1558-1748 (c) 2019 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/JSEN.2020.2964995, IEEE Sensors Journal First Author et al.: Title 1 Abstract—We developed a zinc magnesium oxide–based nanosensor platform for pH sensing. pH is a parameter strongly influential in various chemical, biological, and biomedical applications. Oxide-based semiconductors are preferred as pH sensing materials because of their robustness, size modulation, high sensitivity, cost effectiveness, reversibility of the sensing process, and long lifetime. Vertical nanorods of zinc magnesium oxide were fabricated for the nanosensor platform. Their high crystalline quality was confirmed through various structural characterization techniques such as high-resolution X-ray diffraction and scanning and transmission electron microscopy. Absorption spectroscopy revealed a bandgap of 3.56 eV corresponding to 12% magnesium. pH dependent photoluminescence (PL) measurements showed a shift in the visible range spectrum with decrease in PL intensity. The developed sensor showed high sensitivity of 44.4 ± 3.8 mV/pH, close to the theoretical value, in the 2.4–10 pH range. AC- and DC-based current measurements were performed to study the sensing mechanism. Conductance-based pH measurement, a unique and precise technique, yielded a high sensitivity of 4.59 mS/pH. The proposed nanosensors, which are low cost and easy to fabricate and use, exhibited rapid response, long-term stability, high sensitivity (in both potentiometric as well as conductance-based measurements), and high repeatability. Index Terms— pH nanosensors, Zinc magnesium oxide nanorods, Hydrothermal synthesis, Electrochemical voltage, Conductance-based pH I. INTRODUCTION dvances in nanoscience and nanotechnology have paved the way for development of next generation devices such as sensors and detectors. The optical and electrical properties of such devices depend on the particle size of the material and it can be tuned depending on the desired application. Nanostructures are extensively used in diverse domains such as medicine, astronomy, defense, agriculture, and industry. The advantages of nanostructure-based portable devices are its low This paper was submitted on 23 rd of May,2019. The authors acknowledge the financial support from the Department of Science and Technology, India and the partial financial support from the Department of Information Technology. Authors acknowledge Indian Institute of Technology Bombay Nanofabrication (IITBNF) and SAIF facility at IIT Bombay to carry out the corresponding experiments. Hemant Ghadi * (email: ghadihemant16@gmail.com) 1 Electrical Engineering, The Ohio State University, Columbus, Ohio 43210, United States, cost, ease of fabrication, high performance, and biocompatibility [1], [2] [3]. The pH of a mixture or solution is a useful parameter as it can be used in medical applications, such as early disease diagnostics and treatment optimization, as well as in biological applications [4], such as precision agriculture (wherein maintaining the optimal soil pH improves crop efficiency) [5]. Numerous researchers have improved the efficiency of pH sensing by using modified sensor structures (e.g., ion-sensitive field-effect transistors [6] and hydrogel films [7]), adding optical fibers [8], and employing flexible electronics [9]. However, in these approaches, the increase in device efficiency entails several drawbacks, for example, increased cost of sensors and associated accessories, increased power consumption, and more complex device circuitry. Oxide materials are a potential solution to these problems as they are cost-effective, abundant, biocompatible, and ecofriendly, with high sensitivity and selectivity; in addition, their characteristics (i.e., formation of 1D, 2D, and 3D confinement) can be modulated by controlling the synthesis and deposition processes [10], [11], [12], [13], [14], [15], [16], [17]. Sensitivity, selectivity, and stability are crucial parameters for any sensor. Oxide-based semiconductors, such as zinc oxide (ZnO) [10], Indium oxide (In 2 O 3 ) [12], titanium dioxide (TiO 2 ) [13], tantalum pentoxide (Ta 2 O 5 ) [14], tin dioxide (SnO 2 ) [15], tungsten oxide (WO 3 ) [9], ruthenium oxide (RuO 2 ) [16], and iridium oxide (IrO x )[17], have been effectively implemented in pH sensors with high sensitivity. Oxide-based materials typically have a wide bandgap, making them suitable for a wide range of applications, including high- power devices and light-harvesting photodiodes and switches. Most studies on oxide-based materials have explored their sensing capabilities [10], [12], [13], [14], [15], [16], [17]. Conventionally, sensitivity is measured through the potentiometric method as it is easy to implement in an electronic circuit [18]. However, this approach is not highly accurate as it relies on the oxidation–reduction process, which results in the formation of in-built or electrochemical voltage in the structure; the maximum voltage this process can achieve is on the order of tens of millivolts, thus necessitating an amplification circuit for real-time applications [18], [19], [20]. Punam Murkute, Centre for Research in Nanotechnology & Science, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India Sheetal Patil, Department of Electrical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, Maharashtra, India Subhananda Chakrabarti is Professor at Department of Electrical Engineering, Indian Institute of Technology Bombay, Mumbai 400076, India (email : subho@ee.iitb.ac.in) Hemant Ghadi, Punam Murkute, Sheetal Patil, Subhananda Chakrabarti, Senior Member, IEEE Zinc magnesium oxide based nanorods for high-precision pH sensing A