Featured paper: Disclosing structural disorder in nanomaterials.

[Paper: Decreasing Nanocrystal Structural Disorder by Ligand Exchange: An Experimental and Theoretical Analysis. Gabriel R. Schleder, Gustavo M. Azevedo, Içamira C. Nogueira, Querem H. F. Rebelo, Jefferson Bettini, Adalberto Fazzio, Edson R. Leite. J. Phys. Chem. Lett. 2019 10 1471-1476. https://doi.org/10.1021/acs.jpclett.9b00439]

Disclosing structural disorder in nanomaterials

It is known that it is very important to know and control the structure of a material (how its atoms are arranged in three-dimensional space) as it is largely responsible for the properties of the material and therefore for its applications. For example: regions of disorder in crystalline materials (whose atoms, ideally, are ordered in regular patterns) change some expected behaviors for these materials. Unfortunately, knowing the structure of some materials in detail can be a difficult task – particularly when it comes to nanomaterials.

Concentrating various skills and experimental and theoretical resources, a Brazilian team developed a method to establish the degree and location of disorder in the structure of crystalline and non-crystalline nanomaterials, interfaces and surfaces. The method, which is based on the combination of an experimental technique (transmission electron microscopy), a data analysis method (pair distribution function) and computational simulations, is already available to the scientific community at the Brazilian National Nanotechnology Laboratory (LNNano), and should help develop better performing materials.

In addition to developing the technique, the team applied it in the study of structural disorder in nanocrystals, which are basic elements of nanotechnology and are used for example, in solar cells and electronic devices. Although by definition they have ordered structures, these crystals of nanometric dimension can exhibit, in practice, regions with structural disorder.

In order to carry out the study, the scientists produced faceted nanocrystals of about 3.2 nm in diameter, formed by a core of zirconium dioxide (ZrO2), inorganic material, and a shell made up of organic substances known as ligands, whose atoms form chemical bonds with atoms that are on the surface of the inorganic nucleus. Ligands have the important role of stabilizing the nanocrystals, thus preventing them from aggregating.

The team produced a first series of nanoparticles with ligands containing an aromatic ring and analyzed it using the developed method. The samples were then subjected to a process known as ligand exchange in which chemical reactions occur in the material in the presence of a solvent at a temperature above its boiling point. In these reactions, some connections break down and new connections occur. As a result of the ligand exchange, the team was able to produce nanoparticles with shells containing oleic acid, which were also analyzed using the developed method.

This figure refers to a nanocrystal of ZrO2 before and after the ligand exchange. The figure includes high-resolution images of transmission electron microscopy, structural models and PDF patterns obtained by the developed method.
This figure refers to a nanocrystal of ZrO2 before and after the ligand exchange. The figure includes high-resolution images of transmission electron microscopy, structural models and PDF patterns obtained by the developed method.

The scientists concluded that, unlike the ideal nanocrystal of zirconium dioxide, the two types of nanocrystals analyzed had a degree of structural disorder located on the surface of the nucleus.  In addition, in the second group of nanoparticles, the disorder was significantly lower. The researchers interpreted this reduction as a result of the high temperature of the ligand exchange process, which altered the tensions of the network of atoms.

“In our work, we were able to directly assess the degree and location of disorder in the nanocrystals, which until then was not technically feasible,” says Gabriel Schleder, PhD candidate in the Graduate Program in Nanosciences and Advanced Materials of the Brazilian Federal University of the ABC (UFABC).

By better understanding structural disorder and its causes, the researchers were able to point out a way to control it. “Any property that significantly depends on surface-located structural disorder could be in principle controlled by this kind of ligand exchange process,” says Schleder. “Mechanical properties, photoluminescence, electronic transport and catalytic properties are some of them,” he adds.

The research was reported in a recently published article in The Journal of Physical Chemistry Letters (impact factor = 8,709).

Overcoming the challenge through collaborations

The initial idea of the study appeared in a meeting held at the end of 2017 at the National Center for Research in Energy and Materials (CNPEM), located in the city of Campinas, São Paulo. At the meeting, a group of reserachers discussed the implementation in Sirius (the next Brazilian synchrotron light source) of a technique that allows locally analyzing structural issues such as disorder and defects, called pair distribution function (PDF). The technique describes the distances between pairs of atoms by means of a mathematical function. To apply it, the specialist generally uses the results of X-ray diffraction measurements – an experimental technique that provides information about the structure of materials. However, in order to implement the analysis by PDF, the X-ray beam focused on the sample must be of very high energy – higher than that provided by the current Brazilian synchrotron light source.

During the meeting at CNPEM, Professor Gustavo de Medeiros Azevedo, researcher at the National Laboratory of Synchrotron Light (LNLS), and Professor Edson Leite, LNNano’s scientific director, decided to begin applying PDF using electron diffraction results, a specialty of LNNano’s researcher Jefferson Bettini. The electron beams would be generated by the transmission electron microscope (TEM) of LNNano. In fact, this instrument allows the control of the electron beam so that it focuses a small area of the sample, allowing the desired local analysis of the structure. Besides that, when switching from the “diffraction mode” to the “image mode”, the microscope would made possible to choose precisely the area of the sample to be analyzed.

Simulation of an ideal ZrO2 nanocrystal.
Simulation of an ideal ZrO2 nanocrystal.

The development team also involved professors Içamira Costa Nogueira, from the Federal University of Amazonas (UFAM) and Querem Hapuque Felix Rebelo, from the Federal University of the West of Pará (UFOPA), who contributed with the synthesis of nanocrystals that would be studied and with the development of the analysis methodology.

During the development of the technique, another challenge had to be faced. To interpret the PDF results, it would be necessary to have a simulation of an ideal nanocrystal – a nanocrystal model without structural disorganization that could be used as a reference.

New skills were then incorporated into the team, which was then joined by Professor Adalberto Fazzio, director general of LNNano and leader of a UFABC research group dedicated to computational techniques applied to materials, and his doctoral student Gabriel Schleder. Based on the Density Functional Theory (DFT), a computational modeling method in the field of Quantum Physics, the researchers were able to simulate the ideal nanocrystal that served as the analysis model.

“Something very positive we perceived is that the main results arose from the process of interaction, discussion and exchange of information mainly between theory/computational simulation and experiments. Without this, we certainly would not have good final conclusions,” says Schleder.

The authors of the paper. From the left: Gabriel R. Schleder, Gustavo M. Azevedo, Içamira C. Nogueira, Querem H. F. Rebelo, Jefferson Bettini, Adalberto Fazzio and Edson R. Leite.
The authors of the paper. From the left: Gabriel R. Schleder, Gustavo M. Azevedo, Içamira C. Nogueira, Querem H. F. Rebelo, Jefferson Bettini, Adalberto Fazzio and Edson R. Leite.

Featured paper: Synergistic anticancer films.

[Paper: Antimicrobial Activity and Cytotoxicity to Tumor Cells of Nitric Oxide Donor and Silver Nanoparticles Containing PVA/PEG Films for Topical Applications. Wallace R. Rolim, Joana C. Pieretti, Débora L. S. Renó, Bruna A. Lima, Mônica H. M. Nascimento, Felipe N. Ambrosio, Christiane B. Lombello, Marcelo Brocchi, Ana Carolina S. de Souza, and Amedea B. Seabra. ACS Appl. Mater. Interfaces, 2019, 11 (6), pp 6589–6604. DOI: 10.1021/acsami.8b19021. ]

Synergistic anticancer films

A team of researchers from Brazilian universities developed a new film material that contains and releases, simultaneously, silver nanoparticles (AgNPs) and nitric oxide (NO) – two active substances known for their antimicrobial and anticancer activity. Tested by the scientific team, the material proved to be effective in eliminating various types of bacteria and cells from certain types of cancer. The characteristics of the film make it promising to topically treat malignant tumors or infectious lesions.

The main authors of the paper: from the left, Wallace Rosado Rolim (doctoral student at UFABC), Amedea Barozzi Seabra (Professor at UFABC) and Joana Claudio Pieretti (Master´s student at UFABC).
The main authors of the paper: from the left, Wallace Rosado Rolim (doctoral student at UFABC), Amedea Barozzi Seabra (Professor at UFABC) and Joana Claudio Pieretti (Master´s student at UFABC).

The study, recently published in ACS Applied Materials & Interfaces (Impact Factor 8.097), was developed during the Master’s research work of Wallace Rosado Rolim, guided by Professor Amedea Barozzi Seabra, and defended this year in the postgraduate program in Science and Chemical Technology of the Federal University of ABC (UFABC). The work also involved, through scientific collaborations, knowledge and experimental techniques of Biology and Biomedicine areas. “I emphasize the importance of interdisciplinarity and teamwork for the success of scientific and technological research,” says Professor Seabra, who is the corresponding author of the article.

The idea of developing this biomaterial (a material planned to interact with a biological system for medical diagnostic or treatment) came up in discussions between Rolim and his advisor. “We were looking for new strategies for controlled, localized and sustained release of actives such as nitric oxide molecules associated with silver nanoparticles, for biomedical applications,” reports Professor Seabra. The scientific duo had the idea of bringing together the two therapeutic assets in a single material that was able to topically release them. “We were looking for a synergistic action of these two assets,” says Seabra.

Thus, Professor Seabra and Rolim, with the collaboration of the Master’s student Joana Claudio Pieretti, endeavored to develop the material. The team was able to prepare films made from a composite material, whose matrix consists of a polymer, known as PVA, added with another polymer, called PEG, which made the matrix more flexible. Both polymers are non-toxic and biocompatible. During the preparation of the films, they added silver nanoparticles and a nitric oxide donor substance (the GSNO molecule, which, spontaneously, decompose and generate nitric oxide).

The same group prepared the silver nanoparticles using a simple, inexpensive method that is friendly with the environment and living organisms, also developed by Rolim in his Master’s work. In the method, which was reported in an article published earlier this year (https://doi.org/10.1016/j.apsusc.2018.08.203), green tea extract is used to generate the nanoparticles from silver nitrate, as shown in this figure:


image 1

In order to compare the antimicrobial and anticancer effects, the team prepared several types of films: some formed by the pure matrix (PVA/PEG), others containing silver nanoparticles or nitric oxide donors in different concentrations, and the last containing both therapeutic agents in the same matrix. After analyzing all the films using various characterization techniques to accurately determine their composition and morphology, Professor Seabra and her students studied how the release of nitric oxide and silver nanoparticles occurred.

Finally, the films were sent to the collaborators from other research groups to perform the biological assays, which were performed in vitro (i.e., outside living organisms and within environments with controlled conditions). At UFABC, the groups of professors Ana Carolina Santos de Souza Galvão and Christiane Bertachini Lombello focused on the anticancer action of the biomaterial, using cervical and prostate cancer cells. On the other hand, the tests related to the antibacterial activity of the films were carried out at the São Paulo State University of Campinas (UNICAMP), by Professor Marcelo Brocchi’s group, which involved tests with several types of bacteria, including the well-known Escherichia coli and Staphylococus aureus.

The tests showed that the films containing both therapeutic assets presented the best results in the elimination of bacteria and mainly of cancerous cells, as this figure illustrates:


image 2

As a result, the synergism between silver and nitric oxide nanoparticles, which Seabra and Rolim had looked for since the beginning of the Master’s research work, was proven. In one of the assays, to cite one example, less than 25% of the cancer cells remained alive (viable) after being treated with these films for 24 hours.

The material developed by the UFABC team brings the possibility of implementing a new therapeutic strategy for some cancerous tumors and infectious lesions, based on the simultaneous release of nitric oxide and silver nanoparticles, directly at the affected site, from a film. Seabra explains that “In practice, this film can be applied, for example, in a tissue (such as the skin or mucosa) or an organ, for antimicrobial or antitumor actions.” By releasing therapeutic amounts of the agents directly at the site of interest, it avoids unwanted release in healthy organs and/or tissues and thus prevents possible side effects, Seabra adds.

This work received financial support from the Brazilian agencies CNPq, FAPESP and CAPES. The first author of the paper, Wallace Rosado Rolim, developed his master’s research work with a grant from UFABC.

Postdoctoral fellowship in Physics.

Area of interest: Condensed Matter

FAPESP process number: 2017/02317-2

Project title: Synthesis and physical properties characterization of Halide Perovskites

Principal investigator: Prof. Gustavo Dalpian and Dr. Jose Antonio Souza

Institution: Federal University of ABC – Campus Santo André

Deadline for applications: December 30th, 2018. Expected starting date: February or March/2019.

Location: Avenida dos Estados, 5001, Bairro Bangu – Santo André, SP

E-mail for applications: (gustavo.dalpian@ufabc.edu.br); (joseantonio.souza@ufabc.edu.br)

Applications are invited for a post-doctoral position supported by the State of Sao Paulo Research Foundation (FAPESP-Brazil) in experimental condensed matter field. This fellowship is part of broader Thematic project “Interfaces in materials: electronic, magnetic, structural and transport properties” under the coordination by Prof. Adalberto Fazzio (LNNano, CNPEM – Campinas). The postdoctoral supervisor will be Prof. Dr. Gustavo Dalpian in collaboration with Prof. Dr. Jose Antonio Souza at the Federal University of ABC (UFABC), Santo André – São Paulo.

We intend to develop research on the synthesis and physical properties characterization of Halide Perovskites. Applicants are required to have good experimental knowledge on synthesis and/or physical properties characterization of halide perovskites in the form of nanostructures and/or thin films and/or heterostructures and/or quantum dots and/or bulk. The research will be developed at the Federal University of ABC – Campus Santo André.

The opportunity is open to both Brazilian and foreign candidates with a PhD degree, in Brazil or abroad, in areas related to the proposed subject. It is mandatory that the candidate has international experience, as well as publications in the areas related to the project in journals of relevant worldwide impact.

The following documents are required for application:

  1. Curriculum vitae, presenting the candidate’s academic experience and the list of published papers. The curriculum must be submitted in electronic format (pdf, Portable Document Format), where the articles must be identified by their DOI;
  2. Document proving that the candidate holds a PhD degree;
  3. At least two recommendation letters, in English, which should be sent directly to the email with the subject “Fellowship PD – Recommendation Letter”.

The implementation of the scholarship is conditioned to the approval of the candidate selected by FAPESP. If the decision is approved by FAPESP, the selected candidate will receive a scholarship in the amount of R$ 7,174.80/month and a technical reserve equivalent to 15% of the annual amount of the scholarship, destined to only carry-out expenses directly related to the research activity. More information on the scholarship can be found at: www.fapesp.br/bolsas/pd.

The candidate should send all the documentation to the electronic address cited above under the title “Fellowship PD – Application”. The deadline for submissions is 02/01/18. Only applications in which all the documents (including recommendation letters) are received by midnight 02/01/2018, Brasília time (UTC-3, Brazilian summer time) will be considered.

UFABC abre inscrições para Pós-Graduação em Nanociências e Materiais Avançados.

O aumento da importância e competitividade tecnológica no domínio de nanomateriais e na ciência de materiais é reconhecido como um dos grandes pilares do desenvolvimento científico, tecnológico e social no século XXI. A possibilidade de desenvolver moléculas e materiais que podem substituir os materiais tradicionais terá um profundo impacto em muitos aspectos do desenvolvimento de diversos produtos. O campo emergente de materiais funcionais é, portanto uma tecnologia estratégica para o futuro.

Diante desta realidade o programa de Pós-Graduação em Nanociências e Materiais Avançados da Universidade Federal do ABC (UFABC) busca capacitar profissionais com formação interdisciplinar que apresente uma visão abrangente e diferenciada, qualificando-o para a pesquisa de ponta e as inovações tecnológicas nas áreas do programa.

As inscrições para o processo seletivo para o Mestrado e Doutorado estão abertas até o dia 24 de Junho.

Mais informações em http://nano.ufabc.edu.br.