Sensors molecule-sensitive electrodes

Haga et al. developed another type of immunosensor by combining an enzyme membrane immunoassay and an enzyme sensor using oxygen electrodes (HI). In this assay antigen molecules (theophylline) are attached on the surface of the liposomes and an enzyme (horseradish peroxidase) is encapsulated in the sensitized liposome. When antibody (antitheophylline antibody) and complement are added, the enzyme is released by the liposome lysis. The enzyme activity with the NADH-NAD reaction can be determined by the oxygen electrode. When antigen is added, it competitively binds to antibodies, then liposome lysis and enzyme activity are decreased. The sensitivity of this method for theophylline determination was reported as 0.7 ng/ml. 

So far, there are two types of label-free DNA molecule detection techniques widely studied in laboratories. In the past decades, optical-based label-free detection of DNA molecules gains great development. The sensitivity of the technique has reached the order of pico-mole level. In contrast, although electrochemical method has obtained more and more attentions in the area of detection of DNA molecules because of the effectiveness and costless of the method, the sensitivity of DNA sensors with sihcon electrodes is in the order of p to nano-mole [4], which is low for the propose of detection of ultra-low concentration of DNA molecules, although sensitivity of electrochemistiy based sensors has been greatly improved with the incorporation of microelectronic techniques. 

The use of conducting polymers in sensor technologies involves employing the conducting polymers as an electrode modification in order to improve sensitivity, to impart selectivity, to suppress interference, and to provide a support matrix for sensor molecules [7,9,16,18,22,25,26,113-216]. All electrochemical transducer principles can also be realized with conducting-polymer-modified electrodes. The role of the conducting polymer may be active (for instance, when used as a catalytic layer, as a redox mediator, as a switch, or as a chemically modulated resistor, a so-called chemiiesistor ) or passive (for instance, when used as a matrix) [7,9,16,22,23,26,122,123,167,168,176,177]. 

Modification of electrode with conducting polymers can improve sensitivity, impart selectivity, and provide a support matrix for sensor molecules. These approaches are intensively studied for gas sensors, electroanalysis, and biosensors. The composite film of conducting polymers and metal nanoparticles on electrode often catalyzes electrode reactions (electrocatalysis). 

These host mercuracarborand molecules were applied in Ion Selective Electrodes (ISE) and membrane formulations, as selective optical chloride sensors, as sensitive liquid/polymeric membrane electrodes for anions and as catalysts. ... 

Other sensor applications can be considered if some sensitive biological molecules (such as antibodies or receptors) are attached to the nanogranule. If, for example, an antibody molecule is attached to it, then the granule is placed between two electrodes, and single-electron current flows between them. The step value of the coulomb staircase depends on the capacity of the junctions. When the antibody molecule binds specific antigen, the capacity value will be changed, and, therefore, the step value of the VH characteristics will also change. 

The high specificity required for the analysis of physiological fluids often necessitates the incorporation of permselective membranes between the sample and the sensor. A typical configuration is presented in Fig. 7, where the membrane system comprises three distinct layers. The outer membrane. A, which encounters the sample solution is indicated by the dashed lines. It most commonly serves to eliminate high molecular weight interferences, such as other enzymes and proteins. The substrate, S, and other small molecules are allowed to enter the enzyme layer, B, which typically consist of a gelatinous material or a porous solid support. The immobilized enzyme catalyzes the conversion of substrate, S, to product, P. The substrate, product or a cofactor may be the species detected electrochemically. In many cases the electrochemical sensor may be prone to interferences and a permselective membrane, C, is required. The response time and sensitivity of the enzyme electrode will depend on the rate of permeation through layers A, B and C the kinetics of enzymatic conversion as well as the charac-... 

Due to their response mechanism the polyion-selective electrodes are not sensitive to the small fragments of polyionic macromolecules. Thus, if an enzyme cleaves the polyionic molecule these sensors can be used for detection of enzyme activity. Polycation protamine is rich in arginine residues that make it a suitable substrate for protease-sensitive electrochemical assays. Real-time detection of trypsine activity was demonstrated with the protamine-selective electrode as a detector [38],... 

The enhancement of electrochemical reactions usually occurs at modified electrode surfaces. The large NP surface area facilitates oxidation or reduction of small molecules at the electrode. For example, Niwa et al. modified a carbon film electrode with electrocatalytic platinum NPs to create a sensitive H2C>2 sensor.62 Co-sputtering of carbon and platinum produces platinum NPs of 2.5 nm diameter embedded in a carbon matrix. The platinum NPs catalyze the oxidation of H2O2 at the electrode... 

A CO Sensor Based Upon Self-assembled Ferrocenyl Ferraazetine. Having demonstrated the CO dependent solid-state electrochemistry of ferrocenyl ferraazetine, we synthesized a ferrocenyl ferraazetine molecule with disulfide functionality (Id). Scheme III. The specific aim was to design a CO sensitive molecule that could be confined to the working electrode of a two-terminal device via monolayer self-assembly techniques. Disulfides have been shown to irreversibly adsorb to Au and Pt surfaces (3-10). NMR and mass spectrometry are consistent with the proposed structure for compound Id. The FTIR spectrum of Id in THF exhibits metal carbonyl bands at 2067,2024,1989,1985 cm similar to the spectra for other ferraazetine derivatives la-c (2,5-6). Like derivatives la-c. Id reacts with CO (1 atm) at 298 K in CH2C12 to form a ferrapyrrolinone complex 2d, equation (3). 

Beyond the complete assembly of biomimetic membranes, interfacial supramolec-ular assemblies which incorporate biocomponents represent an important approach to replicating the biological functions outside of living systems. For example, the ability to link or wire otherwise electro-inactive enzymes to electrodes so that they can efficiently transport electrons allows sensitive and selective sensors to be developed for important bioactive molecules, e.g. glucose, lactate, urea, etc. 

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