Nanofiber Channel Organic Electrochemical Transistors for Low-Power Neuromorphic Computing and Wide-Bandwidth Sensing Platforms.

Organic neuromorphic computing/sensing platforms are a promising concept for local monitoring and processing of biological signals in real time. Neuromorphic devices and sensors with low conductance for low power consumption and high conductance for low-impedance sensing are desired. However, it has been a struggle to find materials and fabrication methods that satisfy both of these properties simultaneously in a single substrate. Here, nanofiber channels with a self-formed ion-blocking layer are fabricated to create organic electrochemical transistors (OECTs) that can be tailored to achieve low-power neuromorphic computing and fast-response sensing by transferring different amounts of electrospun nanofibers to each device. With their nanofiber architecture, the OECTs exhibit a low switching energy of 113 fJ and operate within a wide bandwidth (cut-off frequency of 13.5 kHz), opening a new paradigm for energy-efficient neuromorphic computing/sensing platforms in a biological environment without the leakage of personal information.

Fully Integrated Indium Gallium Zinc Oxide NO2 Gas Detector.

We report an amorphous indium gallium zinc oxide (IGZO)-based toxic gas detection system. The microsystem contains an IGZO thin-film transistor (TFT) as a sensing element and exhibits remarkable selectivity and sensitivity to low concentrations of nitrogen dioxide (NO2). In contrast to existing metal oxide-based gas sensors, which are active either at high temperature or with light activation, the developed IGZO TFT sensor is operable at room temperature and requires only visible light activation to revive the sensor after exposure to NO2. Furthermore, we demonstrate air-stable sensors with an experimental limit of detection of 100 ppb. This is the first report on metal oxide TFT gas sensors without heating or continuous light activation. Unlike most existing gas sensing systems that take care of identifying the analytes alone, the developed IGZO microsystem not only quantifies NO2 gas concentration but also yields a 5-bit digital output. The compact microsystem, incorporating readout and analog-to-digital conversion modules developed using only two TFTs, paves the way for inexpensive toxic gas monitoring systems.

Graphene Field Effect Transistor-Based Immunosensor for Ultrasensitive Noncompetitive Detection of Small Antigens.

Due to its high carrier mobility, graphene is considered a suitable material for use in field-effect transistors. However, its application to immunosensing of small molecules is still elusive. To investigate the potential of graphene field effect transistors (G-FET) as a sensor for small molecules with small or no charge, we applied the open-sandwich immunoassay (OS-IA), which detects low-molecular-weight antigens noncompetitively, to G-FET. Using an antibody variable fragment VL immobilized on graphene and a hyperacidic region of amyloid precursor protein fused to the other variable fragment VH, we successfully detected a small antigen peptide consisting of 7 amino acids (BGP-C7), with a more than 100-fold increase in sensitivity compared with that measured by enzyme-linked OS-IA. Furthermore, we succeeded in detecting BGP-C7 in the presence of human serum with similar sensitivity, suggesting its potential application in clinical diagnostics.

Continuous Monitoring of pH and Blood Gases Using Ion-Sensitive and Gas-Sensitive Field Effect Transistors Operating in the Amperometric Mode in Presence of Drift.

Accurate and cost-effective integrated sensor systems for continuous monitoring of pH and blood gases continue to be in high demand. The capacity of ion-selective and Gas-sensitive field effect transistors (FETs) to serve as low-power sensors for accurate continuous monitoring of pH and blood gases is evaluated in the amperometric or current mode of operation. A stand-alone current-mode topology is employed in which a constant bias is applied to the gate with the drain current serving as the measuring signal. Compared with voltage-mode operation (e.g., in the feedback mode in ion-selective FETs), current-mode topologies offer the advantages of small size and low power consumption. However, the ion-selective FET (ISFET) and the Gas-sensitive FET (GasFET) exhibit a similar drift behavior, imposing a serious limitation on the accuracy of these sensors for continuous monitoring applications irrespective of the mode of operation. Given the slow temporal variation associated with the drift characteristics in both devices, a common post-processing technique that involves monitoring the variation of the drain current over short intervals of time can potentially allow extraction of the measuring signal in presence of drift in both sensor types. Furthermore, in the amperometric mode the static sensitivity of a FET-based sensor, given by the product of the FET transconductance and the sensitivity of the device threshold voltage to the measurand concentration, can be increased by adjusting the device design parameters. Increasing the sensitivity, while of interest in its own right, also enhances the accuracy of the proposed method. Rigorous analytical validation of the method is presented for GasFET operation in the amperometric mode. Moreover, the correction algorithm is verified experimentally using a Si3N4-gate ISFET operating in the amperometric mode to monitor pH variations ranging from 3.5 to 10.

Fully Packaged Portable Thin Film Biosensor for the Direct Detection of Highly Pathogenic Viruses from On-Site Samples.

The thin film transistor (TFT) is a promising biosensor system with great sensitivity, label-free detection, and a quick response time. However, even though the TFT sensor has such advantageous characteristics, the disadvantages hamper the TFT sensor's application in the clinical field. The TFT is susceptible to light, noise, vibration, and limited usage, and this significantly limits its on-site potential as a practical biosensor. Herein, we developed a fully packaged, portable TFT electrochemical biosensor into a chip form, providing both portability through minimizing the laboratory equipment size and multiple safe usages by protecting the semiconductor sensor. Additionally, a safe environment that serves as a miniature probe station minimizes the previously mentioned disadvantages, while providing the means to properly link the TFT biosensor with a portable analyzer. The biosensor was taken into a biosafety level 3 (BSL-3) laboratory setting to analyze highly pathogenic avian influenza virus (HPAIV) samples. This virus quickly accumulates within a host, and therefore, early stage detection is critical to deterring the further spread of the deadly disease to other areas. However, current on-site methods have poor limits of detection (105-106 EID50/mL), and because the virus has low concentration in its early stages, it cannot be detected easily. We have compared the sample measurements from our device with virus concentration data obtained from a RT-PCR (virus range: 100-104 EID50/mL) and have identified an increasing voltage signal which corresponds to increasing virus concentration.

Characterization of MOSFET Dosimeter Angular Response Using a Spherical Phantom for Fluoroscopic Dosimetry.

Metal-Oxide Semiconductor Field-Effect Transistor (MOSFET) dosimeters, placed in anthropomorphic phantoms, are a standard method for organ dosimetry in medical x-ray imaging applications. However, many x-ray applications, particularly fluoroscopy procedures, use variable projection angles. During dosimetry, the MOSFET detector active area may not always be perpendicular to the x-ray beam. The goal of this study was to characterize the dosimeter's angular response in the fluoroscopic irradiation involved in pediatric cardiac catheterization procedures, during which a considerable amount of fluoroscopic x-ray irradiation is often applied from various projection angles. A biological x-ray irradiator was used to simulate the beam quality of a biplane fluoroscopy imaging system. A custom-designed acrylic spherical scatter phantom was fabricated to measure dosimeter response (in mV) in two rotational axes, axial (ψ) and normal-to-axial (θ), in 30° increments, as well as four common oblique angles used in cardiac catheterization: a) 90° Left Anterior Oblique (LAO); b) 70° LAO/ 20° Cranial; c) 20° LAO/ 15° Cranial; and d) 30° Right Anterior Oblique (RAO). All results were normalized to the angle where the dosimeter epoxy is perpendicular to the beam or the Posterior-Anterior projection angle in the clinical setup. The relative response in the axial rotation was isotropic (within ± 10% deviation); that in the normal-to-axial rotation was isotropic in all angles except the ψ = 270° angle, where the relative response was 83 ± 9%. No significant deviation in detector response was observed in the four common oblique angles, with their relative responses being: a) 102 ± 3%; b) 90 ± 3%; c) 92 ± 3%; and d) 95 ± 3%, respectively. These angular correction factors will be used in future dosimetry studies for fluoroscopy. The spherical phantom may be useful for other applications, as it allows the measurement of dosimeter response in virtually all angles in the 3-dimensional spherical coordinates.

A NOVEL APPROACH FOR EFFECTIVE DOSE MEASUREMENTS IN DUAL-ENERGY CT.

A novel method was presented for the effective dose (ED) measurement with metal-oxide-semiconductor field-effect transistor (MOSFET) detectors in dual-energy (DE) dual-source (DS) computed tomography (CT) scanner. This study demonstrated that the mean energy of the combined spectrum in dual-source computed tomography can be used to measure the ED. For validation, the MOSFET dose at the centre cavity of a CT dose index (CTDI) body phantom was compared with the dose measured with an energy-independent ion chamber (IC). A clinical abdomen/pelvis scan was performed with an adult anthropomorphic phantom, and ED was compared between the MOSFET method and the dose length product (DLP) method. The tissue doses in the CTDI phantom were 2.08±(2.70 %) with IC and 2.20±(4.82 %) cGy with MOSFET; the per cent difference was 5.91 %, and the t-test showed that there was no statistically significant difference. EDs for the abdomen/pelvis scans were 5.01±(2.34 %) mSv with MOSFET and 5.56 mSv with the DLP method.

Development of an ion sensitive field effect transistor based urea biosensor with solid state reference systems.

Ion sensitive field-effect transistor (ISFET) based urease biosensors with solid state reference systems for single-ended and two-ended differential readout electronics were investigated. The sensing membranes of the biosensors were fabricated with urease immobilized in a conducting polymer-based matrix. The responses of 12.9∼198.1 mV for the urea concentrations of 8∼240 mg/dL reveal that the activity of the enzyme was not significantly decreased. Biosensors combined with solid state reference systems were fabricated, and the evaluation results demonstrated the feasibility of miniaturization. For the differential system, the optimal transconductance match for biosensor and reference field-effect transistors (REFET) pair was determined through the modification of the membranes of the REFETs and enzyme field-effect transistors (EnFETs). The results show that the transconductance curve of polymer based REFET can match with that of the EnFET by adjusting the photoresist/Nafion™ ratio. The match of the transconductance curves for the differential pairs provides a wide dynamic operating measurement range. Accordingly, the miniaturized quasi-reference electrode (QRE)/REFET/EnFET combination with differential arrangement achieved similar urea response curves as those measured by a conventional large sized discrete sensor.

Water-stable organic transistors and their application in chemical and biological sensors.

The development of low-cost, reliable sensors will rely on devices capable of converting an analyte binding event to an easily read electrical signal. Organic thin-film transistors (OTFTs) are ideal for inexpensive, single-use chemical or biological sensors because of their compatibility with flexible, large-area substrates, simple processing, and highly tunable active layer materials. We have fabricated low-operating voltage OTFTs with a cross-linked polymer gate dielectric, which display stable operation under aqueous conditions over >10(4) electrical cycles using the p-channel semiconductor 5,5'-bis-(7-dodecyl-9H-fluoren-2-yl)-2,2'-bithiophene (DDFTTF). OTFT sensors were demonstrated in aqueous solutions with concentrations as low as parts per billion for trinitrobenzene, methylphosphonic acid, cysteine, and glucose. This work demonstrates of reliable OTFT operation in aqueous media, hence opening new possibilities of chemical and biological sensing with OTFTs.

Calibrated LCD/TFT stimulus presentation for visual psychophysics in fMRI.

Standard projection techniques using liquid crystal (LCD) or thin-film transistor (TFT) technology show drastic distortions in luminance and contrast characteristics across the screen and across grey levels. Common luminance measurement and calibration techniques are not applicable in the vicinity of MRI scanners. With the aid of a fibre optic, we measured screen luminances for the full space of screen position and image grey values and on that basis developed a compensation technique that involves both luminance homogenisation and position-dependent gamma correction. By the technique described, images displayed to a subject in functional MRI can be specified with high precision by a matrix of desired luminance values rather than by local grey value.

Transistor array with an organotypic brain slice: field potential records and synaptic currents.

Linear transistor arrays on a silicon chip were used to map evoked extracellular field potentials in organotypic brain slices of rat hippocampus. The shape and amplitude of the transients were similar to those from records with micropipette electrodes. The spatial resolution was 21 and 4.6 microm. The sampled profile of the field potential showed a wide and shallow trough of transients in the stratum radiatum and a narrow but higher ridge in the stratum pyramidale. Due to the high resolution, the profile could be interpreted quantitatively in terms of synaptic currents. Transistor chips may become a novel tool for neurophysiological and pharmacological studies in brain slices.

Comparison of angular free-in-air and tissue-equivalent phantom response measurements in p-MOSFET dosimeters.

Metal Oxide Semiconductor Field Effect Transistor (MOSFET) radiation dosimeters have found recent application in providing real-time measurement in diagnostic radiology as well as in radiotherapy. Due to the design of the MOSFET dosimeter, the response is dependent on both energy and angulation with respect to the direction of primary radiation. The axial angular dependence has been characterized for both free-in-air and for tissue-equivalent phantoms. However, neither the angular dependence normal (90-degree) to the axial rotation, nor the effects of various tissue compositions on angular dependence, have been investigated for radiation energies in the diagnostic range. To characterize the angular dependence normal to the axial rotation, we exposed three "high sensitivity" MOSFET dosimeters simultaneously to x-rays from a medical diagnostic x-ray unit over a 360-degree rotation, at 22.5-degree increments, for both free-in-air and in lung, skeletal, and soft tissue-equivalent phantoms. The MOSFET dosimeters clearly showed an angular dependence in the orientation normal-to-axial as well as in the axial rotation, both for free-in-air and in tissue-equivalent phantoms. Significant variations in response occurred when the MOSFETs were exposed at incident angles between 90 degrees and 180 degrees normal-to-axial, as compared to the normal position (i.e., the zero-degree position with the bubble-side of the MOSFETs facing the radiation source). A maximum decrease in response to 32% of normal was observed when the distal ends (end opposite the wire lead) of the dosimeters were pointing directly away from the x-ray source (270-degree position). To avoid significant errors in MOSFET dosimeter readings, placement of the dosimeters should be consistent, and care should be taken to avoid orienting the dosimeter with its sensitive region (bubble side) facing away from the source of primary radiation at particular angles.

Annealing of the Co/Hf bilayer on single Si, polycrystalline Si and SiO(2).

Silicidation of the Co/refractory metal/Si system in which the refractory metal is used as an epitaxy promoter for CoSi(2) has recently received much attention. Hf is one of the candidates for the epitaxy promoter of cobalt silicide like Ti. In this paper, we investigated the layer structures of the Co/Hf bilayer on various substrates like single (100)Si, polycrystalline Si and SiO(2) after rapid thermal annealing. Epitaxy of CoSi(2) was obtained on (100)Si by annealing Co/Hf/(100)Si. Co-Hf compounds seem to play an important role of barriers against the reaction between Co and Si during silicidation of Co/Hf/(100)Si. The existence of Co-Hf compounds is helpful in the formation of epitaxial CoSi(2) since they retard the diffusion of cobalt and silicon atoms. The transition temperatures of cobalt silicides in the Co/Hf/poly-Si system were found to be lower than those in the Co/Hf/(100)Si system. The reaction between the metal and the spacer SiO(2) during silicidation is a matter of concern since any conducting residue of this reaction could degrade oxide integrity or produce bridging. In the Co/Hf/SiO(2) system Hf oxides formed as a result of the reaction between Hf and SiO(2) but a conducting material like HfSi(2) was not found to form after annealing. Considering the temperature at which epitaxial CoSi(2) forms along with the one from which the SiO(2) substrate starts collapsing we may conclude that the optimum silicidation annealing temperature for Co/Hf/Si is 600 degrees C.

[Analysis of the place of regulation of C-11 transmitters at the Tele-electronic Works "Telkom-Telfa" in Bydgoszcz from the point of view of visual hygiene]. / Analiza stanowisk regulacji przekaznika C-11 w Zakladach Teleelektronicznych "Telkom-Telfa" w Bydgoszczy pod katem higieny wzroku.

The authors performed a detailed analysis of 100 positions of regulation of the C-11 transmitters in the "Telcom-Telfa" ++Tele-electronic Works in Bydgoszcz. It was determined that the requirements for the condition of the eyes and the lighting at this workstand are considerable. Conclusions and recommendations tending to improvement of the working conditions are drawn up. Proposed is eventual rationale leading to the reduction of the eyestrain and facilitation of the work.

Comparison of potassium ISFETs with the Radiometer KNA1 and the Corning 902 ion selective electrode analysers for whole blood potassium ion estimation.

Evaluation of the performance of potassium ion sensitive field effect transistors (K+ ISFETs), developed by Thorn EMI in a form suitable for mass production and for incorporation in 'near the patient' analysers, showed only very small constant and proportional biases against the Radiometer KNA1 and the Corning 902 for whole blood potassium ion estimation. Between batch imprecision tests with whole blood showed the K+ ISFET was comparable in performance to the Corning 902 but inferior to the Radiometer KNA1. The evaluation demonstrated that ISFET manufacturing technology has now reached a stage of development at which ISFETs should be considered seriously for use in clinical chemical analysers.

Continuous monitoring of interstitial fluid potassium during hemorrhagic shock in dogs.

It appears that ISFET probes can reliably and continuously monitor IF K+ in vivo for intervals of at least several hours. The consistently observed increase in IF K+ in response to hemorrhage, a phenomenon invisible systemically, suggests that such probes may provide clinically valuable information regarding perfusion related events at the cellular level during onset of and resuscitation from hypoperfusion states. Precise correlation of ISFET signal to specific cellular dysfunction awaits investigation in which muscle cell membrane potential, muscle surface pH, and postexperiment cellular histology are studied concurrently.

Design and testing of a transistorized nerve stimulator.

Presently available equipment for nerve stimulation includes the relatively expensive multifunction pulse generators and the disposable dc stimulators. We have designed a semidisposable, two-transistor pulse generator that is portable, inexpensive, and capable of dynamic nerve stimulation.