Tuning the visible photoluminescence in Al doped ZnO thin film and its application in label-free glucose detection

Herein, we study the effect of thermal annealing on the structural and optical properties of Al doped ZnO (AZO) thin film and its application for the label-free detection of glucose based on fluorescence quenching. AZO thin films grown by radio frequency magnetron sputtering are annealed at different temperatures( 250-650 degrees C) in air environment. The post-growth annealing improves the structural quality of the AZO films, as confirmed from the X-ray diffraction, X-ray photoelectron spectroscopy and micro-Raman analyses. The as-grown and annealed samples show strong photoluminescence (PL) in the UV (similar to 3.33 eV) andvisible NIR (1.6-2.2 eV). The UV PL peak is originated from the near band edge emission of crystalline ZnO, while the broad visible-NIR PL is associated with the radiative transition related to oxygen interstitial (O-i) defects in the ZnO structure. The PL peak intensity is strongly enhanced after annealing due to the partial removal of non-radiative defects. The high intensity visible-NIR PL of the annealed samples is used for the label-free enzyme-based detection of glucose with the help of glucose oxidase based on PL quenching via electron transfer mechanism. Our AZO thin films can efficiently detect similar to 20 mu M concentration of glucose in presence of glucose oxidase (GOx). We have attempted to quantify the nature of PL quenching based on the Stern-Volmer plot and explained the quenching mechanism as collisional quenching due to charge transfer in presence of a quencher. The Stern-Volmer plot of PL quenching of AZO thin film reveals the linear relationship between the quenching effect and the glucose concentration. Higher sensitivity of the sensor can be achieved by tuning the structure and doping density of the AZO films. This report opens up avenues for the non-destructive, label-free detection of biomolecules with high sensitivity using a low cost ZnO thin film. (C) 2017 Elsevier B.V. All rights reserved.