Sniffing out the truth: clinical diagnosis using the electronic nose

Identification of acrolein as a novel diagnostic odor biomarker for 1,2,3-trichloropropane-induced hepatotoxicity in Sprague Dawley rats

Body odor is considered a diagnostic indicator of various infectious and chronic diseases. But, few studies have examined the odor markers for various toxic effects in the mammalian system. This study attempted to identify the novel diagnostic odor biomarkers for chemical-induced hepatotoxicity in animals. The changes in the concentration of odors were analyzed in the urine of Sprague Dawley (SD) rats treated with two dosages (100 or 200 mg/kg) of 1,2,3-trichloropropane (TCP) using gas chromatography-mass spectrometry (GC-MS). The TCP treatment induced significant toxicity, including a decrease in body weight, an increase in serum biochemical factors, and histopathological changes in the liver of SD rats. During this hepatotoxicity, the concentrations of six odors (ethyl alcohol, acrolein (2-propenal), methanesulfonyl chloride, methyl ethyl ketone, cyclotrisiloxane, and 2-heptanone) in urine changed significantly after the TCP treatment. Among them, acrolein, an acrid and pungent compound, showed the highest rate of increase in the TCP-treated group compared to the Vehicle-treated group. In addition, this increase in acrolein was accompanied by enhanced spermine oxidase (SMOX) expression, an acrolein metabolic enzyme, and the increased level of IL-6 transcription as a regulator factor that induces SMOX production. The correlation between acrolein and other parameters was conformed using correlagram analyses. These results provide scientific evidence that acrolein have potential as a novel diagnostic odor biomarker for TCP-induced hepatotoxicity.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43188-024-00253-0.

Intrinsic and extrinsic factors affecting axillary odor variation. A comprehensive review

Humans produce odorous secretions from multiple body sites according to the microbiomic profile of each area and the types of secretory glands present. Because the axilla is an active, odor-producing region that mediates social communication via the sense of smell, this article focuses on the biological mechanisms underlying the creation of axillary odor, as well as the intrinsic and extrinsic factors likely to impact the odor and determine individual differences. The list of intrinsic factors discussed includes sex, age, ethnicity, emotions, and personality, and extrinsic factors include dietary choices, diseases, climate, and hygienic habits. In addition, we also draw attention to gaps in our understanding of each factor, including, for example, topical areas such as the effect of climate on body odor variation. Fundamental challenges and emerging research opportunities are further outlined in the discussion. Finally, we suggest guidelines and best practices based on the factors reviewed herein for preparatory protocols of sweat collection, data analysis, and interpretation.

Volatile Organic Compound Identification-Based Tuberculosis Screening among TB Suspects: A Diagnostic Accuracy Study

Tuberculosis (TB) affects a third of the global population, and a large population of infected individuals still remain undiagnosed-making the visible burden only the tip of the iceberg. The detection of tuberculosis in close-proximity patients is one of the key priorities for attaining the Sustainable Development Goals (SDG) of TB elimination by 2030. With the current battery of screening tests failing to cover this need, the authors of this paper examined a simple and inexpensive point-of-care breath analyzer (TSI-3000(I)), which is based on detecting the volatile organic compounds that are emitted from infected cells and released in exhaled breath as a screening tool for the detection of TB. A single-center pilot study for assessing the diagnostic accuracy of the point-of-care Tuberculosis Breath Analyzer was conducted, and it was compared against the WHO-recommended TrueNat assay, which is a rapid molecular test and was also treated as the reference standard in this study. Of the 334 enrolled participants with TB signs/symptoms, 42.51% were TrueNat positive for Mycobacterium tuberculosis. The sensitivity of the Tuberculosis Breath Analyzer was found to be 95.7%, with a specificity of 91.3% and a ROC area of 0.935. The test kit showed considerable/significant high sensitivity and specificity as reliability indicators. The performance of the Tuberculosis Breath Analyzer tested was found to be comparable in efficiency to that of the TrueNat assay. A large cohort-based multicentric study is feasibly required to further validate and extrapolate the results of the pilot study.

Smelling the Disease: Diagnostic Potential of Breath Analysis

Breath analysis is a relatively recent field of research with much promise in scientific and clinical studies. Breath contains endogenously produced volatile organic components (VOCs) resulting from metabolites of ingested precursors, gut and air-passage bacteria, environmental contacts, etc. Numerous recent studies have suggested changes in breath composition during the course of many diseases, and breath analysis may lead to the diagnosis of such diseases. Therefore, it is important to identify the disease-specific variations in the concentration of breath to diagnose the diseases. In this review, we explore methods that are used to detect VOCs in laboratory settings, VOC constituents in exhaled air and other body fluids (e.g., sweat, saliva, skin, urine, blood, fecal matter, vaginal secretions, etc.), VOC identification in various diseases, and recently developed electronic (E)-nose-based sensors to detect VOCs. Identifying such VOCs and applying them as disease-specific biomarkers to obtain accurate, reproducible, and fast disease diagnosis could serve as an alternative to traditional invasive diagnosis methods. However, the success of VOC-based identification of diseases is limited to laboratory settings. Large-scale clinical data are warranted for establishing the robustness of disease diagnosis. Also, to identify specific VOCs associated with illness states, extensive clinical trials must be performed using both analytical instruments and electronic noses equipped with stable and precise sensors.

Air-permeable redox mediated transcutaneous CO2 sensor

Standard clinical care of neonates and the ventilation status of human patients affected with coronavirus disease involves continuous CO2 monitoring. However, existing noninvasive methods are inadequate owing to the rigidity of hard-wired devices, insubstantial gas permeability and high operating temperature. Here, we report a cost-effective transcutaneous CO2 sensing device comprising elastomeric sponges impregnated with oxidized single-walled carbon nanotubes (oxSWCNTs)-based composites. The proposed device features a highly selective CO2 sensing response (detection limit 155 ± 15 ppb), excellent permeability and reliability under a large deformation. A follow-up prospective study not only offers measurement equivalency to existing clinical standards of CO2 monitoring but also provides important additional features. This new modality allowed for skin-to-skin care in neonates and room-temperature CO2 monitoring as compared with clinical standard monitoring system operating at high temperature to substantially enhance the quality for futuristic applications.

Wearing N95 masks decreases the odor discrimination ability of healthcare workers: a self-controlled before-after study

Objective

During the coronavirus disease 2019 (COVID-19) pandemic, the N95 mask is an essential piece of protective equipment for healthcare workers. However, the N95 mask may inhibit air exchange and odor penetration. Our study aimed to determine whether the use of N95 masks affects the odor discrimination ability of healthcare workers.

Methods

In our study, all the participants were asked to complete three olfactory tests. Each test involved 12 different odors. The participants completed the test while wearing an N95 mask, a surgical mask, and no mask. The score for each olfactory test was documented.

Results

The olfactory test score was significantly lower when the participants wore N95 masks than when they did not wear a mask (7 vs. 10, p < 0.01). The score was also lower when the participants wore N95 masks than surgical masks (7 vs. 8, p < 0.01).

Conclusion

Wearing N95 masks decreases the odor discrimination ability of healthcare workers. Therefore, we suggest that healthcare workers seek other clues when diagnosing disease with a characteristic odor.

Study on the Discrimination of Possible Error Sources That Might Affect the Quality of Volatile Organic Compounds Signature in Dairy Cattle Using an Electronic Nose

Simple Summary

In recent decades, remarkable progress in the development of electronic nose (EN) technologies, particularly for disease detection, has been accomplished through the disclosure of novel methods and associated devices, mainly for the detection of volatile organic compounds (VOCs). Herein, we assessed the ability of a novel EN technology (MENT-EGAS prototype) to respond to direct sampling and to evaluate the influence of possible error sources that might affect the quality of VOC signatures. Principal Component Analyses (PCA) evidenced the presence in the analyzed samples of sufficient information to consent the discrimination of different environmental backgrounds, feed headspaces and exhalated breath between two groups of cows fed with two different types of feed. Moreover, discrimination was also observed within the same group between exhalated breaths sampled before and after feed intake. Based on these findings, we provided evidence that the MENT-EGAS prototype can identify error sources with accuracy. Livestock precision farming technologies are powerful tools for monitoring animal health and welfare parameters in a continuous and automated way.

Abstract

Electronic nose devices (EN) have been developed for detecting volatile organic compounds (VOCs). This study aimed to assess the ability of the MENT-EGAS prototype-based EN to respond to direct sampling and to evaluate the influence of possible error sources that might affect the quality of VOC signatures. This study was performed on a dairy farm using 11 (n = 11) multiparous Holstein-Friesian cows. The cows were divided into two groups housed in two different barns: group I included six lactating cows fed with a lactating diet (LD), and group II included 5 non-lactating late pregnant cows fed with a far-off diet (FD). Each group was offered 250 g of their respective diet; 10 min later, exhalated breath was collected for VOC determination. After this sampling, 4 cows from each group were offered 250 g of pellet concentrates. Ten minutes later, the exhalated breath was collected once more. VOCs were also measured directly from the feed’s headspace, as well as from the environmental backgrounds of each. Principal component analyses (PCA) were performed and revealed clear discrimination between the two different environmental backgrounds, the two different feed headspaces, the exhalated breath of groups I and II cows, and the exhalated breath within the same group of cows before and after the feed intake. Based on these findings, we concluded that the MENT-EGAS prototype can recognize several error sources with accuracy, providing a novel EN technology that could be used in the future in precision livestock farming.

Changes in the urine volatile metabolome throughout growth of transplanted hepatocarcinoma

Trained detection dogs distinguish between urine samples from healthy organisms and organisms with malignant tumors, suggesting that the volatile urine metabolome contains information about tumor progression. The aim of this study was to determine whether the stage of tumor growth affects the chemical differences in the urine of mice and to what extent the "olfactory image of disease" perceived by dogs coincides with the "image of disease" recorded by the mass spectrometer. We used a novel laser ionization mass spectrometry method and propose a mass spectrometric analysis without detailed interpretation of the spectrum of volatile metabolomes in urine. The mass spectrometer we use works without sample preparation and registers volatile organic compounds in air at room temperature without changing the pH of the sample, i.e. under conditions similar to those in which dogs solve the same problem. The experimental cancer models were male BDF-f1 hybrid mice transplanted with hepatocarcinoma tissue, and similar mice transplanted with healthy liver tissue were used as controls. Our data show that both dogs and our proposed laser mass spectrometry method are able to detect both the entire spectrum of volatile organic compounds associated with the disease and minor changes in this spectrum during its course.

Non-verbal communication: an update on smell

Non-verbal communication is an important aspect of communication skills and sometimes involves making assumptions with smell being one aspect of non-verbal communication. Here the subconscious associations that come with smell are highlighted and by increasing self- awareness, the doctor-patient relationship in the consultation may be improved.

Application and Development of Artificial Intelligence and Intelligent Disease Diagnosis

With the continuous development of artificial intelligence (AI) technology, big data-supported AI technology with considerable computer and learning capacity has been applied in diagnosing different types of diseases. This study reviews the application of expert systems, neural networks, and deep learning used by AI technology in disease diagnosis. This paper also gives a glimpse of the intelligent diagnosis and treatment of digestive system diseases, respiratory system diseases, and osteoporosis by AI technology.

The electronic nose technology in clinical diagnosis: A systematic review

Supplemental Digital Content is available in the text

Background:

Volatile organic compounds (VOC) are end products of human metabolism (normal and disease-associated) that can be mainly excreted in breath, urine, and feces. Therefore, VOC can be very useful as markers of diseases and helpful for clinicians since its sampling is noninvasive, inexpensive, and painless. Electronic noses, or eNoses, provide an easy and inexpensive way to analyze gas samples. Thus, this device may be used for diagnosis, monitoring or phenotyping diseases according to specific breathprints (breath profile).

Objective:

In this review, we summarize data showing the ability of eNose to be used as a noninvasive tool to improve diagnosis in clinical settings.

Methods:

A PRISMA-oriented search was performed in PubMed and Cochrane Library. Only studies performed in humans and published since 2000 were included.

Results:

A total of 48 original articles, 21 reviews, and 7 other documents were eligible and fully analyzed. The quality assessment of the selected studies was conducted according to the Standards for Reporting of Diagnostic Accuracy. Airway obstructive diseases were the most studied and Cyranose 320 was the most used eNose.

Conclusions:

Several case–control studies were performed to test this technology in diverse fields. More than a half of the selected studies showed good accuracy. However, there are some limitations regarding sampling methodology, analysis, reproducibility, and external validation that need to be standardized. Additionally, it is urgent to test this technology in intend-to-treat populations. Thus, it is possible to think in the contribution of VOC analysis by eNoses in a clinical setting.

Biosensors to Monitor Water Quality Utilizing Insect Odorant-Binding Proteins as Detector Elements

In the developing world, the identification of clean, potable water continues to pose a pervasive challenge, and waterborne diseases due to fecal contamination of water supplies significantly threaten public health. The ability to efficiently monitor local water supplies is key to water safety, yet no low-cost, reliable method exists to detect contamination quickly. We developed an in vitro assay utilizing an odorant-binding protein (OBP), AgamOBP1, from the mosquito, Anopheles gambiae, to test for the presence of a characteristic metabolite, indole, from harmful coliform bacteria. We demonstrated that recombinantly expressed AgamOBP1 binds indole with high sensitivity. Our proof-of-concept assay is fluorescence-based and demonstrates the usefulness of insect OBPs as detector elements in novel biosensors that rapidly detect the presence of bacterial metabolic markers, and thus of coliform bacteria. We further demonstrated that rAgamOBP1 is suitable for use in portable, inexpensive "dipstick" biosensors that improve upon lateral flow technology since insect OBPs are robust, easily obtainable via recombinant expression, and resist detector "fouling." Moreover, due to their wide diversity and ligand selectivity, insect chemosensory proteins have other biosensor applications for various analytes. The techniques presented here therefore represent platform technologies applicable to various future devices.

The role of body odors and olfactory ability in the initiation, maintenance and breakdown of romantic relationships - A review

The aim of this review is to present direct and indirect lines of converging evidence that highlight the many ways our body odors and sense of smell may influence the three broad stages of romantic relationships; initiation, maintenance and breakdown. This emerging area of study requires a multidisciplinary empirical approach. Here we survey research findings that taken together, suggest that body odor perception moderates mate choice, provides a source of comfort in existing relationships and may signal the breakdown of a relationship through disgust processes. In terms of olfactory ability, having a good sense of smell may facilitate identifying a healthy mate, enhance sexual experiences, relationship security and ensure empathic responsivity, predictors of relationship longevity. We therefore conclude that olfaction plays an important - yet understudied - role in romantic relationships.

Differentiation between infected and non-infected wounds using an electronic nose

OBJECTIVES

The aim of this study was to explore whether an electronic nose, Aetholab, is able to discriminate between infected versus non-infected wounds, based on headspace analyses from wound swabs.

METHODS

A total of 77 patients participated in this pilot study. Each wound was assessed for infection based on clinical judgment. Additionally, two wound swabs were taken, one for microbiological culture and one for measurement with Aetholab. Diagnostic properties with 95% confidence intervals (95%CIs) of Aetholab were calculated with clinical judgment and microbiological culture results as reference standards.

RESULTS

With clinical judgment as reference standard, Aetholab had a sensitivity of 91% (95%CI 76-98) and a specificity of 71% (95%CI 55-84). Diagnostic properties were somewhat lower when microbiological culture results were used as reference standard: sensitivity 81% (95%CI 64-91), specificity 63% (95%CI 46-77).

CONCLUSIONS

Aetholab seems a promising diagnostic tool for wound infection given the diagnostic properties presented in this pilot study. A larger study is needed to confirm our results.

Ab initio conformational analysis of 1,2,3,4-tetrahydroquinoline and the high-resolution rotational spectrum of its lowest energy conformer

The tight combination of rotational spectroscopy and quantum-chemical calculations provides an insight into the molecular physics of the lowest energy conformer of 1,2,3,4-tetrahydroquinoline.

Diagnosis of bovine tuberculosis using a metal oxide-based electronic nose

Electronic noses (e-noses) have been used for environmental monitoring, standardization of medicinal flavourings, food safety tests and diagnosis of infectious diseases based on the statistical analysis of volatile organic compounds (VOCs). Bovine tuberculosis (bTB) is officially diagnosed using the intradermal skin test (IST), which is time-consuming and labour-intensive. Therefore, a more convenient and rapid test with greater sensitivity would be advantageous as prescreening test. In this study, we used a metal oxide sensor (MOS) type e-nose to analyse VOCs in a bTB-infected (n = 11) and bTB-free (n = 10) sera, from cattle whose health status was confirmed using the IST, and pathological and bacteriological examinations. The differences in VOCs from bTB-infected and bTB-free sera detected by the e-nose were statistically analysed using principal components and discriminant factor analyses. bTB-infected and bTB-free sera could be discriminated by MOS type e-nose, and analysing time per sample was only 20 min. VOC analysis using a MOS e-nose was a rapid and automated prescreening method to diagnose bTB, and can be used to select bTB-suspect cattle for IST confirmation. Further studies are required to estimate test sensitivity and specificity. Significance and impact of the study: Bovine tuberculosis (bTB) in cattle is diagnosed using the intradermal skin test (IST); however, this method is very time-consuming and labour-intensive. We analysed volatile organic compounds that are obtained from serum using a metal oxide sensor type of electronic nose to discriminate between TB-infected and TB-free sera. This simple and automated technique will be useful to prescreen bTB-suspects and reduce the time and labour required to perform the IST.

Glucose prediction by analysis of exhaled metabolites - a systematic review

Background

In critically ill patients, glucose control with insulin mandates time– and blood–consuming glucose monitoring. Blood glucose level fluctuations are accompanied by metabolomic changes that alter the composition of volatile organic compounds (VOC), which are detectable in exhaled breath. This review systematically summarizes the available data on the ability of changes in VOC composition to predict blood glucose levels and changes in blood glucose levels.

Methods

A systematic search was performed in PubMed. Studies were included when an association between blood glucose levels and VOCs in exhaled air was investigated, using a technique that allows for separation, quantification and identification of individual VOCs. Only studies on humans were included.

Results

Nine studies were included out of 1041 identified in the search. Authors of seven studies observed a significant correlation between blood glucose levels and selected VOCs in exhaled air. Authors of two studies did not observe a strong correlation. Blood glucose levels were associated with the following VOCs: ketone bodies (e.g., acetone), VOCs produced by gut flora (e.g., ethanol, methanol, and propane), exogenous compounds (e.g., ethyl benzene, o–xylene, and m/p–xylene) and markers of oxidative stress (e.g., methyl nitrate, 2–pentyl nitrate, and CO).

Conclusion

There is a relation between blood glucose levels and VOC composition in exhaled air. These results warrant clinical validation of exhaled breath analysis to monitor blood glucose levels.

Analysis of breath samples for lung cancer survival

Analyses of exhaled air by means of electronic noses offer a large diagnostic potential. Such analyses are non-invasive; samples can also be easily obtained from severely ill patients and repeated within short intervals. Lung cancer is the most deadly malignant tumor worldwide, and monitoring of lung cancer progression is of great importance and may help to decide best therapy. In this report, twenty-two patients with diagnosed lung cancer and ten healthy volunteers were studied using breath samples collected several times at certain intervals and analysed by an electronic nose. The samples were divided into three sub-groups; group d for survivor less than one year, group s for survivor more than a year and group h for the healthy volunteers. Prediction models based on partial least square and artificial neural nets could not classify the collected groups d, s and h, but separated well group d from group h. Using artificial neural net, group d could be separated from group s. Excellent predictions and stable models of survival day for group d were obtained, both based on partial least square and artificial neural nets, with correlation coefficients 0.981 and 0.985, respectively. Finally, the importance of consecutive measurements was shown.

Exhaled breath analysis by electronic nose in airways disease. Established issues and key questions

Exhaled air contains many volatile organic compounds (VOCs) that are the result of normal and disease-associated metabolic processes anywhere in the body. Different omics techniques can assess the pattern of these VOCs. One such omics technique suitable for breath analysis is represented by electronic noses (eNoses), providing fingerprints of the exhaled VOCs, called breathprints. Breathprints have been shown to be altered in different disease states, including in asthma and COPD. This review describes the current status on clinical validation and application of breath analysis by electronic noses in the diagnosis and monitoring of chronic airways diseases. Furthermore, important methodological issues including breath sampling, modulating factors and incompatibility between eNoses are raised and discussed. Next steps towards clinical application of electronic noses are provided, including further validation in suspected disease, assessment of the influence of different comorbidities, the value in longitudinal monitoring of patients with asthma and COPD and the possibility to predict treatment responses. Eventually, a Breath Cloud may be constructed, a large database containing disease-specific breathprints. When collaborative efforts are put into optimization of this technique, it can provide a rapid and non-invasive first line diagnostic test.

Clinical application of volatile organic compound analysis for detecting infectious diseases

This review article introduces the significance of testing of volatile organic compounds (VOCs) in clinical samples and summarizes important features of some of the technologies. Compared to other human diseases such as cancer, studies on VOC analysis in cases of infectious diseases are limited. Here, we have described results of studies which have used some of the appropriate technologies to evaluate VOC biomarkers and biomarker profiles associated with infections. The publications reviewed include important infections of the respiratory tract, gastrointestinal tract, urinary tract, and nasal cavity. The results highlight the use of VOC biomarker profiles resulting from certain infectious diseases in discriminating between infected and healthy subjects. Infection-related VOC profiles measured in exhaled breath as well as from headspaces of feces or urine samples are a source of information with respect to disease detection. The volatiles emitted in clinical matrices may on the one hand represent metabolites of the infecting pathogen or on the other hand reflect pathogen-induced host responses or, indeed, a combination of both. Because exhaled-breath samples are easy to collect and online instruments are commercially available, VOC analysis in exhaled breath appears to be a promising tool for noninvasive detection and monitoring of infectious diseases.

Production of bioactive volatiles by different Burkholderia ambifaria strains

Increasing evidence indicates that volatile compounds emitted by bacteria can influence the growth of other organisms. In this study, the volatiles produced by three different strains of Burkholderia ambifaria were analysed and their effects on the growth of plants and fungi, as well as on the antibiotic resistance of target bacteria, were assessed. Burkholderia ambifaria emitted highly bioactive volatiles independently of the strain origin (clinical environment, rhizosphere of pea, roots of maize). These volatile blends induced significant biomass increase in the model plant Arabidopsis thaliana as well as growth inhibition of two phytopathogenic fungi (Rhizoctonia solani and Alternaria alternata). In Escherichia coli exposed to the volatiles of B. ambifaria, resistance to the aminoglycoside antibiotics gentamicin and kanamycin was found to be increased. The volatile blends of the three strains were similar, and dimethyl disulfide was the most abundant compound. Sulfur compounds, ketones, and aromatic compounds were major groups in all three volatile profiles. When applied as pure substance, dimethyl disulfide led to increased plant biomass, as did acetophenone and 3-hexanone. Significant fungal growth reduction was observed with high concentrations of dimethyl di- and trisulfide, 4-octanone, S-methyl methanethiosulphonate, 1-phenylpropan-1-one, and 2-undecanone, while dimethyl trisulfide, 1-methylthio-3-pentanone, and o-aminoacetophenone increased resistance of E. coli to aminoglycosides. Comparison of the volatile profile produced by an engineered mutant impaired in quorum-sensing (QS) signalling with the corresponding wild-type led to the conclusion that QS is not involved in the regulation of volatile production in B. ambifaria LMG strain 19182.

Human skin volatiles: a review

Odors emitted by human skin are of great interest to biologists in many fields; applications range from forensic studies to diagnostic tools, the design of perfumes and deodorants, and the ecology of blood-sucking insect vectors of human disease. Numerous studies have investigated the chemical composition of skin odors, and various sampling methods have been used for this purpose. The literature shows that the chemical profile of skin volatiles varies greatly among studies, and the use of different sampling procedures is probably responsible for some of these variations. To our knowledge, this is the first review focused on human skin volatile compounds. We detail the different sampling techniques, each with its own set of advantages and disadvantages, which have been used for the collection of skin odors from different parts of the human body. We present the main skin volatile compounds found in these studies, with particular emphasis on the most frequently studied body regions, axillae, hands, and feet. We propose future directions for promising experimental studies on odors from human skin, particularly in relation to the chemical ecology of blood-sucking insects.

Clinical use of exhaled volatile organic compounds in pulmonary diseases: a systematic review

There is an increasing interest in the potential of exhaled biomarkers, such as volatile organic compounds (VOCs), to improve accurate diagnoses and management decisions in pulmonary diseases. The objective of this manuscript is to systematically review the current knowledge on exhaled VOCs with respect to their potential clinical use in asthma, lung cancer, chronic obstructive pulmonary disease (COPD), cystic fibrosis (CF), and respiratory tract infections. A systematic literature search was performed in PubMed, EMBASE, Cochrane database, and reference lists of retrieved studies. Controlled, clinical, English-language studies exploring the diagnostic and monitoring value of VOCs in asthma, COPD, CF, lung cancer and respiratory tract infections were included. Data on study design, setting, participant characteristics, VOCs techniques, and outcome measures were extracted. Seventy-three studies were included, counting in total 3,952 patients and 2,973 healthy controls. The collection and analysis of exhaled VOCs is non-invasive and could be easily applied in the broad range of patients, including subjects with severe disease and children. Various research groups demonstrated that VOCs profiles could accurately distinguish patients with a pulmonary disease from healthy controls. Pulmonary diseases seem to be characterized by a disease specific breath-print, as distinct profiles were found in patients with dissimilar diseases. The heterogeneity of studies challenged the inter-laboratory comparability. In conclusion, profiles of VOCs are potentially able to accurately diagnose various pulmonary diseases. Despite these promising findings, multiple challenges such as further standardization and validation of the diverse techniques need to be mastered before VOCs can be applied into clinical practice.

Diagnosis of active tuberculosis by e-nose analysis of exhaled air

Tuberculosis (TB), a highly infectious airborne disease, remains a major global health problem. Many of the new diagnostic techniques are not suited for operation in the highly-endemic low-income countries. A sensitive, fast, easy-to-operate and low-cost method is urgently needed. We performed a Proof of Principle Study (30 participants) and a Validation Study (194 participants) to estimate the diagnostic accuracy of a sophisticated electronic nose (DiagNose, C-it BV) using exhaled air to detect tuberculosis. The DiagNose uses a measurement method that enables transfer of calibration models between devices thus eliminating the most common pitfall for large scale implementation of electronic noses in general. DiagNose measurements were validated using traditional sputum smear microscopy and culture on Löwenstein-Jensen media. We found a sensitivity of 95.9% and specificity of 98.5% for the pilot study. In the validation study we found a sensitivity of 93.5% and a specificity of 85.3% discriminating healthy controls from TB patients, and a sensitivity of 76.5% and specificity of 87.2% when identifying TB patient within the entire test-population (best-case numbers). The portability and fast time-to-result of the DiagNose enables a proactive screening search for new TB cases in rural areas, without the need for highly-skilled operators or a hospital center infrastructure.

Chemiresistive sensing with chemically modified metal and alloy nanoparticles

This review describes the use of chemically modified pure and alloyed metal nanoparticles for chemiresistive sensing applications. Chemically modified metal nanoparticles consist of a pure or alloyed metallic core with some type of chemical coating. Researchers have studied the electronic properties of 1D, 2D, and 3D assemblies of chemically modified metal nanoparticles, and even single individual nanoparticles. The interaction with the analyte alters the conductivity of the sensitive material, providing a signal to measure the analyte concentration. This review focuses on chemiresistive sensing of a wide variety of gas- and liquid-phase analytes with metal nanoparticles coated with organothiols, ions, polymers, surfactants, and biomolecules. Different strategies used to incorporate chemically modified nanoparticles into chemiresistive sensing devices are reviewed, focusing on the different types of metal and alloy compositions, coatings, methods of assembly, and analytes (vapors, gases, liquids, biological materials), along with other important factors.

Laboratory diagnosis of tuberculosis in resource-poor countries: challenges and opportunities

With an estimated 9.4 million new cases globally, tuberculosis (TB) continues to be a major public health concern. Eighty percent of all cases worldwide occur in 22 high-burden, mainly resource-poor settings. This devastating impact of tuberculosis on vulnerable populations is also driven by its deadly synergy with HIV. Therefore, building capacity and enhancing universal access to rapid and accurate laboratory diagnostics are necessary to control TB and HIV-TB coinfections in resource-limited countries. The present review describes several new and established methods as well as the issues and challenges associated with implementing quality tuberculosis laboratory services in such countries. Recently, the WHO has endorsed some of these novel methods, and they have been made available at discounted prices for procurement by the public health sector of high-burden countries. In addition, international and national laboratory partners and donors are currently evaluating other new diagnostics that will allow further and more rapid testing in point-of-care settings. While some techniques are simple, others have complex requirements, and therefore, it is important to carefully determine how to link these new tests and incorporate them within a country's national diagnostic algorithm. Finally, the successful implementation of these methods is dependent on key partnerships in the international laboratory community and ensuring that adequate quality assurance programs are inherent in each country's laboratory network.

Advances in electronic-nose technologies developed for biomedical applications

The research and development of new electronic-nose applications in the biomedical field has accelerated at a phenomenal rate over the past 25 years. Many innovative e-nose technologies have provided solutions and applications to a wide variety of complex biomedical and healthcare problems. The purposes of this review are to present a comprehensive analysis of past and recent biomedical research findings and developments of electronic-nose sensor technologies, and to identify current and future potential e-nose applications that will continue to advance the effectiveness and efficiency of biomedical treatments and healthcare services for many years. An abundance of electronic-nose applications has been developed for a variety of healthcare sectors including diagnostics, immunology, pathology, patient recovery, pharmacology, physical therapy, physiology, preventative medicine, remote healthcare, and wound and graft healing. Specific biomedical e-nose applications range from uses in biochemical testing, blood-compatibility evaluations, disease diagnoses, and drug delivery to monitoring of metabolic levels, organ dysfunctions, and patient conditions through telemedicine. This paper summarizes the major electronic-nose technologies developed for healthcare and biomedical applications since the late 1980s when electronic aroma detection technologies were first recognized to be potentially useful in providing effective solutions to problems in the healthcare industry.

Discrimination and characterization of breath from smokers and non-smokers via electronic nose and GC/MS analysis

The objective of this study was to prove the general applicability of an electronic nose for analyzing exhaled breath considering the dependency on smoking. At first, odor compounds from spices (n=6) were detected via the electronic nose and further characterized and classified with gas chromatography/ mass spectrometry to demonstrate the principle ability of the electronic nose. Then, the exhaled breath from smokers and non-smokers were analyzed to prove the influence of smoking on breath analyses with the electronic nose. The exhaled breath was sampled from 11 smokers and 11 non-smokers in a special sampling bag with the mounted sensor chip of the electronic nose. Additionally, solid phase micro-extraction (SPME) technique was established for detection of the specific chemical compounds with gas chromatography and mass spectrometry (GC/MS). For analyses of the sensor signals the principle component analysis (PCA) was applied and the groups were differentiated by linear discriminant function analysis. In accordance to the discrimination between the different spices and between smokers and non-smokers the PCA analysis leads to an optimum accuracy of 100%. The results of this study show that an electronic nose has the ability to detect different changes of odor components and provides separation of smoking side effects in smelling different diseases.

The reactions of H(3)O(+), NO(+) and O(2) (+) with several flavourant esters studied using selected ion flow tube mass spectrometry

The reactions of H(3)O(+), NO(+), and O(2) (+) with nineteen ester compounds occurring naturally in plants, and having important flavourant properties, were examined using selected ion flow tube mass spectrometry (SIFT-MS). The H(3)O(+) reactions primarily generate [R(1)COOR(2).H](+), and may also produce [R(2)](+) fragment ions and/or fragmentation within the ester linkage. Collisional association/adduct ions, [R(1)COOR(2).NO](+), are the main products formed in the NO(+) reactions, although the carboxyl fragment ion is also detected frequently. The identification of the parent compound may be made more easily in the H(3)O(+) and NO(+) reactions. The inclusion of O(2) (+) reactions in the analysis provides additional information, which may be applied when the identity of a parent compound cannot be determined solely from the H(3)O(+) and NO(+) analysis. Consideration of the product ions generated with the three precursors suggests that SIFT-MS can differentiate between many of the esters investigated, including isomers, although the product ions generated in the reactions with some esters are too similar to allow independent quantification. Our data therefore suggest that SIFT-MS may be a useful tool to rapidly analyse and quantify flavourant esters in complex gas mixtures.

Breath biomarkers of active pulmonary tuberculosis

BACKGROUND

Volatile organic compounds (VOCs) in breath may contain biomarkers of active pulmonary tuberculosis derived from the infectious organism (metabolites of Mycobacterium tuberculosis) and from the infected host (products of oxidative stress).

METHODS

We analyzed breath VOCs in 226 symptomatic high-risk patients in USA, Philippines, and UK, using gas chromatography/mass spectroscopy. Diagnosis of disease was based on sputum culture, smear microscopy, chest radiography and clinical suspicion of tuberculosis (CSTB). Chromatograms were converted to a series of 8s overlapping time slices. Biomarkers of active pulmonary tuberculosis were identified with a Monte Carlo analysis of time-slice alveolar gradients (abundance in breath minus abundance in room air).

RESULTS

Breath VOCs contained apparent biomarkers of active pulmonary tuberculosis comprising oxidative stress products (alkanes and alkane derivatives) and volatile metabolites of M. tuberculosis (cyclohexane and benzene derivatives). Breath biomarkers identified active pulmonary tuberculosis with C-statistic (area under curve of receiver operating characteristic)=0.85 (i.e. 85% overall accuracy, sensitivity=84.0%, specificity=64.7%) when sputum culture, microscopy, and chest radiography were either all positive or all negative. Employing a single criterion of disease, C-statistic=0.76 (smear microscopy), 0.68 (sputum culture), 0.66 (chest radiography) and 0.65 (CSTB).

CONCLUSION

A breath test identified apparent biomarkers of active pulmonary tuberculosis with 85% accuracy in symptomatic high-risk subjects.

Chemiresistive sensing of volatile organic compounds with films of surfactant-stabilized gold and gold-silver alloy nanoparticles

Here we describe the chemiresistive sensing of volatile organic compounds (VOCs) with films of chemically synthesized approximately 4 nm diameter Au and AuAg alloy nanoparticles (NPs) stabilized by a surfactant, tetraoctylammonium bromide (TOABr). The chemiresistive sensing properties were measured over a concentration range of 100 to 0.04% saturation for methanol (MeOH), ethanol (EtOH), 2-propanol (IPA), and toluene (Tol) vapor analytes and compared directly to the chemiresistive sensing properties of films of 1.6 nm diameter hexanethiolate (C6S)-coated Au monolayer-protected clusters (MPCs). Films of TOABr-stabilized Au NPs exhibit the opposite response compared to those of C6S-coated Au MPCs. The details are unclear, but the mechanism likely involves changes in capacitive charging in the film or improved conductive pathways through the Au NPs upon incorporation of VOCs into the film for the former as opposed to the well-known change in electron hopping conductivity for the latter. This leads to a decrease in resistance in the presence of VOCs for TOABr Au as opposed to an increase for C6S Au. The TOABr Au sensors are more sensitive, especially for polar analytes, and have greater long-term stability compared to C6S Au. The limit of detection (LOD) for films of TOABr-coated Au NPs is 3, 2, 12, and 37 ppm for IPA, MeOH, EtOH, and Tol, respectively, as compared to 106, 326, 242, and 48 for C6S Au. Films of TOABr-stabilized AuAg alloy NPs exhibit the same type of response, but the sensitivity decreases dramatically with increasing Ag content, showing that the metal composition of the NPs in the film plays a role in the sensing properties, which has not been well-recognized in the literature.

Predicting the receptive range of olfactory receptors

Although the family of genes encoding for olfactory receptors was identified more than 15 years ago, the difficulty of functionally expressing these receptors in an heterologous system has, with only some exceptions, rendered the receptive range of given olfactory receptors largely unknown. Furthermore, even when successfully expressed, the task of probing such a receptor with thousands of odors/ligands remains daunting. Here we provide proof of concept for a solution to this problem. Using computational methods, we tune an electronic nose to the receptive range of an olfactory receptor. We then use this electronic nose to predict the receptors' response to other odorants. Our method can be used to identify the receptive range of olfactory receptors, and can also be applied to other questions involving receptor–ligand interactions in non-olfactory settings.

A key goal in biology is to identify specific ligands for specific receptors. One example is where the ligand is a drug. In turn, in the olfactory system the ligand is the odorant that binds to olfactory receptors. There are many olfactory receptor types, and which odorants will activate which receptors remains largely unknown. One way to answer this is to systematically vary the molecular features of ligands and to measure the olfactory receptor response. However, the vast number of molecular features and their combinations renders such an effort potentially unsolvable. Here, rather than looking at the trees (each molecular feature), we looked at the forest (the smell they generate). We used a device called an electronic nose that generates a patterned response to odorants. We then obtained the response to a set of odorants that are known to activate a particular olfactory receptor, and we used this pattern to predict the response of that receptor to other odorants. We found that, on average in three out of four we could predict the response of olfactory receptors. This result provides a new method for probing the olfactory system, and also suggests a novel method for identifying potential drugs.

An investigation into the suitability of using three electronic nose instruments for the detection and discrimination of bacteria types

The use of electronic nose (e-nose) technology for detection of food-borne bacteria has several practical advantages over current laboratory procedures, such as lower cost and reduced testing time. In this work, we are interested in using electronic nose systems to detect E. coli and Listeria in a nutrient broth, and discriminate between these bacteria types at various concentrations. To do this, we use instruments based on three different technologies - fingerprint mass spectrometry, metal oxide sensors, and conductive polymer sensors. Our results indicate that separation between groups can be achieved. We describe the relative merits and drawbacks of each technology and discuss how this rich multimodal dataset can be used to build a classification system.

Facing the crisis: improving the diagnosis of tuberculosis in the HIV era

Although the human immunodeficiency virus (HIV) infection pandemic has had a catastrophic impact on tuberculosis (TB) control efforts, especially in sub-Saharan Africa, most of the fundamental concepts reflected in the directly observed treatment, short course (DOTS) strategy still hold true in the HIV era. What has changed, and dramatically, is the importance of speedy and accurate TB diagnosis and the difficulty of achieving this. The disproportionate amount of smear-negative disease in sub-Saharan Africa, which shoulders two-thirds of the global burden of HIV infection and acquired immunodeficiency syndrome, has greatly complicated TB case detection and disease control. Now, 15 years after TB rates began to soar in countries where HIV infection is prevalent, we have learned that the conventional approach -- passively waiting for patients with advanced symptomatic disease to make their way to microscopy centers for diagnosis -- has disastrous consequences. Without better diagnostic tools for TB and effective strategies for their implementation, transmission will not be interrupted, mortality will not be checked, and TB will not be controlled in areas where HIV infection is prevalent. Fortunately, a number of technical opportunities exist for the creation of improved diagnostic tests. Developing and exploiting such tests to support TB control in HIV-infected populations is an urgent priority. A substantial public sector effort is under way to work in partnership with the biotechnology industry to accelerate progress toward that goal. In this article, we will define the need for better TB tests and describe technologies being developed to meet that need.

Prospects for clinical application of electronic-nose technology to early detection of Mycobacterium tuberculosis in culture and sputum

Ziehl-Neelsen (ZN) staining for the diagnosis of tuberculosis (TB) is time-consuming and operator dependent and lacks sensitivity. A new method is urgently needed. We investigated the potential of an electronic nose (EN) (gas sensor array) comprising 14 conducting polymers to detect different Mycobacterium spp. and Pseudomonas aeruginosa in the headspaces of cultures, spiked sputa, and sputum samples from 330 culture-proven and human immunodeficiency virus-tested TB and non-TB patients. The data were analyzed using principal-component analysis, discriminant function analysis, and artificial neural networks. The EN differentiated between different Mycobacterium spp. and between mycobacteria and other lung pathogens both in culture and in spiked sputum samples. The detection limit in culture and spiked sputa was found to be 1 x 10(4) mycobacteria ml(-1). After training of the neural network with 196 sputum samples, 134 samples (55 M. tuberculosis culture-positive samples and 79 culture-negative samples) were used to challenge the model. The EN correctly predicted 89% of culture-positive patients; the six false negatives were the four ZN-negative and two ZN-positive patients. The specificity and sensitivity of the described method were 91% and 89%, respectively, compared to culture. At present, the reasons for the false negatives and false positives are unknown, but they could well be due to the nonoptimized system used here. This study has shown the ability of an electronic nose to detect M. tuberculosis in clinical specimens and opens the way to making this method a rapid and automated system for the early diagnosis of respiratory infections.

Medical applications of electronic nose technology

Electronic nose technology has been developed over the past 15 years in the field of chemistry as an electronic equivalent of the biologic mechanism of smell. Since its inception, it has been well recognized that there is great potential in applying this technology to the field of medicine. This review discusses those areas of medicine in which electronic nose technology has been applied. For each area, this review addresses the scope of the medical problem that has been studied, how the electronic nose technology may help address the medical problem, and the results of such studies to date. Next generation electronic noses will be refined to better analyze specific disease states. This will require further evaluation of the specific volatiles to be tested. This information may then be brought to bear on refinement of the chemistry of the electronic nose sensors, making them more sensitive and specific for the particular disease of interest. The ultimate goal of work in this arena is to make an electronic nose that is portable, fast, inexpensive and, therefore, suitable for use in the examination room or at the bedside, making it facile as a diagnostic tool.

Chemiresistive Vapor Sensing with Microscale Films of Gold Monolayer Protected Clusters

Here we report the stability, conductivity, and vapor-sensing properties of microcontact-printed films of 1.6-nm average diameter hexanethiolate-coated gold monolayer protected clusters (C6 Au MPCs). The C6 Au MPCs were stamped into parallel lines (approximately 1.2 microm wide and 400 nm thick) across two Au electrodes separated by a 1-microm gap. The chemiresistive vapor-sensing properties were measured for saturated toluene and 2-propanol vapors. As-prepared patterned Au MPC films were unstable in the presence of saturated toluene vapor, and their current response was irreversible. Chemically linking the films with vapor-phase hexanedithiol greatly improves their stability and leads to reversible responses. The extent of Au MPC cross-linking and vapor response to organic vapors varies with different exposure times to dithiol vapor. The response to toluene changed from 61 to 8% for exposures of 1 and 60 min, respectively, which is likely due to greater film flexibility with less dithiol exposure. The current measured through the films varies from 10(-11) to 10(-3) Angstroms as a function of the temperature between 250 and 320 degrees C, which correlates with the loss of organic material as measured by FT-IR spectroscopy and the change in thickness and width of the film as measured by atomic force microscopy. The vapor-sensing properties vary with temperature, current, and organic content in the film, which are all interrelated. Response to toluene decreased with increasing temperature and conductivity, while the response to 2-propanol was less predictable. Reducing the size of vapor-sensing devices based on Au MPCs is important for creating highly portable devices that can simultaneously detect multiple analytes. This work demonstrates a simple method for reducing the size of such devices down to the microscale and describes methods for maximizing response, stability, and reversibility.

Body Odor Similarity in Noncohabiting Twins

There is currently considerable interest in biometric approaches using human odor as a marker of disease or genetic individuality. Body odor is also thought to be used during mate choice to select genetically compatible mates. The idea that body odor reveals information about both genetic identity and genetic similarity is most readily tested by examining odor in twin pairs. However, although this idea can be traced back 130 years to Francis Galton in 1875, most studies using dogs fail to control for shared environmental effects associated with cohabitation. Here we show that odors of identical twins (but not dizygotic twins) can be matched by human sniffers at rates better than chance, even when the twins are living apart. In addition, matching frequencies for identical twin odors were not significantly different from those for duplicate odors from the same individual. These results indicate an important genetic influence on body odor and the potential for developing technologies for human odor printing in relation to underlying genotype.

Medical applications of odor-sensing devices

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

Use of an electronic nose to diagnose Mycobacterium bovis infection in badgers and cattle

It is estimated that more than 50 million cattle are infected with Mycobacterium bovis worldwide, resulting in severe economic losses. Current diagnosis of tuberculosis (TB) in cattle relies on tuberculin skin testing, and when combined with the slaughter of test-positive animals, it has significantly reduced the incidence of bovine TB. The failure to eradicate bovine TB in Great Britain has been attributed in part to a reservoir of the infection in badgers (Meles meles). Accurate and reliable diagnosis of infection is the cornerstone of TB control. Bacteriological diagnosis has these characteristics, but only with samples collected postmortem. Unlike significant wild animal reservoirs of M. bovis that are considered pests in other countries, such as the brushtail possum (Trichosurus vulpecula) in New Zealand, the badger and its sett are protected under United Kingdom legislation (The Protection of Badgers Act 1992). Therefore, an accurate in vitro test for badgers is needed urgently to determine the extent of the reservoir of infection cheaply and without destroying badgers. For cattle, a rapid on-farm test to complement the existing tests (the skin test and gamma interferon assay) would be highly desirable. To this end, we have investigated the potential of an electronic nose (EN) to diagnose infection of cattle or badgers with M. bovis, using a serum sample. Samples were obtained from both experimentally infected badgers and cattle, as well as naturally infected badgers. Without exception, the EN was able to discriminate infected animals from controls as early as 3 weeks after infection with M. bovis, the earliest time point examined postchallenge. The EN approach described here is a straightforward alternative to conventional methods of TB diagnosis, and it offers considerable potential as a sensitive, rapid, and cost-effective means of diagnosing M. bovis infection in cattle and badgers.