Wearable colorimetric sensors for biodiagnostic applications Finnegan, M. and Morrin, A. Insight SFI Research Centre for Data Analytics, National Centre for Sensor Research, Ireland Wearable sensors have become of widespread interest in the medical and scientific communities in recent years due to their powerful potential in monitoring human health. These sensors offer a non-invasive method of sampling which can allow for pain-free sampling of the patient’s skin which is then analysed in order to probe information from the body. Volatile organic compounds are emitted from the skin and specific volatile profiles have been linked to various diseases such as atopic dermatitis, wound infection and melanoma. Also linked to the health of an individual is the hydrogen ion content/pH of the skin. Many studies have suggested that there is a relationship between skin surface pH and disease. In addition to this, aldehyde emission from skin is of interest and is thought to be a biomarker of oxidative stress on the skin. Our group has studied skin volatile emission for several years [1][2] using gas-chromatography mass-spectrometry workflows. Aldehyde emission from skin has been identified in these studies. More recently, we have established evidence for a correlation between the emission rate of volatile fatty acids from skin and skin surface pH [3]. This research investigates the use of simple, cost-effective wearable colorimetric sensor platforms to monitor volatile emission from skin. A simple pH indictor dye, incorporated into a wearable platform, is used to monitor skin surface pH via the volatile ammonia emission from skin [4]. The wearable platform was then adapted to contain sensor spots of aniline-containing dyes to monitor aldehyde emission from skin. Many of the sampling and analysis methods for these applications discussed in previous literature require complex electronics and instrumentation. This flaw prompted revisiting to the pre-electronic era of analytical chemistry by the use of colorimetric sensors. The lack of these bulky components in the colorimetric sensor platform used here allows the sensor to have a more flexible, conformable design which can adhere to skin with ease. Overall, this work aims to present the challenges involved in developing these wearable colorimetric sensors as well as highlighting their potential use for the monitoring of volatile emission from skin. References 1. Duffy E, Jacobs M R, Kirby B and Morrin A 2017 Probing skin physiology through the volatile footprint: Discriminating volatile emissions before and after acute barrier disruption Exp. Dermatol. 26 919–25 2. Duffy E, Guzman K D, Wallace R, Murphy R and Morrin A 2017 Non-Invasive Assessment of Skin Barrier Properties: Investigating Emerging Tools for In Vitro and In Vivo Applications Cosmetics 4 44 3. Shetewi T, Finnegan M, Fitzgerald S, Xu S, Duffy E and Morrin A 2021 Investigation of the relationship between skin-emitted volatile fatty acids and skin surface acidity in healthy participants—a pilot study J. Breath Res. 15 037101 4. Finnegan M, Duffy E and Morrin A 2022 The determination of skin surface pH via the skin volatile emission using wearable colorimetric sensors Sensing and Bio-Sensing Research 35 100473
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