Vertical standing copper nanowires for electrochemical sensor of nitrate in water

Nitrogen, in the forms of nitrate (NO3-), nitrite, or ammonium, is a nutrient needed for plant growth and it is a common constituent of fertilizers [1]. When fertilizers are overused, they contaminate the ground water and then the food chain. For humans, a low level of nitrate is advisable because it increases the blood flow and has a good effect on both blood pressure and cardiovascular system. On the contrary, a high concentration of nitrate can be dangerous for humans. Nitrate ions undergoes different chemical transformations (i.e. to nitrite ions by Escherichia coli) producing different nitrogen-based compound such as nitrite ions, nitric oxide and ammonia [2]. These chemicals lead to several problems such as cancer, neurodegenerative disease and gastritis. Furthermore, nitrate ions are responsible of the blu-baby disease because they oxide hemoblogin to methemoglobine which has a lower capability to transport oxygen [3]–[4]. Considering all these hazards, the Environmental Protection Agency (EPA) has fixed the maximum allowed concentration of nitrates in drinking water to 44 ppm [5]. Nowadays, nitrate ions quantification is performed by spectroscopy ensuring Limit Of Detection (LOD) in the ppb range [6]–[7]. However, this technique consists of hard procedure (conversion of nitrates to nitrite using cadmium or zinc salts) and requires skilled personnel. Furthermore, it lacks of sensitivity when coloured or opaque samples are analysed. Such disadvantages confine this technique to a lab-based analysis making impossible to detect nitrate ions in real time and/or in situ.