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ABSTRACT: The development of biosensors using electrochemical methods is a promising application in the field of biotechnology. High sensitivity sensors for the bio-detection of proteins have been developed using several kinds of nanomaterials. The performance of the sensors depends on the type of nanostructures with which the biomaterials interact. One dimensional (1-D) structures such as nanowires, nanotubes and nanorods are proven to have high potential for bio-applications. In this paper we review these three different kinds of nanostructures that have attracted much attention at recent times with their great performance as biosensors. Materials such as polymers, carbon and zinc oxide have been widely used for the fabrication of nanostructures because of their enhanced performance in terms of sensitivity, biocompatibility, and ease of preparation. Thus we consider polymer nanowires, carbon nanotubes and zinc oxide nanorods for discussion in this paper. We consider three stages in the development of biosensors: (a) fabrication of biomaterials into nanostructures, (b) alignment of the nanostructures and (c) immobilization of proteins. Two different methods by which the biosensors can be developed at each stage for all the three nanostructures are examined. Finally, we conclude by mentioning some of the major challenges faced by many researchers who seek to fabricate biosensors for real time applications.
Sensors 01/2011; 11(5):5087-111. · 1.74 Impact Factor
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ABSTRACT: Field-controllable pentacene-semiconductor-based strain sensors were fabricated with hybrid gate dielectrics using polyvinyl phenol (PVP) and high- k inorganic tantalum pentoxide (Ta<sub>2</sub>O<sub>5</sub>) onto polyethylene naphthalate films. The Ta<sub>2</sub>O<sub>5</sub> gate-dielectric layer combined with a thin PVP layer to form very smooth and hydrophobic surfaces turns out to improve the molecular structures of pentacene films significantly. The PVP-Ta<sub>2</sub>O<sub>5</sub> hybrid-gate-dielectric films exhibit a high dielectric constant of 19.27 and a leakage-current density of as low as 100 nA/cm<sup>2</sup> . The sensors employing a thin-film-transistor-like Wheatstone bridge configuration able to operate at reduced voltage (~ 4 V) show good device characteristics with a field-effect mobility of 1.89 cm<sup>2</sup>/V · s and a threshold voltage of -0.5 V. The strain sensor characterized with bending at 45° with respect to the bridge bias direction with different bending radii of 50-, 40-, 30-, 20-, and 8-mm displays output signals improved in linearity in a low range of operating voltages.
IEEE Transactions on Electron Devices 03/2010; · 2.32 Impact Factor
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ABSTRACT: Variations in concentrations of ions in biological systems can be important events in the onset of a physiological disorder. In an episode of myocardial ischemia, acidosis and elevation of potassium ion concentration has been observed in the extra-cellular matrix of the myocardium. As a spectrum of markers, they can help detect onset of ischemia as well as infarctions. In this study, Flexible Organic Ion-Sensitive Field-Effect Transistors (ISFETs) have been characterized to detect Ischemia-like variations in pH and potassium ion concentration. Detection capabilities, of the sensors, have been shown as pure chemical concentration to current signal transduction of the ISFET. Independent of peripheral amplifier-converter circuits, they are standalone sensors. The sensors have been evaluated for their sensitivity and signal resolution. Calibration expression, following a thermo-electric model for device operation, represents an explicit relations between transistor drain current and ion concentrations. Signal conditioning, by normalization, has been attempted to make the calibration expression explicit in ion-concentration. Finally a reliable detection strategy, in differential mode, is proposed for a reference electrode free device.
IEEE Sensors Journal 01/2010; · 1.52 Impact Factor
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ABSTRACT: Acute myocardial ischemia is a state of trauma of the heart muscle caused by occlusion of oxygenated blood supply. It is accompanied by an increase in potassium and hydrogen ion concentrations in the heart muscles. A flexible substrate based ion-sensitive field effect transistor (ISFET) has been designed to measure the concentration of potassium and hydrogen ions with high specificity. Double exponential smoothing technique was used to calculate background noise and explain the dependence of drain current on reference voltage and ion concentration in saturation mode of the ISFET.
Applied Physics Letters 07/2008; · 3.84 Impact Factor
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ABSTRACT: In this letter, we present the first flexible strain sensor based on pentacene semiconductors, employing a transistor-like Wheatstone bridge configuration, where the ON/OFF state of the sensor is controlled by the bottom gate bias. The sensor was characterized with bending at 0deg, 45deg, and 90deg with respect to the bridge bias direction for different strains of 1deg/<sub>infin</sub>, 1.25deg/<sub>infin</sub>, 1.67deg/<sub>infin</sub>, and 2.5deg/<sub>infin</sub>. The sensitivity values at the ON state for the 0deg, 45deg, and 90deg bending exhibit 1.6, 7.2, and 4.1 nA/deg/<sub>infin</sub>, respectively, revealing the highest sensitivity for the diagonal (45deg) direction. It is expected that this field-controllable strain sensor leads to a reduced circuit complexity and a reduced cost when embedded into a large-area sensor array system by eliminating the need for additional switching devices.
IEEE Electron Device Letters 01/2008; · 2.85 Impact Factor
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ABSTRACT: In this study, we present the first flexible strain sensors based on pentacene-carbon nanotubes (CNTs) composite thin Alms employing a Wheatstone bridge configuration. The sensors were characterized with bending at 0, 45, and 90 degrees with respect to the bridge bias direction, applying strains of 1, 1.25, 1.67, and 2.5 <sup>0</sup>/<sub>00</sub>, respectively. It was noted that the output signal of the sensors is substantially enhanced with the addition of CNTs, resulting from the improvement in conductivity of the sensing active layer. This strain sensor using the CNTs-organic semiconductor matrix composite thin films as the active layer fabricated on flexible substrates is expected to possess better reliability as compared with conventional metallic foils and inorganic semiconductor strain sensors because of their low Young's modulus (~5 GPa).
Nanotechnology, 2007. IEEE-NANO 2007. 7th IEEE Conference on; 09/2007
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ABSTRACT: In this letter, a temperature sensor based on an organic thin film transistor is proposed and discussed in terms of its linearity and reliability of the variation in the subthreshold drain current with temperature. The saturation mobility exhibits thermally activated hopping and temperature-deactivated behavior in different temperature ranges, but the saturation current shows very little change compared to the subthreshold current that is linearly varied with temperature from 273 to 453 K. In addition, sensor reliability can be ensured by placing a time delay between consecutive measurements to release the charges trapped in the dielectric/semiconductor interface, the so-called bias-stress effect.
Applied Physics Letters 02/2007; 90(6):062105-062105-3. · 3.84 Impact Factor
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ABSTRACT: Advances in smart sensors, miniaturization, and related technologies leading to the emergence of smart fabrics are prerequisites to the construction of a point-of-care (POC) system for continuous health monitoring and illness prevention. Low manufacturing cost, light weight, portability and flexibility are among the requirements for smart sensors when embedded into smart fabrics. Organic semiconductor technology has recently been envisioned to meet these requirements, and to encourage the development of organic semiconductor based sensors because of its low process temperature and potential for very low cost manufacturing. In this paper, we present flexible sensors based on an organic semiconductor capable of measuring physiological parameters such as strain and temperature, adopting pentacene thin film transistors (TFTs) and Wheatstone bridge structures. It is expected that these sensors, integrated into textile structures, will enable real time POC monitoring of a patient's respiration rate, skin temperature, body heat flow and body temperature at an early stage.
Smart Materials and Structures 11/2006; 15(6):1872. · 2.09 Impact Factor
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ABSTRACT: We present two different kinds of semiconductor strain sensors: ungated n+ micro-crystalline silicon (n+ μC-Si), and gated hydrogenated amorphous silicon (a-Si:H). Both sensor types are fabricated on flexible polyimide substrates. The sensors were characterized with bending perpendicular, parallel, and at 45° with respect to the sensor bias direction, and for several bending diameters. Sensor size and power consumption are significantly reduced compared to metallic foil strain sensors. Small sensor size and ease of integration with a-Si:H thin-film transistors also allows arrays of strain sensors or combinations of strain sensors with varying geometric orientation to allow strain direction as well as magnitude to be unambiguously determined.
IEEE Transactions on Electron Devices 03/2006; · 2.32 Impact Factor
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ABSTRACT: In this paper, the authors report the first strain sensors using an organic semiconductor as the active element. The authors have used a doped organic semiconductor as the active element for low Young's modulus strain sensors. The sensor cross-section is shown. For these sensors 2 nm thick Ti and 20 nm thick Au were deposited on 50 micron thick polyimide substrates by thermal evaporation and patterned to form sensor electrodes and wiring. Next, a 50 nm thick pentacene layer was deposited, again by thermal evaporation. The pentacene layer was then doped p-type by exposure to a 1 % solution of ferric chloride in water. The doped pentacene film was then patterned using an aqueous polyvinyl alcohol photolithography step and oxygen reactive ion etching. The maximum process temperature used to fabricate the organic strain sensors is 110 degC
Device Research Conference Digest, 2005. DRC '05. 63rd; 02/2005
