Can graphene help us avoid sunburn?

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Australian researchers combine titanium dioxide and graphene to develop a novel, low-power sun sensor

Sunlight is vital to human health. Without regular exposure to ultraviolet B (UVB), our bodies can struggle to make sufficient vitamin D to support the development of strong bones. But too much sunlight can cause sunburn, and if unchecked over extended periods, can even lead to skin cancer. This has prompted the development of wearable sun sensors that change appearance – or notify users via smartphone – when their exposure to sunlight exceeds recommended levels.

In the November issue of Carbon [DOI: 10.1016/j.carbon.2018.06.010], researchers from the University of New South Wales propose a new design for a UV sensor – one based on the photoreduction of graphene oxide (GO). The sensor was fabricated by the simultaneous deposition of GO sheets and titanium dioxide (TiO2) nanoparticles onto interdigitated electrodes. Thanks to its large band gap, TiO2 is a UV-sensitive photocatalyst. When illuminated in the presence of carbon and ethanol, photogenerated electrons from the TiO2 transfer to the sheets of GO, reducing it, and altering its conductivity.

In this paper, Gooding et al. found a gradual decrease in resistance (or increase in conductivity) during a short, initial period of UV exposure. However, after extended UV exposure (36 hours), the resistance of the graphene sheets dropped significantly from 192 kΩ to 0.84 kΩ. Exposure to visible light had no impact on the sample, which suggests that the sensor is particularly tuned to the UV wavelengths that can cause sunburn. In addition, each cycle of UV exposure produced a change in the baseline conductivity – in other words, the sensor ‘remembered’ each incident of sun exposure.

These results suggest that the sensor accurately mimics the response of human skin to sun. The initial response to UV exposure is minimal, but as the dose increases, changes – be it an increase in sample conductivity or the onset of sunburn – quickly accumulate. The ‘memory’ effect of the sensor means that the amount of sun exposure is constantly being logged, without power, and it can be read at any time. The authors also suggest that the oxidation of the sensor could also be tuned, so as to reflect the behaviour of different skin types. In this way, they say it can act as a reliable sun sensor for the real-time monitoring of sun exposure.

This story first appeared on Materials Today on 29th October:

Original research paper ($): Parisa S. Khiabani, Mehran B. Kashi, Xiao Zhang, Raheleh Pardehkhorram, Bijan P. Markhali, Alexander H. Soeriyadi, Adam P. Micolich, J. Justin Gooding. “A graphene-based sensor for real time monitoring of sun exposure” Carbon 138 (2018) 215-218. DOI: 10.1016/j.carbon.2018.06.010