A biosensor is a device for the detection of an analyte that combines a biological component with a physicochemical detector component. An analyte is a substance or Chemical constituent that is determined in an analytical procedure such as a Titration. [1]
It consists of 3 parts:
- the sensitive biological element (biological material (eg. tissue, microorganisms, organelles, cell receptors, enzymes, antibodies, nucleic acids, etc), a biologically derived material or biomimic) The sensitive elements can be created by biological engineering. Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins Antibodies (also known as immunoglobulins, abbreviated Ig) are Gamma globulin Proteins that are found in Blood or other Bodily A nucleic acid is a Macromolecule composed of chains of monomeric Nucleotides In Biochemistry these Molecules carry Genetic information Biological Engineering (including Biological systems engineering and Bioengineering) is a form of Biotechnology that uses broad-based
- the transducer or the detector element (works in a physicochemical way; optical, piezoelectric, electrochemical, etc. ) that transforms the signal resulting from the interaction of the analyte with the biological element into another signal (i. e. , transducers) that can be more easily measured and quantified;
- associated electronics or signal processors that is primarily responsible for the display of the results in a user-friendly way. [2]
The most widespread example of a commercial biosensor is the blood glucose biosensor, which uses the enzyme glucose oxidase to break blood glucose down. The glucose oxidase enzyme (GOx ( binds to beta-D-glucose (an Isomer of the six-carbon sugar Glucose) and aids in breaking the sugar down into its Metabolites In doing so it first oxidizes glucose and uses two electrons to reduce the FAD (a component of the enzyme) to FADH2. This in turn is oxidized by the electrode (accepting two electrons from the electrode) in a number of steps. The resulting current is a measure of the concentration of glucose. In this case, the electrode is the transducer and the enzyme is the biologically active component.
Recently, arrays of many different detector molecules have been applied in so called electronic nose devices, where the pattern of response from the detectors is used to fingerprint a substance. An electronic nose is a device intended to detect odors or flavors Current commercial electronic noses, however, do not use biological elements.
A canary in a cage, as used by miners to warn of gas could be considered a biosensor. Many of today's biosensor applications are similar, in that they use organisms which respond to toxic substances at a much lower level than us to warn us of their presence. Toxicity is the degree to which a substance is able to damage an exposed organism Such devices can be used both in environmental monitoring and in water treatment facilities.
Contents |
Principles of Detection
Photometric
Optical biosensors based on the phenomenon of surface plasmon resonance are evanescent wave techniques. The excitation of Surface plasmons by light is denoted as a surface plasmon resonance (SPR for planar surfaces or localized surface plasmon resonance (LSPR for nanometer-sized An evanescent wave is a nearfield standing Wave exhibiting Exponential decay with distance This utilises a property shown of gold and other materials; specifically that a thin layer of gold on a high refractive index glass surface can absorb laser light, producing electron waves (surface plasmons) on the gold surface. Gold (ˈɡoʊld is a Chemical element with the symbol Au (from its Latin name aurum) and Atomic number 79 This occurs only at a specific angle and wavelength of incident light and is highly dependent on the surface of the gold, such that binding of a target analyte to a receptor on the gold surface produces a measurable signal.
Surface plasmon resonance sensors operate using a sensor chip consisting of a plastic cassette supporting a glass plate, one side of which is coated with a microscopic layer of gold. This side contacts the optical detection apparatus of the instrument. The opposite side is then contacted with a microfluidic flow system. The contact with the flow system creates channels across which reagents can be passed in solution. This side of the glass sensor chip can be modified in a number of ways, to allow easy attachment of molecules of interest. Normally it is coated in carboxymethyl dextran or similar compound.
Light, at a fixed wavelength is reflected off the gold side of the chip, at the angle of total internal reflection and detected inside the instrument. This induces the evanescent wave to penetrate through the glass plate and someway into the liquid flowing over the surface.
The refractive index at the flow side of the chip surface has a direct influence on the behaviour of the light reflected off the gold side. 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. A widely used research tool, the micro-array, is basically a biosensor.
Electrochemical
Electrochemical biosensors are normally based on enzymatic catalysis of a reaction that produces or consumes electrons (such enzymes are rightly called redox enzymes). The sensor substrate usually contains three electrodes, a reference electrode, an active electrode and a sink electrode. An electrode is an Electrical conductor used to make contact with a nonmetallic part of a circuit (e Reference electrode is an Electrode which has a stable and well-known Electrode potential. A counter electrode may also be present as an ion source. Greg Landau says The Auxiliary electrode, often also called the counter electrode, is an Electrode used in an electrochemical cell with a Working electrode The target analyte is involved in the reaction that takes place on the active electrode surface, and the ions produced create a potential which is subtracted from that of the reference electrode to give a signal. We can either measure the current (rate of flow of electrons is now proportional to the analyte concentration) at a fixed potential or the the potential can be measured at zero current (this gives a logarithmic response). Note that potential of the working or active electrode is space charge sensitive and this is often used.
Another example, the potentiometric biosensor, works contrary to the current understanding of its ability. Such biosensors are screenprinted, conducting polymer coated, open circuit potential biosensors based on conjugated polymers immunoassays. They have only two electrodes and are extremely sensitive, robust and accurate. They enable the detection of analytes at levels previously only achievable by HPLC and LC/MS and without rigorous sample preparation. The signal is produced by electrochemical and physical changes in the conducting polymer layer due to changes occurring at the surface of the sensor. Such changes can be attributed to ionic strength, pH, hydration and redox reactions, the latter due to the enzyme label turning over a substrate([1]).
Others
Piezoelectric sensors utilise crystals which undergo an elastic deformation when an electrical potential is applied to them. Piezoelectricity is the ability of some materials (notably Crystals and certain Ceramics including bone to generate an Electric potential in response to An alternating potential (A. C. ) produces a standing wave in the crystal at a characteristic frequency. This frequency is highly dependent on the elastic properties of the crystal, such that if a crystal is coated with a biological recognition element the binding of a (large) target analyte to a receptor will produce a change in the resonance frequency, which gives a binding signal. In a mode that uses surface waves (SAW), the sensitivity is greatly increased. This is a special application of the Quartz crystal microbalance in biosensor. A quartz crystal microbalance (QCM measures a mass per unit area by measuring the change in Frequency of a Quartz crystal resonator
Thermometric and magnetic based biosensors are rare.
Applications
There are many potential application of biosensors of various types. 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. Some examples are given below:
- Glucose monitoring in diabetes patients <-- historical market driver
- Other medical health related targets
- Environmental applications e. g. the detection of pesticides and river water contaminants
- Remote sensing of airborne bacteria e. A pesticide is a substance or mixture of substances used to kill a pest. The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have g. in counter-bioterrorist activities
- Detection of pathogens[3]
- Determining levels of toxic substances before and after bioremediation
- Detection and determining of organophosphate
- Routine analytical measurement of folic acid, biotin, vitamin B12 and pantothenic acid as an alternative to microbiological assay
- Determination of drug residues in food, such as antibiotics and growth promoters, particularly meat and honey. Bioremediation can be defined as any process that uses Microorganisms Fungi, green plants or their Enzymes to return the natural environment altered An organophosphate (sometimes abbreviated OP) is the general name for Esters of Phosphoric acid. Folic acid (also known as Vitamin M and Folacin) and Folate (the Anionic form are forms of the water-soluble Vitamin B9 Vitamin H redirects here In medical slang "vitamin H" may also refer to Haloperidol. Pantothenic acid, also called Vitamin B5 (a B vitamin) is a water- Soluble vitamin required to sustain life ( In modern usage an antibiotic is a Chemotherapeutic agent with activity against Microorganisms such as Bacteria, fungi or Protozoa
- Drug discovery and evaluation of biological activity of new compounds.
- Detection of toxic methabolites such as mycotoxins [4]
See also
References
- ^ International Union of Pure and Applied Chemistry. A DNA field-effect transistor (DNAFET is a Field-effect transistor which uses the field-effect due to the partial charges of DNA molecules to function as a Biosensor The International Union of Pure and Applied Chemistry ( IUPAC) (aɪjuːpæk or ay-yoo-pec) is an international Non-governmental organization "biosensor". Compendium of Chemical Terminology Internet edition. Compendium of Chemical Terminology (ISBN 0-86542-684-8 is a book published by IUPAC containing internationally accepted definitions for terms in Chemistry.
- ^ Cavalcanti A, Shirinzadeh B, Zhang M, Kretly LC (2008). "Nanorobot Hardware Architecture for Medical Defense". Sensors 8 (5): 2932-2958.
- ^ Pohanka M, Skladal P, Kroca M (2007). "Biosensors for biological warfare agent detection". Def. Sci. J. 57(3):185-93.
- ^ Pohanka M, Jun D, Kuca K (2007). "Mycotoxin assay using biosensor technology: a review. Drug Chem. Toxicol. 30(3):253-61.
External links
Dapyx Software network: MP3 Explorer | Ebook Manager | Zenithic