Extended-gate Field-effect Transistor Sensor Research Articles

Aptamer-Based Electric-Double -Layer (EDL) Extended-Gated FET Biosensor for Detection of Cadmium Ion

Cadmium ion (Cd2+) is a highly toxic heavy metal pollutant. It causes irreversible damage to human health even at low doses due to a long biological half-life and strong bioaccumulation. Common heavy metal detection includes Inductively Coupled Plasma with Atomic Emission, Spectroscopy (ICP-AES), Inductively coupled plasma mass spectrometry (ICP-MS), Flame Atomic Absorption Spectrophotometry (FAAS), and Graphite Furnace Atomic Absorption Spectrometry (GFAAS), and. However, these technologies are high-cost, time-consuming, complicated operations, and can't be detected immediately and accurately.In this study, we developed an electric double-layer (EDL) extended-gate field effect transistor sensor based on aptamers to detect cadmium ions (Cd2+). Use N-channel enhanced-mode MOSFETs to connect the extended-gate array chips with aptamer modified. The aptamers were self-assembled on the gold electrode surface through Au-S bonds. Since the aptamer has a specific binding ability to cadmium ions, it will bind to the aptamer to form a stem-loop structure. The gate voltage changes caused by the structure change and then amplify the electrical signal through the transconductance of the field effect transistor. The linear detection range of this sensor for cadmium ions is from 1nM to 10uM. The Cd2+ calibration curve is shown a high correlation coefficient (R2 = 0.99001) and an excellent detection limit as low as 99.5 nＭ. Importantly, it responds to Cd2+ within 10 seconds. The sensor exhibits high selectivity in the presence of other heavy metals such as arsenic, chromium, lead, and mercury for electrical signal measurements. It also can be reused without significant signal attenuation.The advantages of this method are convenient portability, short detection time, high sensitivity, and simple operation. It has a good prospect for detection in the daily life of cadmium environmental pollution. Figure 1

Rapid Fluorescence-Free Detection of DNA Loop-Mediated Isothermal Amplification on Bare ITO Surface Under EG-FET Scheme

An extended gate field effect transistor (EG-FET)-based chip with a precision temperature control system is developed for real-time and fluorescence-free loop-mediated isothermal amplification (LAMP) detection. A label-free, non-optical instant method was used to detect the hydrogen ions released during nucleic acid amplification, rather than indirect measurements. The system comprises an EG-FET sensor, a temperature sensor, a heating block, and a signal processing system. Industrial grade bare indium tin oxide (ITO) is firstly demonstrated as the sensing material for nucleic acid amplification detection, such that stable and high hydrogen ion detection performance of -80.1±0.03 mV/pH with R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of 0.998 is achieved with the developed sensor. Moreover, a printed circuit board (PCB) with high thermal conductivity was used as the sensor base to provide a uniform temperature distribution during the reaction. The results show that the system maintains a stable LAMP assay temperature of 63°C with a variation of just 0.25°C. Moreover, in a pH-sensitive LAMP assay, the developed sensor achieves a limit-of-detection down to 10 genomic copies per reaction of lambda phage DNA within 17 minutes. The novel and performance iso-thermal EG-FET system is capable of real-time detecting the LAMP DNA amplification, and thus has significant potential for future biomedical applications.

Aptamer-Based Electric-Double -Layer (EDL) Extended-Gated FET Biosensor for Detection of Cadmium Ion

In this study, we developed an electric double-layer (EDL) extended-gate field effect transistor sensor based on aptamers to detect cadmium ions (Cd2+). Since the aptamer has a specific binding ability to cadmium ions. The signal is amplified through the transconductance of the FET. The linear detection range of this sensor for cadmium ions is from 1 nM to 10 uM. The Cd2+ calibration curve is shown a high correlation coefficient (R2 = 0.981) and an excellent detection limit as low as 0.094 nM. Importantly, it responds to Cd2+ within 10 seconds. The sensor exhibits high selectivity in the presence of other heavy metals. It also can be reused without significant signal attenuation. The advantages of this method are convenient portability, short detection time, high sensitivity, and simple operation. It has a good prospect for detection in the daily life of cadmium environmental pollution.

Determination of tumor necrosis factor-α in serum using extended-gate field-effect transistor-based chemosensors with molecularly imprinted polymer-coated gold dendrites

Here, we developed extended-gate field-effect transistor (EG-FET)-based chemosensors with molecularly imprinted polymers (MIPs) on a gold-dendritic (AD) electrode to detect tumor necrosis factor-α (TNF-α) in serum. The poly(β-cyclodextrin) film was electrochemically prepared on the AD electrode using a potentiodynamic technique, followed by TNF-α immobilization by host-guest interaction. The MIP film was formed via electropolymerization of thiophene-3-amidoxime (T3A) monomer in PBS solution with one scan cycle at an applied voltage of 0–1.2 V. After electrochemical optimization, the sensing behavior (based on drain current, Ids) of the MIP films was investigated to explore the validity of the sensors, resulting in excellent reproducibility, reusability, and stability. Based on the ΔIds – CTNF-α regression curves obtained in serum containing various analyte concentrations, the imprinting factor (IF) of MIP-based EG-FET sensor was 5.55. The selectivity was evaluated by comparing sensing property using analogous cytokine proteins (interleukin 1β [IL-1β] and interleukin-6 [IL-6]). The MIP-based EG-FET sensors exhibited high sensitivity (LOD: 0.55 pg/mL, LOQ: 1.82 pg/mL) and excellent selectivity (coefficient (α)> 3). Based on the excellent sensing performances, including high sensitivity and selectivity, excellent reproducibility, robustness, reusability, and stability, our (EG-FET)-based chemosensor with TNF-α-recognizing MIP film can be used for the early diagnosis and point–of–care of immune-related diseases.

Label-free and portable field-effect sensor for monitoring RT-LAMP products to detect SARS-CoV-2 in wastewater

The COVID-19 pandemic caused by the coronavirus SARS-CoV-2 has proven the need for developing reliable and affordable technologies to detect pathogens. Particularly, the detecting the genome in wastewater could be an indicator of the transmission rate to alert on new outbreaks. However, wastewater-based epidemiology remains a technological challenge to develop affordable technologies for sensing pathogens. In this work, we introduce a label-free and portable field-effect transistor (FET)-based sensor to detect N and ORF1ab genes of the SARS-CoV-2 genome. Our sensor integrates the reverse transcription loop-mediated isothermal amplification (RT-LAMP) reaction as a cost-effective molecular detection exhibiting high specificity. The detection relies upon pH changes, due to the RT-LAMP reaction products, which are detected through a simple, but effective, extended-gate FET sensor (EGFET). We evaluate the proposed device by measuring real wastewater samples to detect the presence of SARS-CoV-2 genome, achieving a limit of detection of 0.31 × 10−3 ng/μL for end-point measurement. Moreover, we find the ability of the sensor to perform real-time-like analysis, showing that the RT-LAMP reaction provides a good response after 15 min for concentrations as low as 0.37 ng/μL. Hence, we show that our EGFET sensor offers a powerful tool to detect the presence of the SARS-CoV-2 genome with a naked-eye method, in a straightforward way than the conventional molecular methods for wastewater analysis.

Highly Sensitive and Selective Detection of Diabetic Nephropathy Markers by a Perovskite LaNiO3−x Based Potentiometric Sensor

This work describes the fabrication of efficient biosensors to detect diabetic nephropathy markers (pH, glucose, and creatinine) by constructing a layer-wise sol-gel deposited perovskite LaNiO3−x (LNO) thin-film combined with intermedial annealing (500°C to 700°C). The structural, morphological, and compositional properties of LNO were analyzed by X-ray diffraction, Raman spectroscopy, field emission scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. The bilayer-coated LNO thin film annealed at 600°C exhibited the highest pH sensitivity of 65.83 mV pH−1 with 99.36% linearity for pH 2 to pH 12, a minimum hysteresis of 0.6 mV, and an almost unvarying drift rate of 2.04 mV h−1 in an extended gate field effect transistor (EGFET). Furthermore, the optimized film was utilized to detect glucose and creatinine by immobilizing different enzymes on the LNO surface. The glucose sensor was able to detect glucose with a sensitivity of 20.5 mV mM−1, whereas the sensitivity of the creatinine sensor was 126.4 mVpCcreatinine −1 for an acceptable linear range, with high selectivity for their respective target molecules. Hence, an LNO-based EGFET sensor can be considered a decisive solicitant for diagnosing diabetic nephropathy.

Rapid and label-free detection of the troponin in human serum by a TiN-based extended-gate field-effect transistor biosensor

In this article, the TiN sensitive film as a sensing membrane was deposited onto n+-type Si substrate by a DC sputtering technique for extended-gate field-effect transistor (EGFET) pH sensors and detection of cardiac troponin-I (cTn-I) in the patient sera for the first time. The crystal structure, Raman spectrum, element profile, surface roughness, and surface morphology of the TiN sensitive film were characterized by X-ray diffraction, Raman spectroscopy, secondary ion mass spectroscopy, atomic force microscopy, and scanning electron microscopy, respectively. The sensing performance of the TiN sensitive film is correlated with its relative structural feature. A high sensitivity of 57.49 mV/pH, a small hysteresis voltage of ∼1 mV, and a low drift rate of 0.31 mV/h were obtained in the TiN sensitive film. In addition, the pH sensitivity of this TiN EGFET sensor was preserved approximately 57 mV/pH after operation time of 180 days. Subsequently, the cTn-I antibodies with carboxyl groups activated by 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) along with N-hydroxysuccinimide (NHS) were immobilized on the TiN sensitive film functionalizing with 3-aminopropyl triethoxysilane (APTES). After obtaining the successful immobilization of cTn-I antibodies on the TiN EGFET biosensor, the cTn-I antigen specifically binds with its relative antibody. The cTn-I EGFET biosensor showed a high sensitivity of 21.88 mV/pCcTn-I in a wide dynamic range of 0.01–100 ng/mL. Furthermore, the concentrations of cTn-I in patient sera measured by our TiN EGFET biosensors are comparable to those determined by commercial enzyme-linked immuno-sorbent assay kits.

High-Performance Extended-Gate Field-Effect Transistor for Kinase Sensing in Aβ Accumulation of Alzheimer’s Disease

An amyloid-beta peptide (Aβ) is generally believed to be a pathological marker of Alzheimer's disease (AD), but it is still of great significance to explore the upstream and downstream relationship of Aβ in AD. It is previously reported that c-Abl, a nonreceptor tyrosine kinase, can be activated by Aβ, but the interaction between Aβ and c-Abl is still unknown. Herein, an extended-gate field-effect transistor (EG-FET)-based sensor has been developed to monitor the level of c-Abl with high sensitivity and selectivity. Our peptide-functionalized EG-FET sensor as the signal transducer can follow c-Abl activity with electron transfer by its specific phosphorylation. The sensor presents a good linear correlation over c-Abl concentrations of 1 pg/mL to 3.05 μg/mL. The sensor was successfully applied to quantify c-Abl activity in the brain tissue of AD transgenic mice, and the interaction between c-Abl and Aβ in AD mice was explored by administering the c-Abl inhibitor (imatinib) and the agonist (DPH). Our work is expected to provide an important reference for early diagnosis and treatment of AD.

Structural properties and sensing performances of CoNxOy ceramic films for EGFET pH sensors

This paper describes the impact of both Ar/N2 flow rate and rapid thermal annealing (RTA) on the structural properties and sensing characteristics of CoNxOy ceramic films formed through reactive sputtering and then used in extended-gate field-effect transistor (EGFET) pH sensors. The CoNxOy ceramic films were prepared under three different Ar/N2 flow rates (20/5, 20/10, and 20/15) and then annealed at three different RTA temperatures (200, 300, and 400 °C). X-ray diffraction revealed that all of the CoNxOy ceramic films featured amorphous structures. X-ray photoelectron spectroscopy demonstrated that the Co3+ content of the CoNxOy film prepared at the 20/10 flow rate was higher than those of the films prepared at the other flow rates. Atomic force microscopy indicated that the surface roughnesses of the CoNxOy films obtained at flow rates of 20/10 and 20/15 were higher than that of the film prepared at 20/5. High pH-sensitivity (64.36 mV/pH), a small drift rate (0.27 mV/h), and a low hysteresis voltage (1.4 mV) were achieved for the CoNxOy EGFET sensor that had been fabricated at a flow rate of 20/10 with subsequent RTA at 300 °C. This high performance was due to its CoNxOy film having a rough surface, a high Co3+ ion content, and a low number of oxygen vacancies or defects.

Enhancing pH Sensors Performance of ZnO Nanorods With Au Nanoparticles Adsorption

In this work, the sensing membrane of extended-gate field-effect-transistor (EG-FET) sensor with zinc oxide (ZnO) nanorods (NRs) and Au adsorbed on ZnO NRs were fabricated by hydrothermal method and DC magnetron sputtering. The Pt sheet as a reference electrode, put in sensing membrane and reference electrode to defferent pH valuse buffer solution for linearity and sensitivity analysis. Results showed the both of the ZnO based EG-FET pH sensors exhibited high linearity and sensitivity, and Au-adsorbed exhibited significantly improved sensing performance, the average voltage sensitivity and average current sensitivity of the ZnO NRs based EG-FET sensor was 24.67 mV/pH and <inline-formula> <tex-math notation="LaTeX">$21.4~\mu \text{A}$ </tex-math></inline-formula>/pH, and linearity was 0.986 and 0.994, whereas that of the Au-adsorbed ZnO NRs based EG-FET pH sensor was 76.75 mV/pH and <inline-formula> <tex-math notation="LaTeX">$45.66~\mu \text{A}$ </tex-math></inline-formula>/pH with a linearity of 0.990 and 0.980.

Amorphous ZnSn x O y Fabricated at Room-Temperature for Flexible pH-EGFET Sensor

In this article, the zinc-tin oxide (ZnSn x O y ) based sensing membrane fabricated on a flexible polyethylene terephthalate substrate at room temperature as an extended-gate field-effect transistor (EGFET) is investigated for pH-sensing applications. The ZnSn x O y -based EGFET sensor showed a super-Nernstian pH response (70.79 mV/pH) with very good linearity (0.997), a low hysteresis voltage (6 mV), and a low drift rate (0.25 mV/h). The high pH sensing behavior is attributed to the redox reaction of amphoteric zinc oxide (ZnO) in different pH solutions. Furthermore, good flexibility and bendability were shown by the ZnSn x O y -based EGFET sensor after 400 bending cycles.

Ultrasensitive dopamine detection of indium-zinc oxide on PET flexible based extended-gate field-effect transistor

With the aim of a simple, label-free, and highly specific dopamine detection, we proposed an indium-zinc oxide (InZnxOy) sensing film on flexible PET using a simple sol-gel method for an extended gate field-effect transistor (EGFET) sensor. In this study, X-ray diffraction, atomic force spectroscopy, and X-ray photoelectron spectroscopy were used to characterize the structural, morphological, and chemical features, respectively. The InZnxOy based EGFET sensor showed a super Nernstian pH response of 61.53 mV/pH with an excellent linearity of 0.995 (in the range of pH 2–12), a low hysteresis voltage of ∼ 3 mV (in the pH loop of 7→4→7→10→7) and a small drift rate of 3.52 mV/h (in the pH 7). Correspondingly, to investigate the impact of mechanical bending on the pH performances of InZnxOy based flexible EGFET sensor, a couple of bending tests, which include different bending radius and bending cycles, were performed. The device showed better mechanical durability up to 1500 bending cycles for pH sensitivity. In order to achieve the label-free detection of dopamine, the InZnxOy on PET-based EGFET was functionalized using a synthetic receptor named 4-carboxylphenylboronic acid, for the covalent binding of dopamine on the sensing surface. The sensitivity of dopamine is 10.69 mV/log(dopamine) with linearity 0.998 within the dopamine concentration range of 1 fM–1 nM and the limit of detection value is 0.523 fM. In addition, this InZnxOy based EGFET biosensor showed excellent selectivity to dopamine over other interfering chemicals. Our proposed InZnxOy EGFET biosensor was successfully applied to detect dopamine level in the real samples like rat blood serum and rat brain.

Sensing Performance of Stable TiN Extended-Gate Field-Effect Transistor pH Sensors in a Wide Short Annealing Temperature Range

In this letter, the structural properties and sensing performances of TiN sensing films deposited on a n+-type Si through the reactive DC sputtering method with rapid thermal annealing at a wide temperature range of 200 °C to 800 °C were investigated for extended-gate field-effect transistor (EGFET) pH sensors. We used X-ray diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy to study the structural characteristics of these films. These TiN EGFET sensors exhibited almost the same sensing performances, such as pH sensitivity ~58 mV/pH), hysteresis voltage ~2 mV), and drift rate (~0.45 mV/h), indicating that they contained similar or identical in the film composition and surface roughness.

Study of acidosis, neutral and alkalosis media effects on the behaviour of activated carbon threads decorated by zinc oxide using extended gate FET for glucose sensor application

In recent times, semiconductor-carbon composite microstructure offers new prospects in bio-chemical sensor research. In this study, hexagonally structured zinc oxide micro rods (ZnOMRs) were synthesized on activated carbon threads (ACTs) using the chemical bath in the absence of a ZnO seed layer. The ZnOMRs/ACTs based extended gate field effect transistor (EGFET) was characterized as a bio-chemical sensor for pH and glucose in acidosis, neutral and alkalosis media. The ZnOMRs/ACTs based EGFET sensor exhibited glucose sensitivities in terms of reference voltage (VRef) of (20.71, 18.21, and 16.72) mV/mM and drain source current (IDS) of (29.00, 25.60, and 23.62) μA/mM for pH values of 7.2, 7.4, and 7.6, respectively, at room temperature. Thus, the glucose sensitivity of the ZnOMRs/ACTs based EGFET increased with decrease in pH, due to the increased participation of hydrogen ions in the electrochemical exchange reaction between the solution and ZnOMRs/ACTs electrode. Based on the high sensitivity, ZnOMRs/ACTs composite could be a favourable micromaterial for bio-chemical sensor applications.

Solution processed ZnInxOy sensing membranes on flexible PEN for extended-gate field-effect transistor pH sensors

This work describes the impact of indium content of the structural properties and sensing characteristics of ZnInxOy sensing films for extended-gate field-effect transistor (EGFET) sensors. The synthesis of the ZnInxOy sensing films was made by a solution processing technique directly deposited on flexible polyethylene naphthalate (PEN) through a simple spin-coating method. The synthesized ZnInxOy films at three different indium concentrations (10%, 20% and 30% moles) were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, and atomic force microscopy to examine their chemical features, film structures and surface morphologies, respectively. Experiments were performed to explore the pH sensitivity, drift rate, and hysteresis voltage in the ZnInxOy EGFET sensors. Compare with these conditions, a higher pH sensitivity of 61.76 mV/pH, a lower drift rate of 1.08 mV/h, and a smaller hysteresis voltage of ∼1 mV were obtained in the ZnInxOy EGFET sensor fabricated at the 20% condition. Moreover, after 500 bending cycles, the ZnInxOy EGFET sensor fabricated at the 20% condition showed good mechanical flexibility. The ZnInxOy EGFET sensor also demonstrated a high selective response towards H+. This result indicates that the ZnInxOy sensing film with a rougher surface and a higher Zn–O–In content to generate lower crystal deformities, imperfections and oxygen vacancies.

Super Nernstian pH response and enzyme-free detection of glucose using sol-gel derived RuOx on PET flexible-based extended-gate field-effect transistor

In this paper, we fabricated a sol-gel derived RuOx, with low-temperature thermal oxidation, on polyethylene terephthalate (PET) flexible based extended-gate field-effect transistor (EGFET) as a pH sensor for the assessment of glucose for the first time. Structural identification, surface morphology, and film composition of the sensing membrane were investigated by X-ray diffraction, atomic force microscopy, and X-ray photoelectron microscopy, respectively. The RuOx on PET based EGFET sensor exhibited a pH sensitivity of 65.11 mV/pH in the wide range of pH 2–12 with an excellent linearity of 0.999. This sensor showed good reversibility in terms of a lower hysteresis voltage of ∼1 mV and a better stability for 12 h named as drift rate ∼2.08 mV/h. The RuOx-based EGFET sensor also demonstrated a high selective response towards H+. In addition, the pH performace of this RuOx EGFET flexible sensor kept unchanged after 500 repeated bending cycles. Subsequently, the RuOx on PET based EGFET was functionalized by 4-carboxyphenyl boronic acid (4-CPBA), which is a synthetic receptor for covalent attachment of glucose on the sensing surface. The sensitivity of glucose was 6.89 mV/mM with the linearity of 0.993 within the glucose concentration from 1 to 8 mM. The concentration of serum glucose measured by our 4-CPBA functionalized RuOx EGFET biosensor is comparable to that determined by commercial blood glucose monitoring system. In addition, this RuOx EGFET biosensor exhibited an elevated reference voltage shift response to glucose compared with other saccharides (e.g. fructose, sucrose and mannose).

An Extended-Gate FET-Based pH Sensor With an InZnxOyMembrane Fabricated on a Flexible Polyimide Substrate at Room Temperature

In this letter, a room-temperature synthesized amorphous indium-zinc oxide (InZn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> ) sensing membrane on flexible polyimide is employed as an extended-gate field-effect transistor (EGFET) pH sensor for the first time. The InZn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> -based EGFET sensor exhibited a high pH sensitivity of 56.29 mV/pH with an excellent linearity of 0.999. Furthermore, it also demonstrated good stability in terms of a low hysteresis voltage of 4.6 mV and a small drift rate of 2.08 mV/h, presumably suggesting the formation of uniform, dense, small grains, and stoichiometric InZn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> thin film, which facilitates high conductivity and provides a large number of surface binding sites. The InZn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> -based EGFET pH sensor showed an excellent mechanical bendability after more than 500 bending cycles.

Determination of Selectivity Coefficients of Sodium and Potassium Ion-Selective Electrode Using Porous Silicon N-Type (100) Based Extended Gate Field Effect Transistor

Ion-selective electrode (ISE) was able to accurately detect the ions, precisely for laboratory analysis purposes. The selection of the material varies to select a particular ion, according to the electrode response, and the decisive factor for the optimal selection of ISE for specific ion is the selectivity coefficient. This study used porous silicon (PSi) (100) as an ISE based on extended gate field effect transistor (EGFET) to characterize the selection's preference for sodium (Na+) as a target ion and potassium (K+) is an interference ion. The potential response in the linear region of the EGFET sensor between the detection electrode (PSi) and a reference electrode Ag/AgCl was measured in NaCl, KCl, and a mixed solution of the two salts along ions’ concentration (10-4-1 M) under drain-source voltage 0.3 V at temperature room. The potentiometric selectivity coefficient was calculated by two methods: (1) separate solution method (SSM) at the same activity (0.1 M) and (2) two solution method (TSM). The SSM method, KpotNa,K was 0.581, while the result of TSM method was 0.743. The results showed a slight superiority of Na+ selectivity and acceptable interference resistant for K+.

Direct correlation between potentiometric and impedance biosensing of antibody-antigen interactions using an integrated system

A fully integrated system that combines extended gate field-effect transistor (EGFET)-based potentiometric biosensors and electrochemical impedance spectroscopy (EIS)-based biosensors has been demonstrated. This integrated configuration enables the sequential measurement of the same immunological binding event on the same sensing surface and consequently sheds light on the fundamental origins of sensing signals produced by FET and EIS biosensors, as well as the correlation between the two. Detection of both the bovine serum albumin (BSA)/anti-BSA model system in buffer solution and bovine parainfluenza antibodies in complex blood plasma samples was demonstrated using the integrated biosensors. Comparison of the EGFET and EIS sensor responses reveals similar dynamic ranges, while equivalent circuit modeling of the EIS response shows that the commonly reported total impedance change (ΔZtotal) is dominated by the change in charge transfer resistance (Rct) rather than surface capacitance (Csurface). Using electrochemical kinetics and the Butler-Volmer equation, we unveil that the surface potential and charge transfer resistance, measured by potentiometric and impedance biosensors, respectively, are, in fact, intrinsically linked. This observation suggests that there is no significant gain in using the FET/EIS integrated system and leads to the demonstration that low-cost EGFET biosensors are sufficient as a detection tool to resolve the charge information of biomolecules for practical sensing applications.

Characteristics of Extended-Gate Field-Effect Transistor (EGFET) Based on Porous n-Type (111) Silicon for Use in pH Sensors

Following the advances in pH sensors based on porous silicon (p-Si) in the late 20th century, several studies have been carried out to take advantage of the intrinsic properties of p-Si for development of chemical sensors. This study investigates the characteristics and pH sensitivity of an extended-gate field-effect transistor (EGFET) based on n-type p-Si with (111) orientation. Porous silicon was applied directly without coating. The x-ray diffractogram revealed only n-type (111) crystal orientation. p-Si was comparatively analyzed against a silicon wafer (flat and porous surface) in the pH range from 2 to 12. Regarding EGFET operation, p-Si exhibited significantly enhanced pH sensitivity of 56.13 mV/pH and linearity of 0.9857 (at drain–source current I DS of 0.1 mA, temperature of 300 K, and immersion time of 300 s) because of its high surface area, whereas the silicon wafer (flat and porous surface) exhibited comparatively poor sensitivity of 25.41 mV/pH and linearity of 0.99 under similar conditions. In addition, we demonstrate use of current as a second parameter with high linearity for pH sensing. The low hysteresis depth (9 mV) of the EGFET sensor based on p-Si indicates good stability and reversibility.