Electrochemical Sensors Modified with Combinations of Sulfur Containing Phthalocyanines and Capped Gold Nanoparticles: A Study of the Influence of the Nature of the Interaction between Sensing Materials.

Voltametric sensors formed by the combination of a sulfur-substituted zinc phthalocyanine (ZnPc ^RS ) and gold nanoparticles capped with tetraoctylammonium bromide (AuNP ^tOcBr ) have been developed. The influence of the nature of the interaction between both components in the response towards catechol has been evaluated. Electrodes modified with a mixture of nanoparticles and phthalocyanine (AuNP ^tOcBr /ZnPc ^RS ) show an increase in the intensity of the peak associated with the reduction of catechol. Electrodes modified with a covalent adduct-both component are linked through a thioether bond-(AuNP ^tOcBr -S-ZnPc ^R ), show an increase in the intensity of the oxidation peak. Voltammograms registered at increasing scan rates show that charge transfer coefficients are different in both types of electrodes confirming that the kinetics of the electrochemical reaction is influenced by the nature of the interaction between both electrocatalytic materials. The limits of detection attained are 0.9 × 10 ^-6 mol∙L ^-1 for the electrode modified with the mixture AuNP ^tOcBr /ZnPc ^RS and 1.3 × 10 ^-7 mol∙L ^-1 for the electrode modified with the covalent adduct AuNP ^tOcBr -S-ZnPc ^R . These results indicate that the establishment of covalent bonds between nanoparticles and phthalocyanines can be a good strategy to obtain sensors with enhanced performance, improving the charge transfer rate and the detection limits of voltammetric sensors.