Volatile emissions from compressed tissue

Detecting bacterial infections in wounds: a review of biosensors and wearable sensors in comparison with conventional laboratory methods

Review on laboratory-based methods and biosensors and wearable sensors for detecting wound infection by aerobic and anaerobic bacteria.

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.

Detection of axillary perspiration metabolites using ion mobility spectrometry coupled to rapid gas chromatography

The composition of human sweat-and as a consequence the composition of volatiles released from human skin-strongly depends on genetic preconditions, diet, stress, personal hygiene but also on health status and medication. Accordingly, the composition is a carrier of information on the physical and mental states of a person. Therefore, rapid on-site analysis of the relevant substances may be used for medical diagnosis and medication control or even for psychological characterisation. Ion mobility spectrometry coupled to rapid gas chromatography (GC-IMS) was applied to the analysis of human axillary sweat as a sensitive, selective, rapid, and non-invasive method in a feasibility study. For this purpose, a sampling chamber was designed and manufactured. The design and the experimental setup were validated successfully. At least 179 human metabolites could be detected by GC-IMS from the skin of 7 volunteers. Fifteen metabolites were available in all samples from all volunteers and therefore can be characterised as basic sweat compounds which might enable the localisation of hidden persons. Furthermore, in a preliminary feasibility study, the potential of GC-IMS for differentiating the composition of sweat after physical exercises and in a stressful situation-even gender specific-could be demonstrated. Thus, with GC-IMS, a rapid and mobile analytical tool for the analysis of skin volatiles is available for a broad range of applications, e.g. with regard to axillary odour, human health, nutrition, consumption of remedies or drugs of abuse, the localisation of trapped or hidden persons, or even the characterisation of the reaction on stressful situations. Graphical abstract.

Factors influencing breath analysis results in patients with diabetes mellitus

Breath analysis is used to detect the composition of exhaled gas. As a quick and non-invasive detection method, breath analysis provides deep insights into the progression of various kinds of diseases, especially those with metabolism disorders. Abundant information on volatile compounds in diabetic patients has been studied in numerous articles in the literature. However, exhaled gas in diabetic patients can be altered by various complications. So far, little attention has been paid to this alteration. In our paper, we found that under air pollution conditions, diabetic patients exhale more nitric oxide. Diabetic patients with heart failure exhale more acetone than those without heart failure. After ¹³C-labeled glucose intake, patients infected with Helicobacter pylori exhaled more ¹³C and less ¹⁸O than those without infection. Exhalation with chronic kidney disease changes volatile organic compounds on a large scale. Diabetic patients with ketoacidosis exhale more acetone than those without ketoacidosis. Some specific volatile organic compounds also emanate from diabetic feet. By monitoring breath frequency, diabetic patients with obstructive sleep apnea syndrome exhibit a unique breath pattern and rhythm as compared with other diabetic patients, and sleep apnea is prevalent among diabetic patients. In addition to clinical findings, we analyzed the underlying mechanisms at the levels of molecules, cells and whole bodies, and provided suggestions for further studies.

Real-time monitoring of skin ethanol gas by a high-sensitivity gas phase biosensor (bio-sniffer) for the non-invasive evaluation of volatile blood compounds

In this study, a highly sensitive and selective biochemical gas sensor (bio-sniffer) and real-time monitoring system with skin gas cell was constructed for the determination of ethanol gas concentration on human skin. This bio-sniffer measured the concentration of ethanol according to the change in fluorescence intensity of nicotinamide adenine dinucleotide (NADH), which is produced in an enzymatic reaction by alcohol dehydrogenase (ADH). The NADH detection system used an ultraviolet light emitting diode (UV-LED) as the excitation light, and a highly sensitive photomultiplier tube as a fluorescence intensity detector. The calibration range of the ethanol bio-sniffer was validated from 25 ppb to 128 ppm. To measure the concentration of ethanol within skin gas, subjects ingested an alcohol beverage, and the sensor output was monitored. We chose the central part of the palm, a back of the hand, and a wrist as targets. The real-time concentration of skin ethanol gas at each target was measured after drinking. The maximum output values were reached at approximately 70 min after drinking and then gradually decreased. We showed that ethanol release kinetics were different depending on the part of the hand measured with the developed monitoring system. Accordingly, this highly sensitive and selective bio-sniffer with a skin gas cell could be used to measure ethanol on the skin surface and could be applied for breath and skin gas research, as well as investigation of volatile blood compounds used as biomarkers for clinical diagnosis.

Volatile compounds emission from teratogenic human pluripotent stem cells observed during their differentiation in vivo

Several investigations point out that the volatile fraction of metabolites, often called volatilome, might signal the difference processes occurring in living beings, both in vitro and in vivo. These studies have been recently applied to stem cells biology, and preliminary results show that the composition of the volatilome of stem cells in vitro changes along the differentiation processes leading from pluripotency to full differentiation. The identification of pluripotent stem cells is of great importance to improve safety in regenerative medicine avoiding the formation of teratomas. In this paper, we applied gas chromatography and gas sensor array to the study of the volatilome released by mice transplanted with human induced pluripotent stem cells (hiPSCs) or embryoid bodies (EBs) derived from hiPSCs at 5 days and spontaneously differentiated cells at 27 day. Gas chromatography analysis finds that, in mice transplanted with hiPSCs, the abundance of 13 volatile compounds increases four weeks after the implant and immediately before the formation of malignant teratomas (grade 3) become observable. The same behaviour is also followed by the signals of the gas sensors. Besides this event, the gas-chromatograms and the sensors signals do not show any appreciable variation related neither among the groups of transplanted mice nor respect to a placebo population. This is the first in vivo observation of the change of volatile metabolites released by human induced pluripotent stem cells and hiPSCs-derived cells during the differentiation process. These results shed further light on the differentiation mechanisms of stem cells and suggest possible applications for diagnostic purposes for an early detection of tumor relapse after surgery.

Activated carbon-plasticised agarose composite films for the adsorption of thiol as a model of wound malodour

Conditions such as diabetes, cardiovascular disease and long-term immobilisation can precipitate the development of chronic dermal ulcers. Such wounds are associated with inflammation and bacterial contamination which in turn can lead to the liberation of offensive odours that cause patient embarrassment and, in some instances, social isolation. Activated carbon-containing dressings have been used to manage the odours from such wounds. However, these can be bulky and can become fouled by wound exudate. Agarose is a natural polysaccharide derived from seaweed that forms brittle free-standing films that can be made pliable by addition of a plasticiser. In this study, activated carbon-containing plasticised agarose films were evaluated for their ability to sequester thiol-containing molecules from solution and the gaseous phase. The water vapour transmission rate was also evaluated to determine the potential breathability of these films should they be considered for application to the skin. It was found that the adsorption of thiols was directly proportional to the activated carbon content of the films. Water vapour was found to pass relatively freely through the films indicating that sweat-induced tissue maceration would be unlikely to occur if applied clinically. In conclusion, activated carbon-containing plasticised agarose films have some potential in the sequestration of malodourous molecules such as those liberated from chronic dermal wounds.