It is preferred to chemical monitoring because the latter does not take into account factors of biological significance such as combined effects of the contaminants on DNA, protein, or membrane. Onwurah et al. Microorganisms can be used as an indicator organism for toxicity assay or in risk assessment.
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Tests performed with bacteria are considered to be most reproducible, sensitive, simple, economic, and rapid [ 40 ] Table 3. A biosensor is an analytical device consisting of a biocatalyst enzyme, cell, or tissue and a transducer, which can convert a biological or biochemical signal or response into a quantifiable electrical signal [ 46 ].
A biosensor could be divided into two component analytical devices comprising of a biological recognition element that outputs a measurable signal to an interfaced transducer [ 24 ].
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Biorecognition typically relies on enzymes, whole cells, antibodies, or nucleic acids, whereas signal transduction exploits electrochemical amperometric, chronoamperometric, potentiometric, field-effect transistors, conductometric, capacitative , optical absorbance, reflectance, luminescence, chemiluminescence, bioluminescence, fluorescence, refractive index, light scattering , piezoelectric mass sensitive quartz crystal microbalance , magnetic, or thermal thermistor, pyroelectric interfaces [ 24 ]. The biocatalyst component of most biosensors is immobilized on to a membrane or within a gel, such that the biocatalyst is held in intimate contact with the transducer and may be reused.
Biosensors are already of major commercial importance, and their significance is likely to increase as the technology develops [ 46 ]. Biosensors are still emerging biotechnology for the future in environmental biomonitoring since they have specific limitations. Biosensors on a general sense are often employed for continuous monitoring of environmental contamination or as bioremediation process monitoring and biocontrol tools to provide informational data on what contaminants are present, where they are located, and a very sensitive and accurate evaluation of their concentrations in terms of bioavailability.
Ripp et al. As the name suggests they are biological instruments that detest and signal the presence of harmful contaminants in the environment. There are different types based on the biological components on which their sensitivities are based Figure 4. Some of them, though not exhaustive are the following.
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Anatomy of a Biosensor. The interaction between the target analyte and the biorecognition element creates a signalling event detectable by the interfaced transducer element. Modified from source: Ripp et al. Leyland Clark in the s used an enzyme biosensor which consists of glucose oxidase enzyme immobilized on an oxygen electrode for blood glucose sensing. This historical application of enzyme-based biosensor has found a world-wide lucrative application in medical diagnosis. Nevertheless, enzyme-based biosensor gradually gained application in environmental monitoring.
According to Ripp et al. Since enzymes are highly specific for their particular substrate, the simplest and most selective enzyme-based biosensors merely monitor enzyme activity directly in the presence of the substrate. Michel et al. Enzymatic biosensor using cytochrome C 3 as the recognition element. The current produced by the electrochemical regeneration of reduced cytochrome C 3 is proportional to the amount of oxidized cytochrome C 3 and, therefore, the Cr IV concentration. When tested under simulated groundwater conditions, the biosensors reacted with several other metal species, albeit at lower sensitivities, and were affected by environmental variables such as pH, temperature, and dissolved oxygen.
Another type of enzyme biosensor relies on enzyme activation upon interaction with the target of interest. Heavy metals, for example, in the form of cofactors-inorganic ions that binds to and activate the enzyme can be detected based on this integral association. Metalloenzymes such as alkaline phosphatase, ascorbate oxidase, glutamine synthetase, and carbonic anhydrase require association of a metal ion cofactor with their active sites for catalytic activity and can thus be used as recognition element for heavy metal [ 24 ]. Alkaline phosphatase, for example, can be applied in this regard as a biosensor for zinc [Zn II ] or ascorbate oxidase for biosensing copper II with detection limits down to very low part-per-billion levels [ 51 ].
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Immobilization provides the biosensor longevity and with recent integration of redox active carbon-based nanomaterials nanofibers, nanotubes, nanowires, and nanoparticles as transducers and their unique ability to interact with biological material, a promising advancement in enzyme biosensor design and sensitivity is in sight. Optical transducers absorption, reflectance, luminescence, chemiluminescence, evanescent wave, surface plasma resonance are also commonly employed in enzyme-based biosensor [ 24 ].
This can be as simple as optically registering a pH change using a pH reactive dye; for example, bromocresol purple can be immobilized with an acetylcholinesterase-based biosensor to monitor pH changes related to this enzyme's activity upon exposure to pesticides. Andreou et al. A great application of optical biosensor is in the Luminol, widely used as an electrochemiluminescent indicator. These types of biosensors make use of antibodies as recognition elements immunosensors. They are used widely as environmental monitors because antibodies are highly specific, versatile, and bind stably and strongly to target analytes antigens [ 24 ].
Antibodies can be highly effective detectors for environmental contaminants, and advancements in techniques such as phage display for the preparation and selection of recombinant antibodies with novel binding properties assures their continued environmental application. Perhaps the best introduction to antibody-based biosensing is the Automated Water Analyzer Computer Supported System AWACSS environmental monitoring system developed for remote, unattended, and continuous detection of organic pollutants for water quality control [ 54 ].
AWACSS uses an optical evanescent wave transducer and fluorescently labelled polyclonal antibodies for multiplexed detection of targeted groups of contaminants, including endocrine disruptors, pesticides, industrial chemicals, pharmaceuticals, and other priority pollutants, without requisite sample preprocessing. Antibody binding to a target sample analyte occurs in a short 5-minute preincubation step, followed by microfluidic pumping of the sample over the transducer element, which consists of an optical waveguide chip impregnated with 32 separate wells of immobilized antigen derivatives [ 24 ].
Thus, antibodies with both of their binding sites bound with analyte will not attach to the surface and will pass through the detector.
A semiconductor laser then excites the fluorophore label of bound antibodies, allowing for their quantification, with high fluorescence signals indicating high analyte concentrations. A fibre optic array tied to each well permits separation and identification of signals by the well, thereby yielding a simultaneous measurement of up to 32 different sample contaminants. Another design by Glass et al. Their time of assay was approximately 26 minutes, with detection limits at picomolar concentrations. Although not as elaborate as the AWACSS, a multitude of other antibody-based biosensors have been applied as environmental monitors, traditionally serving as biosensors for pesticides and herbicides, but their target analytes have broadened considerably over the past several years to include heavy metals, polycyclic aromatic hydrocarbons PAHs , polychlorinated biphenyls PCBs , explosives TNT and RDX , phenols, toxins such as microcystin, pharmaceutical compounds, and endocrine disruptors [ 56 ].
The principle underlying the DNA-based biosensor is the ability of a transducer to monitor a change in the nucleic acid's structure occurring after exposure to a target chemical. Immobilizing the nucleic acid as a recognition layer on the transducer surface forms the biosensor, and detection of the chemically induced nucleic acid conformational change is then typically achieved electrochemically i. Nucleic acid biosensors are generally nonselective and provide an overall indication of a potentially harmful genotoxic, carcinogenic, cytotoxic chemical or chemical mix in the test environment and, depending on the biosensor format, an estimate of concentration.
Bagni et al. Double-stranded DNA was immobilized on a single-use disposable screen-printed electrochemical cell operating off a handheld battery-powered potentiostat [ 59 ]. In a very discrete application of this DNA biosensor, the authors also applied it to the detection of this DNA biosensor and also to the detection of PAHs in fish bile, using the accumulation of PAH compounds in live fish to monitor for water contamination events [ 60 ]. Nucleic acid can be manipulated similarly to create target specific aptamers using a process called SELEX systematic evolution of ligands by exponential enrichment [ 24 ].
By iteratively incubating nucleic acid with the desired target, one can select for oligonucleotide sequences or aptamers with the greatest affinity for the target. Kim et al. Predominant aptasensor development and application is in the clinical fields, but it is slowly and inevitably encroaching upon environmental sensing.
senjouin-renshu.com/wp-content/53/2772-como-localizar.php Hydrazine and aromatic amine compounds in fresh and groundwater, hydroxyl radicals in uranium mine drainage waters, herbicides such as atrazine, general toxicity events in wastewater, industrially contaminated soils, and various other environmental sources have all been screened using DNA biosensors [ 24 ]. Metals are also relevant detection targets, due to their various affinities for nucleic acid. Lead, Cadmium, Nickel, Arsenic, Copper, Iron, Chromium, and others have been detected through DNA biosensing, incorporating both single- and double-stranded DNA as the sensing element, but again, nonselectivity [ 24 ].
These engineered catalytic oligonucleotides can mediate nucleic acid cleavages or ligation, phosphorylation, or other reactions.
However, the rapidity only a few minutes to detect but sample processing is often necessary , sensitivity typically down to low part-per-billion levels , ease of use, and cost-effectiveness screen environmental sites for toxic chemical intrusions or monitoring operational endpoints of bioremediation efforts. A calorimetric DNAzyme-based biosensor for lead has also been demonstrated [ 65 ]. Their objectives are toward miniaturization, portability, redundancy, and a reduction in sample size, time of response, and cost.
The majority of these biosensors serves biomedical rather than environmental causes, but they are slowly and inevitably being adapted for the environmental monitoring community. BioMEMs most often utilize optical transducers interfaced with enzyme, whole-cell, antibody, or nucleic acid-type receptors. Several recent examples should illustrate their various design and performance characteristics.
PUBLISHED THESES (2018)
Yakovleva et al. Islam et al. This 1. The BBIC converts the bioluminescently derived photodiode current into a digital signal, the frequency of which is proportional to the concentration of pollutant to which the bioreporter has been exposed.