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Several studies investigated the development of a non-invasive and early diagnostic method for cancer. Recently, the volatile organic compounds (VOCs) exhaled from cancer patients have been shown to act as a potential biomarker for cancer. However, the gas profile of breath is highly variable and not conducive to identification of biomarkers accurately. Accordingly, we identified a cancer-specific VOC as a biomarker using an in vitro cancer system in order to exclude the variables from patient condition. VOCs were collected from the headspace gas of lung cancer cell line (SK-MES) and normal lung cell line (MRC-5), followed by analysis using solid-phase microextraction (SPME)-GC/MS. As a result, 2-ethyl-1-hexanol was detected from headspace gas of SK-MES and decided as a potential biomarker for lung cancer. By screening human olfactory receptor libraries to detect a lung cancer biomarker, human olfactory receptor 4D11P (hOR4D11P) was identified as a receptor specific for 2-ethyl-1-hexanol and expressed heterologously in HEK293 cells. Additionally, we generated nanovesicles containing hOR4D11P from HEK293 cells and confirmed the expression and functionality of hOR4D11P in nanovesicles. [ABSTRACT FROM AUTHOR]

It is known that a dog possesses much better sense of smell than a human. It has been reported that a dog has advantages (compared to a human) in the number of olfactory receptor (OR) genes, proteins and cells, and also nasal structure. However, a definitive reason for superior sensitivity of the canine olfactory system remains controversial. In this study, we compared sensitivity of human and canine olfactory receptors relative to the same condition. Human OR (hOR2W1) and canine OR (cfOR0312), previously identified to recognize hexanal, were inserted to the pcDNA3 vector. This vector was transfected to HEK293 cells. Hexanal-discriminating ability of ORs was confirmed using Fura-2 AM, a dye which illuminates when binding to calcium ions flowing into cells once olfactory signaling occurs. Consequently, cfOR0312 was more sensitive to hexanal than hOR2W1. Comparison of OR sensitivity would be one of the major factors in clarifying difference of sensitivity between human and canine olfactory systems. [ABSTRACT FROM AUTHOR]

Food intake is the primary method for obtaining energy and component materials in the human being. Humans evaluate the quality of food by combining various facets of information, such as an item of food's appearance, smell, taste, and texture in the mouth. Recently, bioelectronic noses and tongues have been reported that use human olfactory and taste receptors as primary recognition elements, and nanoelectronics as secondary signal transducers. Bioelectronic sensors that mimic human olfaction and gustation have sensitively and selectively detected odor and taste molecules from various food samples, and have been applied to food quality assessment. The portable and multiplexed bioelectronic nose and tongue are expected to be used as next-generation analytical tools for rapid on-site monitoring of food quality. In this review, we summarize recent progress in the bioelectronic nose and tongue using olfactory and taste receptors, and discuss the potential applications and future perspectives in the food industry. [ABSTRACT FROM AUTHOR]

Odors are perceived differently as a function of individual human experience, and communicating about odors between individuals is therefore very difficult. There is a need to classify and standardize odors, but appropriate tools have not yet been developed. A bioelectronic nose mimics human olfaction and detects target molecules with high sensitivity and selectivity. This new tool has great potential in many applications and is expected to accelerate odor classification and standardization. In particular, a multiplexed bioelectronic nose can provide complex odor information using pattern recognition techniques, and could even reproduce odors via an integrated olfactory display system. We expect that a bioelectronic nose will be a useful tool for odor standardization by providing codes for odors that enable us to communicate odor information. [ABSTRACT FROM AUTHOR]

Nerve agents are organophosphorus toxic chemicals that can inhibit acetylcholinesterase, leading to paralysis of the nervous system and death. Early detection of nerve agents is important for safety issues. Dimethyl methylphosphonate (DMMP) is widely used as a simulant of nerve agents, and many studies have been conducted using DMMP as a substitute for detecting nerve agents. Despite many studies on sensors for detecting DMMP, they have limitations in sensitivity and selectivity. To overcome these limitations, a nickel-decorated reduced graphene oxide (Ni-rGO) sensor with human olfactory receptor hOR2T7 nanodiscs was utilized to create a bioelectronic nose platform for DMMP gas detection. hOR2T7 was produced and reconstituted into nanodiscs for enhancing the sensor's stability, especially for detection in a gas phase. It could detect DMMP gas selectively and repeatedly at a concentration of 1 ppb. This sensitive and selective bioelectronic nose can be applied as a practical tool for the detection of gaseous chemical warfare agents in military and safety fields.

A multiplexed bioelectronic sensor was developed for the purpose of rapid, on-site, and simultaneous detection of various target molecules. Olfactory and taste receptors were produced in Escherichia coli , and the reconstituted receptors were immobilized onto a multi-channel type carbon nanotube field-effect transistor. This device mimicked the human olfactory/taste system and simultaneously measured the conductance changes with high sensitivity and selectivity following treatment with various odor and taste molecules commonly known to be indicators of food contamination. Various pattern recognition of odorants and tastants was available with a customized platform for the simultaneous measurement of electrical signals. The simple portable bioelectronic device was suitable for efficient monitoring of food freshness and is expected to be used as a rapid on-site sensing platform with various applications. [ABSTRACT FROM AUTHOR]

A bioelectronic nose for the real-time assessment of water quality was constructed with human olfactory receptor (hOR) and single-walled carbon nanotube field-effect transistor (swCNT-FET). Geosmin (GSM) and 2-methylisoborneol (MIB), mainly produced by bacteria, are representative odor compounds and also indicators of contamination in the water supply system. For the screening of hORs which respond to these compounds, we performed CRE-luciferase assays of the two odorants in heterologous cell system. Human OR51S1 for GSM and OR3A4 for MIB were selected, and nanovesicles expressing the hORs on surface were produced from HEK-293 cell. Carbon nanotube field-effect transistor was functionalized with the nanovesicles. The bioelectronic nose was able to selectively detect GSM and MIB at concentrations as low as a 10 ng L −1 . Furthermore, detection of these compounds from the real samples such as tap water, bottled water and river water was available without any pretreatment processes. [ABSTRACT FROM AUTHOR]

Olfactory receptors (ORs), belonging to the Gprotein coupled receptor (GPCR) family, are very difficult to be overexpressed, purified and reconstituted because of their hydrophobicity and complicated structure. These receptors bind to their specific ligands, thus their specificity is very useful for application as a bioelectronic nose. Furthermore, highly purified and well-reconstituted human olfactory receptor (hOR) can be used in various fields, such as in protein-interaction research, drug screening, and analysis of the hOR structure. In this study, human olfactory receptor, hOR2AG1, was produced with high purity and functionally reconstituted in detergent micelles. The hOR2AG1 was overexpressed in Escherichia coli ( E. coli) with glutathione S-transferase (GST) and 6xHis-tag as an inclusion body. The hOR2AG1 fusion protein was solubilized in buffer containing sodium dodecyl sulfate (SDS) and purified using Ni-NTA chromatography. The GST domain was removed using proteolytic cleavage before elution from the column. After purification, the hOR2AG1 was successfully reconstituted using nonionic detergents and methyl-ß-cyclodextrin. Finally highly purified and well-reconstituted hOR was obtained, and its biological characteristics were confirmed by using circular dichroism (CD) spectrum and tryptophan fluorescence assay. These results can be applied to develop protein-based sensing systems including a bioelectronic nose and to analyze the native hOR structure using solid-state NMR, X-ray crystallography, or neutron scattering. [ABSTRACT FROM AUTHOR]

Olfaction plays a critical role in several aspects of the human life. Odorants are detected by hundreds of odorant receptors (ORs) which belong to the superfamily of G protein-coupled receptors. These receptors are expressed in the olfactory sensory neurons of the nose. The information provided by the activation of different combinations of ORs in the nose is transmitted to the brain, leading to odorant perception and emotional and behavioral responses. There are ~400 intact human ORs, and to date only a small percentage of these receptors (~10%) have known agonists. The determination of the specificity of the human ORs will contribute to a better understanding of how odorants are discriminated by the olfactory system. In this work, we aimed to identify human specific ORs, that is, ORs that are present in humans but absent from other species, and their corresponding agonists. To do this, we first selected 22 OR gene sequences from the human genome with no counterparts in the mouse, rat or dog genomes. Then we used a heterologous expression system to screen a subset of these human ORs against a panel of odorants of biological relevance, including foodborne aroma volatiles. We found that different types of odorants are able to activate some of these previously uncharacterized human ORs. [ABSTRACT FROM AUTHOR]

Rapid and precise discrimination of various odorants is vital to fabricating enhanced sensing devices in the fields of disease diagnostics, food safety, and environmental monitoring. Here, we demonstrate an ultrasensitive and flexible field-effect transistor (FET) olfactory system, namely, a bioelectronic nose (B-nose), based on plasma-treated bilayer graphene conjugated with an olfactory receptor. The stable p- and n-type behaviors from modified bilayer graphene (MBLG) took place after controlled oxygen and ammonia plasma treatments. It was integrated with human olfactory receptors 2AG1 (hOR2AG1: OR), leading to the formation of the liquid-ion gated FET-type platform. ORs bind to the particular odorant amyl butyrate (AB), and their interactions are specific and selective. The B-noses behave as flexible and transparent sensing devices and can recognize a target odorant with single-carbon-atom resolution. The B-noses are ultrasensitive and highly selective toward AB. The minimum detection limit (MDL) is as low as 0.04 fM (10–15; signal-to-noise: 4.2), and the equilibrium constants of OR-oxygen plasma-treated graphene (OR-OG) and ammonia plasma-treated graphene (-NG) are ca. 3.44 × 1014 and 1.47 × 1014 M–1, respectively. Additionally, the B-noses have long-term stability and excellent mechanical bending durability in flexible systems. [ABSTRACT FROM AUTHOR]

Abstract: We developed a nanovesicle-based bioelectronic nose (NBN) that could recognize a specific odorant and mimic the receptor-mediated signal transmission of human olfactory systems. To build an NBN, we combined a single-walled carbon nanotube-based field effect transistor with cell-derived nanovesicles containing human olfactory receptors and calcium ion signal pathways. Importantly, the NBN took advantages of cell signal pathways for sensing signal amplification, enabling ∼100 times better sensitivity than that of previous bioelectronic noses based on only olfactory receptor protein and carbon nanotube transistors. The NBN sensors exhibited a human-like selectivity with single-carbon-atomic resolution and a high sensitivity of 1fM detection limit. Moreover, this sensor platform could mimic a receptor-meditated cellular signal transmission in live cells. This sensor platform can be utilized for the study of molecular recognition and biological processes occurring at cell membranes and also for various practical applications such as food screening and medical diagnostics. [Copyright &y& Elsevier]

Abstract: Sensing smell is a highly complex biological process, and characterizing and mimicking the interaction between the olfactory receptor (OR) protein and its ligands is extremely challenging. Herein, we report a highly sensitive and selective human nose-like nanobioelectronic nose (nbe-nose), which responds to gaseous odorants sensitively and selectively, has a signal specificity pattern similar to that in the cellular signal transduction pathway, and maintains an antagonistic behavior similar to the human nose. The human olfaction mechanism was mimicked by using carboxylated polypyrrole nanotubes (CPNTs) functionalized with human OR protein. The nbe-nose was able to detect gaseous odorants at a concentration as low as 0.02 parts-per-trillion (ppt), which was comparable to a highly trained, human expert’s nose. The nbe-nose can be used scientifically for smell mechanism studies. It can be also applied to various fields that rely on smell monitoring for industrial and public purposes. [Copyright &y& Elsevier]

Abstract: Single-walled carbon nanotubes (swCNTs) hold great promise for use as molecular wires because they exhibit high electrical conductivity and chemical stability. However, constructing swCNT-based transducer devices requires controlled strategies for assembling biomolecules on swCNTs. In this study, we proposed a chemically modified swCNT. The swCNT was functionalized with 1,5-diaminonaphthalene via π-stacking, for reliable attachment of the human olfactory receptor 2AG1 (hOR2AG1). The human olfactory receptor was then anchored. We investigated the use of this functionalized CNT in the fabrication of a highly sensitive and selective bioelectronic nose. For the bioelectronic nose, the swCNT-field effect transistor (FET) platform was composed of polyethylene glycol (PEG)-coated regions to prevent non-specific absorption and chemically modified swCNTs regions containing hOR2AG1, which can bind to the specific odorant. This approach allowed us to create well-defined micron-scale patterns of hOR2AG1 on the swCNTs. Our bioelectronic nose displayed ultrahigh sensitivity down to concentrations as low as 1fM due to the enhanced hOR2AG1–odorant interaction through the tight binding of hOR2AG1 on the chemically modified swCNTs. In addition, the approach described here may provide an alternative route for multiplexed detection of diverse odorants and to improve the sensitivity of sensor devices. [Copyright &y& Elsevier]

Ligands for only two human olfactory receptors are known. One of them, OR1D2, binds to Bourgeonal, a volatile chemical constituent of the fragrance of the mythical flower, Lily of the valley or Our Lady's tears, Convallaria majalis (also the national flower of Finland). OR1D2, OR1D4 and OR1D5 are three full-length olfactory receptors present in an olfactory locus in the human genome. These receptors are more than 80% identical in DNA sequences and have 108 base pair mismatches among them. Apparently, these mismatch positions show no striking pattern using computer pattern recognition tools. In an attempt to find a mathematical rule in those mismatches, we find that an L-system generated sequence can be inserted into the OR1D2 subfamily-specific star model and novel full-length olfactory receptors can be generated. This remarkable mathematical principle could be utilized for making new subfamily olfactory receptor members from any olfactory receptor subfamily. The aroma and electronic nose industry might utilize this rule in future. [ABSTRACT FROM AUTHOR]

Abstract: The human olfactory receptor OR 17–40 co-expressed with α-subunit of Golf protein in yeast was attempted as a bio recognition part of impedimetric biosensor. The receptor in its natural membrane environment was anchored to a gold-coated glass substrate modified with thiol-based multilayer. Step-by-step building-up of the OR 17–40 based biofilm was monitored using surface plasmon resonance technique. Stimulation of the OR 17–40 with its cognate odorant helional in phosphate-buffered saline was probed by means of electrochemical impedance spectroscopy under various conditions. Activation of OR 17–40 in the presence of GTP-γ-S at 4 °C was found to improve the sensitivity of the developed label-free biosensor, probably via the enhancement of the specific biochemical signal. [Copyright &y& Elsevier]

Abstract: The forced expiratory volume in the first second (FEV1.0)/the forced vital capacity (FVC) is an important index of a single forced expiration. Ectopic expression of the human olfactory receptor (OR) gene family in the lungs has suggested its potential involvement of respiratory physiology. We hypothesized that the individual variability of FEV1.0/FVC value may be attributed to the genetic variance of the OR gene family caused by the nonfunctioning SNPs (nSNPs). We conducted quantitative trait locus (QTL) analyses of population having the 7 OR gene nSNPs and FEV1.0/FVC values by ANOVA, in 2970 samples in the Yamagata Takahata cohort. We found significant association of one nSNP [rs10838851, OR, family 4, subfamily X, member 1 (OR4X1) gene, Tyr273Ter∗] with FEV1.0/FVC (%) (P =0.008). The FEV1.0/FVC value (%) of population having OR4X1 gene nSNP Ter∗/Ter∗, Ter∗/Tyr, and Tyr/Tyr were 78.9±0.2, 78.2±0.2, and 77.7±0.4, respectively. Haplotype-based analysis of the OR4X1 gene with FEV1.0/FVC values demonstrated that two exclusive haplotypes [Hap-1/Hap-2 (frequency 0.669/0.330): SNP1 (rs7106648)T/A-SNP2 (rs871249)G/A-SNP3 (rs713325)G/A-SNP4 (rs10838851)A (Ter∗)/T (Tyr)-SNP5 (rs4752923)G/A-SNP6 (rs960640)G/A] were significantly associated with FEV1.0/FVC values (global P =0.005). These results suggest that OR4X1 may be one of the genes that contribute to the individual variability of FEV1.0/FVC value in pulmonary function test. [Copyright &y& Elsevier]

This work shows the feasibility of an olfactory biosensor based on the immobilization of Saccharomyces cerevisiae yeast cells genetically modified to express the human olfactory receptor OR17-40 onto interdigitated microconductometric electrodes. This olfactory biosensor has been applied to the detection of its specific odorant (helional) with a high sensitivity (threshold 10−14 M). In contrast, no significant response was observed using a non-specific odorant (heptanal), which suggests a good selectivity. Thus, this work may represent a first step towards a new kind of bioelectronic noses based on whole yeast cells and allowing a real time monitoring of olfactory receptor activation. [ABSTRACT FROM AUTHOR]