Synergistic Effects between Phthalocyanines and Nanoparticles in Nanostructured Voltammetric Sensors - Applications in the Food Industry
Authors: Garcia-Hernandez Celia , Salvo-Comino Coral , Garcia-Cabezon Cristina , Martin-Pedrosa Fernando , Rodriguez-Mendez Maria Luz 
Published: February 2020

The food industry requires the development of new sensors with improved performance in terms of sensitivity, detection limit and selectivity. Electrochemical sensors are an excellent choice because they fulfill these requirements with the advantage of their low cost and portability.
A variety of voltammetric sensors has been used to analyze components usually found in foods including phenols, amines, organic acids, vitamins, etc. In such devices, the working electrode is chemically modified with electrocatalytic materials that enhance the intensity of the signals and decrease the voltages at which the analytes are oxidized.
Classical electrocatalytic materials such as phthalocyanines or conducting polymers such as PEDOT or pyrrol have demonstrated to be excellent electrocatalytic materials for the detection of phenols, acids or amines. Nanomaterials such as metallic nanoparticles, nanotubes or graphene have also successfully been used as electrocatalytic elements.
The objective of this work is to demonstrate the existence of synergistic effects when combinations of electrocatalytic materials are used as chemical modifiers. For this purpose, combinations of two different electrochemical materials –phthalocyanines and gold nanoparticles- [1] has been carried out to ameliorate voltammetric responses, as well as combination of -conducting polymers with gold nanoparticles- [2, 3] and -conducting polymers with phthalocyanines- [3] will be used as the sensing materials in voltammetric sensors dedicated to the assessment of phenols or organic acids present in foods. The performance of the sensors will be tested in terms of sensitivity, limit of detection and reproducibility.
The synergistic effect of several combinations of electrocatalytic materials was tested by immersing the electrodes in phenols (catechol, hydroquinone) or in organic acid (citric acid) solutions and calculating the limits of detection. For example, combinations of AuNPs and LuPc2 deposited on ITO glass by means of the LB technique immersed in phenols showed an increase of the 22% in the intensity of the peaks associated to the oxidation of hydroquinone to the quinoid form and LOD of 10-7 were obtained.
The sensing properties of electrodes chemically modified with PEDOT:PSS towards catechol and hydroquinone have been successfully improved by combining layers of PEDOT:PSS with layers of a secondary electrocatalytic material (EM) such as gold nanoparticles (PEDOT:PSS/AuNPs), or lutetium bisphthalocyanine (PEDOT:PSS/LuPc2) (Figure 1). Layered composites exhibit synergistic effects that strongly enhance the electrocatalytic activity as indicated by the increase in intensity and the shift of the redox peaks to lower potentials.

Figure 1. Cyclic voltammograms of PEDOT:PSS sensor and PEDOT:PSS/LuPc2 sensor immersed in (a) 1.5·10-4 mol·L-1 catechol and (b) 1.5·10-4 mol·L-1 hydroquinone. Scan rate 100 mV.s-1

Figure 1