Abstract
The synthesis of ordered monolayers of gold nano-urchin (Au-NU) nanostructures with controlled size, directly on thin films using a simple electrochemical method is reported in this study. In order to demonstrate one of the vast potential applications, the developed Au-NUs were formed on the electrodes of transducers (QCM) to selectively detect low concentrations of elemental mercury (Hg0) vapor. It was found that the sensitivity and selectivity of the sensor device is enhanced by increasing the size of the nanospikes on the Au-NUs. The Au-NU-12 min QCM (Au-NUs with nanospikes grown on it for a period of 12 min) had the best performance in terms of transducer based Hg0 vapor detection. The sensor had 98% accuracy, 92% recovery, 96% precision (repeatability) and significantly, showed the highest sensitivity reported to date, resulting in a limit of detection (LoD) of only 32 μg/m3 at 75 °C. When compared to the control counterpart, the accuracy and sensitivity of the Au-NU-12 min was enhanced by ~2 and ~5 times, respectively. The results demonstrate the excellent activity of the developed materials which can be applied to a range of applications due to their long range order, tunable size and ability to form directly on thin-films.
Highlights
One of the most important chemical sensing applications that is currently sought-after by the scientific community around the world are mercury sensors[27,28,29,30,31,32,33]
One quartz crystal microbalance (QCM) having no polystyrene nanospheres (PSNS) was fabricated as the control device and is referred to as Au-control
These observations are better demonstrated in the higher scanning electron microscopy (SEM) magnification of each sample that is shown in the Supplementary information (Fig. S1)
Summary
Recent studies have found that among other applications[44,45], gold nanostructures can be modified to exhibit extraordinarily high activity when used in Hg0 vapor sensor devices[42] These findings are driving the recent interest in Au chemistry and Au-based nanomaterials to develop transducer based devices that have LoDs comparative to the commercially available spectroscopic systems. Gold nano-urchins have been reported to have extraordinary properties such as distinct and size-dependent tunable surface plasmon resonance (SPR) bands as well as morphological surface defects generating ‘hot-spots’ essential for surface enhanced Raman spectroscopy (SERS) based sensing applications[46,47,48,49] These structures have so far only been successfully synthesized in the form of colloids thereby limiting their use for thin-film based applications including optics, catalysis, batteries, electrocatalysis, photo-catalysis and chemical/bio-chemical sensing. To the best of the authors’ knowledge, this is the most sensitive QCM based mercury vapor sensor reported to date and is a step forward in developing a non-spectroscopic, transducer based mercury vapor sensor for industrial and environmental applications
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