A non-enzymatic highly stable electrochemical sensing platform based on allylamine capped copper nanoparticles for the detection of the soil nitrate content†

Abstract

Nitrate (NO₃⁻) ion contamination of water is a major issue that affects many parts of the world due to excessive usage of nitrogen containing fertilizers in the soil. Hence, quantification of NO₃⁻ ions in the soil is of utmost importance. In the present research work, we have developed an efficient and highly stable non-enzymatic electrochemical sensor for NO₃⁻ ion detection based on allylamine capped copper nanoparticles (Alym@CuNPs) decorated on exfoliated multi-walled carbon nanotubes (Exf-CNTs). Herein, we have addressed the sensor surface storage stability issue of copper nanoparticle based electrochemical sensors for the first time and confirmed the superior storage stability of the Alym@CuNPs modified glassy carbon electrode (GCE) over uncapped copper nanoparticles (uCuNPs) and electrodeposited copper nanoparticles (eCuNPs) modified GCEs. In comparison to the bare GCE, Exf-CNT/GCE and Alym@CuNPs/Exf-CNT/GCE, the proposed Alym@CuNPs-Nafion (NF)/Exf-CNT/GCE demonstrated enhanced catalytic activity towards the electro-reduction of NO₃⁻ ions (pH = 2) under optimal experimental conditions, with a considerable increase in cathodic peak currents. Along with that, no inert gas was purged into the electrolyte medium prior to the detection of NO₃⁻ ions which makes the sensor more reliable under real environmental conditions. The sensor displayed broad linear ranges from 10 to 1000 μM (R² = 0.997), with a limit of detection (LOD) of 5.28 μM (n = 3) for NO₃⁻ ion detection. The sensor surface shows excellent storage stability even up to 45 days with 97.8% retention in current value which is much higher compared to the previously reported works. Additionally, the sensor surface shows promising reproducibility and repeatability results with RSD values of 1.78% and 0.91%, respectively. Moreover, the proposed sensor is successfully utilized to detect NO₃⁻ ions in real soil samples.