Editing Nanosensor (section)

== Mechanisms of operation ==
There are multiple mechanisms by which a recognition event can be [[Transducer|transduced]] into a measurable signal; generally, these take advantage of the nanomaterial sensitivity and other unique properties to detect a selectively bound analyte.

Electrochemical nanosensors are based on detecting a [[Electrical resistance and conductance|resistance]] change in the nanomaterial upon binding of an analyte, due to changes in [[scattering]] or to the depletion or accumulation of [[charge carrier]]s.  One possibility is to use nanowires such as [[Carbon nanotube field-effect transistor|carbon nanotubes]], [[conductive polymer]]s, or metal oxide nanowires as gates in [[field-effect transistor]]s, although as of 2009 they had not yet been demonstrated in real-world conditions.<ref name=":0" />{{Rp|12–26}} Chemical nanosensors contain a chemical recognition system (receptor) and a physiochemical transducer, in which the receptor interacts with analyte to produce electrical signals.<ref>Chemical Sensors. http://nano-bio.ehu.es/files/chemical_sensors1.doc_definitivo.pdf (accessed Dec 6, 2018)</ref> In one case,<ref>Agnivo Gosai, Brendan Shin Hau Yeah, Marit Nilsen-Hamilton, Pranav Shrotriya,
Label free thrombin detection in presence of high concentration of albumin using an aptamer-functionalized nanoporous membrane,
Biosensors and Bioelectronics,
Volume 126,
2019,
Pages 88-95,
ISSN 0956-5663,
https://doi.org/10.1016/j.bios.2018.10.010.</ref> upon interaction of the analyte with the receptor, the nanoporous transducer had a change in impedance which was determined as the sensor signal. Other examples include electromagnetic or [[Plasmonics|plasmonic]] nanosensors, spectroscopic nanosensors such as [[surface-enhanced Raman spectroscopy]], magnetoelectronic or [[Spintronics|spintronic]] nanosensors, and mechanical nanosensors.<ref name=":0" />{{Rp|12–26}}

Biological nanosensors consist of a bio-receptor and a transducer. The transduction method of choice is currently fluorescence because of the high sensitivity and relative ease of measurement.<ref name=":1">{{Cite journal|last1=Fehr|first1=M.|last2=Okumoto|first2=S.|last3=Deuschle|first3=K.|last4=Lager|first4=I.|last5=Looger|first5=L. L.|last6=Persson|first6=J.|last7=Kozhukh|first7=L.|last8=Lalonde|first8=S.|last9=Frommer|first9=W. B.|date=2005-02-01|title=Development and use of fluorescent nanosensors for metabolite imaging in living cells|url=https://portlandpress.com/biochemsoctrans/article/33/1/287/66035/Development-and-use-of-fluorescent-nanosensors-for|journal=Biochemical Society Transactions|language=en|volume=33|issue=1|pages=287–290|doi=10.1042/BST0330287|pmid=15667328|issn=0300-5127|url-access=subscription}}</ref><ref>{{Cite journal|last=Aylott|first=Jonathan W.|date=2003-04-07|title=Optical nanosensors—an enabling technology for intracellular measurements|url=http://xlink.rsc.org/?DOI=b302174m|journal=The Analyst|volume=128|issue=4|pages=309–312|doi=10.1039/b302174m|pmid=12741632|bibcode=2003Ana...128..309A|url-access=subscription}}</ref> The measurement can be achieved by using the following methods: binding active nanoparticles to active proteins within the cell, using [[site-directed mutagenesis]] to produce indicator proteins, allowing for real-time measurements, or by creating a nanomaterial (e.g. nanofibers) with attachment sites for the bio-receptors.<ref name=":1" /> Even though electrochemical nanosensors can be used to measure [[intracellular]] properties, they are typically less selective for biological measurements, as they lack the high specificity of bio-receptors (e.g. antibody, DNA).<ref name=":2">{{Cite journal|last1=Cullum|first1=Brian M.|last2=Vo-Dinh|first2=Tuan|date=2000-09-01|title=The development of optical nanosensors for biological measurements|url=https://www.cell.com/trends/biotechnology/abstract/S0167-7799(00)01477-3|journal=Trends in Biotechnology|language=en|volume=18|issue=9|pages=388–393|doi=10.1016/S0167-7799(00)01477-3|issn=0167-7799|pmid=10942963|hdl=11603/36051|hdl-access=free}}</ref><ref name=":1" />

[[Photonics|Photonic]] devices can also be used as nanosensors to quantify concentrations of clinically relevant samples. A principle of operation of these sensors is based on the chemical modulation of a hydrogel film volume that incorporates a [[Fiber Bragg grating|Bragg grating]]. As the [[hydrogel]] swells or shrinks upon chemical stimulation, the Bragg grating changes color and diffracts light at different wavelengths. The diffracted light can be correlated with the concentration of a target analyte.<ref>{{cite journal | last1 = Yetisen | first1 = AK | last2 = Montelongo | first2 = Y | last3 = Vasconcellos | first3 = FC | last4 = Martinez-Hurtado | first4 = JL | last5 = Neupane | first5 = S | last6 = Butt | first6 = H | last7 = Qasim | first7 = MM | last8 = Blyth | first8 = J | last9 = Burling | first9 = K | last10 = Carmody | first10 = JB | last11 = Evans | first11 = M | last12 = Wilkinson | first12 = TD | last13 = Kubota | first13 = LT | last14 = Monteiro | first14 = MJ | last15 = Lowe | first15 = CR | year = 2014 | title = Reusable, Robust, and Accurate Laser-Generated Photonic Nanosensor | journal = Nano Lett | volume = 14 | issue = 6| pages = 3587–3593 | doi = 10.1021/nl5012504 | pmid = 24844116 | bibcode = 2014NanoL..14.3587Y | doi-access = free }}</ref>

Another type of nanosensor is one that works through a [[Colorimetry|colorimetric]] basis. Here, the presence of the [[analyte]] causes a [[chemical reaction]] or morphological alteration for a visible color change to occur. One such application, is that gold [[nanoparticle]]s can be used for the detection of heavy metals.<ref>{{Cite journal|last1=Priyadarshini|first1=E.|last2=Pradhan|first2=N.|date=January 2017|title=Gold nanoparticles as efficient sensors in colorimetric detection of toxic metal ions: A review|journal=Sensors and Actuators B: Chemical|volume=238|pages=888–902|doi=10.1016/j.snb.2016.06.081}}</ref> Many harmful gases can also be detected by a colorimetric change, such as through the commercially available [https://www.draeger.com/en-us_us/Applications/Products/Mobile-Gas-Detection/Draeger-Tubes-and-CMS/Draeger-Tubes/Sampling-Tubes-and-Systems Dräger Tube]. These provide an alternative to bulky, lab-scale systems, as these can be miniaturized to be used for point-of-sample devices. For example, many chemicals are regulated by the [[United States Environmental Protection Agency|Environmental Protection Agency]] and require extensive testing to ensure [[Contamination|contaminant]] levels are within the appropriate limits. Colorimetric nanosensors provide a method for on-site determination of many contaminants.<ref>{{Cite journal|last1=Palomares|first1=E.|last2=Martínez-Díaz|first2=M. V.|last3=Torres|first3=T.|last4=Coronado|first4=E.|date=2006-06-06|title=A Highly Sensitive Hybrid Colorimetric and Fluorometric Molecular Probe for Cyanide Sensing Based on a Subphthalocyanine Dye|journal=Advanced Functional Materials|volume=16|issue=9|pages=1166–1170|doi=10.1002/adfm.200500517|s2cid=94134700 |issn=1616-301X}}</ref><ref>{{Cite journal|last1=Wei|first1=Qingshan|last2=Nagi|first2=Richie|last3=Sadeghi|first3=Kayvon|last4=Feng|first4=Steve|last5=Yan|first5=Eddie|last6=Ki|first6=So Jung|last7=Caire|first7=Romain|last8=Tseng|first8=Derek|last9=Ozcan|first9=Aydogan|date=2014-02-25|title=Detection and Spatial Mapping of Mercury Contamination in Water Samples Using a Smart-Phone|journal=ACS Nano|volume=8|issue=2|pages=1121–1129|doi=10.1021/nn406571t|issn=1936-0851|pmc=3949663|pmid=24437470}}</ref><ref>{{Cite journal|last1=El Kaoutit|first1=Hamid|last2=Estévez|first2=Pedro|last3=García|first3=Félix C.|last4=Serna|first4=Felipe|last5=García|first5=José M.|date=2013|title=Sub-ppm quantification of Hg( ii ) in aqueous media using both the naked eye and digital information from pictures of a colorimetric sensory polymer membrane taken with the digital camera of a conventional mobile phone|journal=Anal. Methods|volume=5|issue=1|pages=54–58|doi=10.1039/C2AY26307F|s2cid=98751207|issn=1759-9660}}</ref>