Our group has developed an electrochemical UV sensor utilizing carbon quantum dots as the photoactive material functionalizing a graphene semiconductor layer. When used as a photoactive electrode in contact with a solid polymer electrolyte in a photoelectrochemical cell, illumination under UV radiation at 365 nm induces a photocurrent with a corresponding change in device voltage. The time-dependent change in voltage is a function of UV radiation intensity. Varying the UV LED power density from 26.6 mW/cm 2 (approximately 100% intensity) to 5.1 mW/cm 2 (approximately 20% intensity) results in time-dependent potential changes (dU/dt) ranging from approximately 4.0 mV/s to 0.5 mV/s. The dU/dt vs. LED power density trend is nearly linear (r 2 = 0.97). Similarly, when a constant bias potential is applied to the cell, a sustained photocurrent is observed under UV illumination, with the magnitude of the photocurrent a linear function of the LED power density. In that case, the coefficient of determination r 2 = 0.98. These results indicate that a graphene semiconductor, when functionalized with a photoactive material like carbon quantum dots, has application as a UV sensor with the ability to quantify the intensity of UV radiation. Nano-scale carbon-based materials, such as carbon quantum dots (CQDs), have received significant attention recently due to their unique optical and electronic properties.1 Depending on the particular synthesis procedure and the carbon source, carbon quantum dots can be environmentally and biologically benign.2 It is interesting to note that practically any carbon-containing material can be used as the source for carbon quantum dots. Literature reports on a host of starting materials exist. For example, Meiling and co-workers have used starch and tris-acetate-EDTA buffer as carbon sources.3 Du and co-workers prepared carbon quantum dots from orange pericarp in a hydrothermal treatment method. 4 Zhou, et al., used watermelon peel as a carbon source.5 Often, carbon quantum dots are simply obtained from more typical laboratory chemicals like citric acid. [6][7][8] There are also many possible CQD synthesis techniques, including hydrothermal methods, 9,10 electrochemical methods 11 and microwave-assisted methods.12,13 The combination of widely-variable carbon sources and facile synthesis procedures has ensured that CQD research continues to grow. It is likely that organic CQDs will make up a large share of the growing nanomaterial market. In fact, CQDs have been suggested as markers for biosensing and bioimaging, It is generally accepted that size and surface properties determine CQD optical and electronic behavior. Modification of the surface properties could be achieved by doping the CQDs, often with nitrogen. 24,25 For example, it has been demonstrated that N-doping of CQDs increases quantum yield and electron transfer.26 These N-doped CQDs (henceforth referred to as N-CQDs in this paper) possess unique properties like electrocatalytic activity, controllable luminescence and are also biologic...
Skin cancer is a pressing public health issue, especially in rural communities like Appalachia.1 Increasing public awareness about the risk of exposure to UV radiation and its correlation to the prevalence of skin cancer could change public behavior in a positive way. Such behavioral changes could ultimately reduce the rate of skin cancer and directly address public health. Wearable UV sensors that provide easy-to-understand, accurate and reproducible results is one possible avenue to impact public awareness and behavior. Our group has developed nitrogen-doped carbon quantum dot/graphene (N-CQD/graphene) photoactive electrodes that generate a sustained photocurrent upon illumination with UV radiation. The sensor consists of the N-CQD/graphene photoactive electrode and a nonphotoactive graphene electrode sandwiching a Nafion® polymer electrolyte membrane. Critically, the magnitude of the photocurrent response is proportional to the intensity of the incident UV radiation.2 Incorporating the photoactive electrode into a sensor using a solid polymer electrode could lead to flexible UV sensors ideal for wearable applications by the general public. This presentation will detail synthesis and evaluation procedures for the electrochemical UV sensor. We will discuss current limitations that must be overcome before such a wearable device can be made technically feasible. [1]. Appalachia Community Cancer Network. Addressing the Cancer Burden in Appalachian Communities, 2010. Retrieved from http://www.accnweb.com/pages/cancer-burden-app.pdf [2]. Y. Wang, M. Myers and J.A. Staser, J. Electrochem. Soc., 164: H3001-H3007 (2018).
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