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Methodological variation in headspace analysis of liquid samples using electronic nose
Get PDFIn past years, numerous electronic nose (e-nose) developments have been published describing analyses of solid-, liquid- or gaseous media in microbiological-, environmental-, agricultural- or medical applications. However, little has been reported about complex methodological pitfalls that might be associated with commercially available e-nose technology. In this paper, some of these pitfalls such as temperature, the use of filters and mass flow using different sampling methods (static- and dynamic sampling) are described for two generations of conducting polymer e-noses (ST114/214, CPs, both Scensive Tech. Ltd.). A comparison with metal oxide semiconducting field effect transistor/metal oxide semiconductor (MOSFET/MOS) e-noses regarding stability across replicates and over time was made. Changes in temperature were found to give larger sensor responses, whereas the application of filters led to quantitative and qualitative changes in sensor responses due to a change in mass flow which was also affected by the sampling method. Static sampling provided more stable flows across replicates. Variation was investigated for CPs and MOSFET/MOS e-noses that gave different responses over time and across replicates. These methodological factors cause a lack of stability and reproducibility, demonstrating the pitfalls of e-nose technology and therefore limit their utility for discriminating between samples
Bifurcation Analysis of a Coupled Nose Landing Gear-Fuselage System
Get PDFUnder certain conditions during takeoff and landing, pilots may sometimes experience vibrations in the cockpit. Because the cockpit is located right above the nose landing gear, which is known to potentially be prone to self-excited vibrations at certain velocities, an explanation for those vibrations might be oscillations of the landing gear feeding into the fuselage. However, the fuselage dynamics itself may also influence the dynamics of the landing gear, meaning that the coupling must be considered as bidirectional. A mathematical model is developed to study a coupled nose-landing-gear–fuselage system, which allows to assess the overall influence of the coupling on the system dynamics. Bifurcation analysis reveals that this interaction may be significant in both directions and that the system behavior depends strongly on the modal characteristics of the fuselage
Potential for detection of microorganisms and heavy metals in potable water using electronic nose technology.
Get PDFStudies have been carried out to determine the potential for the detection of different microbial species (Enterobacter aerogenes, Escherichia coli, Pseudomonas aeruginosa), alone and in the presence of low concentrations of different heavy metals (As, Cd, Pb and Zn) in bottled, reverse osmosis (RO) and tap water, using an electronic nose. Studies show that it is possible to discriminate control water samples from water contaminated with 0.5 ppm of a mixture of metals. The presence of heavy metals may modify the activity of microorganisms and thus the volatile production patterns. Bacterial species at 102–104 colony forming units (CFUs) ml−1 could be detected after 24 h of incubation. Work is in progress to identify the limits of detection for a range of other microorganisms, including, fungi and cyanobacteria, and chlorinated phenols using electronic nose technology
Electronic nose responses and acute phase proteins correlate in blood using a bovine model of respiratory infection
Get PDFThis study aimed (i) to assess the ability of electronic nose (e-nose) technology to differentiate
between blood samples of experimentally infected and non-infected subjects, and (ii) to evaluate
e-nose responses given by volatile organic compounds in relation to the acute phase reaction
generated in the host. In an animal model of gram-negative bacterial infection (20 calves;
intratracheal inoculation of Mannheimia haemolytica A1), the concentrations of the acute phase
proteins (APPs; i.e. lipopolysaccharide binding protein and haptoglobin) were measured in serum
samples before and after challenge, and headspaces of pre- and post-inoculation serum samples
were analysed using a conducting polymer based e-nose. Significant changes of certain e-nose
sensor responses allowed discrimination between samples before and after challenge. The
maximal changes in responses of sensitive e-nose sensors corresponded to the peak of clinical
signs. Significant correlations linked decreasing responses of multiple e-nose sensors to
increasing concentrations of APPs in the peripheral blood
Early detection and differentiation of microbial spoilage of bread using electronic nose technology
Get PDFThis study investigated the potential for use of electronic noses (e-noses) for early
rapid detection and differentiation of bread spoilage before visible signs of growth
occur. After 24 h incubation at 25°C it was possible to distinguish Penicillium
verrucosum, Aspergillus ochraceus, and Pichia anomala from 3 different species of
filamentous fungi before visible growth was observed on unmodified wheat agar using
a conducting polymer based e-nose (BH114). Discrimination of controls was possible
after 48 h. The BH114 e-nose was able to differentiate between Pseudomonas fragi,
Saccharomyces cerevisiae and P. verrucosum growing on 0.97 aw modified flour-based
media after only 24 h. The BH114 e-nose was able to discriminate between P. fragi
and S. cerevisiae growing in broth cultures and between different aw controls in
exponential growth (13.5 h). Discrimination of Staphylococcus aureus growing in
different aw broths and from uninoculated controls was achieved after 4.5 h.
The BH114 e-nose was also able to detect and differentiate microbial spoilage in situ
using bread analogues. Discrimination was improved using an incubation temperature
of 25°C when compared to 15°C. Discrimination of microbial and physiological
(enzymic) spoilage of bread analogues was possible using e-nose technology, cfu
counts and gas chromatograph-mass spectrometry (GC-MS) using an initial population
of 106 spores/cells ml-1. After 48 h differentiation of the spoilage types and between
some of the microbial spoilage organisms was possible using the e-nose. A significant
increase in populations was noted between 24 and 48 h. There were significant
differences between microbial populations detected after 48 and 72 h. Analysis of
volatile compounds produced, using GC-MS, showed that after 24 h P. anomala was
the only treatment to produce 2-propanol, ethyl acetate, and pentanol. P. anomala also
produced greater amounts of 3-methylbutanol when compared to P. verrucosum, B.
subtilis, lipoxygenase spoilage and controls.
Differentiation between toxigenic and non-toxigenic strains of Aspergillus parasiticus
in vitro was not achieved. However, in vitro on unmodified 2% wheat agar it was
possible to differentiate a non-toxigenic P. verrucosum strain from 4 citrinin producing
strains and controls using the BH114 e-nose. On bread analogues it was possible to discriminate two ochratoxin A (OTA) producing P. verrucosum strains after 24 h using
an initial population of 106 spore ml-1. Increased incubation resulted in only controls
being discriminated. Using a lower initial population of 103 spores ml-1 only controls
were discriminated after 24 h. However, after 48 h an OTA producing strain could also
be differentiated.
The potential for use of e-noses as a tool for screening novel antioxidants was also
investigated. It was possible to differentiate between broth samples with and without
the antioxidants propyl paraben and butylated hydroxyanisole using both the
conductance based e-nose (BH114) and a metal oxide and metal ion based e-nose
(NST3220 lab emission analyser). When samples without antioxidant were removed it
was possible to differentiate treatments containing antioxidant that had been inoculated
with micro-organism and those that had not. The e-noses were also able to
discriminate between sample times. Microbial populations and carbon dioxide levels
increased with incubation time. P. verrucosum and P. anomala populations were
greater in treatments without antioxidant whereas B. subtilis populations were greater
in 0.97 aw treatments containing antioxidant. CO2 production was greater in inoculated
treatments without an antioxidant except at 0.95 aw P. verrucosum produced greater
volumes in the presence of the antioxidant.
Using natural bread cross validation studies of 4 unknown contaminants (P. anomala,
P. verrucosum and B. subtilis and controls) was performed. This showed that using
initial populations of 103 spores/cells ml-1 the BH114 e-nose was able to differentiate
between all the unknown treatments after 48 h and the NST3220 lab emission analyser
after 72 h. CO2 production could be used to detect controls but it was not possible to
differentiate between the micro-organisms
The detection of patients at risk of gastrointestinal toxicity during pelvic radiotherapy by electronic nose and FAIMS : a pilot study
Get PDFIt is well known that the electronic nose can be used to identify differences between human health and disease for a range of disorders. We present a pilot study to investigate if the electronic nose and a newer technology, FAIMS (Field Asymmetric Ion Mobility Spectrometry), can be used to identify and help inform the treatment pathway for patients receiving pelvic radiotherapy, which frequently causes gastrointestinal side-effects, severe in some. From a larger group, 23 radiotherapy patients were selected where half had the highest levels of toxicity and the others the lowest. Stool samples were obtained before and four weeks after radiotherapy and the volatiles and gases emitted analysed by both methods; these chemicals are products of fermentation caused by gut microflora. Principal component analysis of the electronic nose data and wavelet transform followed by Fisher discriminant analysis of FAIMS data indicated that it was possible to separate patients after treatment by their toxicity levels. More interestingly, differences were also identified in their pre-treatment samples. We believe these patterns arise from differences in gut microflora where some combinations of bacteria result to give this olfactory signature. In the future our approach may result in a technique that will help identify patients at “high risk” even before radiation treatment is started
Differentiation of Agaricus species and other homobasidiomycetes based on volatile production patterns using an electronic nose system
Get PDFComparisons of the qualitative volatile production patterns between seven species of Agaricus, and between two of Volvariella and Pleurotus and one Coprinus species when grown at 25°C on agar media for 14d were made. There was good reproducibility between the volatile production patterns of the same species using an electronic nose unit with a 14 conducting sensor polymer array. Principle Component Analysis (PCA) showed that it was possible to discriminate between five of the seven Agaricus species, but that some overlap occurred between the others. Cluster analysis showed that there was also overlap between some species with the tropical collection of A. bitorquis separating out from the others. The volatile production profile of the commercial A. bisporus was close to that of a wild species, A. campestris. A. bisporus could be readily differentiated from other non-Agaricus species. This study demonstrates the potential for using electronic nose systems to rapidly differentiate mycelial cultures of homobasidiomycete mushrooms
Combined electronic nose and tongue for a flavour sensing system
Get PDFWe present a novel, smart sensing system developed for the flavour analysis of liquids. The system comprises both a so-called "electronic tongue" based on shear horizontal surface acoustic wave (SH-SAW) sensors analysing the liquid phase and a so-called "electronic nose" based on chemFET sensors analysing the gaseous phase. Flavour is generally understood to be the overall experience from the combination of oral and nasal stimulation and is principally derived from a combination of the human senses of taste (gustation) and smell (olfaction). Thus, by combining two types of microsensors, an artificial flavour sensing system has been developed. Initial tests conducted with different liquid samples, i.e. water, orange juice and milk (of different fat content), resulted in 100% discrimination using principal components analysis; although it was found that there was little contribution from the electronic nose. Therefore further flavour experiments were designed to demonstrate the potential of the combined electronic nose/tongue flavour system. Consequently, experiments were conducted on low vapour pressure taste-biased solutions and high vapour pressure, smell-biased solutions. Only the combined flavour analysis system could achieve 100% discrimination between all the different liquids. We believe that this is the first report of a SAW-based analysis system that determines flavour through the combination of both liquid and headspace analysis
Bifurcation analysis of nose landing gear shimmy with lateral and longitudinal bending
No full textWe develop and study a model of an aircraft nose landing gear with torsional, lateral and longitudinal degrees of freedom. The corresponding three modes are coupled in a nonlinear fashion via the geometry of the landing gear in the presence of a nonzero rake angle, as well as via the nonlinear tyre forces. Their interplay may lead to different types of shimmy oscillations as a function of the forward velocity and the vertical force on the landing gear. Methods from nonlinear dynamics, especially numerical continuation of equilibria and periodic solutions, are used to asses how the three modes contribute to different types of shimmy dynamics. We conclude that the longitudinal mode does not actively participate in the nose landing gear dynamics over the entire range of forward velocity and vertical force
Development of medical point-of-care applications for renal medicine and tuberculosis based on electronic nose technology
Get PDFINTRODUCTION: Current clinical diagnostics are based on biochemical,
immunological or microbiological methods. However, these methods are operator
dependent, time consuming, expensive and require special skills, and are therefore not
suitable for point-of-care testing. Recent developments in gas-sensing technology and
pattern recognition methods make electronic nose technology an interesting
alternative for medical point-of-care devices. METHODS: We applied a gas sensor
array based on 14 conducting polymers to monitor haemodialysis in vitro and to
detect pulmonary tuberculosis in both culture and sputum. RESULTS and
DISCUSSION: The electronic nose is able to distinguish between control blood and
“uraemic” blood. Furthermore, the gas sensor array is not only capable of
discriminating pre- from post-dialysis blood (97% accuracy) but also can follow the
volatile shift occurring during a single haemodialysis session. The electronic nose can
be used for both dialysate side and blood-side monitoring of haemodialysis. The pattern observed for post- and pre-dialysis blood might reflect the health status of the
patients and can therefore be related to the long-term outcome. Furthermore, the gas
sensor array was also able to discriminate between Mycobacterium spp. and other
lung pathogens such as Pseudomonas aeruginosa. More importantly the gas sensor
array was capable of resolving different Mycobacterium spp. such as Mycobacterium
tuberculosis, M. scrofulaceum, and M. avium in both liquid culture and spiked sputum
samples. The detection limit for M. tuberculosis in both sputum and liquid culture is 1
x 104 mycobacteria ml-1 and therefore partially fulfils the requirement set by the
WHO. The gas sensor array was able to detect culture proven TB with a sensitivity of
89% and a specificity of 91%. CONCLUSIONS: In conclusion, this study has shown
the ability of an electronic nose as a point-of-care device in these areas
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