Integration of Selective Area Anodized AgCl Thin Film with AlGaN/GaN HEMTs for Chloride Ion Detection

Abstract

We have demonstrated a selective area AgCl anodization process, which can be integrated with the fabrication of AlGaN/GaN high electron mobility transistors ͑HEMTs͒ for chloride ion detection. A limit of detection of chloride ion concentration achieved was 1 ϫ 10 −8 M using a 20 ϫ 50 m anodized Ag/AgCl layer on the HEMT gate sensing area. Unlike the conventional open-circuit potential measurement used for the electrochemical measurement, the drain current of the HEMT was monitored as the output signal in our sensor. The effects of anodization bias voltage and time on the AgCl film properties were investigated. A continuous anodized AgCl film was achieved with the bias voltage of 0.5 or 1 V. However, AgCl films anodized at higher biases ͑5 V͒ were not continuous and a larger grain size was obtained. Energy-dispersive X-ray analysis was used to analyze the composition of the anodized AgCl and showed that slightly chloride deficient films ͑around Ag:Cl = 57:43͒ were obtained.Chlorine is used to kill bacteria and other microbes in drinking water supplies and waste water treatment. Excess chlorine also reacts with organics and forms disinfection by-products such as carcinogenic chloroform, which is harmful to human health. Thus, to ensure the safety of public health, it is very important to accurately and effectively monitor chlorine residues, typically in the form of chloride ion concentration, during the treatment and transport of drinking water. 1,2 In addition, the chloride ion is an essential mineral for humans, and is maintained to a total body chloride balance in body fluids such as serum, blood, urine, exhaled breath condensate, etc., by the kidneys. Variations in the chloride ion concentration in serum may serve as an index of renal diseases, adrenalism, and pneumonia; thus, the measurement of this parameter is clinically important. 3 Several analytical methods like colorimetry, 4 ionselective electrode, 5 activation analysis, 6 X-ray fluorescence spectrometry, 7 and ion chromatography 8,9 have been used for the analysis of chlorine in various samples. However, these methods are not portable and require expensive instrumentation. An accurate and fast determination of the inorganic ion content of various aqueous samples at low detection limits has been of great interest for a long time.Electrochemical sensor methods offer an excellent sensitivity compared to that of fluorescence approaches and in addition offer tunable selectivity and compatibility with microfabrication techniques needed to produce completely integrated microanalytical systems. 10 The open-circuit potential ͑OCP͒ measurement was employed as an electric output signal for the electrochemical detection systems via simple electrodes; the OCP signal can be quantified and transmitted wirelessly. The overall system can be compact and used for remote sensing as well as monitoring. The development of miniaturized electrodes is essential for realizing compact electrochemical sensors. Among different reference electrodes, silver/silver chloride ͑Ag/AgCl͒...

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Aluminum Gallium Nitride (GaN)/GaN High Electron Mobility Transistor-Based Sensors for Glucose Detection in Exhaled Breath Condensate

“…The HEMT sensor immobilized with the AgCl thin film has also demonstrated an excellent response to chloride ion concentrations. 25,26 As illustrated in Figure 8, the sensor showed rapid responses with the chloride ion concentrations in the exposed solutions. This encouraging result shows the possibility of using chloride ion concentrations to calibrate the dilution factor during the measurement of biomarkers in EBC.…”

Long-term stability study of botulinum toxin detection with AlGaN/GaN high electron mobility transistor based sensors

“…GaN based materials are chemically stable, biocompatible, and stable in high temperature and reliable detections of biological agents in real time have been proved by using AlGaN/GaN HEMT based biosensors [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. These sensors also (F. Ren).…”

“…have small size and low cost, and only need small quantity of test samples, thanks to the matured semiconductor microfabrication technique [8][9][10][11][12][13][14][15][16][17][18][19][20][21]. The antibody-immobilized AlGaN/GaN HEMT-based biosensors have been used to detect Botulinum toxin type-A with a limit of detection (LOD) below 1 ng/ml with good reproducibility [8].…”

“…Recently, Chennamsetty et al used a full antibody atomistic molecular dynamics simulation to prove that aggregation leads to a decrease in antibody activity, and they identified the location and size of these aggregation prone regions [6]. However, to date, there are only few reports on the stability of antibody-based immunosensors [3][4][5]7].AlGaN/GaN high electron mobility transistors (HEMTs) based sensors have been demonstrated for gas, chemical, and bio-sensing applications [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. GaN based materials are chemically stable, biocompatible, and stable in high temperature and reliable detections of biological agents in real time have been proved by using AlGaN/GaN HEMT based biosensors [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23].…”