Editing Glucose (section)

==Analysis==
When a glucose molecule is to be detected at a certain position in a larger molecule, [[nuclear magnetic resonance spectroscopy]], [[X-ray crystallography]] analysis or [[lectin]] [[immunostaining]] is performed with [[concanavalin A]] reporter enzyme conjugate, which binds only glucose or mannose.

===Classical qualitative detection reactions===
These reactions have only historical significance:

====Fehling test====
The [[Fehling test]] is a classic method for the detection of aldoses.<ref name="Fehling-Harn">H. Fehling: ''Quantitative Bestimmung des Zuckers im Harn''. In: ''[[Archiv für physiologische Heilkunde]]'' (1848), volume 7, p.&nbsp;64–73 (in German).</ref> Due to mutarotation, glucose is always present to a small extent as an open-chain aldehyde. By adding the Fehling reagents (Fehling (I) solution and Fehling (II) solution), the aldehyde group is oxidized to a [[carboxylic acid]], while the Cu<sup>2+</sup> tartrate complex is reduced to Cu<sup>+</sup> and forms a brick red precipitate (Cu<sub>2</sub>O).

====Tollens test====
In the [[Tollens test]], after addition of ammoniacal [[Silver nitrate|AgNO<sub>3</sub>]] to the sample solution, glucose reduces Ag<sup>+</sup> to elemental [[silver]].<ref>B. Tollens: [https://babel.hathitrust.org/cgi/pt?id=uiug.30112025692838;view=1up;seq=535 ''Über ammon-alkalische Silberlösung als Reagens auf Aldehyd''] {{Webarchive|url=https://web.archive.org/web/20220219063751/https://babel.hathitrust.org/cgi/pt?id=uiug.30112025692838;view=1up;seq=535 |date=19 February 2022 }}. In ''[[Berichte der Deutschen Chemischen Gesellschaft]]'' (1882), volume 15, p. 1635–1639 (in German).</ref>

====Barfoed test====
In [[Barfoed's test]],<ref name="barfoed">{{Cite journal |doi=10.1007/BF01462957 |title=Ueber die Nachweisung des Traubenzuckers neben Dextrin und verwandten Körpern |language=de |journal=Zeitschrift für Analytische Chemie |volume=12 |pages=27–32 |year=1873 |last1=Barfoed |first1=C. |issue=1 |s2cid=95749674 |url=https://zenodo.org/record/1594255 |access-date=1 July 2019 |archive-date=29 July 2020 |archive-url=https://web.archive.org/web/20200729234027/https://zenodo.org/record/1594255 |url-status=live }}</ref> a solution of dissolved [[copper acetate]], [[sodium acetate]] and acetic acid is added to the solution of the sugar to be tested and subsequently heated in a water bath for a few minutes. Glucose and other monosaccharides rapidly produce a reddish color and reddish brown [[copper(I) oxide]] (Cu<sub>2</sub>O).

====Nylander's test====
As a reducing sugar, glucose reacts in the [[Nylander's test]].<ref>Emil Nylander: ''Über alkalische Wismuthlösung als Reagens auf Traubenzucker im Harne'', [[Zeitschrift für physiologische Chemie]]. Volume 8, Issue 3, 1884, p.&nbsp;175–185 [http://www.degruyter.com/dg/viewarticle/j$002fbchm1.1884.8.issue-3$002fbchm1.1884.8.3.175$002fbchm1.1884.8.3.175.xml Abstract]. {{Webarchive|url=https://web.archive.org/web/20150923213720/http://www.degruyter.com/dg/viewarticle/j$002fbchm1.1884.8.issue-3$002fbchm1.1884.8.3.175$002fbchm1.1884.8.3.175.xml |date=23 September 2015 }} (in German).</ref>

====Other tests====
{{See also|Maillard reaction|Lye roll}}
Upon heating a dilute [[potassium hydroxide]] solution with glucose to 100&nbsp;°C, a strong reddish browning and a caramel-like odor develops.<ref name="Schwedt 102">Georg Schwedt: ''Zuckersüße Chemie''. John Wiley & Sons, 2012, {{ISBN|978-3-527-66001-8}}, p.&nbsp;102 (in German).</ref> Concentrated [[sulfuric acid]] dissolves dry glucose without blackening at room temperature forming sugar sulfuric acid.<ref name="Schwedt 102" />{{Verify source|date=April 2022}} In a yeast solution, alcoholic fermentation produces carbon dioxide in the ratio of 2.0454 molecules of glucose to one molecule of [[Carbon dioxide|CO<sub>2</sub>]].<ref name="Schwedt 102" /> Glucose forms a black mass with [[stannous chloride]].<ref name="Schwedt 102" /> In an ammoniacal silver solution, glucose (as well as lactose and dextrin) leads to the deposition of silver. In an ammoniacal [[lead acetate]] solution, white [[lead glycoside]] is formed in the presence of glucose, which becomes less soluble on cooking and turns brown.<ref name="Schwedt 102" /> In an ammoniacal copper solution, yellow [[copper oxide]] hydrate is formed with glucose at room temperature, while red copper oxide is formed during boiling (same with dextrin, except for with an ammoniacal copper acetate solution).<ref name="Schwedt 102" /> With [[Picric acid|Hager's reagent]], glucose forms [[mercury oxide]] during boiling.<ref name="Schwedt 102" /> An alkaline [[bismuth]] solution is used to precipitate elemental, black-brown bismuth with glucose.<ref name="Schwedt 102" /> Glucose boiled in an [[ammonium molybdate]] solution turns the solution blue. A solution with [[indigo carmine]] and [[sodium carbonate]] destains when boiled with glucose.<ref name="Schwedt 102" />

===Instrumental quantification===
====Refractometry and polarimetry====
In concentrated solutions of glucose with a low proportion of other carbohydrates, its concentration can be determined with a polarimeter. For sugar mixtures, the concentration can be determined with a [[refractometer]], for example in the [[Oechsle scale|Oechsle]] determination in the course of the production of wine.

====Photometric enzymatic methods in solution====
{{main|Glucose oxidation reaction}}
The enzyme glucose oxidase (GOx) converts glucose into gluconic acid and hydrogen peroxide while consuming oxygen. Another enzyme, peroxidase, catalyzes a chromogenic reaction (Trinder reaction)<ref>{{Cite journal |doi=10.1177/000456326900600108 |title=Determination of Glucose in Blood Using Glucose Oxidase with an Alternative Oxygen Acceptor |journal=Annals of Clinical Biochemistry |volume=6 |pages=24–27 |year=1969 |last1=Trinder |first1=P. |issue=1 |s2cid=58131350 |doi-access=free }}</ref> of [[phenol]] with [[4-Aminoantipyrine|4-aminoantipyrine]] to a purple dye.<ref name="purpuled">{{cite book |doi=10.1016/bs.pmbts.2019.01.004 |chapter=Fasting blood glucose levels in patients with different types of diseases |title=Glycans and Glycosaminoglycans as Clinical Biomarkers and Therapeutics - Part A |series=Progress in Molecular Biology and Translational Science |date=2019 |volume=162 |pages=277–292 |isbn=978-0-12-817738-9 | vauthors = Zhang Q, Zhao G, Yang N, Zhang L |publisher=Elsevier |pmid=30905457 }}</ref>

====Photometric test-strip method====
The test-strip method employs the above-mentioned enzymatic conversion of glucose to gluconic acid to form hydrogen peroxide. The reagents are immobilised on a polymer matrix, the so-called test strip, which assumes a more or less intense color. This can be measured reflectometrically at 510&nbsp;nm with the aid of an LED-based handheld photometer. This allows routine blood sugar determination by nonscientists. In addition to the reaction of phenol with 4-aminoantipyrine, new chromogenic reactions have been developed that allow photometry at higher wavelengths (550&nbsp;nm, 750&nbsp;nm).<ref name="purpuled"/><ref>{{Cite journal |doi=10.1039/A709038B |title=Water-soluble chromogenic reagent for colorimetric detection of hydrogen peroxide—an alternative to 4-aminoantipyrine working at a long wavelength |journal=Analytical Communications |volume=35 |issue=2 |pages=71–74 |year=1998 |last1=Mizoguchi |first1=Makoto |last2=Ishiyama |first2=Munetaka |last3=Shiga |first3=Masanobu}}</ref>

====Amperometric glucose sensor====
The electroanalysis of glucose is also based on the enzymatic reaction mentioned above. The produced hydrogen peroxide can be amperometrically quantified by anodic oxidation at a potential of 600 mV.<ref>{{Cite journal |pmid=18154363 |year=2008 |last1=Wang |first1=J. |title=Electrochemical glucose biosensors |journal=Chemical Reviews |volume=108 |issue=2 |pages=814–825 |doi=10.1021/cr068123a}}.</ref> The GOx is immobilized on the electrode surface or in a membrane placed close to the electrode. Precious metals such as platinum or gold are used in electrodes, as well as carbon nanotube electrodes, which e.g. are doped with boron.<ref>{{Cite journal |doi=10.1016/j.talanta.2008.04.023 |pmid=18656655 |year=2008 |last1=Chen |first1=X. |title=Amperometric glucose biosensor based on boron-doped carbon nanotubes modified electrode |journal=Talanta |volume=76 |issue=4 |pages=763–767 |last2=Chen |first2=J. |last3=Deng |first3=C. |last4=Xiao |first4=C. |last5=Yang |first5=Y. |last6=Nie |first6=Z. |last7=Yao |first7=S.}}</ref> Cu–CuO nanowires are also used as enzyme-free amperometric electrodes, reaching a detection limit of 50&nbsp;μmol/L.<ref>{{Cite journal |doi=10.1007/s00604-009-0260-1 |title=Enzyme-free amperometric sensing of glucose using Cu-CuO nanowire composites |journal=Microchimica Acta |volume=168 |issue=1–2 |pages=87–92 |year=2010 |last1=Wang |first1=Guangfeng |last2=Wei |first2=Yan |last3=Zhang |first3=Wei |last4=Zhang |first4=Xiaojun |last5=Fang |first5=Bin |last6=Wang |first6=Lun |s2cid=98567636 }}</ref> A particularly promising method is the so-called "enzyme wiring", where the electron flowing during the oxidation is transferred via a molecular wire directly from the enzyme to the electrode.<ref>{{Cite journal |doi=10.1021/ac00087a008 |pmid=8092486 |year=1994 |last1=Ohara |first1=T. J. |title="Wired" enzyme electrodes for amperometric determination of glucose or lactate in the presence of interfering substances |journal=Analytical Chemistry |volume=66 |issue=15 |pages=2451–2457 |last2=Rajagopalan |first2=R. |last3=Heller |first3=A.}}</ref>

====Other sensory methods====
There are a variety of other chemical sensors for measuring glucose.<ref name="Borisov">{{Cite journal |doi=10.1021/cr068105t |pmid=18229952 |year=2008 |last1=Borisov |first1=S. M. |title=Optical biosensors |journal=Chemical Reviews |volume=108 |issue=2 |pages=423–461 |last2=Wolfbeis |first2=O. S.}}</ref><ref>{{Cite journal |doi=10.1177/193229681100500507 |pmc=3208862 |pmid=22027299 |year=2011 |last1=Ferri |first1=S. |title=Review of glucose oxidases and glucose dehydrogenases: A bird's eye view of glucose sensing enzymes |journal=Journal of Diabetes Science and Technology |volume=5 |issue=5 |pages=1068–76 |last2=Kojima |first2=K. |last3=Sode |first3=K. }}</ref> Given the importance of glucose analysis in the life sciences, numerous optical probes have also been developed for saccharides based on the use of boronic acids,<ref>{{Cite journal |doi=10.1007/s00604-008-0947-8 |title=Boronic acid based probes for microdetermination of saccharides and glycosylated biomolecules |journal=Microchimica Acta |volume=162 |issue=1–2 |pages=1–34 |year=2008 |last1=Mader |first1=Heike S. |last2=Wolfbeis |first2=Otto S. |s2cid=96768832 }}</ref> which are particularly useful for intracellular sensory applications where other (optical) methods are not or only conditionally usable. In addition to the organic boronic acid derivatives, which often bind highly specifically to the 1,2-diol groups of sugars, there are also other probe concepts classified by functional mechanisms which use selective glucose-binding proteins (e.g. concanavalin A) as a receptor. Furthermore, methods were developed which indirectly detect the glucose concentration via the concentration of metabolized products, e.g. by the consumption of oxygen using fluorescence-optical sensors.<ref>{{Cite journal |doi=10.1016/S0956-5663(99)00073-1 |pmid=10826645 |title=Sol–gel based glucose biosensors employing optical oxygen transducers, and a method for compensating for variable oxygen background |journal=Biosensors and Bioelectronics |volume=15 |issue=1–2 |pages=69–76 |year=2000 |last1=Wolfbeis |first1=Otto S. |last2=Oehme |first2=Ines |last3=Papkovskaya |first3=Natalya |last4=Klimant |first4=Ingo}}</ref> Finally, there are enzyme-based concepts that use the intrinsic absorbance or fluorescence of (fluorescence-labeled) enzymes as reporters.<ref name="Borisov" />

====Copper iodometry====
Glucose can be quantified by copper iodometry.<ref name="Galant">{{Cite journal |doi=10.1016/j.foodchem.2015.04.071 |pmid=26041177 |year=2015 |last1=Galant |first1=A. L. |title=Glucose: Detection and analysis |journal=Food Chemistry |volume=188 |pages=149–160 |last2=Kaufman |first2=R. C. |last3=Wilson |first3=J. D.}}</ref>

===Chromatographic methods===
In particular, for the analysis of complex mixtures containing glucose, e.g. in honey, chromatographic methods such as [[high performance liquid chromatography]] and [[gas chromatography]]<ref name="Galant" /> are often used in combination with [[mass spectrometry]].<ref>{{cite journal | last1 = Sanz | first1 = M. L. | last2 = Sanz | first2 = J. | last3 = Martínez-Castro | first3 = I. | year = 2004| title = Gas chromatographic-mass spectrometric method for the qualitative and quantitative determination of disaccharides and trisaccharides in honey. | journal = [[Journal of Chromatography A]] | volume = 1059 | issue = 1–2| pages = 143–148 | pmid = 15628134 | doi = 10.1016/j.chroma.2004.09.095 }}</ref><ref name="mpg-210190">{{cite web|title=Glucose mass spectrum|periodical=Golm Metabolome Database|url=http://gmd.mpimp-golm.mpg.de/Spectrums/8dee81a1-8d98-4a73-b55d-9de42f10e190.aspx|access-date=4 June 2018|last=[[Max Planck Institute of Molecular Plant Physiology]] in Golm Database|date=19 July 2007|archive-url=https://web.archive.org/web/20180909000409/http://gmd.mpimp-golm.mpg.de/Spectrums/8dee81a1-8d98-4a73-b55d-9de42f10e190.aspx|archive-date=9 September 2018|url-status=live}}</ref> Taking into account the isotope ratios, it is also possible to reliably detect honey adulteration by added sugars with these methods.<ref>{{cite journal | last1 = Cabañero | first1 = A. I. | last2 = Recio | first2 = J. L. | last3 = Rupérez | first3 = M. | year = 2006| title = Liquid chromatography coupled to isotope ratio mass spectrometry: a new perspective on honey adulteration detection. | journal = [[J Agric Food Chem]] | volume = 54 | issue = 26| pages = 9719–9727 | pmid = 17177492 | doi = 10.1021/jf062067x | bibcode = 2006JAFC...54.9719C }}</ref> Derivatization using silylation reagents is commonly used.<ref>{{Cite journal |pmid=24054643|year=2013|last1=Becker|first1=M.|title=Ethoximation-silylation approach for mono- and disaccharide analysis and characterization of their identification parameters by GC/MS|journal=Talanta|volume=115|pages=642–51|last2=Liebner|first2=F.|last3=Rosenau|first3=T.|last4=Potthast|first4=A.|doi=10.1016/j.talanta.2013.05.052}}</ref> Also, the proportions of di- and trisaccharides can be quantified.

====In vivo analysis====
Glucose uptake in cells of organisms is measured with [[2-deoxy-D-glucose]] or [[fluorodeoxyglucose]].<ref name="Dwyer">Donard Dwyer: ''Glucose Metabolism in the Brain''. Academic Press, 2002, {{ISBN|978-0-123-66852-3}}, p.&nbsp;XIII.</ref> (<sup>18</sup>F)fluorodeoxyglucose is used as a tracer in [[positron emission tomography]] in oncology and neurology,<ref name="gdch">[[Gesellschaft Deutscher Chemiker]]: [http://www.gdch.de/strukturen/fg/nuklear/posi2.pdf wayback=20100331071121 ''Anlagen zum Positionspapier der Fachgruppe Nuklearchemie''] {{Webarchive|url=https://web.archive.org/web/20100331071121/http://www.gdch.de/strukturen/fg/nuklear/posi2.pdf |date=31 March 2010 }}, February 2000.</ref> where it is by far the most commonly used diagnostic agent.<ref>{{Cite journal |doi=10.1155/2014/214748 |pmc=4058687 |pmid=24991541|year=2014 |last1=Maschauer |first1=S. |title=Sweetening pharmaceutical radiochemistry by (18)f-fluoroglycosylation: A short review |journal=BioMed Research International |volume=2014 |pages=1–16 |last2=Prante |first2=O. |doi-access=free }}</ref>