Low-Cost and Mobile Ultraviolet Radiation Sensor using Electrochemical and Electrochromic Detection

Abstract

My project involved the development of a low-cost and mobile ultraviolet radiation (UVR) sensor. UVR overexposure is associated with health issues such as an increased risk of skin cancer development. Current technology primarily involves the use of chromophores that change color with UVR exposure. Colorimetric sensors are however less sensitive and worsen as the chromophores degrade over time. The use of spectrometers as the transduction element for colorimetric sensors make them less useful as wearable sensors due to bulkiness and cost. My work focuses on a wearable sensor based on electrochemical and electrochromic detection. The sensor was fabricated using layer-by-layer assembly. The sensor was comprised of: i) flexible polydimethylsiloxane (PDMS) base; ii) conductive silver nanoparticles (Ag-NPs) with cellulose nanocrystal (CNC) ink; iii) carbon nanotubes (CNTs)/CNC/titanium dioxide (TiO2); iv) Prussian Blue redox poly(isopropylacrylamide) polymer microgel. To ensure the four layers were permanently glued to the PDMS base, (3-glycidyloxypropyl)trimethoxy-silane (GOPS) was used as an adhesive. The sensor mechanism involves TiO2 reacting with UVR to create electron/hole pairs, which—in presence of moisture—results in the formation of H2O2. The H2O2 oxidizes the redox microgel from Fe2+ to Fe3+, which induces polymer shrinkage. The shrunk polymer compacts the CNC/CNT conductive layer reducing its conductivity. The change in conductivity of the sensor was quantified by cyclic voltammetry to determine the effect of UVR and H2O2 on the sensor. Both the CNC/CNT control sensor cathodic and anodic capacitance displayed greater reactivity than the UV sensor cathodic and anodic capacitance in response to increasing H2O2 concentrations. The time studies provided inconsistent results which emphasize the need for more tests to be performed and stricter laboratory conditions applied. The oxidation of the redox microgel produced a successful colorimetric change which was used for verification of the electrochromic detection mechanism. The sensor was found to need optimization to enable better sensitivity to ensure its viability in application, however, the confirmation of the electrochromic color detection mechanism indicates the sensors current ability to provide naked eye detection of UVR exposure.

Faculty Mentor: Samuel Mugo

Department: Chemistry