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Eletrodos baseados em grafeno obtidos por gravação a laser: eletroanálise de amostras ambientais, biológicas e de alimento

2026-08-18T06:22:02Z

Title: Eletrodos baseados em grafeno obtidos por gravação a laser: eletroanálise de amostras ambientais, biológicas e de alimento Abstract: Laser engraving has emerged as a promising technique for the rapid, simple, and low-cost fabrication of electrochemical sensors. In this thesis, laser-induced graphene (LIG) electrodes were fabricated through the direct engraving of polyimide using a CO₂ laser, aiming at the development of electrochemical methods for applications in food, environmental, and biological samples. To achieve this goal, the work was conducted in three stages. Initially, using unmodified LIG electrodes, a method was developed for the determination of total antioxidant capacity (TAC) in tea samples through the quantification of the consumption of the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical, employing batch injection analysis (BIA) with amperometric detection. The method exhibited a linear range from 2 to 900 μmol L⁻¹, a limit of detection (LOD) of 0.6 μmol L⁻¹, and high precision (relative standard deviation, RSD < 4.0%). The TAC of the samples followed the order: mixed tea < black tea < green tea < green tea with hibiscus, in agreement with the conventional spectrophotometric method. In a second stage, the applicability of these unmodified devices was extended to the determination of chloramphenicol in honey samples by adsorptive stripping differential pulse voltammetry (AdSDPV). This method showed linearity in the range of 10 to 160 μmol L⁻¹, an LOD of 1.0 μmol L⁻¹, and recovery values ranging from 86% to 109%. Finally, it was demonstrated, for the first time, that the application of only 3.0 μL of dimethyl sulfoxide (DMSO) onto the surface of LIG electrodes significantly enhances the electrochemical activity of the material. Physicochemical and electrochemical characterizations revealed changes in the chemical composition, structure, and surface morphology of LIG, including an increased concentration of oxygen-containing functional groups, structural reorganization favoring the formation of graphitic domains, enhanced hydrophilicity, increased surface roughness, and reduced charge-transfer resistance. Based on this surface modification strategy, a method was developed for the determination of sulfanilamide in water and synthetic urine samples using differential pulse cathodic stripping voltammetry (DPCSV). The method exhibited a linear response in the range of 0.3 to 9.0 μmol L⁻¹, an LOD of 0.09 μmol L⁻¹, and recovery values ranging from 90% to 104%. Overall, the results demonstrate that LIG-based electrodes constitute a versatile, efficient, and low-cost analytical platform. Furthermore, surface treatment with DMSO proved to be a simple and effective strategy for enhancing the electrochemical performance of LIG, thereby expanding its potential for the development of electrochemical sensors.

Estudos in silico da proteína TcP21 no contexto da doença de Chagas

2026-08-07T06:23:36Z

Title: Estudos in silico da proteína TcP21 no contexto da doença de Chagas Abstract: Chagas disease, caused by Trypanosoma cruzi, remains a significant public health concern, with still limited therapeutic options. In this context, the TcP21 protein, secreted by extracellular amastigote forms, has emerged as a molecular target of interest, involved in alternative and still poorly explored infection pathways. This thesis aimed to characterize TcP21 in silico from two complementary perspectives: the identification and characterization of binding sites on its surface, and the elucidation of potential interaction interfaces in the TcP21–CXCR4 complex. The integration of mixed-solvent molecular dynamics simulations, fragment-based molecular docking, and pharmacophore-based molecular docking followed by molecular dynamics, driven by occupancy-based volumetric maps, enabled the convergent identification of a binding site on TcP21. This site involved the key residues GLU55, ASP52, VAL70, ILE62, and TRP77. The observed interactions, including salt bridges, hydrogen bonds, charge–charge interactions, and π–alkyl contacts, formed an intermolecular network consistent with the recognition of protonated amino, acetamido, and phenyl functional groups. Binding modes of the TcP21–CXCR4 complex were generated by molecular docking and subsequently refined through multireplica molecular dynamics simulations in a biomimetic environment. Consensus analysis of the trajectories, based on a ΔSASA-driven multimetric scoring function and on the evaluation of intermolecular contacts (number, frequency, and temporal stability), revealed a continuous segment in TcP21 (LYS23–PHE39) with typical protein–protein interface properties. In CXCR4, the transmembrane domains TM5, TM6, and TM7 formed a stabilized structural core within the extracellular vestibule, whereas regions such as ECL2 and the N-terminal domain exhibited greater conformational flexibility. The resulting interface displayed a modular organization, predominantly stabilized by van der Waals interactions, with additional electrostatic and polar contributions conferring directional specificity to the molecular recognition process. The integrated analysis of the studies indicated the presence of two functionally specialized regions in TcP21, potentially associated with pharmacophore ligand binding and host receptor recognition, respectively

Filmes finos baseados em hexacianoferratos de ferro e bismuto e nanomateriais de carbono para aplicação em dispositivos de armazenamento de energia

2026-07-24T06:19:59Z

Title: Filmes finos baseados em hexacianoferratos de ferro e bismuto e nanomateriais de carbono para aplicação em dispositivos de armazenamento de energia Abstract: The objective of this work was the development and characterization of nanocomposite thin films based on iron (HCFFe) and bismuth (HCFBi) hexacyanoferrates combined with carbon nanomaterials (carbon nanotubes and reduced graphene oxide) for application in aqueous rechargeable batteries. The motivation of this study stems from the growing demand for efficient, safe, and low-cost energy storage technologies, such as aqueous electrolyte rechargeable batteries, which emerge as promising alternatives to lithium-ion batteries due to the abundance of metals like sodium and potassium, in addition to the higher intrinsic safety of aqueous systems. The nanocomposite films (HCFFe/NTC, HCFFe/rGO, HCFBi/NTC, and HCFBi/rGO) were prepared using the liquid-liquid interfacial synthesis method. This method allowed the attainment of integral structures, albeit with an irregular compositional distribution, at the toluene-water interface, facilitating their subsequent transfer onto ITO substrates. The materials were structurally and morphologically characterized by Fourier-transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. The analyses confirmed the formation of HCFFe nanoparticles and HCFBi microparticles distributed within the carbon matrices, and an unprecedented diamond-shaped morphology was observed for HCFBi. The electrochemical performance of the films was optimized through a 23 factorial design, evaluating the influence of the cation type (Na+ or K+), pH, and electrolyte concentration. Cyclic voltammetry results, combined with Dunn’s method, indicated that the HCFFe/rGO film exhibited a predominantly faradaic behavior associated with ion intercalation, whereas the HCFBi/rGO film showed more pronounced capacitive and pseudocapacitive contributions. In galvanostatic charge-discharge tests, the HCFFe/rGO composite reached a specific capacity of 160 mA h g-1, while HCFBi/NTC, despite presenting a lower specific capacity (35.85 mA h g-1), demonstrated remarkable cycling stability after 300 cycles. Additionally, the HCFBi/rGO film presented a specific capacitance of 113.30 F g-1, highlighting its potential for capacitor applications.

Integração de sensores de cor e construção de dispositivos analíticos para medidas em solução e em papel

2026-07-24T06:19:36Z

Title: Integração de sensores de cor e construção de dispositivos analíticos para medidas em solução e em papel Abstract: This work describes the development and application of analytical devices based on the integration of digital multispectral color sensors (TCS34721, AS7262, AS7341, AS7343, and AS7265x) with microcontrollers, aiming at the construction of intelligent platforms for analytical measurements by reflectance in aqueous solutions and in paper-based analytical devices. Initially, a comparative study was carried out among the TCS34721, AS7262, and AS7341 sensors for the quantification of dyes in aqueous solution. The dyes tartrazine, indigo carmine, ponceau 4R, and sunset yellow were selected because they cover a wide range of the visible spectrum, allowing the evaluation of analytical performance across different spectral regions. The results demonstrated that the AS7341 exhibited superior spectral performance due to its higher multichannel resolution, enabling linear calibration curves, low limits of detection (1 µmol L⁻¹), and adequate precision (RSD = 1.0%). The results obtained with this sensor were comparable to those from a commercial spectrophotometer. Based on these findings, a procedure was developed for the determination of sunset yellow in isotonic beverages, juices, and gelatin, yielding results in agreement with UV–Vis spectrophotometry. Subsequently, the Smart-Sense device was developed, a portable embedded system integrating the AS7341 sensor, electronic control, and a smartphone-based graphical interface, which was successfully applied to the determination of ammonium, iron(II), and nitrite. This system exhibited performance compatible with spectrophotometric methods, in addition to advantages related to portability, low cost, analytical speed, and connectivity. Additionally, the Smart-PAD platform was proposed, consisting of a mechanized system for the reading of paper-based analytical devices. Parameters such as drying time, gain, and integration time were evaluated, with temporal control being critical due to the slow kinetics of the modified Berthelot reaction and the degradation of the reaction product on paper. The platform performs measurements within 8.2 minutes for 18 spots, minimizing the effects of substrate heterogeneity. Its application to ammonium determination showed good linearity (R = 0.997), an RSD of 2.7%, and a detection limit of 6 mg L⁻¹. Overall, the developed devices demonstrate the potential of integrating multispectral sensors with embedded systems as a viable and accessible alternative for chemical analyses, contributing to the democratization of analytical instrumentation and to the advancement of the Internet of Analytical Things (IoAT).