Cu-Based Nanoneedle Array for Electrochemical Detection of Nitrate

The extensive usage of nitrogen-based fertilizers, food preservatives and explosive chemicals in various industries has led to the accumulation of nitrate in the ecosystems, especially in soil and water bodies. Several severe environmental and human health issues, including eutrophication, diseases related to N-nitroso compounds (such as Cancer, Parkinson and Gastritis) and blue-baby syndrome (methemoglobinemia), have arisen from the excessive nitrate concentration in the environment. Consequently, various government and regulatory agencies, such as the U.S. Environmental Protection Agency (EPA), have established the maximum nitrate ion concentration in drinkable water at 44 mg/L (0.71 mM). In this context, an accurate monitoring of the level of nitrate becomes important in environmental pollution control, food, clinical analysis, and other industries. While the spectroscopy techniques are of the most use due to its high precision and low limit of detection (LOD), these methods frequently require skilled workforces and specific instrumentations to operate. The electrochemical sensors benefit from recent developments of new nanomaterials to detect nitrate with a quick response, ability of continuously monitoring, small and simple instrumentation as well as easy to use. Several studies have utilized different strategies to fabricate Cu-based nanostructures (such as nanoparticles, nanoclusters, nanowires, and single-crystals) to achieve a low LOD. However, the sensitivity that has been achieved so far is still relatively low compared to the requirements for the real sampling applications. In this work, we utilized a one-step electrodeposition method to prepare Cu-based nano-array electrodes with high active surface sites, aiming for a fast and sensitive electrochemical detection of nitrate. The morphology of the array can be fine-tuned between nanoneedle and nanowire structures ( Figure 1a and 1b ). The x-ray diffraction (XRD) measurements indicate that the Cu-based nanoneedle array exhibited an abundant Cu(220) facet than the nanowire systems, which is usually associated with the active edge sites on copper ( Figure 1c ). The nanoneedle array was used for nitrate sensing via Cyclic Voltammetry methods which showed a sensitivity of 2.8 μA/μM*cm 2 , about 5-fold higher than the Cu foil control electrode ( Figure 1d ). The main reason of the sensitivity enhancement is that the nanoneedle structure resulted in a 30 times enrichment in the surface area compared to the Cu foil as shown in the electrochemical surface area (ECSA) measurement. Overall, our study provides a novel and convenient design of highly ordered Cu nanoneedle array structure for the sensitive electrochemical detection of nitrate. Figure 1