Combined electronic nose and tongue for a flavour sensing system

We 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

CMOS and SOI CMOS FET-based gas sensors

In recent years, there has been considerable interest in the use of gas/vapour monitors and electronic nose instruments by the environmental, automotive and medical industries. These applications require low cost and low power sensors with high yield and high reproducibility, with an annual prospective market of 1 million pounds. Present device and sensor technologies suffer a major limitation, their incompatibility with a standard silicon CMOS process. These technologies have either operating/annealing temperatures unsuited for MOSFET operation or an inappropriate sensing mechanism. The aim of this research is the development of CMOS compatible gas/vapour sensors, with a low cost of fabrication, high device repeatability and, in the future, transducer sensor amalgamation. Two novel approaches have been applied, utilising bulk CMOS and SOI BiCMOS. The bulk CMOS designs use a MOSFET sensing structure, with an active polymeric gate material, operating at low temperatures (<100°C), based on an array device of four elements, with channel lengths of 10 μm or 5 μm. The SOI designs exploit a MOSFET heater with a chemoresistive or chemFET sensing structure, on a thin membrane formed by the epi-taxial layer. By applying SOI technology, the first use in gas sensor applications, operating temperatures of up to 300 °C can be achieved at a power cost of only 35 mW (simulated). Full characterisation of the bulk CMOS chemFET sensors has been performed using electrochemically deposited (e.g. poly(pyrrole)/BSA)) and composite polymers (e.g. poly(9-vinylcarbazole)) to ethanol and toluene vapour in air. In addition, environmental factors (humidity and temperature) on the response and baseline were investigated. This was carried out using a newly developed flow injection analysis test station, which conditions the test vapour to precise analyte (<15 PPM of toluene) and water concentrations at a fixed temperature (RT to 105°C +- 0.1), with the sensor characterised by either I-V or constant current instrumentation. N-channel chemFET sensors operated at constant current (10 μA) with electrochemically deposited and composite polymers showed sensitivities of up to 1.1 μV/PPM and 4.0 μV/PPM to toluene vapour and to 1.1 μV/PPM and 0.4 μV/PPM for ethanol vapour, respectively, with detection limits of <20 PPM and <100 PPM to toluene and <20 PPM and 10+ PPM to ethanol vapour (limited by baseline noise), respectively. These responses followed either a power law (composite polymers) or a modified Langmuir isotherm model (electrochemically deposited polymers) with analyte concentration. It is proposed that this reaction-rate limited response is due to an alteration in polymers work function by either a partial charge transfer from the analyte or a swelling effect (polymer expansion). Increasing humidity caused, in nearly all cases a reduction in relative baseline, possible by dipole formation at the gate oxide surface. For the response, increasing humidity had no effect on sensors with composite polymers and an increase for sensors with electrochemically-deposited polymers. Higher temperatures caused a reduction in baseline signal, by a thermal expansion of the polymer, and a reduction in response explained by the analyte boiling point model describing a reduction in the bulk solubility of the polymer. Electrical and thermal characterisation of the SOI heaters, fabricated by the MATRA process, has been performed. I-V measurements show a reduction in drain current for a MOSFET after back-etching, by a degradation of the carrier mobility. Dynamic measurement showed a two stage thermal response (dual exponential), as the membrane reaching equilibrium (100-200 ms) followed by the bulk (1-2 s). A temperature coefficient of 8 mW/°C was measured, this was significantly higher than expected from simulations, explained by the membrane being only partially formed. Diode and resistive temperature sensors showed detection limits under 0.1°C and shown to measure a modulated heater output of less than 1°C at frequencies higher than 10Hz. The principal research objectives have been achieved, although further work on the SOI device is required. The results and theories presented in this study should provide a useful contribution to this research area

Development of a compact, IoT-enabled electronic nose for breath analysis

In this paper, we report on an in-house developed electronic nose (E-nose) for use with breath analysis. The unit consists of an array of 10 micro-electro-mechanical systems (MEMS) metal oxide (MOX) gas sensors produced by seven manufacturers. Breath sampling of end-tidal breath is achieved using a heated sample tube, capable of monitoring sampling-related parameters, such as carbon dioxide (CO2), humidity, and temperature. A simple mobile app was developed to receive real-time data from the device, using Wi-Fi communication. The system has been tested using chemical standards and exhaled breath samples from healthy volunteers, before and after taking a peppermint capsule. Results from chemical testing indicate that we can separate chemical standards (acetone, isopropanol and 1-propanol) and different concentrations of isobutylene. The analysis of exhaled breath samples demonstrate that we can distinguish between pre- and post-consumption of peppermint capsules; area under the curve (AUC): 0.81, sensitivity: 0.83 (0.59–0.96), specificity: 0.72 (0.47–0.90), p-value: <0.001. The functionality of the developed device has been demonstrated with the testing of chemical standards and a simplified breath study using peppermint capsules. It is our intention to deploy this system in a UK hospital in an upcoming breath research study

Low cost optical electronic nose for biomedical applications

Here we report on the development of a Non-Dispersive Infrared Sensor (NDIR) optical electronic nose, which we intend to target towards healthcare applications. Our innovative electronic nose uses an array of four different tuneable infra-red detectors to analyse the gas/volatile content of a sample under test. The instrument has the facility to scan a range of wavelengths from 3.1 μm and 10.5 μm with a step size of 20 nm. The use of a tuneable filter, instead of expensive lasers, reduces the overall cost of the system. We have tested our instrument to a range of gases and vapours and our electronic nose is able to detect, for example, methane down to single figure ppm at two different wavelengths. It is also able to discriminate between complex odours, here we present the results from 6 different chemicals. In this case, fixed frequency measurements were used as “virtual sensors” and their output then analysed by (PCA), which for all but one case, showed good separation

The detection of wound infection by ion mobility chemical analysis

Surgical site infection represents a large burden of care in the National Health Service. Current methods for diagnosis include a subjective clinical assessment and wound swab culture that may take several days to return a result. Both techniques are potentially unreliable and result in delays in using targeted antibiotics. Volatile organic compounds (VOCs) are produced by micro-organisms such as those present in an infected wound. This study describes the use of a device to differentiate VOCs produced by an infected wound vs. colonised wound. Malodourous wound dressings were collected from patients, these were a mix of post-operative wounds and vascular leg ulcers. Wound microbiology swabs were taken and antibiotics commenced as clinically appropriate. A control group of soiled, but not malodorous wound dressings were collected from patients who had a split skin graft (SSG) donor site. The analyser used was a G.A.S. GC-IMS. The results from the samples had a sensitivity of 100% and a specificity of 88%, with a positive predictive value of 90%. An area under the curve (AUC) of 91% demonstrates an excellent ability to discriminate those with an infected wound from those without. VOC detection using GC-IMS has the potential to serve as a diagnostic tool for the differentiation of infected and non-infected wounds and facilitate the treatment of wound infections that is cost effective, non-invasive, acceptable to patients, portable, and reliable

A novel, low-cost, portable PID sensor for detection of VOC

A low cost portable photoionization (PID) sensor was successfully designed and manufactured. Unlike existing commercial PID sensors, our device provides two outputs, one associated with the total chemical components and a second that provides some level of compositional information. We believe that this makes this sensor system more useful than a standard PID, with a similar, if not lower, cost point. Our PID sensor was tested with gas concentrations down to 2 ppm isobutylene. These results indicate that the limit of detection will be well below 1 ppm. Further detection tests were carried out with ethanol, acetone and isobutylene, which showed similar sensitivities. Compositional measurements were also undertaken and the results presented shows our sensor can discriminate successfully between low concentration isobutylene and 2-pentanone

A novel, low-cost, portable PID sensor for the detection of volatile organic compounds

We report on the design, fabrication and verification of a portable, low cost PID. Unlike commercial PID sensors, ours provides two outputs. One output correlates to the total chemical components and a second that provides some level of compositional information. We believe that this makes this sensor system more useful than a standard commercial PID, at a similar cost point. Our PID sensor was tested with gas concentrations down to 2 ppm isobutylene. The results presented indicate that the limit of detection will be well below 1 ppm. Compositional analysis was also carried out and the results presented shows our sensor can successfully discriminate between low concentrations of 2-hexanone, isobutylene, propanol, 2-pentanone, 2-octanone and 2-heptanone

Design and development of a low-cost, portable monitoring device for indoor environment quality

This article describes the design and development of a low-cost, portable monitoring system for indoor environment quality (IEQ). IEQ is a holistic concept that encompasses elements of indoor air quality (IAQ), indoor lighting quality (ILQ), acoustic comfort, and thermal comfort (temperature and relative humidity). The unit is intended for the monitoring of temperature, humidity, PM2.5, PM10, total VOCs (×3), CO2, CO, illuminance, and sound levels. Experiments were conducted in various environments, including a typical indoor working environment and outdoor pollution, to evaluate the unit’s potential to monitor IEQ parameters. The developed system was successfully able to monitor parameter variations, based on specific events. A custom IEQ index was devised to rate the parameter readings with a simple scoring system to calculate an overall IEQ percentage. The advantages of the proposed system, with respect to commercial units, is associated with better customisation and flexibility to implement a variety of low-cost sensors. Moreover, low-cost sensor modules reduce the overall cost to provide a comprehensive, portable, and real-time monitoring solution. This development facilities researchers and interested enthusiasts to become engaged and proactive in participating in the study, management, and improvement of IEQ

A simple, portable, computer-controlled odour generator

In this paper, we report on the on-going development of a simple computer controlled odour generator. The unit comprises of eight “aroma dispensers” that can be loaded with liquid samples (in our case fragrances such as tea-tree oil). These aroma dispensers use a combination of the capillary effect and thermal heating to release aroma to the user. The instrument also includes a controlled fan and a gas sensor to monitor the release of the aroma. Interaction with the aroma generator is through a custom interface that releases aromas in line with either direct control or a preprogrammed sequence. We believe this unit can be used in combination with virtual environments to enhance such experiences

Development of a portable, multichannel olfactory display transducer

In this paper we report on the development of a simple, yet innovative multi-channel olfactory display. Unlike other sensory stimuli (specifically sight and sound), digital olfactory technology has yet to have wide-spread commercial success. Our proposed system will release up to 8 different liquid phase aromas (essential oils) using a thermal mechanism. The unit contains a speed controlled fan, temperature control of the heating element and a gas sensor to provide feedback to inform the release rate. It can be connected (via Bluetooth LE) to a tablet/computer to control the timing and intensity of the aroma. External measurements show that aromas can be detected within a few seconds of release and produce a broad range of intensities from low ppm to 10’s of ppm