In biological and environmental applications, pH is an important parameter that needs to be monitored at a regular basis. Conventionally, the measurement process takes a considerable amount of time involving several calibration steps and handling of fragile electrodes. In this work, we propose a new, robust and reliable way of sensing pH. The sensor has been fabricated based on tungsten oxide nanoparticle modified glassy carbon electrode (WO₃/GCE) (Fig. 1). WO₃ is a promising material for pH sensor because of its availability, stability, good morphological and structural control of the synthesized nanostructures, reversible change of conductivity, high sensitivity, selectivity and biocompatibility.¹ Furthermore, WO₃ is a well-studied wide band gap semiconductor (~2.75 eV) used for several applications as chromogenic material and catalyst.²

In this work, hydrothermal synthesis method was used for the fabrication of WO₃ nanoparticles. For the fabrication of the pH sensor, the nanoparticles were mixed with Nafion and chitosan before drop coating onto the GCE surface. Scanning electron microscopy (SEM), x-ray diffraction (XRD), transmission electron microscopy (TEM) was used to characterize the nanoparticles. Cyclic voltammetry (CV) and square wave voltammetry (SWV) were used to monitor the potential shift based on different pH in the buffer solution. The WO₃/GCE pH sensor showed a sensitivity of 1.15 VpH^-1cm^-2 at 25 °C and a potential drift of less than 5% after three hours of continuous use. The sensor showed good linearity at a pH range of 3 -10 and could retain 95% of its initial sensitivity after 1 week of use. The good sensitivity and long term stability of this WO₃ based sensor may allow the development of a low cost pH sensor for a wider range of applications.³

Acknowledgement

This work is financially supported by Science Foundation Ireland funded project “SweatSens” under the grant agreement No. 14/TIDA/2455 and the University Grant Commission (research support and publication division), Bangladesh.

Corresponding authors' email addresses: mamun.jamal@chem.kuet.ac.bd and kafil.mahmood@tyndall.ie

Reference

1. D. Vernardou, H. Drosos, E. Spanakis, E. Koudoumas, C. Savvakis, N. Katsarakis, J. Mater. Chem., 2011, 21, 513.

2. M. Natan, T. E. Mallouk, M. S. Wrighton, J. Phys. Chem. 1987, 91, 648.

3. L. Devlin, M. Jamal and K. M. Razeeb, Anal. Meth. 2013, 5, 880.

Figure 1. Schematic diagram of WO₃ nanoparticle based pH sensor.