Biosensors, development using

In the field of electrochemical biosensors, the utilization of biomolecules such as antibodies, DNA, enzymes or another kind of proteins adhered to Langmuir-Blodgett films confer specificity to the system [48-50]. Concerned the development of modified electrodes for enzymes immobilization, Langmuir-Blodgett films has been considered an important path for biosensors fabrication and many kinds of arquitectures has been reported in the last decades as very promissing approaches for biosensors development. Examples of biosensors development using LB method has been extensively reported on literature for application in several biosensing approaches [51, 52]. 

Examples of chemical sensors and biosensors developed using the ISFET, EGFET, SEGFET, EIS and LAPS structures as transducers are summarized in Table 4.1. 

Oxidation of P-nicotinamide adenine dinucleotide (NADH) to NAD+ has attracted much interest from the viewpoint of its role in biosensors reactions. It has been reported that several quinone derivatives and polymerized redox dyes, such as phenoxazine and phenothiazine derivatives, possess catalytic activities for the oxidation of NADH and have been used for dehydrogenase biosensors development [1, 2]. Flavins (contain in chemical structure isoalloxazine ring) are the prosthetic groups responsible for NAD+/NADH conversion in the active sites of some dehydrogenase enzymes. Upon the electropolymerization of flavin derivatives, the effective catalysts of NAD+/NADH regeneration, which mimic the NADH-dehydrogenase activity, would be synthesized [3]. 

New developments in immobilization surfaces have lead to the use of SPR biosensors to monitor protein interactions with lipid surfaces and membrane-associated proteins. Commercially available (BIACORE) hydrophobic and lipophilic sensor surfaces have been designed to create stable membrane surfaces. It has been shown that the hydrophobic sensor surface can be used to form a lipid monolayer (Evans and MacKenzie, 1999). This monolayer surface can be used to monitor protein-lipid interactions. For example, a biosensor was used to examine binding of Src homology 2 domain to phosphoinositides within phospholipid bilayers (Surdo et al., 1999). In addition, a lipophilic sensor surface can be used to capture liposomes and form a lipid bilayer resembling a biological membrane. 

In recent years, there are more applications based on the layer-by-layer fabrication techniques for CNT-modified electrodes. This technique clearly provides thinner and more isolated CNTs compared with other methods such as CNT-composite and CNT coated electrodes in which CNTs are in the form of big bundles. This method should help biomolecules such as enzymes and DNA to interact more effectively with CNTs than other methods, and sensors based on this technique are expected to be more sensitive. Important biosensors such as glucose sensors have been developed using this technique, and further development of other sensors based on the layer-by-layer technique is expected. 

Some new developments are also proposed such as a system based on the use of electrochemically active bacteria in combination with a microbial fuel cell [34], giving good responses over 60 days, or a biosensor developed for fast... 

Topics discussed above are some basic principles and techniques in voltammetry. Voltammetry in the frequency domain where i-E response is obtained at different frequencies from a single experiment known as AC voltammetry or impedance spectroscopy is well established. The use of ultramicroelectrodes in scanning electrochemical microscopy to scan surface redox sites is becoming useful in nanoresearch. There have been extensive efforts made to modify electrodes with enzymes for biosensor development. Wherever an analyte undergoes a redox reaction, voltammetry can be used as the primary sensing technique. Microsensor design and development has recently received... 

FRET-based protein biosensors have been developed using CPEs as the lightharvesting donors in conjugation of lock-key recognition. Streptavidin is a... 

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]. 

The selection of appropriate microorganisms is a possible way to improve the correlation between BOD and BODj [16,53]. The prerequisite for the use of microorganisms for BOD-sensors is a wide substrate spectrum. Therefore several samples of activated sludge from different wastewater plants were investigated [ 13,14]. One problem with an activated sludge based biosensor is the variability of sensor response with time. These BOD-sensors with an undefined variety of microbial species revealed no reproducible results. For that reason, BOD-sensors were developed using various types of defined cultures of microorganisms (Table 1). 

Many different types of techniques for protein immobilization have been developed using, in most cases, enzyme sensors. Early studies of enzyme biosensors often employed thick polymer membranes (thickness 0.01-1 mm) in which enzymes are physically entrapped or chemically anchored. The electrode surface was covered with the enzyme-immobilized polymer membranes to prepare electrochemical enzyme sensors. Although these biosensors functioned appropriately to... 

By controlling the structural and electronic properties of sNPS which are related to the nanocrystallite dimensions and porosity, their surface selectivity and sensitivity to different gases (nitrogen and carbon oxide, vapors of water and organic substances) can be adjusted. This approach for the effective detection of acetone, methanol and water vapor in air was described in [13-15].The minimal detectable acetone concentration was reported to be 12 pg/mL. Silicon sensors for detection of SO2 and some medicines such as penicillin were created [16-18]. sNPS were used for the development of a number of immune biosensors, particularly using the photoluminescence detection. Earlier we developed similar immune biosensors for the control of the myoglobin level in blood and for monitoring of bacterial proteins in air [19-23]. 

The experimental data presented show that sNPS can be used as transducers, which are stable for a long time after the construction of an immune biosensor. The specific immune complex formed on the sNPS surface may be registered by measuring its photoluminescence or photoconductivity. Such immune biosensors can be applied for control of T2 mycotoxin. The biosensors developed are sensitive and simple and allows for rapid analysis and analysis in field conditions. This approach may be applied for detection of any biochemical substances which can form an immune complex. Further investigations should be directed towards studying the mechanism of the biochemical signal detection by the sNPS and characterization of all the steps of analysis. 

Heat is the most common product of biological reaction. Heat measurement can avoid the color and turbidity interferences that are the concerns in photometry. Measurements by a calorimeter are cumbersome, but thermistors are simple to use. However, selectivity and drift need to be overcome in biosensor development. Changes in the density and surface properties of the molecules during biological reactions can be detected by the surface acoustic wave propagation or piezoelectric crystal distortion. Both techniques operate over a wide temperature range. Piezoelectric technique provides fast response and stable output. However, mass loading in liquid is a limitation of this method. 

The possibilities of these approaches, considering the large numbers of potentially useful biochemical reactions, are enormous. It is expected that significant advances will occur in the field of biosensor development in the near future, especially when newer biotechnological processes and chemical modification approaches are adapted to sensor development. 

Our research group is working on the development of electrochemical biosensors for the detection of microcystin and anatoxin-a(s), based on the inhibition of protein phosphatase and acetylcholinesterase, respectively. These enzyme biosensors represent useful bioanalytical tools, suitable to be used as screening techniques for the preliminary yes/no detection of the toxicity of a sample. Additionally, due to the versatility of the electrochemical approach, the strategy can be applied to the detection of other cyanobacterial toxins. 

However, it should be mentioned that there is a flexible hand-held electrochemical instrument on the market, which can be programmed to be used in a variety of voltammetric/amperometric modes in the field [209]. Although the majority of biosensor applications described in this review were for single analyte detection, it is very likely that future directions will involve development of biosensor arrays for multi-analyte determinations. One example of this approach has been described in an earlier section, where five OPs could be monitored with an array of biosensors based on mutant forms of AChE from D. melanogaster [187]. This array has considerable potential for monitoring the quality of food, such as wheat and fruit. Developments and applications of biosensors in the area of food analysis are expected to grow as consumer demand for improved quality and safety increases. Another area where biosensor developments are likely to increase significantly is in the field of environmental analysis, particularly with respect to the defence of public... 

Some applications of amperometric biosensing strategies for pesticide detection in real or spiked food samples have been recently reported. Most of the applications have been developed for vegetable matrices. Different formats of biosensors have been used disposable screen-printed choline oxidase biosensors [23] using AChE in solution were utilized to detect pesticides in real samples of fruit and vegetables. 

Knowing that the inorganic mercury is biomagnified in the aquatic food chain through bacterial conversion to methyl mercury and then accumulated primarily in fish, this part is focused to the determination of methyl mercury in fish samples. The developed method described above using the combination of biphasic system and glucose oxidase biosensor was used. 

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