Enzyme-modified field effect transistors based on surface-conductive single-crystalline diamond

Enzyme-modified field effect transistors (ENFETs) were realized using surface-conductive single-crystalline diamond films. The enzymes penicillinase and acetylcholinesterase were immobilized onto the active area of diamond-based electrolytic solution gated FETs, using different organic linker molecules and cross-linking chemistries. The active area of the devices was patterned to generate enzyme-modified regions next to surface-conductive regions. Penicillinase was chosen as a robust model system, but the main focus of the present paper is on acetylcholinesterase, an enzyme essential for many neuronal signal transduction processes. All the different ENFETs show a clear and specific response to the corresponding substrate, penicillin and acetylcholine. The device response is based on the pH sensitivity of the surface-conductive active area and is enabled by the local pH change induced during the enzymatic reaction. The devices demonstrate promising stability and characteristic variations of the enzymatic activity with measurement conditions. Furthermore, the results from the ENFET measurements were compared with the results of spectrophotometric experiments, carried out with enzymes immobilized on diamond substrates and also with free enzymes in solution. This allows an analysis of the enzyme kinetics, as well as qualitative comparison of the different functionalization methods employed in this study.     

Neutral lipid enzyme electrode based on ion-sensitive field effect transistors

An enzyme electrode for neutral lipid determination based on hydrogen ion-sensitive field effect transistors (pH-FET's) is described. The electrode is composed of two pH-FET's with an immobilized lipase membrane on one pH-FET, and a platinum wire. Triglycerides are solubilized with 10% (v/v) Triton X-100. The electrode is used to determine triglycerides over wide concentration ranges with response times of ca. 2 min. Relations between signal and the logarithm of the concentration are linear over the ranges 100–400 mM triacetin, 3–50 mM tributylin and 0.6–3 mM triolein. In the case of triolein, the detection limit is 9 μg ml^?1 (signal/noise = 3:1). The effect of Triton X-100 on the electrode response is discussed.     

High-performance low-cost organic field-effect transistors with chemically modified bottom electrodes

The characteristics of organic field-effect transistors (OFETs) were dramatically improved by chemically modifying the surface of the bottom-contact Ag or Cu source-drain (D-S) electrodes with a simple solution method. The contact resistance and energetic mismatch typically observed with Ag D-S electrodes in pentacene bottom-contact OFETs can be properly eliminated when modified by the Ag-TCNQ (TCNQ = 7,7,8,8-tetracyanoquinodimethane). The pentacene transistors with low-cost Ag-TCNQ-modified Ag bottom-contact electrodes exhibit outstanding electrical properties, which are comparable with that of the Au top-contact devices. It thus provides a novel way toward high-performance low-cost bottom-contact OFETs.     

Two-dimensional nanocomposites based on chemically modified graphene

The multiple functional groups and unique two-dimensional (2D) morphology make chemically modified graphene (CMG) an ideal template for the construction of 2D nanocomposites with various organic/inorganic components. Additionally, the recovered electrical conductivity of CMG may provide a fast-electron-transport channel and can thus promote the application of the resultant nanocomposites in optoelectronic and electrochemical devices. This Concept article summarizes the different strategies for the bottom-up fabrication of CMG-based 2D nanocomposites with small organic molecules, polymers, and inorganic nanoparticles, which represent the new directions in the development of graphene-based materials.     

Graphene-based field effect transistors as biosensors

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Optically controlled field effect transistors based on photochromic spiropyran and fullerene C60 films

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Ion-selective field effect transistors with heterogeneous membranes

Polyfluorinated polyphosphazene can be used as an elastomer for the preparation of heterogeneous membranes which can be applied to the ISFETs by solvent casting. The performance characteristics of such devices prepared with AgCl, AgCl-Ag₂S and AgI-Ag₂S membranes are very similar to those found for heterogeneous membranes based on silicone rubber, which have been used in the corresponding ion-selective electrodes. The sensor is suitable for direct determinations of chloride in sweat.     

Ion-selective field effect transistors with polymeric membranes

The construction and operation of ion-selective field effect transistors (ISFET) with polymeric membranes are described, and their electrical and chemical performance are discussed. The H⁺, K⁺, and Ca²⁺ ISFET's all show responses similar to those of the corresponding ion-selective electrodes, with t_95% response times of approximately 40 ms and accurate ion activity measurements for periods up to one month.     

Electrostatically protected ion sensitive field effect transistors

Two type of ISFETs with electrostatic protection have been designed and tested. They both utilize an electrically conductive layer incorporated into the gate of the ISFET. This layer is connected via an on-chip MOSFET switch to the outside circuitry. In the first type the conductor is capacitively coupled to the ion-selective membrane and to the solution. In this case the device output is proportional to the time differential of the concentration change. The applicability of this device to high-speed FIA titrations has been tested.In the second device the gate electrically contacts the membrane. In this case the output is identical to that of a conventional ISFET. The signal-to-noise ratio and the electrostatic protection of this ISFET are considerably improved.     

A novel enzyme biosensor for steroidal glycoalkaloids detection based on pH-sensitive field effect transistors.

For the design of a biosensor sensitive to steroidal glycoalkaloids, pH-Sensitive Field Effect Transistors as transducers and immobilised butyrylcholinesterase as a biorecognition element have been used. The total potato glycoalcaloids can be measured by this biosensor in the concentration range 0.5-100 microM with detection limits of 0.5 microM for alpha-chaconine and of 2.0 microM for alpha-solanine and solanidine, respectively. The responses of the developed biosensors were reproducible with a relative standard deviation of about 1.5% and 5% for intra- and inter-sensor responses (both cases, n=10, for an alkaloid concentration of 5 microM), respectively. Moreover, due to the reversibility of the enzyme inhibition, the same sensor chip with immobilised butyrylcholinesterase can be used several times (for at least 100 measurements) after a simple washing by a buffer solution and can be stored at 4 degrees C for at least 3 months without any significant loss of the enzymatic activity.     

Potentiometric pH sensors based on chemically modified electrodes with electropolymerized metal-tetraaminophthalocyanine

Potentiometric pH sensors based on polymer film were prepared by electropolymerization of the monomer nickel(II)-4,4',4',4'-tetraaminophthalocyanine (NiTAPc) or copper(II)-4,4',4',4'-tetraaminophthalocyanine (CuTAPc) on glassy carbon (GC) electrodes. The polymer of metal tetraaminophthalocyanine (p-MTAPc) film coated electrodes show a slope of 55 +/- 1 mV/pH (at 20 degrees C) and nearly Nernstain potentiometric response to pH over the range of pH 1-13. The electrodes possess good potential reproducibility and high selectivity, and are useful sensing devices in pH determination and end-point indication of acid-base potentiometric titration.     

Fluorometric sensors based on chemically modified enzymes Glucose determination in drinks

In this paper an enzymatic fluorometric sensor for glucose determination in drinks is presented. The sensor film was obtained by immobilisation of glucose oxidase chemically modified with a fluorescein derivative (GOx-FS) in a polyacrylamide polymer. During the enzymatic reaction the changes in the fluorescence intensity of the GOx-FS are related to the glucose concentration. Working in FIA mode, the optimum conditions found were: 0.7 ml min(-1) flow rate, 300 mul sample injection and pH 6.5. The sensor responds to glucose concentrations ranging from 400 to 2000 mg l(-1), the reproducibility is around 3% and the life-time is at least 3 months (more than 350 measurements). The sensor was applied to direct glucose determination in drinks with good accuracy; interference caused by the filter effect was avoided by the kinetics of the reaction.     

Engineering a cationic supramolecular charge switch for facile amino acids enantiodiscrimination based on extended-gate field effect transistors

Chiral recognition of essential amino acids (EAAs) is a huge challenge that keeps plaguing analytical scientists due to their cryptochirality and limited steric interaction sites. Inspired by the superior enantioselectivity of functional supramolecular cyclodextrins (CDs) and strong signal amplification ability of field effect transistors (FETs), this work firstly reports a cationic supramolecular charge switch for facile enantiodiscrimination of EAAs based on extended-gate organic FET (EG-OFET). The cationic phenylcarbamoylated-CD single isomer acts as a charge switch via interacting with different enantiomers and the weak stereo-differentiation intermolecular interaction signals between the cationic perphenylcarbamoylated CDs and EAAs on the EG can be strongly and rapidly amplified through an OFET. Efficient chiral differentiation of six EAAs, including phenylalanine, tryptophan, leucine, isoleucine, lysine and valine, are successfully achieved without any derivation process and the detection limit for d-phenylalanine is down to 10^?13 mol/L. We believe that this study provides a new and facile sensing perspective for natural amino acids and may afford deeper understanding of molecular chirality.     

High yield fabrication of semiconducting thin-film field-effect transistors based on chemically functionalized single-walled carbon nanotubes

Here we report a simple and scalable method to fabricate high performance thin-film field-effect transistors(FETs) with high yield based on chemically functionalized single-walled carbon nanotubes(SWNTs) by organic radical initiators.The UV-Vis-NIR spectra,Raman spectra and electrical characterization demonstrated that metallic species in CoMoCat 65 and HiPco SWNTs could be effectively eliminated after reaction with some organic radical initiators.The effects of the substrate properties on the electrical pr...     

Novel butterfly pyrene-based organic semiconductors for field effect transistors

Novel butterfly pyrene derivatives functionalized with trifluoromethylphenyl and thienyl aromatic groups in the 1-, 3-, 6- and 8-positions of pyrene cores and have been synthesized by Suzuki coupling reactions, and their crystal structures, optical and electrochemical properties investigated; additionally, the field effect transistor using as the active material exhibited a p-type performance.     

High mobility of dithiophene-tetrathiafulvalene single-crystal organic field effect transistors

Single-crystal field effect transistors of the organic semiconductor dithiophene-tetrathiafulvalene (DT-TTF) were prepared by drop casting. Long, thin crystals connected two microfabricated gold electrodes, and a silicon substrate was used as a back gate. The highest hole mobility observed was 1.4 cm2/Vs, which is the highest reported for an organic semiconductor not based on pentacene. A high ON/OFF ratio of at least 7 x 105 was obtained for this device.     

Voltammetric determination of copper at chemically modified electrodes based on crown ethers

The feasibility of fabricating copper-sensitive chemically modified electrodes (CMEs) for trace analysis in aqueous and in 40% (v/v) ethanol-water media was investigated. Carbon paste electrodes modified with crown ethers were constructed by mixing the crown ethers into a graphite powder-paraffin oil matrix. The electrodes so formed were able to bind Cu(II) ions chemically and gave better voltammetric responses than the unmodified ones. The crown ethers studied and compared were 15-crown-5, benzo-15-crown-5 and dibenzo-18-crown-6. With a 3% benzo-15-crown-5 CME, Cu(II) could be quantified at sub-ppm levels by differential pulse voltammetry with a detection limit of 0.05 ppm. By differential pulse anodic stripping voltammetry Cu(II) could be quantified over the range I to 100 ppb. Interference from metal ions like Ni(II), Co(II), Mn(II), Fe(II), etc. have also been studied. The method was successfully applied to artificial as well as commercial samples of alcoholic beverages.     

A study about pH chemically modified electrodes based on amino-derivatives of naphthalene

On the basis of the study of synergistic sensitizing effect of mixed ionic and nonionic surfactants on a series of color reactions, the synergistic effect of mixed solubilizers (or dispersing agents) was investigated. The systems examined included the mixture of a surfactant (either ionic and nonionic) with soluble macromolecular compounds (e.g. PVA or arabic gum) or with -cyclodextrin. The mixed solubilizers often performed synergism of solubilization, sensitization and stabilization on the systems studied, and for certain cases the selectivity was also improved.     

Voltammetric determination of copper at chemically modified electrodes based on crown ethers

The feasibility of fabricating copper-sensitive chemically modified electrodes (CMEs) for trace analysis in aqueous and in 40% (v/v) ethanol-water media was investigated. Carbon paste electrodes modified with crown ethers were constructed by mixing the crown ethers into a graphite powder-paraffin oil matrix. The electrodes so formed were able to bind Cu(II) ions chemically and gave better voltammetric responses than the unmodified ones. The crown ethers studied and compared were 15-crown-5, benzo-15-crown-5 and dibenzo-18-crown-6. With a 3% benzo-15-crown-5 CME, Cu(II) could be quantified at sub-ppm levels by differential pulse voltammetry with a detection limit of 0.05 ppm. By differential pulse anodic stripping voltammetry Cu(II) could be quantified over the range 1 to 100 ppb. Interference from metal ions like Ni(II), Co(II), Mn(II), Fe(II), etc. have also been studied. The method was successfully applied to artificial as well as commercial samples of alcoholic beverages. Received: 12 January 2000 / Revised: 14 March 2000 / Accepted: 16 March 2000