Editing Biosensor (section)

==Surface attachment of the biological elements==
[[File:Sensing negatively charged exosomes bound a graphene surface.svg|thumb|Sensing negatively charged exosomes bound a graphene surface]]

An important part of a biosensor is to attach the biological elements (small molecules/protein/cells) to the surface of the sensor (be it metal, polymer, or glass). The simplest way is to [[Surface engineering|functionalize]] the surface in order to coat it with the biological elements. This can be done by polylysine, aminosilane, epoxysilane, or nitrocellulose in the case of silicon chips/silica glass. Subsequently, the bound biological agent may also be fixed—for example, by [[layer by layer]] deposition of alternatively charged polymer coatings.<ref>{{cite journal | last1 = Pickup | first1 = JC | last2 = Zhi | first2 = ZL | last3 = Khan | first3 = F | last4 = Saxl | first4 = T | last5 = Birch | first5 = DJ | year = 2008 | title = Nanomedicine and its potential in diabetes research and practice | journal = Diabetes Metab Res Rev | volume = 24 | issue = 8| pages = 604–10 | doi=10.1002/dmrr.893 | pmid=18802934| s2cid = 39552342 }}</ref>

Alternatively, three-dimensional lattices ([[hydrogel]]/[[xerogel]]) can be used to chemically or physically entrap these (whereby chemically entrapped it is meant that the biological element is kept in place by a strong bond, while physically they are kept in place being unable to pass through the pores of the gel matrix). The most commonly used hydrogel is [[sol-gel]], glassy silica generated by polymerization of silicate monomers (added as tetra alkyl orthosilicates, such as [[Tetramethyl orthosilicate|TMOS]] or [[Tetraethyl orthosilicate|TEOS]]) in the presence of the biological elements (along with other stabilizing polymers, such as [[Polyethylene glycol|PEG]]) in the case of physical entrapment.<ref>{{cite journal | last1 = Gupta | first1 = R | last2 = Chaudhury | first2 = NK | date = May 2007 | title = Entrapment of biomolecules in sol-gel matrix for applications in biosensors: problems and future prospects | journal = Biosens Bioelectron | volume = 22 | issue = 11| pages = 2387–99 | doi=10.1016/j.bios.2006.12.025 | pmid=17291744}}</ref>

Another group of hydrogels, which set under conditions suitable for cells or protein, are [[Acrylate polymer|acrylate]] hydrogel, which polymerizes upon [[radical initiator|radical initiation]]. One type of radical initiator is a [[peroxide]] radical, typically generated by combining a [[Ammonium persulfate|persulfate]] with [[Tetramethylethylenediamine|TEMED]] ([[Polyacrylamide gel]] are also commonly used for [[protein electrophoresis]]),<ref>{{cite journal | last1 = Clark | first1 = HA | last2 = Kopelman | first2 = R | last3 = Tjalkens | first3 = R | last4 = Philbert | first4 = MA | date = November 1999 | title = Optical nanosensors for chemical analysis inside single living cells. 2. Sensors for pH and calcium and the intracellular application of PEBBLE sensors | journal = Anal. Chem. | volume = 71 | issue = 21| pages = 4837–43 | doi=10.1021/ac990630n| pmid = 10565275 }}</ref> alternatively light can be used in combination with a photoinitiator, such as DMPA ([[2,2-dimethoxy-2-phenylacetophenone]]).<ref>{{cite journal | last1 = Liao | first1 = KC | last2 = Hogen-Esch | first2 = T | last3 = Richmond | first3 = FJ | last4 = Marcu | first4 = L | last5 = Clifton | first5 = W | last6 = Loeb | first6 = GE | date = May 2008 | title = Percutaneous fiber-optic sensor for chronic glucose monitoring in vivo | journal = Biosens Bioelectron | volume = 23 | issue = 10| pages = 1458–65 | doi=10.1016/j.bios.2008.01.012 | pmid=18304798}}</ref> 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.<ref>{{cite web|url=http://www.technologyreview.com/biomedicine/21603/?a=f|title=Mimicking Body Biosensors|first=Katherine|last=Bourzac|website=technologyreview.com}}</ref>