Fabricação de sensores eletroquímicos e dispositivos de fluxo lateral para aplicações bioanalíticas

Abstract

This work presents the development and evaluation of low-cost analytical platforms with potential for portable applications and point-of-care (POC) analysis. Initially, an electrochemical sensor based on conductive tracks directly produced on glass substrates using a laser engraving technique was developed. The fabrication parameters were systematically optimized, and the optimal conditions were established as a power of 2.7 J s⁻¹, a speed of 3.6 mm s⁻¹, and a laser distance of 6 mm, resulting in tracks with minimum electrical resistivity in the range of 27–41 Ω cm. Structural characterization by Raman spectroscopy confirmed the formation of carbonaceous material with graphitic character, evidenced by well-defined D and G bands and a reduction in the ID/IG ratio after chemical treatment with acetic acid, indicating greater structural organization and an increase in sp² domains. FE-SEM analyses revealed a porous and rough surface with a higher density of cavities after acid treatment. The electrochemical performance was evaluated by cyclic voltammetry using the redox probe [Fe(CN)₆]³⁻/⁴⁻, showing reversible behavior, good repeatability, and a diffusion-controlled response. The analytical application of the sensor was investigated for the detection and quantification of midazolam maleate (MID) using differential pulse voltammetry and square wave voltammetry, with the former showing the best performance. The sensor exhibited a linear response in the range of 25 to 150 mg L⁻¹, with limits of detection and quantification of 2.9 mg L⁻¹ and 8.9 mg L⁻¹, respectively. Interference studies demonstrated a low influence of common compounds, and application in real samples of water and fortified alcoholic beverages showed recoveries between 88 and 112%, confirming the potential of the platform for rapid, portable, and lowcost forensic analyses. Additionally, a lateral flow-based analytical device was developed aiming to construct a simple and accessible system for POC diagnostic applications. The device was assembled through the sequential overlap of a glass fiber sample/conjugate pad, a nitrocellulose membrane, and an absorbent pad, allowing continuous and reproducible capillary flow. Different methodologies for depositing test and control lines were evaluated, including manual and semiautomated approaches, revealing reproducibility limitations associated with manual deposition methods. As a molecular recognition strategy, the biotin–streptavidin interaction was explored, involving the immobilization of streptavidin on the membrane and the capture of biotinylated amplicons, whose interaction was confirmed by fluorescence. Furthermore, a controlled deposition system using a linear displacement stage coupled with a syringe pump was developed, enabling greater control in reagent deposition. The results demonstrate the potential of the lateral flow device and the developed deposition system, as well as the need for additional optimization steps to improve line deposition and the analytical performance of the device. Overall, the results highlight the potential of different fabrication strategies for low-cost analytical devices, emphasizing both laser-engraved electrochemical sensors and lateral flow devices as promising alternatives for rapid, portable, and accessible analytical applications.