{"id":173160,"date":"2015-02-28T13:51:31","date_gmt":"2015-02-28T16:51:31","guid":{"rendered":"http:\/\/revistapesquisa.fapesp.br\/?p=173160"},"modified":"2015-03-30T14:03:37","modified_gmt":"2015-03-30T17:03:37","slug":"identification-by-smell","status":"publish","type":"post","link":"https:\/\/revistapesquisa.fapesp.br\/en\/identification-by-smell\/","title":{"rendered":"Identification by smell"},"content":{"rendered":"
\"Set

Eduardo Cesar<\/span>Set of gas sensors used to analyze vapors from volatile substancesEduardo Cesar<\/span><\/p><\/div>\n

from\u00a0Ag\u00eancia FAPESP<\/p>\n

<\/em>Researchers at the University of S\u00e3o Paulo\u2019s Chemistry Institute (IQ-USP) in Brazil have built \u201celectronic noses\u201d capable of identifying and classifying different types of wood and plastic by odor as well as detecting early-stage deterioration of oranges due to fungal contamination.\u00a0 Some of the devices were developed through the FAPESP-funded project \u201cNew conjugated polymers for solar cells and electronic noses.\u201d\u00a0 The technology is very simple and inexpensive and has several applications,\u201d say Jonas Gruber, a professor at IQ-USP and principal investigator for the project.\u00a0 Each \u201ce-nose\u201d consists of an array of gas sensors that change the electrical conductivity of some of the materials that they are made of (including conductive polymer, a type of plastic) as they interact with vapors from volatile substances such as amines, alcohols, ketones and aromatic compounds.
\n<\/em><\/p>\n

Variations in the array\u2019s conductance generate a specific electrical signal that is converted into a digital signal. This signal is read by a computer program, which, in a matter of seconds, identifies the type of volatile substance in contact with the device.\u00a0 \u201cThe e-nose responds differently according to the nature of the gas that comes into contact with the polymeric materials in the sensors,\u201d Gruber explains. One feat in particular permitted the development of these e-noses. Gruber and his group at IQ-USP synthesized and characterized new conductive polymers derived from two specific classes of polymer: poly-p-phenylenevinylene (PPV) and poly-p-xylylene (PPX), which were then used these to build sensors.\u00a0 \u201cWe were the first to use PPV in gas sensors,\u201d Gruber says. \u201cThe advantages are low production cost, low power consumption, and the ease with which the characteristics of the devices can be changed by introducing structural modifications into the polymer chains.\u201d<\/p>\n

The sensor construction technique used by the researchers consists of depositing a conductive polymer film with a thickness of a few hundred nanometers (billionths of a meter) on a board the size of a cell phone chip with two interdigitated metal electrodes (interlocked, but with minute gaps between them) so that the film connects the two materials.\u00a0 When the sensor is exposed to vapor from a volatile substance, the film\u2019s electrical resistance changes. \u201cEach sensor costs one Brazilian Real, and we use between four and seven sensors per e-nose on average,\u201d Gruber says.<\/p>\n

\"Equipment

EDUARDO CESAR<\/span>Equipment differentiates species of wood after loggingEDUARDO CESAR<\/span><\/p><\/div>\n

One of the devices was developed to identify and classify different species of wood. The researchers expect it to be used by environmental police to combat illegal logging of endangered tree species in Brazil\u2019s tropical forests.\u00a0 Protected species such as mahogany (Swietenia macrophylla<\/em>) are often hard to distinguish from species that can be legally logged and marketed, such as Spanish cedar (Cedrela odorata<\/em>).\u00a0 Both belong to the same family and are so similar that mahogany is often marketed as Spanish cedar Gruber explains.<\/p>\n

\u201cYou can distinguish between mahogany and Spanish cedar when you look at them in the forest, but once logged, they can only be distinguished by histological analysis [of the plant tissues] performed in the lab by a botanist,\u201d Gruber says.\u00a0 E-noses facilitate the identification of these and other species, such as Brazilian walnut (Ocotea porosa<\/em>) and Ocotea catharinensis<\/em> (local common name: canela-preta<\/em>). All they need is a small shaving from the trunk, which releases volatile compounds. The sensor array identifies the species in under a minute.\u00a0 \u201cBecause Spanish cedar and mahogany are different species and belong to different genera, e-noses can distinguish them with 100% accuracy,\u201d Gruber says. \u201cIn the case of walnut and canela-preta<\/em> it\u2019s a little harder because they belong to the same genus. Even so, identification by e-nose is correct 95% of the time.\u201d<\/p>\n

\"Prototype

Eduardo Cesar<\/span>Prototype of the e-nose at the USP laboratoryEduardo Cesar<\/span><\/p><\/div>\n

Aged cacha\u00e7a
\n<\/strong>The e-nose for wood identification aroused the interest of researchers at the Cane Spirit Chemistry Development Laboratory (LDQA), part of the University of S\u00e3o Paulo\u2019s S\u00e3o Carlos Chemistry Institute. They wanted a way to distinguish cacha\u00e7a aged in oak casks from cacha\u00e7a aged in barrels composed of other wood species that are considered inferior. According to Gruber, consumers prefer the flavor and odor of cacha\u00e7a aged in oak casks, so it sells for a higher price. Because it is imported from Canada, however, import restrictions often apply. Native species increasingly used to age cacha\u00e7a include cherry (Hymenaea courbaril<\/em>), rosewood (Jacaranda mimosifolia<\/em>), jequitib\u00e1 (Cariniana estrellensis<\/em>) and walnut (Ocotea porosa<\/em>). According to Gruber, the producer may claim that oak has been used.<\/p>\n

\u201cSome distillers sell cacha\u00e7a labeled as aged in cherry for less than oak-aged spirit, but the opposite is also true: you find cacha\u00e7a aged in barrels made from native wood but with oak on the label and selling for R$200 a bottle,\u201d Gruber says.\u00a0 To try to protect consumers from this kind of false advertising, the researchers adapted IQ-USP\u2019s e-nose for the analysis of cacha\u00e7a samples. \u201cThe device is able to \u2018sniff\u2019 a cacha\u00e7a and identify the wood species used,\u201d Gruber says.<\/p>\n

This particular e-nose was developed during the post-doctoral project of Alexandre Ataide da Silva, entitled \u201cDistinguishing hydroalcoholic wood extracts and monitoring their stages of aging using gas sensors, gas chromatography (GC-MS) and multivariate analysis.\u201d<\/p>\n

\"Oranges

L\u00e9o Ramos<\/span>Oranges contaminated by fungi have a different odorL\u00e9o Ramos<\/span><\/p><\/div>\n

Plastic identification
\n<\/strong>Researchers at IQ-USP have also developed a device to identify plastics for recycling.\u00a0 According to Gruber, different types of plastic, such as PVC, polyethylene and polypropylene, cannot be mixed when recycled because they contain incompatible resins.\u00a0 One of the techniques used to identify and classify plastics is infrared spectroscopic analysis of samples dissolved in appropriate solvents. However, infrared spectroscopy requires a laboratory staffed by professionals qualified to operate an infrared spectrometer.<\/p>\n

The e-nose developed by Gruber\u2019s research group identifies plastics from the gas emitted in combustion.\u00a0 The researchers built a small combustion chamber to hold a sample of approximately 300 milligrams for incineration.\u00a0 The e-nose \u201csniffs\u201d the fumes emitted during combustion and identifies the type of plastic from the volatile compounds that the plastic releases.\u00a0 \u201cPolyethylene produces carbon dioxide and water during combustion, whereas a polyamide like nylon, for example, produces nitrogen oxides as well as carbon dioxide and water. The e-nose perceives those differences\u201d Gruber explains.<\/p>\n

The researchers also developed an e-nose for early detection of contamination of oranges (after being harvested) by Penicillium digitatum<\/em>.\u00a0 This fungus, together with Elsinoe australis<\/em> and Guignardia citricarpa<\/em>, causes severe economic losses in countries that are major citrus producers, such as Brazil, Gruber says. The e-nose can detect contamination by the fungus while oranges are in silo storage.\u00a0 \u201cThe device detects contamination as soon as day two and, in a matter of seconds, identifies infection of the oranges by the fungus based on the volatile metabolites that it releases.\u201d<\/p>\n

According to Gruber, some of the e-noses developed by his group are protected by patents. The idea is for interested firms to license the technology to produce and sell the devices.\u00a0 \u201cWe aim to produce low-cost e-noses. Some of the commercially available devices cost as much as $20,000,\u201d Gruber says. One of the reasons for the high price, he explains, is that these devices have 20-30 sensors and are not designed for specific applications.\u00a0 \u201cWe develop e-noses for specific applications so we can reduce the number of sensors that they contain and greatly reduce production costs.\u201d<\/p>\n

Projects<\/strong>
\n1.<\/strong> New conjugated polymers for solar cells and electronic noses (No 2011\/51249-3<\/a>); Grant Mechanism<\/strong>: Regular Research Award: Principal Investigator<\/strong>: Jonas Gruber (USP); Investment<\/strong>: R$80,782.65 US$27,507.50 (FAPESP).
\n2.<\/strong> Distinguishing hydroalcoholic wood extracts and monitoring their stages of aging using gas sensors, gas chromatography (GC-MS) and multivariate analysis (No 2012\/15539-0<\/a>); Grant Mechanism<\/strong>: Scholarships in Brazil \u2013 Doctoral degree (Alexandre Ata\u00edde da Silva); Principal Investigator<\/strong>: Douglas Wagner Franco (USP); Investment<\/strong>: R$160,441.00 (FAPESP).<\/p>\n

Scientific articles<\/em>
\nESTEVES, C. H. A. et al<\/em>. New composite porphyrin-conductive polymer gas sensors for application in electronic noses. Sensors and Actuators B: Chemical<\/a>. V. 193, p. 136-41. March 2014.
\nGRUBER, J. et al<\/em>. A conductive polymer based electronic nose for early detection of penicillium digitatum\u00a0<\/em>in post-harvest oranges<\/a>. Materials Science and Engineering<\/strong>:C.<\/strong> V. 33, No. 5, p. 2766\u201369. July 2013.<\/p>\n

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