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589 results on '"Bertotti, Mauro"'

20. Unusual dark‐field hyperspectral and confocal Raman microscopy features of a nanoporous gold electrode coated with porphyrazine complex.

Author

Ribeiro, Leonardo M. A., Silva, Hiago N., Damasceno, Pedro H. A., Bertotti, Mauro, Toyama, Marcos M., Nakamura, Marcelo, and Toma, Henrique E.

Subjects
RAMAN microscopy, GOLD electrodes, RAMAN scattering, CONFOCAL microscopy, GOLD coatings, SERS spectroscopy
Abstract

Nanoporous gold electrodes are of great interest in electroanalytical chemistry, because of their unusual activity and large surface area. The electrochemical activity can be further improved by coating with molecular catalysts such as the tetraruthenated cobalt‐tetrapyridylporphyrazines investigated in this work. The plasmonic enhancement of the scattered light at the nanoholes and borders modifies the electrode's optical characteristics, improving the transmission through the surface‐enhanced Raman scattering (SERS) effect. When monitored by hyperspectral dark‐field and confocal Raman microscopy, this effect allows probing of the porphyrazine species at the plasmonic nanholes, improving the understanding of the chemically modified gold electrodes. [ABSTRACT FROM AUTHOR]

Published
2024
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21. Manipulation of Energy Migration in Upconversion Nanoparticles for Long-Lived Mn2+ Emission and Enhanced Singlet Molecular Oxygen Generation.

Author

Khan, Zahid U., Khan, Latif U., Prado, Fernanda M., Gul, Iram, Lopes, Thiago, Ribeiro, Leonardo M. A., Bertotti, Mauro, Gidlund, Magnus, Brito, Hermi F., and Di Mascio, Paolo

Abstract

Nanosensitizers having long-lived upconversion emission under near-infrared (NIR) excitation offer unique advantages in terms of reduced background noise and prolonged signal detection for deep tissue therapy of cancer. Herein, we demonstrate a systematic mechanism of energy migration toward achieving long-lived Mn2+ upconversion emission in the multilayered core–shell–shell lattice of NaGdF4:Yb3+,Tm3+,Ca2+/NaGdF4:Yb3+,Ca2+/NaGdF4:Mn2+ upconversion nanoparticles (NPs), following the Yb3+ → Tm3+ → Gd3+ → Mn2+ intermetal ions energy transfer pathway. Furthermore, a rational design of nanosensitizer was achieved by incorporating Er3+ ions into the intermediate shell of multishell NPs, which was subsequently conjugated with the Rose Bengal sensitizer to enable the enhancement in singlet molecular oxygen (1O2) generation under excitation of a 980 nm NIR laser. An intense higher-energy emission in the UV–blue visible region from Tm3+ was achieved by optimizing the amount of Ca2+ in the core–shell NPs, followed by subsequent energy migration to the Mn2+ ion incorporated at the outer shell. The Mn2+ ions were strategically doped in the outer shell of NPs to leverage the catalytic activities of Mn2+ for H2O2 decomposition and decrease the backward energy transfer to the Tm3+ ion. Hence, this approach resulted in a long lifetime of Mn2+ (∼34 ms), attributed to the spin-forbidden 4T1g → 6A1g transition within 3d5 configuration. Additionally, the nanosensitizer demonstrated high 1O2 (∼0.39 μM) generation even at a very low concentration (5 μg/mL) under a laser power of 2 mW cm–2. The hydrogenase-like catalytic activities of Mn2+ exhibited significant oxygen production through decomposition of H2O2. Hence, these findings might contribute to the development of convenient multifunctional nanosensitizers for multimodal bioimaging and therapeutic features, including efficient 1O2 generation and catalytic decomposition of H2O2 (found excessively in a tumor environment) to oxygen for alleviating the hypoxia. [ABSTRACT FROM AUTHOR]

Published
2024
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32. Calibration-Free Analysis with Chronoamperometry at Microelectrodes

Author

Conceição, Valdomiro S., Saraiva, Douglas P. M., Denuault, Guy, and Bertotti, Mauro

Abstract

Analytical methods are crucial for monitoring and assessing the concentration of important chemicals, and there is now a growing demand for methodologies that allow miniaturization, require lower sample volumes, and enable real-time analysis in the field. Most electroanalytical techniques depend on calibrations or standards, and this has several limitations, ranging from matrix interference, to stability problems, time required, cost and waste. Therefore, strategies that do not require standards or calibration curves greatly interest the analytical chemistry community. Here, we propose a new quantification method that does not rely on calibration and is only based on a single chronoamperometric curve recorded with a microelectrode. We show that satisfactory analytical information is obtained with just one chronoamperometric experiment that only takes a few seconds. We propose different data treatments to determine the unknown concentration, we consider the experimental conditions and instrument parameters, we report how parallel reactions affect the results, and we recommend procedures to implement the method in autonomous sensors. We also show that the concentration of several species can be derived if their E° values are sufficiently far apart or the sum of all concentrations if the E° values are too close. The proposed method was validated with a model redox system then further evaluated by determining ascorbic acid concentrations in standard solutions and food supplements, and paracetamol in a pain killer. The results for ascorbic acid were compared with those obtained by coulometry, and a good agreement was found, with a maximum deviation ca. 10.8%. The approach was also successfully applied to ascorbic acid quantification in solutions with different viscosity using ethylene glycol as a thickener.

Published
2024
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46. Deciphering the Atomic Scale Electrocatalytic Sites in Hierarchically Porous Gold Nanostructures: Implications for Ascorbic Acid Electrooxidation.

Author

Kumar, Abhishek, Lüder, Johann, Bertotti, Mauro, Araki, Koiti, Montoro, Fabiano, Herbst, Frederic, Meunier-Prest, Rita, Angnes, Lucio, Bouvet, Marcel, Bettini, Jefferson, and Gonçalves, Josue M.

Abstract

Understanding the structure and origin of catalytic sites at the nanometer/subnanometer scale in porous nanomaterials is essential for an efficient and durable catalyst design. Herein, chemically pure nanoporous gold (NPG) having a hierarchically porous network is electrochemically synthesized, and its microstructure is investigated by electron microscopies, electrochemical methods, and ab initio simulations to unravel the identification of catalytic sites for ascorbic acid (AA) electrochemical oxidation. Experimental characterizations reveal a highly porous NPG film containing polycrystalline and interconnected dendrite fractals. The film growth follows a unique pattern such that at the beginning of the film growth, Au grains are smaller, which at the later growth stage become larger and expose low-index facets and structural defects such as dislocation of Au atoms, atomic steps, and kinks. Such structural defects and facet evolutions in the NPG film cause a remarkable electrocatalytic effect toward the electrochemical oxidation of AA, which is interpreted based on density function theory (DFT) simulation. The simulation predicts stronger binding of AA on the low-indexed Au facets and grain boundaries, leading to a larger electronic charge transfer from AA to the Au atoms. In particular, grain boundary regions provide vacancy-like sites, in which part of AA locks itself, forming a stronger bond with a Au atom of partial covalent character. The low catalytic activity of the thermodynamically stable (111) facet is assigned to its flat topography, over which AA interacts through mainly van der Waals forces, causing weaker binding. [ABSTRACT FROM AUTHOR]

Published
2024
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