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Contoh yang paling umum dari biosensor adalah pengukur [[gula darah]], yang menggunakan enzim [[glukosa oksidase]] untuk memecah gula darah. Biosensor ini bekerja dengan mengoksidasi glukosa terlebih dahulu dengan menggunakan dua [[elektron]] untuk mereduksi FAD (komponen dari enzim) menjadi FADH2. Lalu FADH2 dioksidasi oleh elektrode dan menerima dua elektron dari elektrode dalam beberapa tahap. Hasilnya adalah arus listrik yang mengukur konsentrasi glukosa. Dalam kasus ini, elektrode adalah transduser dan enzim adalah elemen biologis sensitif.
Saat ini, serangkaian detektor molekul, yang disebut dengan [[hidungpenciuman elektronik]], telah diaplikasikan untuk menjadikan pola respon alat tersebut sebagai ''fingerprint'' dari suatu senyawa.<ref>[http://www.microfluidicsolutions.com/apps/blog/show/20808263-ucsb-sensor-sniffs-explosives-through-microfluidics-might-replace-rover-at-the-airport-video- UCSB Electronic Nose]</ref> Berbagai jenis hewan telah digunakan sebagai biosensor dan diidentifikasi melalui perilakunya terhadap rangsangan yang diterimanya, seperti serangga dari ordo [[Hymenoptera]]<ref name="scicentr">{{cite web|title=Wasp Hound|url=http://www.sciencentral.com/articles/view.php3?article_id=218392717|publisher=Science Central|accessdate=23 February 2011}}</ref><ref>Lihat [[:en:Hymenoptera training]]</ref> untuk mendeteksi [[narkoba]] dan [[bahan peledak]], dan [[burung kenari]]<ref>Page, Walter Hines; Page, Arthur Wilson (August 1914). [http://books.google.com/?id=zegeQtMn9JsC&pg=PA474 "Man And His Machines: Resuscitation Cage For Mine Canaries"]. The World's Work: A History of Our Time XLIV (2): 474. Retrieved 2009-08-04.</ref><ref>Lihat [[:en:Domestic Canary#Miner's canary]]</ref> untuk mendeteksi keberadaan gas berbahaya di dalam tambang.
Berbagai jenis hewan telah digunakan sebagai biosensor dan diidentifikasi melalui perilakunya terhadap rangsangan yang diterimanya, seperti serangga dari ordo [[Hymenoptera]]<ref name=scicentr>{{cite web|title=Wasp Hound|url=http://www.sciencentral.com/articles/view.php3?article_id=218392717|publisher=Science Central|accessdate=23 February 2011}}</ref><ref>Lihat [[:en:Hymenoptera training]]</ref> untuk mendeteksi [[narkoba]] dan [[bahan peledak]], dan [[burung kenari]]<ref>Page, Walter Hines; Page, Arthur Wilson (August 1914). [http://books.google.com/?id=zegeQtMn9JsC&pg=PA474 "Man And His Machines: Resuscitation Cage For Mine Canaries"]. The World's Work: A History of Our Time XLIV (2): 474. Retrieved 2009-08-04.</ref><ref>Lihat [[:en:Domestic Canary#Miner's canary]]</ref> untuk mendeteksi keberadaan gas berbahaya di dalam tambang.
<!--Many optical biosensors are based on the phenomenon of [[surface plasmon resonance]] (SPR) techniques. This utilises a property of 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. 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 of a fixed wavelength is reflected off the gold side of the chip at the angle of total internal reflection, and detected inside the instrument. The angle of incident light is varied in order to match the evanescent wave propagation rate with the propagation rate of the surface plasmon plaritons.<ref>{{cite journal |author=Homola J |title= Present and future of surface plasmon resonance biosensors. |year=2003 /8x2n9xhbkqtp76dq}}</ref> This induces the evanescent wave to penetrate through the glass plate and some distance 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. The refractive index of the medium near the surface changes when biomolecules attach to the surface, and the SPR angle varies as a function of this change.
Other evanescent wave biosensors have been commercialised using waveguides where the propagation constant through the waveguide is changed by the absorption of molecules to the waveguide surface. One such example, [[Dual Polarisation Interferometry]] uses a buried waveguide as a reference against which the change in propagation constant is measured. Other configurations such as the [[Mach-Zehnder]] have reference arms lithographically defined on a substrate. Higher levels of integration can be achieved using resonator geometries where the resonant frequency of a ring resonator changes when molecules are absorbed.<ref>M. Iqbal, M. A. Gleeson, B. Spaugh, F. Tybor, W. G. Gunn, M. Hochberg, T. Baehr-Jones, R. C. Bailey, L. C. Gunn, "Label-Free Biosensor Arrays Based on Silicon Ring Resonators and High-Speed Optical Scanning Instrumentation", IEEE J. Sel. Top. Quant. Elec. 16, 654-661 (2010)</ref><ref>{{cite journal|author=J. Witzens, M. Hochberg|title=Optical detection of target molecule induced aggregation of nanoparticles by means of high-Q resonators|journal=Opt. Express|volume=19|pages=7034–7061|year=2011|url = http://www.opticsinfobase.org/oe/fulltext.cfm?uri=oe-19-8-7034&id=211400}}</ref>
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. For example, a fully operational prototype device detecting casein in milk has been fabricated. The device is based on detecting changes in absorption of a gold layer.<ref>H. M. Hiep et al. "A localized surface plasmon resonance based immunosensor for the detection of casein in milk" Sci. Technol. Adv. Mater. 8 (2007) 331 [http://dx.doi.org/10.1016/j.stam.2006.12.010 free download]</ref> A widely used research tool, the micro-array, can also be considered a biosensor.
Nanobiosensors use an immobilized bioreceptor probe that is selective for target analyte molecules. Nanomaterials are exquisitely sensitive chemical and biological sensors. Nanoscale materials demonstrate unique properties. Their large surface area to volume ratio can achieve rapid and low cost reactions, using a variety of designs.<ref>Gerald A Urban 2009 Meas. Sci. Technol. 20 012001 {{doi|10.1088/0957-0233/20/1/012001}}</ref>
Biological biosensors often incorporate a genetically modified form of a native protein or enzyme. The protein is configured to detect a specific analyte and the ensuing signal is read by a detection instrument such as a fluorometer or luminometer. An example of a recently developed biosensor is one for detecting [[cytosol]]ic 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.<ref>Fan, F. et al. (2008) Novel Genetically Encoded Biosensors Using Firefly Luciferase. ACS Chem. Biol. 3, 346–51. [http://pubs.acs.org/doi/abs/10.1021/cb8000414 free download]</ref> Similar systems have been created to study cellular responses to native ligands or xenobiotics (toxins or small molecule inhibitors). Such "assays" are commonly used in drug discovery development by pharmaceutical and biotechnology companies. Most cAMP assays in current use require lysis of the cells prior to measurement of cAMP. A live-cell biosensor for cAMP can be used in non-lysed cells with the additional advantage of multiple reads to study the kinetics of receptor response. -->
== Referensi ==
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