Bacterial electrodes

Bacterial electrodes [11, 31, 33, 46, 48, 49, 60] In this type of electrode, a suspension of suitable bacteria is placed between the sensor proper and a dialysis membrane that prevents passage of high-molecular substances (see fig. 8.3). The sensor is usually a gas probe. In the simple types of bacterial electrode, the determinand is converted by a suitable strain of bacteria into a product sensed by the gas probe. Thus it is possible to determine arginine [46], glutamine [48],/.-aspartic acid [31],/.-histidine [60] and nitrate [33]. Hybrid bacterial - enzyme electrodes contain both a bacterial strain and a suitable enzyme. For example, an extract from ivingas Neurospora chossa can be used as a source of NAD nucleosidase and an Escherichia coli culture as a source of nicotinamide deaminase, so that the electrode responds to NAD [49] as a result of the series of reactions... 

A potentiometric determination of lysozyme is based on a system similar to a bacterial electrode [11]. The cells of the bacteria, Mcrococcus lysodeicticus, readily accept trimethylphenyl ammonium ions (TMPA ) from the solution. Lysozyme decomposes the cell membranes and TMPA is liberated. The rate... 

The determination of the lysozyme activity using the bacterial electrode (see p. 139) can also be used for immuno-analysis of biotine and avidine. The determination is based on the inhibition reaction of avidine with the biotine-lysozyme conjugate. After the reaction, the conjugate is no longer capable of dissolving the cell wall of the bacteria. The determination of biotine is similar [15]. 

Enzyme activity is often enhanced in bacterial cells and remains longer due to the optimal environment. Consequently, lifetimes of bacterial electrodes average around 20 days compared to 14 days for... 

While selectivity in certain instances has been excellent (i.e., the above glutamine sensor), most tissue and bacterial electrodes are plagued by simultaneous response to several biochemical species. This is because there are often several enzymes present in a given cell which liberate the electrode-detectable product. Consequently, in situ type measurements with such... 

Figure 10. (A) Schematic diagram of the bacterial electrode a, bacterial layer b, dialysis membrane c, gas-permeable membrane d, internal sensing element e, internal filling solution and f, plastic electrode body. (B) Detail of the membrane phases (35).

Bacterial electrodes using whole cell suspensions and an ammonia sensing electrode also have been reported by Rechnitz et al (7,8). 

Specific ion and specific gas electrodes, as well as other electrode types, can be employed. Examples of the types of bacterial electrodes include the use of Streptococcus foecium immobilized on an ammonia electrode to sense arginine,the use of Sarcina flava and an ammonium electrode to sense L-glutamine, and the use of Lactobacillus fermenti and a platinum, silver peroxide electrode to sense vitamin... 

Biocomponent or affinity ligand enzyme electrode, whole cell biosensor, tissue-based electrode, bacterial electrode, yeast probe, imunoelectrode, affinity electrode, receptrode, DNA-probe... 

Karube [389] has pioneered in the development of many bacterial electrodes based on this principle using various bacteria depending on the target analyte. Ion-selective electrodes for NH3, O2, CO2, H2S and have all been used in conjunction with immobilized whole cells. Riedel et al. [390] have recently demonstrated that preincubation of certain bacterial electrodes with the desired analyte (substrate) can enhance the sensitivity of a sensor toward that chemical by a factor of as much as 25. This induction approach may prove to be widely applicable. The shelf-life of a wholecell electrochemical sensor can extend up to several weeks with fully optimized storage conditions (low temperature, for example). Microbe thermistors (sensors that respond to the heat evolved during bacterial metabolism of a substrate) have also been developed, but these present problems once again with respect to analyte specificity,... 

Figure 3.12 Schematic diagram of an amperometric bacterial electrode.

Pseudomonas sp.. The characteristics of the two sensors are given in Tables 4.2 and S.l. The en me sensor has a better performance than the bacterial sensor, in terms of both re nse time and concentration range. The purification of the enzyme takes about a week, and the purified enzyme will keep for years without decomposing. This is not the case for the bacteria, which require periodic culture and harvesting. The bacterial sensor is, however, less sensitive to pH and temperature, but is the least selective since it is also sensitive to urea. Ammonia interferes with the response of both the enzyme and the bacterial electrodes, as they both use the same pNHa transducer. 

Cholesterol is de mined using an ampoometric microbial electrode [235]. In contrast, glucose is determined using a potentiometric bacterial electrode, employing the reduction of lipoic acid in the presence of Escherichia coli [236]. The latter is based on bacterial growth, and the response time is very long, between 1 and 2 hours. 

Walters R.R., Moriarty B.E. and Buck R.P. (1980) Pseudomonas bacterial electrode for determination of L-histidine. Anal. Chem., 52, 1680-1684. 

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. 

AN AMPEROMETRIC ENZYME IMMUNOSENSOR BASED ON SCREEN-PRINTED ELECTRODE FOR THE DETERMINATION OF KLEBSIELLA PNEUMONIAE BACTERIAL ANTIGEN... 

The aim of our investigation was the development of the amperometric enzyme immunosensor for the determination of Klebsiella pneumoniae bacterial antigen (Ag), causes the different inflammatory diseases. The biosensing pail of the sensors consisted of the enzyme (cholinesterase) and antibodies (Ab) immobilized on the working surface of the screen-printed electrode. Bovine seiaim albumin was used as a matrix component. 

Oxidation-reduction potential Because of the interest in bacterial corrosion under anaerobic conditions, the oxidation-reduction situation in the soil was suggested as an indication of expected corrosion rates. The work of Starkey and Wight , McVey , and others led to the development and testing of the so-called redox probe. The probe with platinum electrodes and copper sulphate reference cells has been described as difficult to clean. Hence, results are difficult to reproduce. At the present time this procedure does not seem adapted to use in field tests. Of more importance is the fact that the data obtained by the redox method simply indicate anaerobic situations in the soil. Such data would be effective in predicting anaerobic corrosion by sulphate-reducing bacteria, but would fail to give any information regarding other types of corrosion. 

Tissue and Bacteria Electrodes The limited stability of isolated enzymes, and the fact that some enzymes are expensive or even unavailable in the pure state, has prompted the use of cellular materials (plant tissues, bacterial cells, etc.) as a source for enzymatic activity (35). For example, banana tissue (which is rich with polyphenol oxidase) can be incorporated by mixing within the carbon paste... 

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 . 

The concept of a biocatalytic membrane electrode has been extended to the use of a tissue slice as the catalytic layer. An example of this approach is an electrode for AMP which consists of a slice of rabbit muscle adjacent to an ammonia gas electrode. NHj is produced by enzymatic action of rabbit muscle constituents on AMP The electrode exhibits a linear range of 1.4 x 10 to 1.0 x 10 M with a response time varying from 2.5 to 8.5 min, depending on the concentration. Electrode lifetime is about 28 days when stored between use in buffer with sodium azide to prevent bacterial growth. Excellent selectivity enables AMP to be determined in serum. 

Prior to the introduction of ion-selective electrode techniques, in situ monitoring of free copper (II) in seawater was not possible due to the practical limitations of existing techniques (e.g., ligand competition and bacterial reactions). Ex situ analysis of free copper (II) is prone to experimental error, as the removal of seawater from the ocean can lead to speciation of copper (II). Potentially, a copper (II) ion electrode is capable of rapid in situ monitoring of environmental free copper (II). Unfortunately, copper (II) has not been used widely for the analysis of seawater due to chloride interference that is alleged to render the copper nonfunctional in this matrix [288]. 

Zourob et al.22 constructed a flow-cell incorporating the MCLW and ITO electrode as shown in Fig. 15.25. Initial experiments were conducted after treating the surface with BSA overnight. BG bacterial spores were introduced to the sensor system at a constant flow rate of 200 pL min 1 in 50 mM histidine buffer, and the sensor system was operated in real-time scattering mode using a CCD camera. 

DC potential was applied so that BG bacterial spores were either collected onto or repelled from the MCLW sensor surface. Figure 15.26 shows the detected number of bacterial spores on the sensor surface vs. time. At time A, a negative potential was applied to the ITO electrodes and a positive potential to the metal layer of the MCLW sensor, resulting in an increase in the number of BG bacterial spores driven to the sensor surface. At time B, the potential is reversed and a decrease in the number of BG bacterial spores on the sensor surface is observed, hence the bacterial... 

A portable microbial sensing system [58] was developed for detecting the toxicity of pre-treated wastewater. The signal of the modified electrode containing a bacterial culture renewed every 9 h, within 8 min of contact with toxic solutions or samples, is roughly correlated with toxicity. 

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