Coffee-ring effect-driven TiO2 microstructures as sensing layer for redox-free impedimetric detection of Hg(II) in tap water

Abstract

Mercury (Hg(II)) is a deadly heavy metal ion that can cause disabilities and mental retardation. It is increasingly spreading in nature due to the development in industrialization. Current detection techniques of Hg(II) are time consuming, expensive and require highly trained individuals. Therefore, new easy-to-use and low-cost technologies that can be used for the on-site and rapid detection of such heavy metal ions are highly desirable to reduce the impact of toxins spreading in water. In this work, non-faradaic impedimetric sensors were developed for the direct detection of Hg(II) in tap water. The sensor consists of coffee-ring effect-driven titanium dioxide (TiO2) microstructures at interdigitated gold electrodes on plastic substrate. Before performing sensor measurements, we investigated the physical and chemical properties of the TiO2 microstructures on top of Au on silicon substrate. Thereafter, we utilized the TiO2 microstructures as sensing layer for the direct detection of Hg(II) in tap water. The sensor demonstrated excellent sensitivity and LoD of 19.92 nF/log(nM) and 60 pM, respectively. More importantly, the sensor performance is similar to other electrochemical sensors which require the use of redox probes or reference electrodes during detection. The sensor also demonstrated satisfactory selectivity towards Hg(II) when mixed with other common metal ions. Both, fabrication of sensing layer and non-faradaic detection of Hg(II) are direct and simple which emphasize the potential of our developed sensor as low-cost and mass producible sensor for the on-site and direct detection of heavy metal ions in real samples.