Biosensors, bacterial

Potcntiomctric Biosensors Potentiometric electrodes for the analysis of molecules of biochemical importance can be constructed in a fashion similar to that used for gas-sensing electrodes. The most common class of potentiometric biosensors are the so-called enzyme electrodes, in which an enzyme is trapped or immobilized at the surface of an ion-selective electrode. Reaction of the analyte with the enzyme produces a product whose concentration is monitored by the ion-selective electrode. Potentiometric biosensors have also been designed around other biologically active species, including antibodies, bacterial particles, tissue, and hormone receptors. 

It is well known that arsenic is one of the most dangerous elements in terms of its potential impacts to both to human and ecosystem health. Therefore the problem of As detection at ppb level remains very important from the point of environmental hazard investigation. The goal of the present work is the developing of very simple and inexpensive assay for arsenite and arsenate determination in environmental samples using whole-cell bacterial biosensors. 

Stewart G.S.A.B., Loessner M.J. Scherer S. (1996) The bacterial lux gene bioluminescent biosensor revisiXei. Am Soc Microbiol News, 62, 297-301. 

Biocatalytic membrane electrodes have an ISE or a gas sensing electrode in contact with a thin layer of biocatalytic material, which can be an immobilized enzyme, bacterial particles or a tissue slice, as shown in Fig. 3 The biocatalyst converts substrate (the analyte) into product, which is measured by the electrode. Electrodes of this type are often referred to as biosensors . 

Rouch, D.A., Parkhill, J., and Brown, N.L., Induction of bacterial mercury- and copper-responsive promoters Functional differences between inducible systems and implications for their use in gene-fusions for in vivo metal biosensors, J Ind Microbiol and Biotechnol, 14 (3), 349-353, 1995. 

Gautier S.M., Blum L.J., Coulet P.R., Fiber-optic sensor with Co-immobilized bacterial bioluminescence enzymes, Biosensors 1989 4 181. 

Since ideally, a biosensor should be reagentless, that is, should be able to specifically measure the concentration of an analyte without a supply of reactants, attempts to develop such bioluminescence-based optical fibre biosensors were made for the measurements of NADH28 30. For this purpose, the coreactants, FMN and decanal, were entrapped either separately or together in a polymeric matrix placed between the optical fibre surface and the bacterial oxidoreductase-luciferase membrane. In the best configuration, the period of autonomy was 1.5 h during which about twenty reliable assays could be performed. 

Large analytes targeted by affinity biosensor technology include bacterial pathogens such as Escherichia coli, Salmonella enteritidis, and Listeria monocytogenes. Salmonella enteritidis and Listeria monocytogenes were detected by an SPR sensor at concentrations down to 106 cfu/ml27. 

Willardson BM, Wilkins JF, Rand TA, Schupp JM, Hill KK, Keim P, Jackson PJ (1998) Development and testing of a bacterial biosensor for toluene-based environmental contaminants. Appl Environ Microbiol 64 1006-1012... 

Other applications dealt with the development of a luciferin ester substrate to measure the luciferase activity in living cells [141], the detection of toxic compounds such as sodium azide, fluoroacetic acid, and antibiotics [142], the development of a biosensor for the determination of bioavailable mercury [143], the use of eukaryotic luciferases as bacterial markers with different colors of luminescence [144], the determination of complement-mediated killing of bacteria [145], and the development of a bioassay for the determination of HIV type 1 virus and HIV-1 Tat protein activity, valuable also for analysis of HlV-inhibi-tory agents [146],... 

Zourob, M. Elwary, S. Turner A. A. F., Principles of Bacterial Detection Biosensors, Recognition Receptors and Microsystems Springer science + business media, ISBN 978 0 387 75112 2,2008... 

Molecular weight of the main bacterial toxins ranges from 28,000 to 150,000, which makes it possible for most sensitive SPR biosensors to measure their concentrations directly or using a sandwich assay. Examples of food safety-related toxins detected by SPR biosensors include Botulinum toxin (detection limit 2.5 pg/ml " ), . coli enterotoxin (detection limit 6 pg/ml " ) and Staphylococcal enterotoxin B (detection limit 5 ng/ml and 0.5 ng/ml for direct detection and sandwich assay, respectively" ). 

Bacterial pathogens are relatively large targets (> 1pm) and therefore, their presence can be detected directly with an optional amplification by secondary antibodies (sandwich assay). Examples of foodbome bacterial pathogens detected by SPR biosensors include Escherichia coli (detection limit 5x10 cfii/ml " " ), Listeria monocytogenes (detection limit 1 O cfii/ml " ) and Salmonella enteritidis (detection limit lO cfii/ml" ). 

Tissue electrodes [2, 3, 4, 5, 45,57], In these biosensors, a thin layer of tissue is attached to the internal sensor. The enzymic reactions taking place in the tissue liberate products sensed by the internal sensor. In the glutamine electrode [5, 45], a thick layer (about 0.05 mm) of porcine liver is used and in the adenosine-5 -monophosphate electrode [4], a layer of rabbit muscle tissue. In both cases, the ammonia gas probe is the indicator electrode. Various types of enzyme, bacterial and tissue electrodes were compared [2]. In an adenosine electrode a mixture of cells obtained from the outer (mucosal) side of a mouse small intestine was used [3j. The stability of all these electrodes increases in the presence of sodium azide in the solution that prevents bacterial decomposition of the tissue. In an electrode specific for the antidiuretic hormone [57], toad bladder is placed over the membrane of a sodium-sensitive glass electrode. In the presence of the antidiuretic hormone, sodium ions are transported through the bladder and the sodium electrode response depends on the hormone concentration. 

Biosensors based on microbial immobilization have also been used for food applications, e.g., the inexpensive and rapid high-throughput bacterial biosensor developed by Virolainen et al. for rapid detection of tetracyclines and their 4-epimer derivatives in poultry meat [188, 189]. 

Simple or automated offline or online biodegradability tests can be performed by measuring CO2 or CH4 gas production or O2 consumption [13]. Biosensors may utilize either whole bacterial cells or enzymes to detect specific molecules of hazardous substances. Toxicity can be monitored specifically by whole-cell sensors whose bioluminescence may be inhibited by the... 

Bioluminescent reactions have been thoroughly investigated with a view to designing integrated flow-through biosensors using firefly and bacterial... 

Use of optical fiber biosensors for real-time detection of biowarfare agents (BWA) especially those of bacterial cells, toxins, or spores in the air, soil, or environment has been investigated by the Naval Research Laboratory (Taitt et al, 2005). In addition, many laboratories are also employing fiber optic biosensors for detection of wide varieties of foodbome pathogens, which are discussed below. 

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