A high-performance reagent-less sensor based on copper( <scp>ii</scp> ) phthalocyanines supported by multi-walled carbon nanotubes for phosphate detection

Phosphate concentration is an important indicator of water quality, specifically for eutrophication levels in the presence of algae. Several analytical techniques have been proposed for phosphate monitoring, and most of them are based on indirect methods. In this study, we propose a new reagent-less direct method for the electrochemical detection of phosphate in aqueous solutions. For this, carbon screen printed electrodes (CSPE) were modified with copper(ii)-phthalocyanines (CuPc) that offer excellent oxidoreduction and electrocatalytic properties, together with chemically modified multiwalled carbon nanotubes (MWCNTs) to enhance the electrocatalytic performance of the sensor. We implemented two detection methods, which are electrochemical impedance spectroscopy (EIS) and square wave voltammetry (SWV) to compare them. The developed sensor exhibits a remarkable detection limit of 1.15 μM in the range from 10 μM to 100 μM with voltammetry and 0.13 nM in the range from 0.001 μM to 100 μM with impedance, enabling accurate measurement of phosphate concentrations in water samples. Thus, EIS shows a better sensitivity towards phosphate reduction. Furthermore, the developed sensor shows good performance in the presence of possibly interfering species that usually coexist with phosphate ions, as well as the applicability of the sensor in real water samples (tap water and nutrient water from an aquaponic system) at a good recovery rate. The electrode's response is highly reproducible with a relative standard deviation lower than 10%.