INFLUÊNCIA DE SUPERFÍCIES DE OURO MODIFICADAS COM FTALOCIANINAS NA ELETRO-OXIDAÇÃO DE NEUROTRANSMISSORES DE CATECOLAMINAS

Abstract

Catecholamines are a class of biogenetically active compounds found in the brain and central nervous system. One of them, dopamine (DA), functions directly as a neurotransmitter. Understanding the biological processes of these neurotransmitters is essential for understanding their physiological role, as they are associated with diseases such as anxiety, depression, and Parkinson's disease. Thus, the detection and quantification of these molecules can serve as biomarkers for disease stage or to monitor treatment efficacy. In this context, electrochemical application using gold surfaces as electrode substrates for the study of biological reactions has received considerable attention in the field of sensors, as several of these biomolecules strongly adsorb onto their surface. However, the oxidation of dopamine on conventional electrodes does not yield good results, as studies of dopamine oxidation are conducted together with its biological interferents, ascorbic acid (AA), and uric acid (UA), which oxidize at the same potential range as dopamine, hindering its effective detection. Therefore, this work evaluated the effectiveness of inhibiting the oxidation of interferents and/or separating the oxidation regions of these biomolecules by modifying gold surfaces with tetrakisulfonated phthalocyanines (Ftc) with copper and nickel metal cores (Ftc_Cu and Ftc_Ni). In addition to these modified electrodes, polycrystalline gold nanoparticles (AuNPs) were also prepared for the studies. Electrochemical analyses of the oxidations were performed by cyclic voltammetry and differential pulse voltammetry in a 0.1 M phosphate buffer solution at pH 3.0, 7.0, and 12.0, with initial concentrations of 1 mmol L-1 of DA, AA, and UA. The surfaces of the electrode materials were studied using atomic force microscopy, where the results indicate that the spontaneous deposition of Ftc_Cu forms self-oriented monolayers on gold, as they exhibit a homogeneous distribution and regular particle sizes. The images of Ftc_Ni/Au show that the most suitable scanning rate for its deposition is 20 mV s-1, and the images of AuNPs show that spherical structures were produced, characteristic of polycrystalline materials. The results of voltammetry, with the aid of the first derivative of the current (di/dV), for the combined oxidation (DA+AA+UA) at pH 7.0 indicate that Ftc_Cu/Au is the most promising electrode, as it exhibits excellent inhibition of the AA oxidation peak while maintaining the separation of the DA and UA peaks, but it is necessary to ensure a surface coverage above 20%. The Ftc_Ni/Au electrode did not show significant results in the separation or inhibition of any of the interferent peaks. AuNPs show better oxidation results when compared to the gold disk in terms of dopamine detection signal. Keywords: Electro-oxidation; Dopamine; Ascorbic acid, Uric acid; Phthalocyanines.