Fabrication of a flexible UV photodetector and disposable photoresponsive uric acid sensor by direct writing of ZnO pencil on paper

Veerla, Raja Sekhar and Sahatiya, Parikshit and Badhulika, Sushmee (2017) Fabrication of a flexible UV photodetector and disposable photoresponsive uric acid sensor by direct writing of ZnO pencil on paper. Journal of Materials Chemistry C, 5 (39). pp. 10231-10240. ISSN 2050-7526

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Abstract

There are few reports on ZnO being used for flexible substrate based sensors. Most of the studies have documented the use different solvents or inks for the sensor fabrication, which leads to the degradation of the properties of both substrate and sensing materials. This work is the first demonstration of solvent-free direct drawing on a cellulose paper using zinc oxide (ZnO) pencil to fabricate an ultra-violet (UV) light sensor, which was further utilized for photoresponsive uric acid (UA) sensing. The transient analysis was performed for ZnO (with silver (Ag) ohmic contact) and Graphene (Gr)/ZnO (with graphene contact). The recovery time constant observed for Gr/ZnO and ZnO was 8.79 and 18.13 seconds, respectively, which is comparable to that of the photodetector fabricated using the sophisticated cleanroom techniques. The responsivity calculated for ZnO and Gr/ZnO devices under 3.9 mW cm(-2) UV light illumination was found to be 4.12 mA W-1 and 6.27 mA W-1, respectively. The excellent UV sensing property of ZnO was further utilized for photoresponsive UA sensing at several concentrations ranging from 100 mu M to 450 mu M with a sensitivity of 1.99 m mu M-1 (R-2 = 0.984) and the limit of detection (LOD) of 38.4 mu M. In the presence of UA, the photogenerated electrons from ZnO under UV illumination get trapped by oxygen present in UA because of its oxidation in atmospheric air. As the UA concentration increases, the oxidation of UA causes more photogenerated electron traps, which results in the further decrease in the photocurrent. Such a simple and inexpensive way for fabricating ZnO-based devices on paper holds promising applications in the field of flexible and wearable electronic devices, optoelectronic sensors, and medical diagnostic systems etc.

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