Featured paper: Low toxicity magneto-luminescent nanoplatform.


Cover of ACS Applied Nano Materials features the paper.
Cover of ACS Applied Nano Materials features the paper.

In research carried out in a number of Brazilian laboratories, a multidisciplinary scientific team developed a magnetic, luminescent nanomaterial capable of chemically binding to molecules of interest, such as drugs or proteins. This nanomaterial also showed low toxicity in tests with living organisms. With this set of characteristics, the new material can be seen as a multifunctional nanoplatform that is promising for the development of various applications, especially in the areas of biotechnology, health and environment. The study was reported in an article published in ACS Applied Nano Materials (American Chemical Society journal released in 2018), and featured on the cover of the June issue of the journal.

The properties of this nanoplatform derive from the presence of several compounds and elements with distinct properties: iron oxide (Fe3O4, known as magnetite) nanoparticles responsible for magnetism; lanthanide element ions (Gd3 +, Ce3 + and Tb3 +, known as rare earths) responsible for luminescence or light emission, and chitosan (biopolymer obtained from the crustacean exoskeleton), essential for providing chemical bonds of the nanoplatform surface to the external molecules of interest.

The nanoplatform was developed at the Brazilian National Nanotechnology Laboratory of the National Center for Energy and Materials Research (LNNano – CNPEM). The process used for its synthesis comprises a series of steps. Initially, the iron oxide nanoparticles that form the core of the nanoplatforms are synthesized and coated with silicon dioxide (SiO2). Then the luminescent elements and chitosan are incorporated into the nanoparticles forming an outer layer. The result is nanoplatforms of approximately 170 nm in diameter (on average), called Fe3O4@SiO2/GdOF:xCe3+,yTb3+.

On the left, a schematic illustration of one of the nanoplatforms, showing its core. On the right, a solution with nanoplatforms under the effect of a magnetic field (concentrated near the magnets) and irradiated with UV light (generating the emission of green light).
On the left, a schematic illustration of one of the nanoplatforms, showing its core. On the right, a solution with nanoplatforms under the effect of a magnetic field (concentrated near the magnets) and irradiated with UV light (generating the emission of green light).

To study the magnetic and luminescent properties of the nanoplatform and to characterize its structure and morphology, research groups from the State University of Campinas (Unicamp) and the University of São Paulo (USP) participated in the study.

In addition, the main authors of the paper decided to evaluate the toxicity of nanoplatforms with relation to living organisms – a key step when thinking about health or environmental applications, and they decided to conduct a well-established in vivo test, in which zebrafish embryos (scientific name Danio rerio) are exposed to the material whose toxicity is to be evaluated. These freshwater fish, in fact, has a high genetic similarity to humans (about 70%) and at the same time is cheaper and easier to study than mice or rats, among other advantages.

In the toxicity test, a few dozen freshly fertilized zebrafish eggs were placed in aqueous medium containing the nanoplatforms at various concentrations. The embryos were examined at different development stages using an optical microscope to check for mortality, malformation, edema or changes in size. Tests included embryos with and without chorion (membrane that protects the embryo in the early stages of development). The test results carried out at LNNano showed that nanoplatforms, even at high concentrations (100 mg/L), have low toxicity for all embryo groups.

Zebrafish embryos used in nanotoxicity tests. (A) 24-hour embryos in the presence and absence of the chorion, where arrows indicate the chorion (membrane that protects embryos in the early stages of development). (B) Embryos after 96 hours of development.
Zebrafish embryos used in nanotoxicity tests. (A) 24-hour embryos in the presence and absence of the chorion, where arrows indicate the chorion (membrane that protects embryos in the early stages of development). (B) Embryos after 96 hours of development.

“This work brings an unprecedented contribution that involves evaluating the toxicity of hybrid nanomaterials using the zebrafish model, a promising alternative method in nanotoxicology, and the influence of the chorion,” says Diego Stéfani Teodoro Martinez, CNPEM researcher at LNNano and one of the corresponding authors of the article.

The embryos were also analyzed at the Brazilian National Synchrotron Light Laboratory (LNLS – CNPEM) to verify the distribution and concentration of nanoplatforms in the organism of the embryos. To do this, the scientists used the synchrotron light X-ray fluorescence microscopy (SXRF) technique, which can accurately map certain chemical elements in biological systems. This technique is available at one of the LNLS experimental stations, coordinated by the researcher Carlos Alberto Pérez, who is one of the corresponding authors of the article.

X-ray fluorescence microscopy analysis with synchrotron light (SXRF) of two zebrafish embryos after exposure to the nanoplatform for 72 hours. (A) Optical microscopy image of the embryos; (B) SXRF image of embryos demonstrating nanoplatform accumulation in the intestinal tract; and (C) X-ray fluorescence intensity along the white line indicated in (B), demonstrating the spatial co-location of Fe and Gd elements in the intestinal tract of zebrafish embryos.
X-ray fluorescence microscopy analysis with synchrotron light (SXRF) of two zebrafish embryos after exposure to the nanoplatform for 72 hours. (A) Optical microscopy image of the embryos; (B) SXRF image of embryos demonstrating nanoplatform accumulation in the intestinal tract; and (C) X-ray fluorescence intensity along the white line indicated in (B), demonstrating the spatial co-location of Fe and Gd elements in the intestinal tract of zebrafish embryos.

SXRF analysis showed that nanoplatforms had accumulated in the embryos as a function of exposure time, with higher concentrations in the gastrointestinal tract in the case of already developed mouth embryos – a result that may be significant, for example in the context of healthcare applications involving oral nanoplatform ingestion.

The study was carried out in the context of a postdoctoral project by fellow Latif Ullah Khan, also corresponding author of the article. The completion of the project, says Martinez, was made possible by the availability of skills and facilities at CNPEM’s multi-user laboratories. However, partnerships with other laboratories were also crucial, adds the CNPEM researcher. Professor Marcelo Knobel’s group performed the magnetometry studies at Unicamp. The groups of professors Hermi Felinto Brito and Magnus Gidlund carried out the luminescence and functionalization studies at USP. Finally, Professor Diego Muraca (Unicamp) and researcher Jefferson Bettini (CNPEM) contributed to the structural and morphological characterization using transmission electron microscopy techniques.

“This article was the result of integrating the experience of different Brazilian groups; an interdisciplinary study on the frontier of knowledge in nanobiotechnology and nanotoxicology,” says Martinez, adding that one of the main challenges of the work was integrating knowledge and techniques from different areas, such as Materials, Biology and Toxicology, a task that was coordinated by Martinez and Pérez.

The main authors of the paper. From the left: Latif Khan, Carlos Pérez and Diego Stéfani Martinez.
The main authors of the paper. From the left: Latif Khan, Carlos Pérez and Diego Stéfani Martinez.

The study received financial support from Brazilian agencies CAPES (including through the CAPES-CNPEM agreement), FAPESP and CNPq (including through INCT-Inomat); from the Brazilian Ministry of Science, Technology, Innovations and Communications (MCTIC) through SisNANO, and The World Academy of Sciences for advancement of science in developing countries (TWAS). The study also received financial support from the Brazil-China Nanotechnology Research and Innovation Center (CBC-Nano).

Applications: biotechnology, health and the environment

According to Martínez, the nanoplatform developed opens perspectives for applications in biotechnology, health and the environment, such as biological tissue and cell imaging systems, medical diagnostic kits, and environmental systems for pollutant detection and remediation

The applications would take advantage of the interesting set of nanoplatform properties. Because they are magnetic, using an external magnet, nanoplatforms could be directed and retained in a particular biological tissue or isolated from, for example, contaminated blood or water. In addition, the luminescence of the nanomaterial would allow visualizing the nanoplatforms within the biological tissues and cells of interest. Finally, the presence of chitosan would enable the chemical binding of drugs and other molecules that would serve for the diagnosis and/or treatment of diseases. “However, much study is still needed for real applications and commercialization of this nanoplatform, as it is a new material and needs to be tested on different models in the future,” says Martinez Martinez.

 

[Paper: Fe3O4@SiO2 Nanoparticles Concurrently Coated with Chitosan and GdOF:Ce3+,Tb3+ Luminophore for Bioimaging: Toxicity Evaluation in the Zebrafish Model. Latif U. Khan, Gabriela H. da Silva, Aline M. Z. de Medeiros, Zahid U. Khan, Magnus Gidlund, Hermi F. Brito, Oscar Moscoso-Londoño, Diego Muraca, Marcelo Knobel, Carlos A. Pérez, Diego Stéfani T. Martinez. ACS Appl. Nano Mater. 2019, 2,6, 3414-3425. https://doi.org/10.1021/acsanm.9b00339.]

Featured paper: “Green” nanoparticles for water treatment.


The scientific paper by members of the Brazilian community on Materials research featured this month is: “Green” colloidal ZnS quantum dots/chitosan nano-photocatalysts for advanced oxidation processes: Study of the photodegradation of organic dye pollutants. Alexandra A.P. Mansur, Herman S. Mansur, Fábio P. Ramanery, Luiz Carlos Oliveira, Patterson P. Souza. Applied Catalysis B: Environmental158–159 (2014), 269–279. DOI:10.1016/j.apcatb.2014.04.026.

“Green” nanoparticles for water treatment

A group of researchers from Brazilian institutions developed nanoparticles that are triply “green”. They can be used to purify water, one the greatest global challenges of the 21st Century. In addition to that, they coexist harmonically with the environment and biological systems. Finally, they are produced by means of an eco-friendly process.

“We managed to integrate properties and characteristics rarely found in nanostructured systems, which are biocompatibility and environmental compatibility, using a ‘green’ process”, says Professor Herman Sander Mansur from the Federal University of Minas Gerais (UFMG).

The particles are formed by “quantum dots” (fluorescent semiconductor nanocrystals) of zinc sulfide (ZnS) with approximately 3.8 nm in size, coated with “shells” made of chitosan – an abundant, low-cost material, derived from the external skeleton of crustaceans such as shrimps and crabs. The synthesis process of these particles is completed in a single stage, carried out in an aqueous medium, without using toxic substances.

In a study performed by the research team, the nanoparticles displayed the capacity to degrade contaminant organic pigments usually found in water, using only light, including direct sunlight.

“The results were very promising, since we were able to observe that the system was effective for the photodegradation of organic contaminants found in the aqueous solutions we studied,” said Herman Mansur, who is the corresponding author of a paper about the research, recently released by the journal Applied Catalysis B: Environmental.

The research will also be the subject of a patent application, which the authors already started writing. “The following step will be searching potential partners in the private sector, in order to commercialize it as a product for cleaning waters which are polluted by organic pigments”, says Mansur.

Schematic representation of the nanostructured system produced with a ZnS core and chitosan shell for photodegradation of organic pollutants in water.

History of the paper

It was during scientific discussions occurred in the monthly meetings of the Exact Sciences and Materials Board of the Minas Gerais State Research Foundation (FAPEMIG) that the initial idea for the research came up.  In fact, both, Herman Mansur, coordinator of the UFMG Nanosciences, Nanotechnology and Innovation Center, and Luis Carlos de Oliveira, coordinator of the research group in Advanced Materials for Catalysis and Photocatalysis in the same university, were members of said advisory committee between February 2010 and the same month in 2014. According to Mansur, “the main idea was to use nanotechnology to develop innovative environmental solutions to clean up water, as it is an increasingly scarce resource in the world, whether in developed or emergent countries, as well as the ones with low social and economic development”.

Then, the professors prepared a project that combined the experience from the two research groups: Professor Mansur’s team, dedicated for twenty years to the development of nanomaterials and nanostructures by means of the synthesis of quantum dots, and Professor Oliveira’s group, which had been working in the field of chemical catalysis, searching sustainable solutions for the treatment of industrial waste.

Their initial research led to a first article on nanoparticles with cadmium sulfide (CdS) core and niobium oxide shell: L. C Oliveira et. al. One-pot Synthesis of CdS@Nb2O5 Core-Shell Nanostructures with Enhanced Photocatalytic ActivityApplied Catalysis. B, Environmental, v. 152:53, p. 403-412, 2014 (DOI:10.1016/j.apcatb.2014.01.025).

As a result, the group conceived, designed and developed an application for the concept of “green chemistry” in the whole project, producing zinc sulfide and chitosan particles, and their synthesis process. In the following stage, their research also incorporated the collaboration of Professor Patterson P. Souza, from the Federal Center for Technological Education of Minas Gerais (CEFET-MG), who conducted mass spectrometry tests, assessing the degradation of the organic pigments used as models for the polluting chemical species.