The use of a gas chromatograph coupled to a metal oxide sensor for rapid assessment of stool samples from irritable bowel syndrome and inflammatory bowel disease patients.

There is much clinical interest in the development of a low-cost and reliable test for diagnosing inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS), two very distinct diseases that can present with similar symptoms. The assessment of stool samples for the diagnosis of gastro-intestinal diseases is in principle an ideal non-invasive testing method. This paper presents an approach to stool analysis using headspace gas chromatography and a single metal oxide sensor coupled to artificial neural network software. Currently, the system is able to distinguish samples from patients with IBS from patients with IBD with a sensitivity and specificity of 76% and 88% respectively, with an overall mean predictive accuracy of 76%.

Towards point of care testing for C. difficile infection by volatile profiling, using the combination of a short multi-capillary gas chromatography column with metal oxide sensor detection.

Rapid volatile profiling of stool sample headspace was achieved using a combination of short multi-capillary chromatography column (SMCC), highly sensitive heated metal oxide semiconductor (MOS) sensor and artificial neural network (ANN) software. For direct analysis of biological samples this prototype offers alternatives to conventional GC detectors and electronic nose technology. The performance was compared to an identical instrument incorporating a long single capillary column (LSCC). The ability of the prototypes to separate complex mixtures was assessed using gas standards and homogenised in house 'standard' stool samples, with both capable of detecting more than 24 peaks per sample. The elution time was considerably faster with the SMCC resulting in a run time of 10 minutes compared to 30 minutes for the LSCC. The diagnostic potential of the prototypes was assessed using 50 C. difficile positive and 50 negative samples. The prototypes demonstrated similar capability of discriminating between positive and negative samples with sensitivity and specificity of 85% and 80% respectively. C. difficile is an important cause of hospital acquired diarrhoea, with significant morbidity and mortality around the world. A device capable of rapidly diagnosing the disease at the point of care would reduce cases, deaths and financial burden.

A sensor system for monitoring the simple gases hydrogen, carbon monoxide, hydrogen sulfide, ammonia and ethanol in exhaled breath.

A sensor array system was constructed incorporating electrochemical sensors for hydrogen, carbon monoxide, hydrogen sulfide and ethanol, a ceramic sensor for total volatiles and a dye-based optical ammonia sensor. The system was calibrated using standard gases balanced with dry air. Limit of detection and % relative standard deviation values (n = 10) for the sensors in the array are hydrogen (0.1 ppm, 2.6%), carbon monoxide (0.4 ppm, 2.1%), ethanol (0.5 ppm, 1.5%), hydrogen sulfide (0.1 ppm, 1.5%) and ammonia (0.6 ppm, 10.7%). Humidity effects were assessed by calibrating with humidified standard gases (hydrogen, carbon monoxide) or spiked breath samples in Tedlar bags (hydrogen sulfide, ethanol and ammonia). The calibration data were used to establish a cross-sensitivity matrix. The concentration of breath volatiles was found to be dependent on exhalation rate and exhalation volume. A test protocol based on these data required volunteers to exhale 1 litre of breath at a rate between 7.5 and 17.5 l min(-1). Sensor responses were measured for 40 s then purged at 7 l min(-1) (150 s). A longitudinal study was undertaken of ten asymptomatic volunteers over a five-day period. Volunteers ate an ad hoc diet, but fasted prior to giving the first breath sample and then gave samples every hour for 8 h. Breath hydrogen levels for volunteers showed large variations within a day and also from day to day. Fasting levels ranged between 0.3 and 34.1 ppm (mean 9.1 ppm). The carbon monoxide levels for non-smokers were between 0.6 and 4.9 ppm (mean 2.1 ppm), whilst for smokers they were between 8.3 and 18.7 ppm (mean 12.8 ppm). The measured levels of other gases on breath were as follows: hydrogen sulfide (0-1.3 ppm, mean 0.33 ppm), ethanol (0-3.9 ppm, mean 0.62 ppm) and ammonia (0-1.3 ppm mean 0.42 ppm). The system was capable of direct quantitative measurements of low concentrations of a range of volatiles on exhaled breath. The measured values for compounds on the breath of asymptomatic volunteers were in broad agreement with quoted literature ranges. The system will now be assessed in a clinical setting.

The characteristics of novel low-cost sensors for volatile biomarker detection.

For breath analyses, volatile detectors capable of sensing extremely low concentrations in the sub-ppm range are required. Novel room temperature sensors were fabricated based on ultraviolet light activation of nanoparticulate metal oxide surfaces using light emitting diodes. These sensors gave reversible electrical resistance changes in the low ppm/ppb range to volatile organic compounds found in breath, including acetone, acetaldehyde, pentane and ethanol.