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Various organisms, such as dogs and moths, can locate their prey and mates by sensing their smells. Following this manner, if an engineering device with the capability to detect a smell or gas source is realized, it can have a wide range of potential applications, such as searching for landmines, locating gas leaks, and rapid detection of fire. A previous study on the estimation of smell and gas-flow direction successfully detected the smell/gas-source direction in low-wind-velocity environments using a semiconductor gas sensor array. However, some problems are generally associated with the use of semiconductor gas sensors due to the use of heaters. This study aimed to detect the location of a smell/gas source using an integrated CMOS smell sensor array, which operates at room temperature without a heater. The experiment showed that under ideal conditions, the order of gas responses and concentration gradient of the gas enabled the estimation of the direction of the smell/gas-source location on one side of the sensor. [ABSTRACT FROM AUTHOR]

Among the five human senses, light, sound, and force perceived by the eye, ear, and skin, respectively are physical phenomena, and therefore can be easily measured and expressed as objective, univocal, and simple digital data with physical quantity. However, as taste and odor molecules perceived by the tongue and nose are chemical phenomena, it has been difficult to express them as objective and univocal digital data, since no reference chemicals can be defined. Therefore, while the recording, saving, transmitting to remote locations, and replaying of human visual, auditory, and tactile information as digital data in digital devices have been realized (this series of data flow is defined as DX (digital transformation) in this review), the DX of human taste and odor information is not yet in the realization stage. Particularly, since there are at least 400,000 types of odor molecules and an infinite number of complex odors that are mixtures of these molecules, it has been considered extremely difficult to realize "human olfactory DX" by converting all odors perceived by human olfaction into digital data. In this review, we discuss the current status and future prospects of the development of "human olfactory DX", which we believe can be realized by utilizing odor sensors that employ the olfactory receptors (ORs) that support human olfaction as sensing molecules (i.e., human OR sensor). [ABSTRACT FROM AUTHOR]

Expectations for the sensing of very small amounts of gases and odors are increasing in many fields such as medicine, healthcare, and mobility. In recent years, nanomaterials with various forms such as needle-like, beltlike, sheet-like, and dendrite-like have been developed. These nanomaterials have been used to detect very small amounts of gas with a semiconductor gas sensor. In addition, detection of various gases and odor molecules has been realized using these gas sensors. In particular, in the field of ceramics, which requires high-temperature firing at several hundred degrees Celsius, the realization of “cold crystallization”, which has been a longstanding issue, has had a great impact. Nanomaterials with high surface area, unique shape, metastable crystal facets, etc. have been developed with cold crystallization of ceramics. These nanomaterials have improved the low-concentration gas detection characteristics of gas sensors and odor sensors. In this review, I would like to introduce the fabrication of new SnO2 nanomaterials and the development of gas and odor sensors using the SnO2 nanomaterials. [ABSTRACT FROM AUTHOR]

Among the five human senses, light, sound, and force perceived by the eye, ear, and skin, respectively are physical phenomena, and therefore can be easily measured and expressed as objective, univocal, and simple digital data with physical quantity. However, as taste and odor molecules perceived by the tongue and nose are chemical phenomena, it has been difficult to express them as objective and univocal digital data, since no reference chemicals can be defined. Therefore, while the recording, saving, transmitting to remote locations, and replaying of human visual, auditory, and tactile information as digital data in digital devices have been realized (this series of data flow is defined as DX (digital transformation) in this review), the DX of human taste and odor information is not yet in the realization stage. Particularly, since there are at least 400,000 types of odor molecules and an infinite number of complex odors that are mixtures of these molecules, it has been considered extremely difficult to realize “human olfactory DX” by converting all odors perceived by human olfaction into digital data. In this review, we discuss the current status and future prospects of the development of “human olfactory DX”, which we believe can be realized by utilizing odor sensors that employ the olfactory receptors (ORs) that support human olfaction as sensing molecules (i.e., human OR sensor).

The deterioration or oxidation of the mineral oil in transformers poses the risk of short circuits. Convenient and effective methods are expected to be developed. Carbon-based sensor arrays were used in this study to identify the quality variations of mineral oil for oil-filled transformers by odors. The sensitive layers of the odor-sensing system consisted of different types of GC stationary phase materials and carbon black (CB) mixtures. We made a targeted selection of GC materials by utilizing the polarities to make a sensor array based on the distinct components of mineral oil such as alkanes and xylenes by gas chromatography mass spectrometry (GC/MS) analysis. The response characteristics of the sensitive layers were used to recognize the mineral oil odors by machine learning. With laboratory air as the carrier gas, the system could distinguish mineral oil that has been in use for over 20 years from new mineral oil with an accuracy of about 93.8%. The identification accuracy achieved was about 60% for three different concentrations of unused mineral oil and the oxidized mineral oil created by the transformer's leakage. When detecting the oxidized mineral oil with a concentration of more than 50%, the accuracy rate reached more than 80%. The odor-sensing system in this study will help inspect mineral oils in the transformer and make leakage judgments in a short time. [ABSTRACT FROM AUTHOR]

• Colorimetric sensor array (CSA) and chemometric method were combined. • IVSO, CARS and BOSS were used to improve the performance of prediction modeling. • CARS-PLS modeling was most robust for TVB-N proportion prediction in snakehead fillets. • TVB-N of snakehead fillets were effectively measured and quantified. Total volatile basic nitrogen content (TVB-N) is an important index of freshness for snakehead. This paper attempted the feasibility of determining TVB-N content level in snakehead fillets by a colorimetric sensor array (CSA) composed of twelve porphyrin materials and eight pH indicators. The nine feature variables in RGB, HSV and CIE L*a*b* color spaces were obtained by differentiating the images of the CSA before and after exposure to the headspace-gas of the samples. Competitive adaptive reweighted sampling combined with partial least squares regression (CARS-PLS) was used to build the relationship between the TVB-N content and the feature variables of CSA, and to select meaningful color-sensitive materials. The results showed that CARS-PLS had a correlation coefficient of 0.9325 in the prediction set and selected 13 informative color-sensitive materials. This study demonstrated that the CSA with CARS-PLS algorithm could be used successfully to quantify and monitor the TVB-N in snakehead fillets. [ABSTRACT FROM AUTHOR]

An odor sensing system with chemosensitive resistors was used to identify the gases generated from overheated cables to prevent fire. Three different electric cables for a distribution cabinet were used. The cables had an insulation layer made of polyvinyl chloride (PVC) or cross-linked polyethylene (XLPE). The heat resistance of the cables was tested by differential thermal and thermogravimetric analyses. The thermal decomposition products of the cables were investigated by gas chromatography-mass spectrometry (GC-MS). For the odor sensing system, two types of 16-channel array were used to detect the generated gases. One contains high-polarity GC stationary phase materials and the other contains GC stationary phase materials of high to low polarity. The system could distinguish among three cable samples at 270 °C with an accuracy of about 75% through both arrays trained with machine learning. Furthermore, the system could achieve a recall rate of 90% and a precision rate of 70% when the abnormal temperature was set above the cables’ allowable conductor temperature at 130 °C. The odor sensing system could effectively detect the abnormal heating of the cables before the occurrence of fire. Therefore, it is helpful for fire prediction and detection systems in factories and substations.

The technological advantages that biosensors have over conventional technical sensors for odor detection and the role they play in the biological transformation have not yet been comprehensively analyzed. However, this is necessary for assessing their suitability for specific fields of application as well as their improvement and development goals. An overview of biological basics of olfactory systems is given and different odor sensor technologies are described and classified in this paper. Specific market potentials of biosensors for odor detection are identified by applying a tailored methodology that enables the derivation and systematic comparison of both the performance profiles of biosensors as well as the requirement profiles for various application fields. Therefore, the fulfillment of defined requirements is evaluated for biosensors by means of 16 selected technical criteria in order to determine a specific performance profile. Further, a selection of application fields, namely healthcare, food industry, agriculture, cosmetics, safety applications, environmental monitoring for odor detection sensors is derived to compare the importance of the criteria for each of the fields, leading to market-specific requirement profiles. The analysis reveals that the requirement criteria considered to be the most important ones across all application fields are high specificity, high selectivity, high repeat accuracy, high resolution, high accuracy, and high sensitivity. All these criteria, except for the repeat accuracy, can potentially be better met by biosensors than by technical sensors, according to the results obtained. Therefore, biosensor technology in general has a high application potential for all the areas of application under consideration. Health and safety applications especially are considered to have high potential for biosensors due to their correspondence between requirement and performance profiles. Special attention is paid to new areas of application that require multi-sensing capability. Application scenarios for multi-sensing biosensors are therefore derived. Moreover, the role of biosensors within the biological transformation is discussed.

There has been so far few odor sensors with an array of the biosensor elements. However, an odor sensor constructed in this fashion is expected to have high performance in terms of the ability to discriminate between odorants. In this study, a parallel lock‐in measurement circuit was developed to acquire the fluorescent image of the cells even under an ambient light. Since that circuit can extract only the responses of the cells from the fluorescent image, its output represents a specific pattern corresponding to the odorant. Therefore, principal component analysis was applied to that output in order to confirm the availability of the odorant discrimination by using a fluorescent image. It was found that the output pattern from the developed circuit included information enough to discriminate between at least two types of odorants. [ABSTRACT FROM AUTHOR]

The technological advantages that biosensors have over conventional technical sensors for odor detection have not yet been comprehensively analyzed. However, this is necessary for assessing their suitability for specific fields of application as well as their improvement and development goals. In this paper specific market potentials of biosensors for odor detection are identified by applying a tailored methodology that enables the derivation and systematic comparison of both the performance profiles of biosensors as well as the requirement profiles for various application fields. Therefore, the fulfillment of defined requirements is evaluated for biosensors by means of 16 selected technical criteria in order to determine a specific performance profile. Further, a selection of application fields for odor detection sensors is derived to compare the importance of the criteria for each of the fields, leading to market-specific requirement profiles. The analysis reveals that the requirement criteria considered to be the most important ones across all application fields are high specificity, high selectivity, high repeat accuracy, high resolution, high accuracy, and high sensitivity. All these criteria, except for the repeat accuracy, can potentially be better met by biosensors than by technical sensors, according to the results obtained. Therefore, biosensor technology in general has a high application potential for all the areas of application under consideration. Health and safety applications especially are considered to have high potential for biosensors due to their correspondence between requirement and performance profiles.

In this short review, we describe our recent approaches and strategies for the development of quartz crystal microbalance (QCM)-based odor sensor systems for environmental and human health monitoring. QCM electrodes, which were modified with sensitive nanometerthick coatings via layer-by-layer (LbL) deposition, were used to develop a system for measuring significant environmental changes in indoor air. Identification of the origin of environmental changes was possible via the differential signal analysis of obtained data. The sensors showed different responses to humidity changes, hazardous gas (ammonia), or cigarette smoke exposure. In addition, QCM sensors with porous films comprising silica nanoparticles and poly(allylamine hydrochloride) (PAH) were fabricated via an electrostatic self-assembly method and they exhibited considerable sensitivity to relative humidity (RH). The infusion of poly(acrylic acid) (PAA) into the multilayer porous film enabled the construction of a highly sensitive and selective QCM sensor device for the detection of gaseous ammonia. Two types of QCM sensors, with and without PAA, enabled the simultaneous quantitative detection of humidity and ammonia. Preliminary tests were conducted to detect low concentrations of ammonia in human breath, which are of clinical relevance. The results obtained showed that the sensor can detect ammonia in human breath at pathological levels (greater than 3 ppm). [ABSTRACT FROM AUTHOR]

SUMMARY Odor sensing system with high sensitivity and selectivity is expected to be realized by using biological mechanisms such as olfactory receptor. We have already developed a cell-based odor sensing system which acquires odorant concentration as a fluorescent intensity change. In the measurement, however, an artifact is likely to happen due to lack of stable and reproducible methods for delivering odorants to biological cells. Therefore, we developed and evaluated the automated flow measurement system which can simultaneously control pump, solenoid valve, and camera. Our system realized automation of solution supply and fluorescent measurement. As a result, our system could reduce artifacts and repeatedly performed measurements with the same sensor cells. [ABSTRACT FROM AUTHOR]

Mimicking the biological olfaction, large odor-sensor arrays can be used to acquire a broad range of chemical information, with a potentially high degree of redundancy, to allow for enhanced control over the sensitivity and selectivity of artificial olfaction systems. The arrays should consist of the largest possible number of individual sensing elements while being miniaturized. Chemosensitive resistors are one of the sensing platforms that have a potential to satisfy these two conditions. In this work we test viability of fabricating a 16-element chemosensitive resistor array for detection and recognition of volatile organic compounds (VOCs). The sensors were fabricated using blends of carbon black and gas chromatography (GC) stationary-phase materials preselected based on their sorption properties. Blends of the selected GC materials with carbon black particles were subsequently coated over chemosensitive resistor devices and the resulting sensors/arrays evaluated in exposure experiments against vapors of pyrrole, benzenal, nonanal, and 2-phenethylamine at 150, 300, 450, and 900 ppb. Responses of the fabricated 16-element array were stable and differed for each individual odorant sample, proving the blends of GC materials with carbon black particles can be effectively used for fabrication of large odor-sensing arrays based on chemosensitive resistors. The obtained results suggest that the proposed sensing devices could be effective in discriminating odor/vapor samples at the sub-ppm level. [ABSTRACT FROM AUTHOR]

An odor-sensing system based on the insect olfactory receptor (OR) and fluorescent instrumentation has been developed. Cells expressing ORs were responsible for odor detection by monitoring the change in fluorescent light intensity emitted by the cells. Since fluorescent light from the cells is very weak, the measurement quality deteriorates if ambient light is present. A lockin measurement technique was incorporated to the system to overcome the problem of the ambient light together with the fluorescent image. The lock-in technique enables the detection of light synchronous with the modulated excitation light under the ambient light. This technique is useful for improving the signal-to-noise ratio. In this paper, sensitivity improvement by applying the lockin technique to fluorescent instrumentation for a cell-based odor sensor is discussed quantitatively. Experimental results show that the employment of the lock-in technique enhances the sensitivity by three orders of magnitude under the ambient light condition. [ABSTRACT FROM AUTHOR]

Versatile odor sensors that can discriminate among huge numbers of environmental odorants are desired in many fields, including robotics, environmental monitoring, and food production. However, odor sensors comparable to an animal's nose have not yet been developed. An animal's olfactory system recognizes odor clusters with specific molecular properties and uses this combinatorial information in odor discrimination. This suggests that measurement and clustering of odor molecular properties (e.g., polarity, size) using an artificial sensor is a promising approach to odor sensing. Here, adsorbents composed of composite materials with molecular recognition properties were developed for odor sensing. The selectivity of the sensor depends on the adsorbent materials, so specific polymeric materials with particular solubility parameters were chosen to adsorb odorants with various properties. The adsorption properties of the adsorbents could be modified by mixing adsorbent materials. Moreover, a novel molecularly imprinted filtering adsorbent (MIFA), composed of an adsorbent substrate covered with a molecularly imprinted polymer (MIP) layer, was developed to improve the odor molecular recognition ability. The combination of the adsorbent and MIP layer provided a higher specificity toward target molecules. The MIFA thus provides a useful technique for the design and control of adsorbents with adsorption properties specific to particular odor molecules. [ABSTRACT FROM AUTHOR]

Mimicking the biological olfaction, large odor-sensor arrays can be used to acquire a broad range of chemical information, with a potentially high degree of redundancy, to allow for enhanced control over the sensitivity and selectivity of artificial olfaction systems. The arrays should consist of the largest possible number of individual sensing elements while being miniaturized. Chemosensitive resistors are one of the sensing platforms that have a potential to satisfy these two conditions. In this work we test viability of fabricating a 16-element chemosensitive resistor array for detection and recognition of volatile organic compounds (VOCs). The sensors were fabricated using blends of carbon black and gas chromatography (GC) stationary-phase materials preselected based on their sorption properties. Blends of the selected GC materials with carbon black particles were subsequently coated over chemosensitive resistor devices and the resulting sensors/arrays evaluated in exposure experiments against vapors of pyrrole, benzenal, nonanal, and 2-phenethylamine at 150, 300, 450, and 900 ppb. Responses of the fabricated 16-element array were stable and differed for each individual odorant sample, proving the blends of GC materials with carbon black particles can be effectively used for fabrication of large odor-sensing arrays based on chemosensitive resistors. The obtained results suggest that the proposed sensing devices could be effective in discriminating odor/vapor samples at the sub-ppm level.

The detection of low-concentration gases and odors in fields such as healthcare, mobility, and indoor environment control is attracting tremendous attention. The development of high-sensitivity gas sensors capable of detecting low concentrations of gases and molecules is strongly desired. This review focuses on tin oxide nanomaterials, which are substances that are being actively researched as semiconductor-type gas sensors. In particular, the development of novel tin oxide nanomaterials over the last decade and their gas sensing applications are discussed. It is revealed that dimension and morphology affect the sensing performance. Tin oxide nanomaterials having nano-meter size which is similar to size of a depletion layer, and controlled microstructure such as a nanosheet structure shows high sensing performance. The dendritic structure in which 2D nanosheets are connected by crystal growth points the direction for future sensor development. Furthermore, the high gas adsorption performance and reactivity of the metastable crystal plane will be a guide for future sensor development. [ABSTRACT FROM AUTHOR]

Abstract: An odor sensor based on a fluorescent imaging system was developed to detect the sweat odor of human body. Volatile organic acid substances with low molecular weight were supposed to be one of the key contributors to the odor of a sweat sample collected from the human body. Quinine sulfate, a pH-dependent fluorescent compound that shows fluorescent enhancing in the presence of organic acids, was utilized to prepare an agarose-gel supported fluorescent film. The existence of organic acid components with high abundance in the collected sweat sample was confirmed by the analysis of SPME-GC/MS. Sequence images of the fluorescent film in the absence and presence of odors were recorded by a high-resolution CCD camera. The response of the sensor to typical organic acids in sweat odor, such as acetic acid, isovaleric acid, hexanoic acid and octanoic acid, was evaluated by the analysis of subtraction images as well as the real-time change of mean gray value (MGV). The odor of the sweat sample after incubation was successfully visualized, which indicates the application potential of the developed fluorescent imaging sensor in the detection of human body odor. [Copyright &y& Elsevier]

Abstract: The paper reports on development of a method for stabilization of coatings for QCM odor sensors that use liquid GC stationary phase materials. The liquid materials tend to be easily removed from the sensor''s surface when coated directly onto its surface. The proposed method employs chemisorbed lipopolymers and lipids to form a matrix into which the liquid GC materials are encapsulated. The fabrication method is relatively simple as the sensing films are formed in a sorption process from a single solution. The obtained experimental results show significantly enhanced stability of the fabricated sensing films. The obtained sensors reproducibly show high sensitivities to vapors of selected odorants with detection limits in sub-ppm range. They also showed a good capability to discriminate among the odorant samples. [Copyright &y& Elsevier]

Abstract: We review methodological approaches commonly employed for the determination of human-body-odor (BO) components. As a first step, we evaluate the common types of BO and the sampling and/or preconcentration strategies for them. We also emphasize the potential for odor components as a health-diagnosis tool. We critically evaluate gas chromatography-based detection methods in terms of their feasibility for human-BO monitoring. We also discuss recently developed on-line detection methods, especially sensor-based techniques to assess their potential in the determination of odorant components released by the human body. Finally, we highlight the limitations and the future prospects for investigation of human BO. [Copyright &y& Elsevier]

Abstract: The paper reports on development of a novel method for fabrication of highly sensitive spherical surface acoustic wave (Ball-SAW) devices for odor-sensing. The proposed method is based on functionalization of the Ball-SAW devices’ surface by means of chemisorption of self-assembled lipopolymers. Once functionalized, the devices’ surface can be further modified by means of physisorption of various lipid derivatives. More traditional techniques used for sensing-film deposition on Ball-SAW devices (such as AC electrospray) cause a considerable attenuation of the acoustic wave propagation after many circulations. The method proposed here is relatively simple and additional attenuation due to coating is negligible even if the amount of the coating is the same as that in the traditional technique. This makes for a significant enhancement of sensitivity to odorants as compared to the sensors coated with traditional techniques. [Copyright &y& Elsevier]

Abstract: An odor sensing system using a quartz crystal microbalance (QCM) sensor array and pattern recognition technique has been for years a main research topic in our group. For the general field of artificial olfaction using acoustic-wave based sensors such as QCMs it is vital to search for novel sensing materials. Here we present recent results of our ongoing study on application of pegylated lipids as coatings for QCM odor-sensors. The method presented herein is based on self-assembling of lipids and lipid-derivatives on the QCM surfaces. The disulphide-terminated lipids and lipopolymers are co-chemisorbed onto gold electrodes of QCM sensors by simple immersion in ethanolic solutions. This creates porous supports onto which additional layers of lipopolymers are physisorbed. The method allows for fabrication of lipopolymeric QCM odor-sensors with enhanced sensitivity to odorants, capable of very good discrimination among odorant samples—according to the functional group of an odorant. [Copyright &y& Elsevier]

Abstract: We report application of the PEGylated lipids (PEG lipopolymers) containing disulphide as supports for sensing films for quartz crystal microbalance (QCM) odor sensors. The materials are binding covalently to the surface of gold QCM sensor electrode creating self-assembled cushion. Additional amounts of lipid or lipid-derived materials can be physisorbed on that chemisorbed coating. Both processes do not require much labor and can be performed with minimum instruments in a simple process. The sensors fabricated with the chemisorbed supports are more sensitive to the tested odorants than their non-supported counterparts. Enhanced sensitivity is derived from higher fluidity of the supported films in comparison to the non-supported ones. Discrimination capability among odorants is also better for the sensors with chemisorbed supports than for the non-supported ones—there are no overlaps between the sample groups and the samples are clustered closely within the groups. Overall, the studied supported sensors introduce interesting properties that can be utilized in the odor sensing systems using QCM sensors. [Copyright &y& Elsevier]

Abstract: We report on improved ultrasonic atomizer method of depositing the sensing films on quartz crystal microbalance (QCM) sensors. The main objectives of the present work were minimizing the sensor-to-sensor response variation, improving the sensing film stability, and reducing amount of materials used during coating (reducing time of coating). In order to achieve the goals, we have redesigned and refabricated large parts of the atomizer system reported previously. The main principle of the operation—deposition of the fine mist generated by the ultrasonic device remained unchanged. The largest modifications encompass introduction of the new, sealed deposition chamber, considerable reduction of the flow resistance, and control over the flow rates of the mist and air streams in the system. The paper reports the new configuration of the ultrasonic atomizer method, optimization of the atomizer system performance (deposition parameters) and the results of improved quality of sensors fabricated using the new system. [Copyright &y& Elsevier]

Abstract: Lipids play an outstanding role in biological chemoreception schemes. The odorant–lipid interactions can be used as a mean of detecting the odorant molecules. A sensible way to exploit the interaction is coating the quartz crystal microbalance (QCM) sensors with natural or synthetic lipids or lipid-derived materials. Interesting candidates for such coatings are reported in the present paper—the synthetic lipids grafted with poly(ethylene glycol) (pegylated lipids, PEG lipopolymers). Two such materials grafted with PEG chains 2000 and 5000 were used for coating the QCMs. The obtained lipopolymer sensors were compared with pure lipid, pure polymer and lipid–polymer blend sensors. The results revealed very good discrimination power of the fabricated lipopolymer sensors for the range of odorants used in the study. The sensors have high sensor-to-sensor reproducibility and characteristics distinctly different from those for the remaining sensors used. [Copyright &y& Elsevier]

Abstract: Alcohol concentration in the expiration of a subjective person after drinking was examined. Beer, Japanese sake, red wine and shochu were adopted as the alcoholic subjects. The concentration grade was indicated using three metal oxide odor sensors. It became obvious that the alcoholic component in the expiration could remain over 3h after drinking. Japanese elderly people mostly prefer beer and sake according to a questionnaire survey. In this study, the sensor output characteristic as a function of passage time after drinking sake was investigated and the suitable amount could be indicated by a proposed technique. This means an amount of alcohol from which the subject feels refreshment of mind and body. The sensor outputs after 1 and 2h of drinking were adopted in the technique. In the questionnaire, it became obvious that 61% of aged men habitually drunk and 18% of females drunk. Women also preferred wine, plum liquor and shochu cocktails. This system was developed to survey the aged life style and identify whether they moderately drunk or not. [Copyright &y& Elsevier]

Abstract: Despite high significance of the sense of smell, the technique of recording and reproducing the olfactory modality was hardly investigated. The odor recorder developed by our group enables electronic recording of the odors and their reproduction at any time and at properly equipped place. The odor recording technique is expected to be useful in many fields such as virtual environments and e-commerce. To realize the future application of the odor recorder, the range of flavors to be handled by the instrument has to be significantly expanded. However, the expansion has to meet the constraint of reasonable number of odor components. One way to achieve that is using the approximation technique with significant reduction of the flavor components. The alternative way could be blending the complex mixtures of odorants treated as single components. In the present study, we focused on investigating both approaches. In the first part of experiment, we successfully recorded the typical orange flavor, approximating the smell with only 3 of 14 components. Subsequently performed human sensory tests (triangle test) confirmed similarity of reproduced flavor and the target one. In the second part of the experiment, three binary mixtures of essential oils extracted from citrus fruits were successfully recorded using the odor recorder. Results of both parts of the study allowed further expansion of the applicable range of flavors for odor recorder. [Copyright &y& Elsevier]

The Taguchi experimental design method was applied for the systematic and effective investigation of the optimal fabrication conditions of an odorous gas sensor, which would be affected by various parameters, such as a main sensing material, the materials and amounts of additives, as well as several fabrication conditions. From the results of eight experimental runs, for the evaluation of seven factors and two levels, having the equivalent effects of 128 experimental runs, the following results are derived. Most of the experimental conditions in this study showed a good sensitivity to H2S at 7.84 ppm, indicating good sensor performance could be expected at even lower H2S concentrations. As for the additives, PdCl2 and Pt mainly contributed to increases in the sensitivity of the sensor, but the amount of the additives made no significant difference to the sensor performance. In addition, a sintering temperature of 500 °C and mixing with distilled water for 10 min was appeared preferable from the viewpoint of sensor response time. The relationship between the sensor performance and the formation of surface crystals was verified with SEM analysis. As a consequence of the optimal fabrication conditions, the final sensor response time for the sensor was shortened to 20.06 s. [Copyright &y& Elsevier]

A novel odor sensing system which imitates the process of reception of odorants in biological olfactory system had been developed, utilizing surface polarity controlling method as a transducer of the sensor. In biological system, odorants are received by a large number of receptors, which recognize not whole structures but partial structures of molecules. The present sensor responded partial structures of odorants and adsorption interaction of the partial structures were controlled by the surface polarity of the electrode. Sensor output signals were analyzed on the stand point of partial structures of odorants. As a result, the responses to alcohols, aromatic compounds and aromatic alcohols as odorants could be discriminated by similar molecular structures, with principal component analysis (PCA). In addition, regression models of the response to partial structures of odorants were developed by multiple regression analysis, and odor qualities of aromatic alcohols could be evaluated quantitatively by partial structures of odor molecules. [Copyright &y& Elsevier]

The odor recorder has been developed using the odor sensing system based on the active sensing method to electronically record odors and reproduce them anytime and anywhere. The recorder developed in this paper has capability of recording the target odor, the mixture of five odor components, using the odor sensor array composed of quartz crystal microbalance sensors. The difference between the sensor response patterns of the recipe and target odors was minimized so that the recipe of the five components for the target odor was determined. In this paper, the method of selecting the most appropriate sensors to record odors was investigated based on the condition number of the sensor array sensitivity matrix. Moreover, the method of determining the parameters of the odor-recording algorithm was studied. As a result, several apple flavors composed of the five components were successfully recorded. Furthermore, the typical apple flavor composed of nine components was approximated using the mixture of the five components. The approximation result by the sensing system was successfully verified by the human sensory test. [Copyright &y& Elsevier]

An odor sensing system with chemosensitive resistors was used to identify the gases generated from overheated cables to prevent fire. Three different electric cables for a distribution cabinet were used. The cables had an insulation layer made of polyvinyl chloride (PVC) or cross-linked polyethylene (XLPE). The heat resistance of the cables was tested by differential thermal and thermogravimetric analyses. The thermal decomposition products of the cables were investigated by gas chromatography-mass spectrometry (GC-MS). For the odor sensing system, two types of 16-channel array were used to detect the generated gases. One contains high-polarity GC stationary phase materials and the other contains GC stationary phase materials of high to low polarity. The system could distinguish among three cable samples at 270 °C with an accuracy of about 75% through both arrays trained with machine learning. Furthermore, the system could achieve a recall rate of 90% and a precision rate of 70% when the abnormal temperature was set above the cables' allowable conductor temperature at 130 °C. The odor sensing system could effectively detect the abnormal heating of the cables before the occurrence of fire. Therefore, it is helpful for fire prediction and detection systems in factories and substations. [ABSTRACT FROM AUTHOR]

The technological advantages that biosensors have over conventional technical sensors for odor detection and the role they play in the biological transformation have not yet been comprehensively analyzed. However, this is necessary for assessing their suitability for specific fields of application as well as their improvement and development goals. An overview of biological basics of olfactory systems is given and different odor sensor technologies are described and classified in this paper. Specific market potentials of biosensors for odor detection are identified by applying a tailored methodology that enables the derivation and systematic comparison of both the performance profiles of biosensors as well as the requirement profiles for various application fields. Therefore, the fulfillment of defined requirements is evaluated for biosensors by means of 16 selected technical criteria in order to determine a specific performance profile. Further, a selection of application fields, namely healthcare, food industry, agriculture, cosmetics, safety applications, environmental monitoring for odor detection sensors is derived to compare the importance of the criteria for each of the fields, leading to market-specific requirement profiles. The analysis reveals that the requirement criteria considered to be the most important ones across all application fields are high specificity, high selectivity, high repeat accuracy, high resolution, high accuracy, and high sensitivity. All these criteria, except for the repeat accuracy, can potentially be better met by biosensors than by technical sensors, according to the results obtained. Therefore, biosensor technology in general has a high application potential for all the areas of application under consideration. Health and safety applications especially are considered to have high potential for biosensors due to their correspondence between requirement and performance profiles. Special attention is paid to new areas of application that require multi-sensing capability. Application scenarios for multi-sensing biosensors are therefore derived. Moreover, the role of biosensors within the biological transformation is discussed. [ABSTRACT FROM AUTHOR]

Versatile odor sensors that can discriminate among huge numbers of environmental odorants are desired in many fields, including robotics, environmental monitoring, and food production. However, odor sensors comparable to an animal's nose have not yet been developed. An animal's olfactory system recognizes odor clusters with specific molecular properties and uses this combinatorial information in odor discrimination. This suggests that measurement and clustering of odor molecular properties (e.g., polarity, size) using an artificial sensor is a promising approach to odor sensing. Here, adsorbents composed of composite materials with molecular recognition properties were developed for odor sensing. The selectivity of the sensor depends on the adsorbent materials, so specific polymeric materials with particular solubility parameters were chosen to adsorb odorants with various properties. The adsorption properties of the adsorbents could be modified by mixing adsorbent materials. Moreover, a novel molecularly imprinted filtering adsorbent (MIFA), composed of an adsorbent substrate covered with a molecularly imprinted polymer (MIP) layer, was developed to improve the odor molecular recognition ability. The combination of the adsorbent and MIP layer provided a higher specificity toward target molecules. The MIFA thus provides a useful technique for the design and control of adsorbents with adsorption properties specific to particular odor molecules., Competing Interests: The authors declare no conflict of interest.

Abstract: This paper studies the response characteristics of an odor sensor based on organic thin-film transistors (OTFTs) obtained from spin-coated poly-3-hexylthiophene (P3HT) on a thermally grown SiO2/Si wafer. The response characteristics of the odor sensor based on OTFTs are measured for odor gases generated from liquid fumes of 2-mercaptoethanol and 3-methylindole, such as are typically emitted by pig slurry in ambient air conditions. The experiments show that the response characteristics of the OTFT, when exposed to the 2-mercaptoethanol and 3-methylindole gases, result in a threshold voltage shift, a change in drain current, and a change in mobility with the gate bias. [Copyright &y& Elsevier]

To provide a platform to enable the study of simulated olfactory circuitry in context, we have integrated a simulated neural olfactorimotor system with a virtual world which simulates both computational fluid dynamics as well as a robotic agent capable of exploring the simulated plumes. A number of the elements which we developed for this purpose have not, to our knowledge, been previously assembled into an integrated system, including: control of a simulated agent by a neural olfactorimotor system; continuous interaction between the simulated robot and the virtual plume; the inclusion of multiple distinct odorant plumes and background odor; the systematic use of artificial evolution driven by olfactorimotor performance (e.g., time to locate a plume source) to specify parameter values; the incorporation of the realities of an imperfect physical robot using a hybrid model where a physical robot encounters a simulated plume. We close by describing ongoing work toward engineering a high dimensional, reversible, low power electronic olfactory sensor which will allow olfactorimotor neural circuitry evolved in the virtual world to control an autonomous olfactory robot in the physical world. The platform described here is intended to better test theories of olfactory circuit function, as well as provide robust odor source localization in realistic environments.