Cost-effective lab-made graphite- and aluminum oxide-integrated polylactic acid composite electrodes for electrochemical sensing of minoxidil

Abstract

The development of new sensors, which are low-cost, portable, and disposable, is currently highly required. In this sense, this work describes a simple way for lab-made fabrication of new composite electrodes exploiting an environmental friendly matrix based on thermoplastic polylactic acid (PLA). Great conductive features were achieved using graphite and aluminum oxide in PLA. The amount of aluminum oxide has been carefully optimized (0 to 12.25 % m/m). The manufacturing process presented reproducibility (between-device % relative standard deviation (RSD) < 7.3). Additionally, the electrode was characterized by electrochemical, spectroscopy, and morphological techniques. Improved cyclic voltammetric responses regarding Ipa, Ipc, and ΔEp were obtained towards the detection of the redox probes [Fe(CN)6]3-/4- and dopamine using the electrode incorporated with aluminum oxide. Moreover, electrochemical impedance measurements revealed a more facilitated charge transfer process in the alumina-loaded electrode (Rct = 2070 Ω) than without alumina (Rct = 2810 Ω). The developed sensor was associated with batch injection analysis for the simple, fast, and sensitive amperometric monitoring of minoxidil (MXD) in pharmaceuticals, achieving a greater sensitivity with a detection limit of 2.9 µmol/L. A wide linear behavior from 10 to 1000 µmol/L and a between-measurement % RSD of less than 6 were acquired. Also, the method is free of interference from compounds commonly used as excipients in pharmaceutical products. When applied to the pharmaceutical sample, results statistically comparable to the reference method (UV–Vis spectrometry) were achieved, which confirmed the method's accuracy. Thus, the proposed sensor proves to be a powerful alternative tool for MXD monitoring, providing comparable and even better results with other high-cost electrochemical sensors.