oxidase, which are implemented to detect glucose, lactic acid, cholesterol, ethanol, urea, formaldehyde, and oxalate, respectively. These biomolecules are significant markers in many biologically metabolic reactions. In our study, we present a cholesterol sensor based on a high sensitivity hydrogen peroxide sensor with ultra-low detection limit. The sensor can directly test the sample and only need very small amount of sample. And because of the simple structural design and fabrication, the sensor can be used as a cheap, efficient, and portable sensor system. The HRP-modified resistive sensors based on n-alkylated polyaniline(PANI) detect hydrogen peroxide in solution with very high sensitivity, ultra-low limit, and short response time. The sensitivity is higher than that of other sensing methods, such as electrochemical sensors or transistor sensors. The detection limit of PANI sensor is 0.7 nM. It is three orders smaller than that of other common methods with detection limit around 1 μM. To the best of our knowledge, it is the lowest detection limit that has ever been reported. And we combine the hydrogen peroxide sensor with cholesterol oxidase to build up the cholesterol sensor. In our study, the PANI layer and gold electrodes were deposited on silicon nitride substrate, and the PANI was applied to fabricate a thin film between two electrodes. Then the PANI layer was sultonated by propane sultone and modified with HRP. After that, the device was combined with dialysis membrane which was modified with cholesterol oxidase. During the measurement, the sensor was operated at 100mV and different concentrations of cholesterol PBS solutions (pH=7.0) were dropped on it. The cholesterol reacted with the cholesterol oxidase and created hydrogen peroxide on the PANI thin film (Figure 1). The current change was measured when the hydrogen peroxide reacted with the HRP immobilized PANI thin film. According to regular cholesterol level in human blood, we tested the cholesterol solution from 100 mg/dl to 400 mg/dl ,and we get a very good linear result (Figure 2). In summary, the cholesterol sensor can provide a more exact cholesterol concentration detection. The simple process for the sensor fabrication also allows the sensor to be cheap, disposable and combinable with other sensors to build up sensing system. This work was partially supported by National Science Council grant (No.99B20495A & 101-2221-E-007-102-MY3) and by the research grant (100N2049E1) at National Tsing Hua University.

Recently, more and more studies indicate that free radical is the cause of various diseases such as aging, cancer, neurodegenerative diseases and cardiovascular diseases because of uncontrolled oxidation of lipids, protein and DNA in biological system. Hydroxyl radical (OH°) is the highest oxidized species in free radicals. So far, most techniques for hydroxyl radical detection are sophisticated and expensive. Therefore, a simple and cheap method for hydroxyl radical detection is very necessary. Polyaniline (PANI) has been used as the active layer for different type of sensors because of its good electronic conductivity. The conductive polyaniline can neutralize free radicals by donating electrons and thereby changing their oxidation state from emeraldine to pernigraniline. In here, we used a simple and cheap polyaniline microchip to detect hydroxyl radical generated from Fenton reaction. The result shows significant current (or conductance) change. Figure 1 (a) and (b) show the schematic of hydroxyl radical sensor and the top-view of the devices, respectively. The sensor consists of two metal electrodes made by 200 Å Ti and 1000 Å Au deposited with an e-beam evaporator on a Si3N4/Si substrate. The length and the width of the Au electrodes are 500 μm and 100 μm, respectively. The gap between the two metal electrodes is 10 μm. 0.3 g polyaniline emeraldine base powder was dissolved in 5 mL dimethyl sulfoxide (DMSO) with stirring for 6 h. The polyaniline solution was then mixed with the same volume of 0.01 M NaOH. Use centrifuge to separate two different phase in the solution and pipet out the upper layer of the solution. Propane sultone was added into the polyaniline solution with the ratio 3:7 and stood for 6~8 hr over 30 degree Celsius. Also use centrifuge to separate two different phase in the solution and pipet out the upper layer of the solution. 2 μL of the remaining solution was coated on a chip and baked for 2.5 hr. The hydroxyl radical was generated from Fenton reaction as shown below: Fe2+ + H2O2 → Fe3+ + OH°+ OH- Figure 2 (a) shows significant current (or conductance) decrease approximately 84 μA of hydroxyl radical sensor after dropping hydrogen peroxide. It indicates that hydroxyl radical reacted with polyaniline and stole electron from polyaniline inducing current decrease. The current of the sensor was measured at a constant bias of 0.1 V at room temperature by using Agilent B1500 parameter analyzer with the polyaniline layer exposed. The interval time between any two measurement points is 1 minute. The final concentration of ferrous ion and hydrogen peroxide are 25 mM and 100 mM, respectively. Both two solutions were prepared in citrate phosphate buffer solution. Figure 2 (b) shows the current of sensor after dropping the hydrogen peroxide without ferrous ion. The current doesn’t change significantly. It indicates that the sensor doesn’t react with the hydrogen peroxide. Therefore, we can verify that the signal in figure 2 (a) is from hydroxyl radical, not from hydrogen peroxide. In summary, we develop a simple and cheap sensor to detect hydroxyl radical. The sensor shows significant conductance change when reacting with hydroxyl radical. We will further test different concentration of hydroxyl radical and confirm the mechanism in the future. This work was partially supported by National Science Council grant (101-2221-E-007-102-MY3) and by the research grant (101N7047E1) at National Tsing Hua University.

Variation of temperature, pressure, and pH values has been demonstrated for affecting the stability of AlGaN/GaN HEMTs sensors. In addition to the factors above mentioned, we found out other factors which are related to the stability of AlGaN/GaN HEMTs sensors. In this study, we found out the current variation of AlGaN/GaN HEMTs without gate metal sensors is inversely proportional to the viscosity of liquids. We also found out that dipole moment of liquids is related to the current variation of AlGaN/GaN HEMTs without gate metal sensors.