Bioelectronic nose with high sensitivity and selectivity using chemically functionalized carbon nanotube combined with human olfactory receptor

Artificial Olfactory Biohybrid System: An Evolving Sense of Smell

The olfactory system can detect and recognize tens of thousands of volatile organic compounds (VOCs) at low concentrations in complex environments. Bioelectronic nose (B-EN), which mimics olfactory systems, is becoming an emerging sensing technology for identifying VOCs with sensitivity and specificity. B-ENs integrate electronic sensors with bioreceptors and pattern recognition technologies to enable medical diagnosis, public security, environmental monitoring, and food safety. However, there is currently no commercially available B-EN on the market. Apart from the high selectivity and sensitivity necessary for volatile organic compound analysis, commercial B-ENs must overcome issues impacting sensor operation and other problems associated with odor localization. The emergence of nanotechnology has provided a novel research concept for addressing these problems. In this work, the structure and operational mechanisms of biomimetic olfactory systems are discussed, with an emphasis on the development and immobilization of materials. Various biosensor applications and current developments are reviewed. Challenges and opportunities for fulfilling the potential of artificial olfactory biohybrid systems in fundamental and practical research are investigated in greater depth.

Advances in the Production of Olfactory Receptors for Industrial Use

In biological olfactory systems, olfactory receptors (ORs) can recognize and discriminate between thousands of volatile organic compounds with very high sensitivity and specificity. The superior properties of ORs have led to the development of OR-based biosensors that have shown promising potential in many applications over the past two decades. In particular, newly designed technologies in gene synthesis, protein expression, solubilization, purification, and membrane mimetics for membrane proteins have greatly opened up the previously inaccessible industrial potential of ORs. In this review, gene design, expression and solubilization strategies, and purification and reconstitution methods available for modern industrial applications are examined, with a focus on ORs. The limitations of current OR production technology are also estimated, and future directions for further progress are suggested.

Bioelectrical Nose Platform Using Odorant-Binding Protein as a Molecular Transporter Mimicking Human Mucosa for Direct Gas Sensing

Recently, various bioelectronic nose devices based on human receptors were developed for mimicking a human olfactory system. However, such bioelectronic nose devices could operate in an aqueous solution, and it was often very difficult to detect insoluble gas odorants. Here, we report a portable bioelectronic nose platform utilizing a receptor protein-based bioelectronic nose device as a sensor and odorant-binding protein (OBP) as a transporter for insoluble gas molecules in a solution, mimicking the functionality of human mucosa. Our bioelectronic nose platform based on I7 receptor exhibited dose-dependent responses to octanal gas in real time. Furthermore, the bioelectronic platforms with OBP exhibited the sensor sensitivity improved by ∼100% compared with those without OBP. We also demonstrated the detection of odorant gas from real orange juice and found that the electrical responses of the devices with OBP were much larger than those without OBP. Since our bioelectronic nose platform allows us to directly detect gas-phase odorant molecules including a rather insoluble species, it could be a powerful tool for versatile applications and basic research based on a bioelectronic nose.

Progress in the Development of Detection Strategies Based on Olfactory and Gustatory Biomimetic Biosensors

The biomimetic olfactory and gustatory biosensing devices have broad applications in many fields, such as industry, security, and biomedicine. The development of these biosensors was inspired by the organization of biological olfactory and gustatory systems. In this review, we summarized the most recent advances in the development of detection strategies for chemical sensing based on olfactory and gustatory biomimetic biosensors. First, sensing mechanisms and principles of olfaction and gustation are briefly introduced. Then, different biomimetic sensing detection strategies are outlined based on different sensing devices functionalized with various molecular and cellular components originating from natural olfactory and gustatory systems. Thereafter, various biomimetic olfactory and gustatory biosensors are introduced in detail by classifying and summarizing the detection strategies based on different sensing devices. Finally, the future directions and challenges of biomimetic biosensing development are proposed and discussed.

Carbon-Related Materials: Graphene and Carbon Nanotubes in Semiconductor Applications and Design

As the scaling technology in the silicon-based semiconductor industry is approaching physical limits, it is necessary to search for proper materials to be utilized as alternatives for nanoscale devices and technologies. On the other hand, carbon-related nanomaterials have attracted so much attention from a vast variety of research and industry groups due to the outstanding electrical, optical, mechanical and thermal characteristics. Such materials have been used in a variety of devices in microelectronics. In particular, graphene and carbon nanotubes are extraordinarily favorable substances in the literature. Hence, investigation of carbon-related nanomaterials and nanostructures in different ranges of applications in science, technology and engineering is mandatory. This paper reviews the basics, advantages, drawbacks and investigates the recent progress and advances of such materials in micro and nanoelectronics, optoelectronics and biotechnology.

Programmable self-assembly of M13 bacteriophage for micro-color pattern with a tunable colorization

Over the last decade, the M13 bacteriophage has been used widely in various applications, such as sensors, bio-templating, and solar cells. The M13 colorimetric sensor was developed to detect toxic gases to protect the environment, human health, and national security. Recent developments in phage-based colorimetric sensor technologies have focused on improving the sensing characteristics, such as the sensitivity and selectivity on a large scale. On the other hand, few studies have examined precisely controllable micro-patterning techniques in phage-based self-assembly. This paper developed a color patterning technique through self-assembly of the M13 bacteriophages. The phage was self-assembled into a nanostructure through precise temperature control at the meniscus interface. Furthermore, barcode color patterns could be fabricated using self-assembled M13 bacteriophage on micrometer scale areas by manipulating the grooves on the SiO₂ surface. The color patterns exhibited color tunability based on the phage nano-bundles reactivity. Overall, the proposed color patterning technique is expected to be useful for preparing new color sensors and security patterns.

Experiment designs have been developed for tunable colorization film by temperature control during self-assembly processing based on the M13 bacteriophage. The micro-color pattern was fabricated and demonstrated for humidity detection.

Graphene Bioelectronic Nose for the Detection of Odorants with Human Olfactory Receptor 2AG1

A real-time sensor for the detection of amyl butyrate (AB) utilising human olfactory receptor 2AG1 (OR2AG1), a G-protein coupled receptor (GPCR) consisting of seven transmembrane domains, immobilized onto a graphene resistor is demonstrated. Using CVD graphene as the sensor platform, allows greater potential for more sensitive detection than similar sensors based on carbon nanotubes, gold or graphene oxide platforms. A specific graphene resistor sensor was fabricated and modified via non-covalent π–π stacking of 1,5 diaminonaphthalene (DAN) onto the graphene channel, and subsequent anchoring of the OR2AG1 receptor to the DAN molecule using glutaraldehyde coupling. Binding between the target odorant, amyl butyrate, and the OR2AG1 receptor protein generated a change in resistance of the graphene resistor sensor. The functionalized graphene resistor sensors exhibited a linear sensor response between 0.1–500 pM and high selectively towards amyl butyrate, with a sensitivity as low as 500 fM, whilst control measurements using non-specific esters, produced a negligible sensor response. The approach described here provides an alternative sensing platform that can be used in bioelectronic nose applications.

Wearable sensors for continuous oral cavity and dietary monitoring toward personalized healthcare and digital medicine

Oral monitoring plays an essential role in preventing and diagnosing systemic diseases through saliva in the mouth. Dietary monitoring is also crucial to reduce the likelihood of chronic diseases such as hypertension and diabetes by analyzing food types, amounts and diet patterns. Therefore, the oral cavity and dietary monitoring are vital for accurate personalized healthcare management that can improve healthcare. To perform continuous oral cavity and dietary monitoring in real-time, a wearable sensing system capable of continuous analysis is necessary. In this review, we classify chemical and physical biosensing methods and summarize recent progress in wearable sensor development for oral cavity and dietary monitoring for personalized healthcare and digital medicine. We also discuss future perspectives and the potential of wearable sensors to provide robust data for food-intake monitoring and the saliva analysis of super-aged/aging societies, non-face-to-face social life, and global pandemic disease issues. We believe that this review will result in a paradigm shift toward personalized healthcare and digital medicine using wearable sensors through the analysis of massively parallel healthcare data.

Market Perspectives and Future Fields of Application of Odor Detection Biosensors within the Biological Transformation-A Systematic Analysis

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.

Carbon Nanomaterials for Biomedical Application

The use of carbon-based nanomaterials (CNs) with outstanding properties has been rising in many scientific and industrial application fields. These CNs represent a tunable alternative for applications with biomolecules, which allow interactions in either covalent or noncovalent way. Diverse carbon-derived nanomaterial family exhibits unique features and has been widely exploited in various biomedical applications, including biosensing, diagnosis, cancer therapy, drug delivery, and tissue engineering. In this chapter, we aim to present an overview of CNs with a particular interest in intrinsic structural, electronic, and chemical properties. In particular, the detailed properties and features of CNs and its derivatives, including carbon nanotube (CNT), graphene, graphene oxide (GO), and reduced GO (rGO) are summarized. The interesting biomedical applications are also reviewed in order to offer an overview of the possible fields for scientific and industrial applications of CNs.

Bio-Inspired Strategies for Improving the Selectivity and Sensitivity of Artificial Noses: A Review

Artificial noses are broad-spectrum multisensors dedicated to the detection of volatile organic compounds (VOCs). Despite great recent progress, they still suffer from a lack of sensitivity and selectivity. We will review, in a systemic way, the biomimetic strategies for improving these performance criteria, including the design of sensing materials, their immobilization on the sensing surface, the sampling of VOCs, the choice of a transduction method, and the data processing. This reflection could help address new applications in domains where high-performance artificial noses are required such as public security and safety, environment, industry, or healthcare.

A 3D-Printed Hybrid Nasal Cartilage with Functional Electronic Olfaction

Advances in biomanufacturing techniques have opened the doors to recapitulate human sensory organs such as the nose and ear in vitro with adequate levels of functionality. Such advancements have enabled simultaneous targeting of two challenges in engineered sensory organs, especially the nose: i) mechanically robust reconstruction of the nasal cartilage with high precision and ii) replication of the nose functionality: odor perception. Hybrid nasal organs can be equipped with remarkable capabilities such as augmented olfactory perception. Herein, a proof-of-concept for an odor-perceptive nose-like hybrid, which is composed of a mechanically robust cartilage-like construct and a biocompatible biosensing platform, is proposed. Specifically, 3D cartilage-like tissue constructs are created by multi-material 3D bioprinting using mechanically tunable chondrocyte-laden bioinks. In addition, by optimizing the composition of stiff and soft bioinks in macro-scale printed constructs, the competence of this system in providing improved viability and recapitulation of chondrocyte cell behavior in mechanically robust 3D constructs is demonstrated. Furthermore, the engineered cartilage-like tissue construct is integrated with an electrochemical biosensing system to bring functional olfactory sensations toward multiple specific airway disease biomarkers, explosives, and toxins under biocompatible conditions. Proposed hybrid constructs can lay the groundwork for functional bionic interfaces and humanoid cyborgs.

Peptide hormone sensors using human hormone receptor-carrying nanovesicles and graphene FETs

Hormones within very low levels regulate and control the activity of specific cells and organs of the human body. Hormone imbalance can cause many diseases. Therefore, hormone detection tools have been developed, particularly over the last decade. Peptide hormones have a short half-life, so it is important to detect them within a short time. In this study, we report two types of peptide hormone sensors using human hormone receptor-carrying nanovesicles and graphene field-effect transistors (FETs). Parathyroid hormone (PTH) and glucagon (GCG) are peptide hormones present in human blood that act as ligands to G protein-coupled receptors (GPCRs). In this paper, the parathyroid hormone receptor (PTHR) and the glucagon receptor (GCGR) were expressed in human embryonic kidney-293 (HEK-293) cells, and were constructed as nanovesicles carrying the respective receptors. They were then immobilized onto graphene-based FETs. The two hormone sensors developed were able to detect each target hormone with high sensitivity (ca. 100 fM of PTH and 1 pM of GCG). Also, the sensors accurately recognized target hormones among different types of peptide hormones. In the development of hormone detection tools, this approach, using human hormone receptor-carrying nanovesicles and graphene FETs, offers the possibility of detecting very low concentrations of hormones in real-time.

Biosensing with Insect Odorant Receptor Nanodiscs and Carbon Nanotube Field-Effect Transistors

Insect odorant receptors have been reconstituted into lipid nanodiscs and tethered to carbon nanotube field-effect transistors to function as a biosensor. Here, four different insect odorant receptors (ORs) from Drosophila melanogaster (DmelOR10a, DmelOR22a, DmelOR35a, and DmelOR71a) were expressed in Sf9 cells, purified, and reconstituted into lipid nanodiscs. We have demonstrated that each of these ORs produce a selective and highly sensitive electrical response to their respective positive ligands, methyl salicylate, methyl hexanoate, trans-2-hexen-1-al, and 4-ethylguaiacol, with limits of detection in the low femtomolar range. No detection was observed for each OR against control ligands, and empty nanodiscs showed no specific sensor signal for any of the odorant molecules. Our results are the first evidence that insect ORs can be integrated into lipid nanodiscs and used as primary sensing elements for bioelectronic nose technologies.

[Medical diagnosis by breath analysis: odor sensors]

An odor sensor is a device for detecting target odors within a mixture, used in many fields including medical diagnosis. Electronic noses are networks of olfactory sensors, consisting of a surface whose properties are modified in the presence of odors, coupled with a measurement system. Their olfactory signature is analyzed in comparison with databases. Such portable devices can monitor body odors, e.g. in the breath, so as to reliably diagnose various pathologies at an early stage and non-invasively. It is tempting to use the naturally optimized molecular recognition of odorants and intrinsic sensitivity of the animal olfactory system to detect and discriminate minute amounts of odorants. New bioelectronic hybrid devices or "bioelectronic noses" can be designed by replacing the artificial sensory elements of e-noses by proteins naturally binding odorants, particularly olfactory receptors. As in the animal olfactory system, the detection and discrimination of odorants require a network of olfactory receptors. Prototypes of such miniaturized bioelectronic noses yield promising results.

Carbon Nanotube Chemical Sensors

Carbon nanotubes (CNTs) promise to advance a number of real-world technologies. Of these applications, they are particularly attractive for uses in chemical sensors for environmental and health monitoring. However, chemical sensors based on CNTs are often lacking in selectivity, and the elucidation of their sensing mechanisms remains challenging. This review is a comprehensive description of the parameters that give rise to the sensing capabilities of CNT-based sensors and the application of CNT-based devices in chemical sensing. This review begins with the discussion of the sensing mechanisms in CNT-based devices, the chemical methods of CNT functionalization, architectures of sensors, performance parameters, and theoretical models used to describe CNT sensors. It then discusses the expansive applications of CNT-based sensors to multiple areas including environmental monitoring, food and agriculture applications, biological sensors, and national security. The discussion of each analyte focuses on the strategies used to impart selectivity and the molecular interactions between the selector and the analyte. Finally, the review concludes with a brief outlook over future developments in the field of chemical sensors and their prospects for commercialization.

Multifunctional self-assembled monolayers via microcontact printing and degas-driven flow guided patterning

Soft lithography-based patterning techniques have been developed to investigate biological and chemical phenomena. Until now, micropatterning with various materials required multiple procedural steps such as repeating layer-by-layer patterning, aligning of stamps, and incubating printed inks. Herein, we describe a facile micropatterning method for producing chemically well-defined surface architectures by combining microcontact (µCP) and microfluidic vacuum-assisted degas-driven flow guided patterning (DFGP) with a poly(dimethylsiloxane) (PDMS) stamp. To demonstrate our concept, we fabricated a bi-composite micropatterned surface with different functional molecular inks such as fluorescein isothiocyanate labelled bovine serum albumin (FITC-BSA) and polyethylene glycol (PEG)-silane for a biomolecule array, and 3-aminopropyltriethoxysilane (APTES) and PEG-silane pattern for a self-assembled colloid gold nanoparticle monolayer. With a certain composition of molecular inks for the patterning, bi-composite surface patterns could be produced by this µCP-DFGP approach without any supplementary process. This patterning approach can be used in microfabrication and highly applicable to biomolecules and nanoparticles that spread as a monolayer.

Human-like smelling of a rose scent using an olfactory receptor nanodisc-based bioelectronic nose

We report a strategy for the human-like smelling of a rose scent utilizing olfactory receptor nanodisc (ND)-based bioelectronic nose devices. In this strategy, a floating electrode (FE)-based carbon nanotube (CNT) field effect transistor (FET) was functionalized with human olfactory receptor 1A2 (hOR1A2)-embedded NDs (hOR1A2NDs). The hOR1A2NDs responded to rose scent molecules specifically, which were monitored electrically using the underlying CNT-FET. This strategy allowed us to quantitatively assess the contents of geraniol and citronellol, the main components of a rose scent, as low as 1 fM and 10 fM, respectively. In addition, it enabled us to selectively discriminate a specific rose odorant from other odorants. Significantly, we also demonstrated that the responses of hOR1A2NDs to a rose scent could be strongly enhanced by enhancer materials like a human nose. Furthermore, the method provided a means to quantitatively evaluate rose scent components in real samples such as rose oil. Since our method allows one to quantitatively evaluate general rose scent ingredients just like a human nose, it could be a powerful strategy for versatile basic research and various applications such as fragrance development.

Progress in the development of olfactory-based bioelectronic chemosensors

Artificial chemosensory devices have a wide range of applications in industry, security, and medicine. The development of these devices has been inspired by the speed, sensitivity, and selectivity by which the olfactory system in animals can probe the chemical nature of the environment. In this review, we examine how molecular and cellular components of natural olfactory systems have been incorporated into artificial chemosensors, or bioelectronic sensors. We focus on the biological material that has been combined with signal transduction systems to develop artificial chemosensory devices. The strengths and limitations of different biological chemosensory material at the heart of these devices, as well as the reported overall effectiveness of the different bioelectronic sensor designs, is examined. This review also discusses future directions and challenges for continuing to advance development of bioelectronic sensors.

An overview of an artificial nose system

The present review describes recent advances in the development of an artificial nose system based on olfactory receptors and various sensing platforms. The kind of artificial nose, the production of olfactory receptors, the sensor platform for signal conversion and the application of the artificial nose system based on olfactory receptors and various sensing platforms are presented. The associated transduction modes are also discussed. The paper presents a review of the latest achievements and a critical evaluation of the state of the art in the field of artificial nose systems.

Application of Electronic Nose Systems on Animal-Source Food

Electronic nose, which is designed to perceive artificially the odour-active molecules in a sample headspace, has seen an increased use in the food industry as a rapid and reliable tool for quality assessment, classification, and authentication of several food items. The use of chemometrics and pattern recognition methods, together with gas sensors, emerged to be a very powerful analytical approach. In this chapter, an overview of the recent achievements in the field of electronic nose applications on animal-source food is given. Moreover, the authors deal with the recent research trends to overcome the actual sensor shortcomings, including sensor fusion techniques and their applications to evaluate animal-source foods and novel electronic nose systems.

The bioelectronic nose and tongue using olfactory and taste receptors: Analytical tools for food quality and safety assessment

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.

Diverse Applications of Nanomedicine

The design and use of materials in the nanoscale size range for addressing medical and health-related issues continues to receive increasing interest. Research in nanomedicine spans a multitude of areas, including drug delivery, vaccine development, antibacterial, diagnosis and imaging tools, wearable devices, implants, high-throughput screening platforms, etc. using biological, nonbiological, biomimetic, or hybrid materials. Many of these developments are starting to be translated into viable clinical products. Here, we provide an overview of recent developments in nanomedicine and highlight the current challenges and upcoming opportunities for the field and translation to the clinic.

Nanoscale hybrid systems based on carbon nanotubes for biological sensing and control

This paper provides a concise review on the recent development of nanoscale hybrid systems based on carbon nanotubes (CNTs) for biological sensing and control. CNT-based hybrid systems have been intensively studied for versatile applications of biological interfaces such as sensing, cell therapy and tissue regeneration. Recent advances in nanobiotechnology not only enable the fabrication of highly sensitive biosensors at nanoscale but also allow the applications in the controls of cell growth and differentiation. This review describes the fabrication methods of such CNT-based hybrid systems and their applications in biosensing and cell controls.

Molecular cloning, expression profile, odorant affinity, and stability of two odorant-binding proteins in Macrocentrus cingulum Brischke (Hymenoptera: Braconidae)

The polyembryonic endoparasitoid wasp Macrocentrus cingulum Brischke (Hymenoptera: Braconidae) is deployed successfully as a biocontrol agent for corn pest insects from the Lepidopteran genus Ostrinia in Europe and throughout Asia, including Japan, Korea, and China. The odorants are recognized, bound, and solubilized by odorant-binding protein (OBP) in the initial biochemical recognition steps in olfaction that transport them across the sensillum lymph to initiate behavioral response. In the present study, we examine the odorant-binding effects on thermal stability of McinOBP2, McinOBP3, and their mutant form that lacks the third disulfide bonds. Real-time PCR experiments indicate that these two are expressed mainly in adult antennae, with expression levels differing by sex. Odorant-binding affinities of aldehydes, terpenoids, and aliphatic alcohols were measured with circular dichroism spectroscopy based on changes in the thermal stability of the proteins upon their affinities to odorants. The obtained results reveal higher affinity of trans-caryophelle, farnesene, and cis-3-Hexen-1-ol exhibits to both wild and mutant McinOBP2 and McinOBP3. Although conformational flexibility of the mutants and shape of binding cavity make differences in odorant affinity between the wild-type and mutant, it suggested that lacking the third disulfide bond in mutant proteins may have chance to incorrect folded structures that reduced the affinity to these odorants. In addition, CD spectra clearly indicate proteins enriched with α-helical content.

Bioelectronic Nose: An Emerging Tool for Odor Standardization

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.

Current-voltage characteristics of seven-helix proteins from a cubic array of amino acids

The electrical properties of a set of seven-helix transmembrane proteins, whose space arrangement [three-dimensional (3D) structure] is known, are investigated by using regular arrays of the amino acids. These structures, specifically cubes, have topological features similar to those shown by the chosen proteins. The theoretical results show a good agreement between the predicted current-voltage characteristics obtained from a cubic array and those obtained from a detailed 3D structure. The agreement is confirmed by available experiments on bacteriorhodopsin. Furthermore, all the analyzed proteins are found to share the same critical behavior of the voltage-dependent conductance and of its variance. In particular, the cubic arrangement evidences a short plateau of the excess conductance and its variance at high voltages. The results of the present investigation show the possibility to predict the I-V characteristics of a multiple-protein sample even in the absence of detailed knowledge of the proteins' 3D structure.

Dissipation enhanced vibrational sensing in an olfactory molecular switch

Motivated by a proposed olfactory mechanism based on a vibrationally activated molecular switch, we study electron transport within a donor-acceptor pair that is coupled to a vibrational mode and embedded in a surrounding environment. We derive a polaron master equation with which we study the dynamics of both the electronic and vibrational degrees of freedom beyond previously employed semiclassical (Marcus-Jortner) rate analyses. We show (i) that in the absence of explicit dissipation of the vibrational mode, the semiclassical approach is generally unable to capture the dynamics predicted by our master equation due to both its assumption of one-way (exponential) electron transfer from donor to acceptor and its neglect of the spectral details of the environment; (ii) that by additionally allowing strong dissipation to act on the odorant vibrational mode, we can recover exponential electron transfer, though typically at a rate that differs from that given by the Marcus-Jortner expression; (iii) that the ability of the molecular switch to discriminate between the presence and absence of the odorant, and its sensitivity to the odorant vibrational frequency, is enhanced significantly in this strong dissipation regime, when compared to the case without mode dissipation; and (iv) that details of the environment absent from previous Marcus-Jortner analyses can also dramatically alter the sensitivity of the molecular switch, in particular, allowing its frequency resolution to be improved. Our results thus demonstrate the constructive role dissipation can play in facilitating sensitive and selective operation in molecular switch devices, as well as the inadequacy of semiclassical rate equations in analysing such behaviour over a wide range of parameters.

The possibility of inventing new technologies in the detection of cancer by applying elements of the canine olfactory apparatus

In order to find better tools in the diagnosis of cancer in an earlier and more precise manner, researchers have explored the use of volatile organic compound (VOCs) as a way to detect this disease. Interestingly, the canine olfactory apparatus was observed to detect cancer in two anecdotal reports. After the description of these events, researchers began to study this phenomenon in a structured way in order to assess the ability of canines in detecting cancer-related VOCs. Due to the fact that some of these studies have shown that the canine olfactory apparatus is highly proficient in the detection of cancer-related VOCs, in this article we assess the possibility of constructing a bioelectronic-nose, based on canine olfactory receptors (ORs), for the purpose of diagnosing cancer in a more sensitive, specific, and cost effective manner than what is available nowadays. Furthermore, in order to prove the feasibility and the need of the proposed apparatus, we searched for the following type of articles: all of the studies that have examined, to our knowledge, the ability of dogs in detecting cancer; articles that assess the dog olfactory receptor (OR) gene repertoire, since a central part of the proposed bioelectronic nose is being able to recognize the odorant that emanates from the cancerous lesion, and for that purpose is necessary to express the canine ORs in heterologous cells; examples of articles that depict different devices that have been built for the purpose of detecting cancer-related VOCs, so as to assess if the construction of the proposed apparatus is needed; and articles that describe examples of already constructed bioelectronic noses, in order to demonstrate the existence of a technical precedent and thus the plausibility of the proposed device.

Bioelectronic nose combined with a microfluidic system for the detection of gaseous trimethylamine

A bioelectronic nose based on a novel microfluidic system (μBN) was fabricated to detect gaseous trimethylamine (TMA) in real-time. Single-walled carbon nanotube-field effect transistors (SWNT-FETs) were functionalized with olfactory receptor-derived peptides (ORPs) that can recognize the TMA molecules. The ORP-coated SWNT-FETs were assembled with a microfluidic channel and were sealed with top and bottom frames. This simple process was used to complete the μBNs, and a well-defined condition was achieved to detect the gaseous molecules. The μBNs allowed us to detect gaseous TMA molecules down to 10 parts per trillion (ppt) in real-time and showed high selectivity when distinguishing gaseous TMA from other gaseous odorants. The sensor was used to determine the quality of seafood (oysters), and spoiled seafood and other types of spoiled foods were also successfully discriminated without any pretreatment processes. These results indicate that portable-scale platforms can be manufactured by using μBNs and can be applicable for real-time on-site gas analysis.

Ligands binding and molecular simulation: the potential investigation of a biosensor based on an insect odorant binding protein

Based on mimicking biological olfaction, biosensors have been applied for the detection of various ligands in complex environment, which could represent one of the most promising research fields. In this study, the basic characters of one insect odorant binding protein (OBP) as a biosensor were explored. To explore the molecular recognition process, the tertiary structure of the protein was modeled and the protein-ligand interactions with 1,536,550 chemicals were investigated by the molecular docking. The availability of large amount of recombinant SlitOBP1 overcame the difficulty to obtain biological sensing material. After obtained the purified recombinant protein, the result of fluorescence binding assays proved the candidate protein has good affinities with the majority of the tested chemicals. With the aid of simulation docking, the key conserved amino acids within the binding site were identified and then mutated to alanine. After mutation, the protein-ligand binding characteristics were recorded, and the competitive binding assays were carried out to provide experimental verification. The detailed information on its structure and affinities investigated in this study could allow the design of specific mutants with desired characteristics, which provides a solid base for tailoring OBP for biosensor and provides a role model for screening the other elements in olfactory system for different applications.

Bioelectronic tongue using heterodimeric human taste receptor for the discrimination of sweeteners with human-like performance

The sense of taste helps humans to obtain information and form a picture of the world by recognizing chemicals in their environments. Over the past decade, large advances have been made in understanding the mechanisms of taste detection and mimicking its capability using artificial sensor devices. However, the detection capability of previous artificial taste sensors has been far inferior to that of animal tongues, in terms of its sensitivity and selectivity. Herein, we developed a bioelectronic tongue using heterodimeric human sweet taste receptors for the detection and discrimination of sweeteners with human-like performance, where single-walled carbon nanotube field-effect transistors were functionalized with nanovesicles containing human sweet taste receptors and used to detect the binding of sweeteners to the taste receptors. The receptors are heterodimeric G-protein-coupled receptors (GPCRs) composed of human taste receptor type 1 member 2 (hTAS1R2) and human taste receptor type 1 member 3 (hTAS1R3), which have multiple binding sites and allow a human tongue-like broad selectivity for the detection of sweeteners. This nanovesicle-based bioelectronic tongue can be a powerful tool for the detection of sweeteners as an alternative to labor-intensive and time-consuming cell-based assays and the sensory evaluation panels used in the food and beverage industry. Furthermore, this study also allows the artificial sensor to exam the functional activity of dimeric GPCRs.

Nature's chemical signatures in human olfaction: a foodborne perspective for future biotechnology

The biocatalytic production of flavor naturals that determine chemosensory percepts of foods and beverages is an ever challenging target for academic and industrial research. Advances in chemical trace analysis and post-genomic progress at the chemistry-biology interface revealed odor qualities of nature's chemosensory entities to be defined by odorant-induced olfactory receptor activity patterns. Beyond traditional views, this review and meta-analysis now shows characteristic ratios of only about 3 to 40 genuine key odorants for each food, from a group of about 230 out of circa 10 000 food volatiles. This suggests the foodborn stimulus space has co-evolved with, and roughly match our circa 400 olfactory receptors as best natural agonists. This perspective gives insight into nature's chemical signatures of smell, provides the chemical odor codes of more than 220 food samples, and beyond addresses industrial implications for producing recombinants that fully reconstruct the natural odor signatures for use in flavors and fragrances, fully immersive interactive virtual environments, or humanoid bioelectronic noses.

Insights into structural features determining odorant affinities to honey bee odorant binding protein 14

Molecular interactions between odorants and odorant binding proteins (OBPs) are of major importance for understanding the principles of selectivity of OBPs towards the wide range of semiochemicals. It is largely unknown on a structural basis, how an OBP binds and discriminates between odorant molecules. Here we examine this aspect in greater detail by comparing the C-minus OBP14 of the honey bee (Apis mellifera L.) to a mutant form of the protein that comprises the third disulfide bond lacking in C-minus OBPs. Affinities of structurally analogous odorants featuring an aromatic phenol group with different side chains were assessed based on changes of the thermal stability of the protein upon odorant binding monitored by circular dichroism spectroscopy. Our results indicate a tendency that odorants show higher affinity to the wild-type OBP suggesting that the introduced rigidity in the mutant protein has a negative effect on odorant binding. Furthermore, we show that OBP14 stability is very sensitive to the position and type of functional groups in the odorant.

Honey bee odorant-binding protein 14: effects on thermal stability upon odorant binding revealed by FT-IR spectroscopy and CD measurements

In the present work, we study the effect of odorant binding on the thermal stability of honey bee (Apis mellifera L.) odorant-binding protein 14. Thermal denaturation of the protein in the absence and presence of different odorant molecules was monitored by Fourier transform infrared spectroscopy (FT-IR) and circular dichroism (CD). FT-IR spectra show characteristic bands for intermolecular aggregation through the formation of intermolecular β-sheets during the heating process. Transition temperatures in the FT-IR spectra were evaluated using moving-window 2D correlation maps and confirmed by CD measurements. The obtained results reveal an increase of the denaturation temperature of the protein when bound to an odorant molecule. We could also discriminate between high- and low-affinity odorants by determining transition temperatures, as demonstrated independently by the two applied methodologies. The increased thermal stability in the presence of ligands is attributed to a stabilizing effect of non-covalent interactions between odorant-binding protein 14 and the odorant molecule.