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. J. Mater. Chem. C, 5 (39). pp. 10231-10240. ISSN 2050-7526

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Abstract

While there are few reports on ZnO on flexible substrate based sensors, most of them use different solvents/inks for the sensor fabrication thereby leading to degradation of the properties of both substrate and sensing materials. This work is the first demonstration of solvent-free direct drawing of Zinc Oxide (ZnO) pencil based Ultra-Violet (UV) light sensor fabricated on cellulose paper which was further utilized for photoresponsive Uric acid (UA) sensing. A transient analysis was performed for ZnO (silver (Ag) ohmic contact) and Graphene (Gr)/ZnO (Graphene contacts) wherein the recovery time constant observed for Gr/ZnO was 8.79 seconds and 18.13 seconds for ZnO which are comparable to the photo detector fabricated using sophisticated cleanroom techniques. Responsivity calculated for ZnO and Gr/ZnO device was found to be 4.12 mA/W and 6.27 mA/W respectively under 3.9 mW/cm2 UV light illumination. The excellent UV sensing property of ZnO was further utilized for photoresponsive UA sensing for several concentrations ranging from 100 µM-450 µM with a sensitivity of 1.99m/µM (R2= 0.984) and limit of detection (LOD) of 38.4 µM. In the presence of UA, the photo generated electrons from ZnO under UV illumination gets trapped by the oxygen present in UA because of its oxidation with atmospheric air. As the UA concentration increases, the oxidation of UA causes more photo generated electron traps which result in further decrease in photocurrent. Such a simple and inexpensive way of fabricating ZnO based devices on paper holds promising applications in the field of flexible and wearable electronics, optoelectronics, medical diagnostics etc.

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