Caneta de plasma de ar atmosférico para modificação de eletrodos serigrafados: análise de paracetamol e codeína em saliva e fármacos

Abstract

Screen-printed electrodes (SPEs) are widely employed as electrochemical sensors. These three-electrode systems (working, reference, and counter electrodes) involve the preparation of a substrate and the deposition of a composite consisting of an organic binder and a conductive material, typically graphite powder or, more recently, boron-doped diamond (BDD) films. Although the use of SPEs as sensors has shown promising results, they often require surface treatment to enhance electrochemical performance. In this context, plasma stands out as a promising, reagent-free approach compatible with a wide range of electrode materials. In this work, we propose the use of a handheld atmospheric air plasma pen to efficiently (2 min) treat different carbonaceous surfaces, specifically graphite-based electrodes (G-SPE, sp²) and BDD-based electrodes (BDD-SPE, sp³). Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses revealed surface changes after plasma treatment. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) demonstrated an increase in the sp² carbon content on both types of SPE surfaces. Furthermore, electrochemical impedance spectroscopy (EIS) measurements showed a decrease in charge transfer resistance (Rct) and an increase in the heterogeneous electron transfer rate constant (k0) for plasma-treated SPEs. Electrochemical performance was evaluated by cyclic voltammetry in 0.50 mmol L⁻¹ solutions of different electroactive species. To assess the feasibility of the proposed method, plasma-treated G-SPE was employed for the simultaneous determination of paracetamol (PAR) and codeine (COD) in pharmaceutical formulations and synthetic saliva. Using treated electrodes, linear response ranges of 1.00–9.00 µmol L⁻¹ (LOD = 0.15 µmol L⁻¹) for PAR and 1.00–80.00 µmol L⁻¹ (LOD = 0.71 µmol L⁻¹) for COD were obtained. Recovery studies yielded values ranging from 81–116% for saliva and 90–107% for pharmaceutical samples, indicating that the method is accurate and suitable for the analysis of these matrices. Additionally, treatment with the plasma pen also enabled the regeneration of aged G-SPE and BDD-SPE electrodes.