Anions biosensors

Liu, H., Tian, Y., Xia, P., 2008. Pyramidal, rodhke, spherical gold nanostructures for direct electron transfer of copper, zinc-superoxide dismutase apphcation to superoxide anion biosensors. Langmuir 24, 6359-6366. 

In 1994, thiols were firstly used as stabilizers of gold nanoparticles [6a]. Thiols form monolayer on gold surface [18] and highly stable nanoparticles could be obtained. Purification of nanoparticles can be carried out, which makes chemical method of metal nanoparticles a real process for nanomaterial preparation. Various thiol derivatives have been used to functionalize metal nanoparticles [6b, 19]. Cationic and anionic thiol compounds were used to obtain hydrosols of metal nanoparticles. Quaternary ammonium-thiol compounds make the nanoparticle surface highly positively charged [20]. In such cases, cationic nanoparticles were densely adsorbed onto oppositely charged surfaces. DNA or other biomolecule-attached gold nanoparticles have been proposed for biosensors [21]. 

A flow injection optical fibre biosensor for choline was also developed55. Choline oxidase (ChOX) was immobilized by physical entrapment in a photo-cross-linkable poly(vinyl alcohol) polymer (PVA-SbQ) after adsorption on weak anion-exchanger beads (DEAE-Sepharose). In this way, the sensing layer was directly created at the surface of the working glassy carbon electrode. The optimization of the reaction conditions and of the physicochemical parameters influencing the FIA biosensor response allows the measurement of choline concentration with a detection limit of 10 pmol. The DEAE-based system also exhibited a good operational stability since 160 repeated measurements of 3 nmol of choline could be performed with a variation coefficient of 4.5%. 

Tsafack V.C., Marquette C.A., Pizzolato F., Blum L.J., Chemiluminescent choline biosensor using histidine-modified peroxidase immobilized on metal-chelate substituted beads and choline oxidase immobilized on anion-exchanger beads co-entrapped in a photocrosslinkable polymer, Biosens. Bioelectron, 2000 15 125-133. 

Y. Tian, L. Mao, T. Okajima, and T. Ohsaka, Superoxide dismutase-based third-generation biosensor for superoxide anion. Anal. Chem. 74, 2428-2434 (2002). 

Biosensors fabricated on the Nafion and polyion-modified palladium strips are reported by C.-J. Yuan [193], They found that Nafion membrane is capable of eliminating the electrochemical interferences of oxidative species (ascorbic acid and uric acid) on the enzyme electrode. Furthermore, it can restricting the oxidized anionic interferent to adhere on its surface, thereby the fouling of the electrode was avoided. Notably, the stability of the proposed PVA-SbQ/GOD planar electrode is superior to the most commercially available membrane-covered electrodes which have a use life of about ten days only. Compared to the conventional three-dimensional electrodes the proposed planar electrode exhibits a similar... 

Dwight SJ, Gaylord BS, Hong JW, Bazan GC (2004) Perturbation of fluorescence by nonspecific interactions between anionic poly(phenylenevinylene)s and proteins implications for biosensors. J Am Chem Soc 126 16850-16859... 

Application of Ferrocenyl-Containing Dendrimers in the Electrochemical Recognition of Anions and as Electron Transfer Mediators in Amperometric Biosensors... 

Domestic wastewater contains a large amount of detergents, especially anionic surfactants, such as linear alkylbenzene sulfonates (LAS). A sensitive biosensor containing Trichosporon cutaneum has been developed in Japan and used to monitor river water [128,129]. With this sensor a detection limit of 0.2 mg 1" LAS has been reached. 

Phosphate is another anion which is of biological significance as well as being biologically active. Numerous phosphate biosensors have been developed, with one based on a multi-enzyme system immobilised on a cellulose membrane on a Pt electrode being able to detect levels down to 10 8 M [104]. Simpler methods, however, use enzymes such as polyphenol oxidase combined with alkaline phosphatase bound within an electropolymerised layer based on a substituted pyrrole [ 105]. This was reported to give a sensor with a detection... 

There has been some development of optical biosensors. Nitrate reductase was immobilised within a sol-gel matrix, with binding of nitrate ion (down to a limit of 10"6 M) causing a characteristic change in the optical absorption [132]. It is notable that this sensor was reversible, allowed selective nitrate detection over other physiologically significant anions and did not lose activity even over six months. Phosphate-binding protein was immobilised on a fibre-optic detector and could be used to measure phosphate with a detection limit of about 10 6 M [133]. 

Biosensors Based on Entrapment of Enzymes in a Water-Dispersed Anionic Polymer... 

Previously, Nafion was used in electroanalysis as electrode covering membrane to immobilize cationic species (7,8) and as a barrier to anionic species (9,10). In biosensor field, the main limitation in the use of Nafion for enzyme entrapment is related to the solubility of the Nafion in lower aliphatic alcohols which are not compatible with the enzyme activity (11). Until now, only glucose oxidase was successfully immobilized in Nafion. 

More recently, a new series of water dispersed anionic polymers, the AQ 29D, 38D and 55D polymers were released by Eastman Kodak. Since that time, these polymers were used as electrode modifier (12, 13), as covering membrane (14) and as support for enzyme immobilization (15, 16). AQ polymers are high molecular weights (14,000 to 16,000 Da) sulfonated polyester type polymers (17, 18). Their possible structures have been recently presented (18). The AQ polymer serie shows many interesting characteristics useful for the fabrication of biosensors. They are water dispersed polymers and thus compatible with enzymatic activity. They have sulfonated pendant groups similar to Nafion and they can act as a membrane barrier for anionic interferring substances and they offer the possibility to immobilize redox mediators by ion exchange. 

Tetracyanoquinodimethane (TCNQ) and many of its derivatives are easily reduced to anions of the type TCNQ-, which form salts with various cations. With many cations, e.g., tetrathiafulvalene cations (TTF+), and N-methyl phenazinium cations (NMP+), the TCNQ- anions form electronically conducting salts (- molecular metals, -> charge-transfer complexes) that can be used as electrodes, especially because of their electrocatalytic properties (- biosensors, -> electrocatalysis, -> molecular metals) [i,ii]. TCNQ undergoes insertion electrochemical reactions (-> insertion electrochemistry) leading to TCNQ salts [iii, iv]. Polymers... 

Lee TH, Mozsolits H, Aguilar MI (2001) Measurement of the affinity of melittin for zwitterionic and anionic membranes using immobilized lipid biosensors. J Pept Res 58 464-476... 

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