Malodour classification with low-cost flexible electronics.

Understanding body malodour in a measurable manner is essential for developing personal care products. Body malodour is the result of bodily secretion of a highly complex mixture of volatile organic compounds. Current body malodour measurement methods are manual, time consuming and costly, requiring an expert panel of assessors to assign a malodour score to each human test subject. This article proposes a technology-based solution to automate this task by developing a custom-designed malodour score classification system comprising an electronic nose sensor array, a sensor readout interface and a machine learning hardware fabricated on low-cost flexible substrates. The proposed flexible integrated smart system is to augment the expert panel by acting like a panel assessor but could ultimately replace the panel to reduce the test and measurement costs. We demonstrate that it can classify malodour scores as good as or even better than half of the assessors on the expert panel.

Odorant binding proteins fromHermetia illucens: potential sensing elements for detecting volatile aldehydes involved in early stages of organic decomposition.

Organic decomposition processes, involving the breakdown of complex molecules such as carbohydrates, proteins and fats, release small chemicals known as volatile organic compounds (VOCs), smelly even at very low concentrations, but not all readily detectable by vertebrates. Many of these compounds are instead detected by insects, mostly by saprophytic species, for which long-range orientation towards organic decomposition matter is crucial. In the present work the detection of aldehydes, as an important measure of lipid oxidation, has been possible exploiting the molecular machinery underlying odour recognition inHermetia illucens(Diptera: Stratiomyidae). This voracious scavenger insect is of interest due to its outstanding capacity in bioconversion of organic waste, colonizing very diverse environments due to the ability of sensing a wide range of chemical compounds that influence the choice of substrates for ovideposition. A variety of soluble odorant binding proteins (OBPs) that may function as carriers of hydrophobic molecules from the air-water interface in the antenna of the insect to the receptors were identified, characterised and expressed. An OBP-based nanobiosensor prototype was realized using selected OBPs as sensing layers for the development of an array of quartz crystal microbalances (QCMs) for vapour phase detection of selected compounds at room temperature. QCMs coated with four recombinantH. illucensOBPs (HillOBPs) were exposed to a wide range of VOCs indicative of organic decomposition, showing a high sensitivity for the detection of three chemical compounds belonging to the class of aldehydes and one short-chain fatty acid. The possibility of using biomolecules capable of binding small ligands as reversible gas sensors has been confirmed, greatly expanding the state-of the-art in gas sensing technology.

Gravimetric biosensors.

Gravimetric transducers produce a signal based on a change in mass. These transducers can be used to construct gas sensors or biosensors using odorant binding proteins (OBPs) as recognition elements for small volatile organic compounds. The methods described in this chapter are based on the immobilization of the OBPs onto functionalized (activated) self-assembled monolayer (SAMs) on gold and on nanocrystalline diamond surfaces. Depending on the surface immobilization methods used to fabricate the biosensor, recombinant proteins can be engineered to express six histidine tags either on the N-terminal or C-terminal of the proteins and these can also be used to facilitate protein immobilization. These methods are used to produce functional sensors based on quartz crystal microbalances or surface acoustic wave devices and are also applicable to other types of gravimetric transducers.

Modification of an Anopheles gambiae odorant binding protein to create an array of chemical sensors for detection of drugs.

The binding pockets of odorant binding proteins from Anopheles gambiae (OBP1 and OBP47) were analysed using in silico modelling. The feasibility of creating mutant proteins to achieve a protein array capable of detecting drugs of abuse in solution or in vapour phase was investigated. OBP1 was found to be easily adapted and several mutant proteins were expressed and characterised. AgamOBP1_S82P was found to have high affinities to cannabinol, 3,4-methylenedioxy methamphetamine (MDMA/Ecstasy) and cocaine hydrochloride. When these proteins were immobilised on a quartz crystal microbalance, saturated cocaine hydrochloride vapour could be detected. The sensors were stable over a period of at least 10 months in air. The approach taken allows flexible design of new biosensors based on inherently stable protein scaffolds taking advantage of the tertiary structure of odorant binding proteins.

Effects of point mutations in the binding pocket of the mouse major urinary protein MUP20 on ligand affinity and specificity.

The mouse Major Urinary Proteins (MUPs) contain a conserved ß-barrel structure with a characteristic central hydrophobic pocket that binds a variety of volatile compounds. After release of urine, these molecules are slowly emitted in the environment where they play an important role in chemical communication. MUPs are highly polymorphic and conformationally stable. They may be of interest in the construction of biosensor arrays capable of detection of a broad range of analytes. In this work, 14 critical amino acids in the binding pocket involved in ligand interactions were identified in MUP20 using in silico techniques and 7 MUP20 mutants were synthesised and characterised to produce a set of proteins with diverse ligand binding profiles to structurally different ligands. A single amino acid substitution in the binding pocket can dramatically change the MUPs binding affinity and ligand specificity. These results have great potential for the design of new biosensor and gas-sensor recognition elements.

A study on volatile organic compounds emitted by in-vitro lung cancer cultured cells using gas sensor array and SPME-GCMS.

BACKGROUND: Volatile organic compounds (VOCs) emitted from exhaled breath from human bodies have been proven to be a useful source of information for early lung cancer diagnosis. To date, there are still arguable information on the production and origin of significant VOCs of cancer cells. Thus, this study aims to conduct in-vitro experiments involving related cell lines to verify the capability of VOCs in providing information of the cells. METHOD: The performances of e-nose technology with different statistical methods to determine the best classifier were conducted and discussed. The gas sensor study has been complemented using solid phase micro-extraction-gas chromatography mass spectrometry. For this purpose, the lung cancer cells (A549 and Calu-3) and control cell lines, breast cancer cell (MCF7) and non-cancerous lung cell (WI38VA13) were cultured in growth medium. RESULTS: This study successfully provided a list of possible volatile organic compounds that can be specific biomarkers for lung cancer, even at the 24th hour of cell growth. Also, the Linear Discriminant Analysis-based One versus All-Support Vector Machine classifier, is able to produce high performance in distinguishing lung cancer from breast cancer cells and normal lung cells. CONCLUSION: The findings in this work conclude that the specific VOC released from the cancer cells can act as the odour signature and potentially to be used as non-invasive screening of lung cancer using gas array sensor devices.

Development of a new generation of ammonia sensors on printed polymeric hotplates.

Conducting polyaniline-based chemiresistors on printed polymeric micro-hotplates were developed, showing sensitive and selective detection of ammonia vapor in air. The devices consist of a fully inkjet-printed silver heater and interdigitated electrodes on a polyethylene naphthalate substrate, separated by a thin dielectric film. The integrated heater allowed operation at elevated temperatures, enhancing the ammonia sensing performance. The printed sensor designs were optimized over two different generations, to improve the thermal performance through careful design of the shape and dimension of the heater element. A vapor-phase deposition polymerization technique was adapted to produce polyaniline sensing layers doped with poly(4-styrenesulfonic acid). The resulting sensor had better thermal stability and sensing performance when compared with conventional polyaniline-based sensors, and this was attributed to the polymeric dopant used in this study. Improved long-term stability of the sensors was achieved by electrodeposition of gold on the silver electrodes. Response to sub-parts-per-million concentrations of ammonia even under humid conditions was observed.

Structure and biotechnological applications of odorant-binding proteins.

Odorant-binding proteins (OBPs) are small soluble polypeptides found in sensory organs of vertebrates and insects as well as in secretory glands and are dedicated to detection and release of chemical stimuli. OBPs of vertebrates belong to the family of lipocalin proteins, while those of insects are folded into α-helical domains. Both types of architectures are extremely stable to temperature, organic solvents and proteolytic digestion. These characteristics make OBPs suitable elements for fabricating biosensors to be used in the environment, as well as for other biotechnological applications. The affinity of OBPs for small volatile organic compounds is in the micromolar range, and they have broad specificity to a range of ligands. For biotechnological applications, OBPs can be expressed in bacterial systems at low cost and are easily purified. The large amount of information available on their structures and affinities to different molecules should allow the design of specific mutants with desired characteristics and represent a solid base for tailoring OBPs for different applications.

Medical applications of odor-sensing devices.

Many diseases and intoxications are accompanied by characteristic odors, and their recognition can provide diagnostic clues, which in turn may aid in planning a therapy. Arrays of gas and odor sensors, made from different technologies, are finding their way into a variety of specialized applications. This article reviews some clinical applications where this technology can be applied to noninvasive monitoring of patients.