Biosensor
The biosensor reader device connects with the associated electronics or signal processors that are primarily responsible for the display of the results in a user-friendly way.
A biosensor typically consists of a bio-receptor (enzyme/antibody/cell/nucleic acid/aptamer), transducer component (semi-conducting material/nanomaterial), and electronic system which includes a signal amplifier, processor & display.
In one approach to overcome these limitations, recombinant binding fragments (Fab, Fv or scFv) or domains (VH, VHH) of antibodies have been engineered.
[22] The use of affinity binding receptors for purposes of biosensing has been proposed by Schultz and Sims in 1979 [23] and was subsequently configured into a fluorescent assay for measuring glucose in the relevant physiological range between 4.4 and 6.1 mmol/L.
[26][27] Additionally, aptamers can be combined with nucleic acid enzymes, such as RNA-cleaving DNAzymes, providing both target recognition and signal generation in a single molecule, which shows potential applications in the development of multiplex biosensors.
[30] Different research projects aim to develop new portable devices that use cheap, environmentally friendly, disposable cartridges that require only simple handling with no need of further processing, washing, or manipulation by expert technicians.
[34] Microalgae are entrapped on a quartz microfiber and the chlorophyll fluorescence modified by herbicides is collected at the tip of an optical fiber bundle and transmitted to a fluorimeter.
The most commonly used hydrogel is sol-gel, glassy silica generated by polymerization of silicate monomers (added as tetra alkyl orthosilicates, such as TMOS or TEOS) in the presence of the biological elements (along with other stabilizing polymers, such as PEG) in the case of physical entrapment.
[41] Smart materials that mimic the biological components of a sensor can also be classified as biosensors using only the active or catalytic site or analogous configurations of a biomolecule.
Additionally, the label-free and direct electrical detection of small peptides and proteins is possible by their intrinsic charges using biofunctionalized ion-sensitive field-effect transistors.
Such biosensors are often made by screen printing the electrode patterns on a plastic substrate, coated with a conducting polymer and then some protein (enzyme or antibody) is attached.
One such device, based on a 4-electrode electrochemical cell, using a nanoporous alumina membrane, has been shown to detect low concentrations of human alpha thrombin in presence of high background of serum albumin.
[47] By embedding the ion channels in supported or tethered bilayer membranes (t-BLM) attached to a gold electrode, an electrical circuit is created.
Quantitative detection of an extensive class of target species, including proteins, bacteria, drug and toxins has been demonstrated using different membrane and capture configurations.
[49][50] The European research project Greensense develops a biosensor to perform quantitative screening of drug-of-abuse such as THC, morphine, and cocaine [51] in saliva and urine.
Antibodies and artificial families of AgBPs are constituted by a set of hypervariable (or randomized) residue positions, located in a unique sub-region of the protein, and supported by a constant polypeptide scaffold.
The binding of the bioreceptor will affect some of the magnetic particle properties that can be measured by AC susceptometry,[57] a Hall Effect sensor,[58] a giant magnetoresistance device,[59] or others.
The main requirements for a biosensor approach to be valuable in terms of research and commercial applications are the identification of a target molecule, availability of a suitable biological recognition element, and the potential for disposable portable detection systems to be preferred to sensitive laboratory-based techniques in some situations.
Many of today's biosensor applications are similar, in that they use organisms which respond to toxic substances at a much lower concentrations than humans can detect to warn of their presence.
Biosensors could be used to monitor air, water, and soil pollutants such as pesticides, potentially carcinogenic, mutagenic, and/or toxic substances and endocrine disrupting chemicals.
Deneb Karentz, a researcher at the Laboratory of Radio-biology and Environmental Health (University of California, San Francisco) has devised a simple method for measuring ultraviolet penetration and intensity.
Working in the Antarctic Ocean, she submerged to various depths thin plastic bags containing special strains of E. coli that are almost totally unable to repair ultraviolet radiation damage to their DNA.
In this regard, biosensors are very attractive and applicable tools for providing rapid, sensitive, specific, stable, cost-effective and non-invasive detections for early lung cancer diagnosis.
Thus, cancer biosensors consisting of specific biorecognition molecules such as antibodies, complementary nucleic acid probes or other immobilized biomolecules on a transducer surface.
The biorecognition molecules interact specifically with the biomarkers (targets) and the generated biological responses are converted by the transducer into a measurable analytical signal.
Binding to the flow side of the chip has an effect on the refractive index and in this way biological interactions can be measured to a high degree of sensitivity with some sort of energy.
Other optical biosensors are mainly based on changes in absorbance or fluorescence of an appropriate indicator compound and do not need a total internal reflection geometry.
An example of a recently developed biosensor is one for detecting cytosolic concentration of the analyte cAMP (cyclic adenosine monophosphate), a second messenger involved in cellular signaling triggered by ligands interacting with receptors on the cell membrane.
[128] "Nanoantennas" made out of DNA – a novel type of nano-scale optical antenna – can be attached to proteins and produce a signal via fluorescence when these perform their biological functions, in particular for distinct conformational changes.
The ability to absorb and immobilize a variety of proteins, particularly some with carbon ring structures, has proven graphene to be an excellent candidate as a biosensor transducer.
