Subscriber access provided by UOW Library
Article
A Paper Based Sensor for Monitoring Sun Exposure Parisa Sowti Khiabani, Alexander Hertanto Soeriyadi, Peter J. Reece, and J. Justin Gooding ACS Sens., Just Accepted Manuscript • DOI: 10.1021/acssensors.6b00244 • Publication Date (Web): 06 May 2016 Downloaded from http://pubs.acs.org on May 8, 2016
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
ACS Sensors is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 7
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Sensors
A Paper Based Sensor for Monitoring Sun Exposure Parisa S. Khiabani,† Alexander H. Soeriyadi, †‡ Peter J. Reece,§ and J. Justin Gooding*†‡¥ †
School of Chemistry, The University of New South Wales, Sydney,2052, Australia
‡
Australian Centre for NanoMedicine, The University of New South Wales, Sydney, 2052, Australia
§
School of Physics, The University of New South Wales, Sydney, 2052, Australia
ARC Centre of Excellence in convergent Bio-Nano Science and Technology, The University of New South Wales, Sydney, 2052, Australia ¥
KEYWORDS: Sun, sensor, photocatalytic, titanium dioxide, UV, paper sensor
ABSTRACT: An easy to use and easy to make sun exposure sensor was prepared via the ink jet printing of titanium dioxide (TiO2), polyvinyl propylene (PVP) and food dye on paper. The sun exposure sensor works by employing titanium dioxide (TiO2) as a photocatalyst to degrade the food dyes resulting in gradual discoloration of this film. The PVP serves as a binder to allow film formation. The discoloration can be observed by the naked eye or quantitative monitored using UVVis reflectance spectra. Finally, discoloration of the films was calibrated to match UV exposure time of different skin types, by using different UV neutral density filters with the ability of transmit between 1.5 to 70% of the irradiant UV light from the sources to the photoactive film.
Sunburn is the main cause of skin cancer.1 Sun exposure that does not result in burning can still cause damage to skin cells and increase the long term risk of developing skin cancer 1. According to the radiation protection standard by Australian Radiation Protection and Nuclear Safety Agency (ARPNS), the exposure threshold leading to sunburn for human exposure to UVR incident radiation upon the skin or eyes is 30 joule per square meter in an 8 hour working day. To put this into perspective, during summer in Melbourne, Australia, with a UV index of 12 (the UV index is in the range of 2-16 and is reported by media as a measure of maximum daily UVR), the time to reach this threshold (sunburn) can be as low as 7 minutes for fair skin without sunscreen applied.2 The duration that is required to exceed the exposure limit varies with the intensity of solar UVR, skin type of the person who is being exposed to solar UV and the sun protection factor of any applied sunscreen.2 Therefore, it is challenging to judge the appropriate amount of time that is safe under UV sun exposure. Currently, most UV sensor technologies involve integration of the sensing material into other devices (such as smart phones) or other high-technology wearable sensors. An alternative is a single use, disposable, sunburn sensor. Any viable disposable sun exposure sensor would have to be simple, easy to use and inexpensive. However, such products are scarce in the market. One example is the thin film device made by Sun Signal®3 which employs methyl orange as the pH indicating dye and an organic halogen, such as 1,2-dibromotetrachloroethane, as the UVdriven acid-release agent. The Sun Signal® device is fabri-
cated via the deposition of several sequential layers and contains halogenated organic materials that produce acidic compounds after exposure to UV. These acidic compounds are responsible for the change in the colour of the device, which is incorporated onto an adhesive strip so it can be applied to the skin.3 Mills et al. improved upon this disposable UV-dosimeter technology by introducing a base to delay the change in the colour. In this way the sensor performance can be tuned to change colour after different UV exposure times and to match different skin types.4 Furthermore, Mills et al. also reported UV dosimeters based on benzyl viologen and polyvinyl alcohol 5, dichloroindophenol and SnO2 6 and neotetrazolium chloride 7 but just for one skin type. Another important aspect is to fabricate a disposable UV with a process that is not only cheap but also is composed of entirely benign materials. This is what we seek to achieve with the technology described herein entirely using materials that are already approved for human use. The basis of the idea behind the sunburn sensor to be described is a single layer device that incorporates the photocatalytic properties of titanium dioxide. Titanium dioxide (TiO2) is a nontoxic, relatively inexpensive and highly photostable photocatalyst that is already used in sunscreens for blocking UV radiation. This wide band gap semiconductor is inherently UVselective.8-9 Two different crystal structures of TiO2, rutile and anatase, are commonly used in photocatalysis with anatase showing a higher photocatalytic activity.10 In particular, it was found that mixed-phase TiO2 photocatalysts, for example, commercial P25 powder (ca. 25% rutile
ACS Paragon Plus Environment
ACS Sensors
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
and 75% anatase), had higher photocatalytic activities than those in single anatase or rutile phase.11-12 In the case of photocatalytic reactions in aqueous system, two photocatalytic mechanisms have been proposed for titanium dioxide. One suggests that, when UV illuminates TiO2, electron-hole pairs are created. If these electron and holes can avoid recombination and migrate to the surface of TiO2, they can participate in surface reactions with oxygen and water and produce oxygen ion and hydroxyl radicals, respectively (see Supplementary Figure S- 1).8 The other mechanism states that the organic compound has to be firstly adsorbed on the catalyst surface and then reacts with excited superficial hole–electron pairs or OH radicals from adsorbed water to form the final products.13 The purpose of this work is to demonstrate that the discoloration of common food dyes by TiO2 when exposed to UV radiation14-17 can be used as an easy to fabricate, simple to use, disposable sun exposure sensor that can be tuned to different skin types. This single layer paper based sensor was fabricated by inject printing of a suspension containing a Food and Drug administration (FDA) in the USA approved food dye (e.g. brilliant blue FCF), TiO2 and polyvinylpyrrolidone (PVP) as a binder on paper. As a result of the decomposition of this food dye by TiO2 in presence of UV, the film will lose the inherent colour of the dyes. The discoloration time could be adjusted most effectively by coating the device using filters although fabrication parameters such as the actual dye, the ratio of dye to TiO2 or the film thickness also gave some control over the discoloration time. EXPERIMENTAL SECTION Materials and Methods TiO2 anatase (nanopowder,
