Publications

Abstract In the present work, Eu2+/Dy3+ ions doped/co-doped into persistent SrAl2O4 microparticles have been developed through solid-state synthesis followed by homogenization and particle size reduction in a ball milling device. These particles have shown a broad and long-persistent afterglow around the 528 nm wavelength of electromagnetic radiation through a broad excitation at around 400 nm. The luminescence intensity was optimized through the selection of different annealing temperatures in the range of 1100 C-degrees to 1500 C-degrees, with intervals of 100 C-degrees. Several structural and optical characterization techniques, such as XRD, SEM, FTIR, thermogravimetric analysis, and photoluminescence, were utilized to judge the preparation and ability of these particles in possible applications in latent fingermark detection on various difficult surfaces. The persistency and stability of these particles were calculated using a digital lux meter.

Abstract The human normal breast cell line MCF-10A is being widely used as a model in toxicity studies due to its structural similarity to the normal human mammary epithelium. Over the years, application of carbon dots (C-dots) in biomedicine has been increasing due to their photoluminescence properties, biocompatibility, biosafety and possible applications in bioimaging and as drug carriers. In this work we prepared three different C-dots from the same set of carbon and nitrogen precursors (citric acid and urea, respectively) via three distinct bottom-up synthetic routes and their safety was tested against the normal breast cell line MCF-10A. The characterization results demonstrated a similar size range and composition for all the C-dots. The MCF-10A cells were treated with different concentrations of C-dots for 24, 48 and 72 h to evaluate the cell viability over time. For the 24 h incubation, there were no significant decreases in the viability of the MCF-10A cells. For the 48 h treatment, there was a significant decrease in the viability of the cells treated with calcination-based C-dots, but without significant cellular viability changes for microwave and hydrothermal-based C-dots. For 72 h, cells treated with hydrothermal-based C-dots have the most promising viability profile. Also, compared with paclitaxel, these C-dots have a safety profile very close to that of an antineoplastic in non-tumor cells. Our results suggest that these new C-dots have potential as imaging candidates or biosensing tools as well as drug carriers, and further investigation in animal models is needed for future application in medicine.

Abstract <jats:p>Carbon dots (CDs) are fluorescence carbon-based nanomaterials that possess several properties such as photoluminescence, biocompatibility and good water solubility. They can be fabricated from a large variety of precursors; however, most available organic molecules are still expensive and their use or synthesis can lead to significant challenges to the environment and human health. It has become desirable to use biomass waste as alternative precursors in the synthesis of CDs, given that biomass waste material is ubiquitous, nontoxic, cheap and renewable. Spent coffee grounds (SCGs) are the residues of the treatment of coffee powder can be a potential carbon source to a more environmentally sustainable synthesis route. In this work, we fabricated SCG-based CDs via one-pot and solvent-free carbonization at 200 °C of solid samples generating particles with sizes between 2.1 and 3.9 nm. These carbon nanoparticles exhibited blue fluorescence and excitation-dependent emission of carbon dots with moderate quantum yields (2.9–5.8%). The presence of heavy metals in water resources, such as Fe3+, can lead to adverse health effects. SCG-based CDs showed potential for being used as optical Fe3+ optical sensors, with Life Cycle Assessment (LCA) studies validating the SCGs as more sustainable precursors than classical precursors, both considering a weight- or function-based functional unit.</jats:p>

Abstract Spent coffee grounds (SCGs) are known for containing many organic compounds of interest, including carbohydrates, lipids, phenolic compounds and proteins. Therefore, we investigated them as a potential source to obtain carbon dots (CDs) via a nanotechnology approach. Herein, a comparison was performed between CDs produced by SCGs and classic precursors (e.g., citric acid and urea). The SCG-based CDs were obtained via the one-pot and solvent-free carbonization of solid samples, generating nanosized particles (2.1-3.9 nm). These nanoparticles exhibited a blue fluorescence with moderate quantum yields (2.9-5.8%) and an excitation-dependent emission characteristic of carbon dots. SCG-based CDs showed potential as environmentally relevant fluorescent probes for Fe(3+)in water. More importantly, life cycle assessment studies validated the production of CDs from SCG samples as a more environmentally sustainable route, as compared to those using classic reported precursors, when considering either a weight- or a function-based functional unit.

Abstract This work aims to apply photonic-crystal-based nanocoatings with unusual aesthetical orientation to wood application. Structural colors are currently a formula to achieve those colorful coatings including nonfading properties. They can be produced from self-assembled colloidal spheres into photonic crystals, which possess particular optical properties. Herein, photonic crystals with iridescent structural colors were prepared from the self-assembly of monodispersed nanospheres. Particle sizes can be adjusted from 308 to 196 nm, and well-ordered structures are arranged through self-assembly process into films, which exhibit brilliant colors over a wide visible spectrum, from red to violet. Color varies with the angle of observation of incidence light. The present study provided an effective and simple approach to prepare structural color films and their practical application to wood coating for an aesthetic appeal.

Abstract Carbon dots (CDs) are carbon-based nanoparticles with very attractive luminescence features. Furthermore, their synthesis by bottom-up strategies is quite flexible, as tuning the reaction precursors and synthesis procedures can lead to an endless number of CDs with distinct properties and applications. However, this complex variability has made the characterization of the structural and optical properties of the nanomaterials difficult. Herein, we performed a systematic evaluation of the effect of three representative bottom-up strategies (hydrothermal, microwave-assisted, and calcination) on the properties of CDs prepared from the same precursors (citric acid and urea). Our results revealed that these synthesis routes led to nanoparticles with similar sizes, identical excitation-dependent blue-to-green emission, and similar surface-functionalization. However, we have also found that microwave and calcination strategies are more efficient towards nitrogen-doping than hydrothermal synthesis, and thus, the former routes are able to generate CDs with significantly higher fluorescence quantum yields than the latter. Furthermore, the different synthesis strategies appear to have a role in the origin of the photoluminescence of the CDs, as hydrothermal-based nanoparticles present an emission more dependent on surface states, while microwave- and calcination-based CDs present an emission with more contributions from core states. Furthermore, calcination and microwave routes are more suitable for high-yield synthesis (similar to 27-29%), while hydrothermal synthesis present almost negligible synthesis yields (similar to 2%). Finally, life cycle assessment (LCA) was performed to investigate the sustainability of these processes and indicated microwave synthesis as the best choice for future studies.

Abstract The selective fluorescence sensing of fructose was achieved by fluorescence quenching of the emission of hydrothermal-synthesized carbon quantum dots prepared by 3-hydroxyphenylboronic acid. Quantification of fructose was possible in aqueous solutions with pH of 9 (Limit of Detection L-OD and Limit of Quantification L-OQ of 2.04 and 6.12mM), by quenching of the emission at 376nm and excitation similar to 380nm with a linearity range of 0-150mM. A Stern-Volmer constant (K-SV) of 2.11x10(-2)mM(-1) was obtained, while a fluorescent quantum yield of 31% was calculated. The sensitivity of this assay towards fructose was confirmed by comparison with other sugars (such as glucose, sucrose and lactose). Finally, the validity of the proposed assays was further demonstrated by performing recovery assays in different matrixes.

Abstract Diabetes mellitus is a chronic disease and leading cause of death worldwide, affecting more than 420 million people. High blood glucose levels are a common effect of uncontrolled diabetes, which can cause serious health damage. Diabetic individuals must measure their blood glucose levels regularly in order to control glycemic levels and minimize the effects of the disease. Glucose sensors have been used in the management of diabetes for more than 50 years, when Clark and Ann Lyons developed the first glucose enzyme electrode in 1962. Electrochemical sensors have become the leading technology for glucose concentration measuring with most of the commercially available devices being based on amperometric detection. However, the detection of glucose in the blood is still an object of intense research. The development of new fluorescent nanomaterials begins to constitute an alternative for glucose blood quantification. These sensors include carbon dots, quantum dots, graphene quantum dots, gold, silver and upconversion nanoparticles. This paper reviews the last 10 year fluorescent nanoparticles based technologies proposed for glucose monitoring and provide an insight into emerging optical fluorescence glucose biosensors.

Abstract Carbon dots have attracted great attention from the research community given their very attractive luminescent properties. However, the recent discovery that some of these properties may result from fluorescent impurities originating from the synthesis process, and not from the carbon dots themselves, constitute a significant setback to our knowledge of these materials. Herein, we proceeded to the study of carbon dots generated from citric acid and urea via a microwave-assisted synthesis, focusing on their analysis by AFM, HR-TEM, XPS, FT-IR, ESI-MS, UV-Vis and fluorescence spectroscopy. We have found that this synthesis process does generate molecular fluorophores that can mask the luminescence of the carbon dots. More importantly, our data demonstrates that when present in the same solution, the carbon dots and these fluorophores do not behave as separated species with individual emission. Instead, they interact to produce a hybrid luminescence, which excited state properties and reactivity are different from the properties of the individual species. These results indicate the possibility for the development of hybrid materials composed by carbon dots and related molecular fluorophores with new and improved properties.

Abstract Coelenterazine, a member of the imidazopyrazinone class of chemiluminescent substrates, presents significant potential as a dynamic probe of reactive oxygen species in a biological environment, such as a superoxide anion, in which these species are important in cellular biology and pathology. The objective of the current study was to understand in what way the efficiency of singlet and triplet chemiexcitation could be modulated, towards a more efficient use of imidazopyrazinone-based compounds as dynamic chemiluminescent probes. To this end the thermolysis of imidazopyrazinone dioxetanone, substituted at the C-8-position with electron-donating or electron-withdrawing groups, was characterized with a theoretical approach based on density functional theory. Substituents with different electron-donating/withdrawing characters have only a limited effect on the singlet chemiexcitation of anionic dioxetanone. For neutral dioxetanone, both electron-withdrawing and weak electron-donating substituents increase singlet chemiexcitation, to the contrary of strong electron-donating groups. During their thermolysis reaction, all molecules presented regions of degeneracy with triplet states, thereby indicating the possibility of triplet chemiexcitation.