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Category: News
Featured paper: Photoelectrochemical biosensor for point-of-care diagnosis of diseases.
Using a set of carefully prepared and combined materials, Brazilian researchers have developed a portable photoelectrochemical immunosensor with potential for use in the early diagnosis of diseases. The device allows rapid and accurate detection of diseases such as cancer, even at an early stage. The immunosensor was tested, with very good results, in the detection of prostate-specific antigen (PSA), which is the most used marker to diagnose and monitor cases of prostate cancer from blood samples.
In a compact system, which fits in one hand, the device gathers all the elements necessary to carry out the diagnosis without needing laboratories nor specialized professionals. In this way, the device is part of the point-of-care testing paradigm, an expression that designates, in the health area, the possibility of performing medical tests at the time and place of the patient´s medical care.
“The technology we developed has the potential to facilitate cancer diagnoses and make it faster and more accurate, especially at the early stage. The method allows the detection of biomarkers at low concentration levels and in the doctor’s office”, says Thiago Serafim Martins, one of the corresponding authors of the article that reports this research and was featured on cover of ACS Applied Materials & Interfaces. Martins participated in this work during his doctorate, whose thesis was defended this year at the São Carlos Institute of Chemistry (IQSC-USP).
The challenge
Immunosensors form a class of detection devices whose operation is based on the interaction between antibodies and their antigens. In these biosensors, antibodies are immobilized on the surface of the detection platform so that, when they come into contact with their respective antigens, and only with them, a chemical reaction occurs – the one that, in the body, allows us to defend ourselves from pathogens.
At that moment, another component of the immunosensor comes into play, the transducer, which translates this immunochemical information into another type of signal that can be easily interpreted (usually an electrical current). When this translation is based on electrochemical reactions, the device is called an electrochemical immunosensor. And when the generation of electric current is encouraged by the action of light on a sensitive material, the immunosensor is said to be photoelectrochemical.
“Photoelectrochemical biosensors belong to a sensitive and low-cost analytical approach to detecting molecules of clinical and environmental interest”, says José Luiz Bott-Neto, postdoctoral fellow at the São Carlos Institute of Physics (IFSC-USP) and corresponding co-author of the paper. However, he explains, before this work, this technology required the use of large, high-power light sources, which made its use in portable devices unfeasible.
Faced with this limitation, the team from USP São Carlos set out to develop a photocatalyst (a nanomaterial capable of increasing the system’s ability to absorb light and transform it into electric current) that would allow the use of smaller light sources. The researchers started with two materials that, in addition to having photocatalyst properties, are non-toxic, inexpensive and easy to prepare: titanium dioxide (TiO2) and graphitic carbon nitride (gC3N4). Then, they inserted nickel atoms into the graphitic carbon nitride structure, forming the Ni-gC3N4 compound, and combined this material with titanium dioxide nanoparticles, resulting in the formation of the Ni-gC3N4/TiO2 composite. Finally, they treated the surface of the composite with aryl diazonium salt. “The latter acted as a signal amplifier at the same time that it made it possible to immobilize the antibodies on the nanoparticles”, says Bott-Neto. The photocatalyst was used to coat the carbon electrodes of the photoelectrochemical system.
The result
Always looking for simplicity and miniaturization, the authors assembled a prototype of the device with the photocatalysts, the anti-PSA antibodies immobilized on them, an electrical system and, as a light source, a 3-watt LED, in addition to parts produced through 3D printing. In performance tests, the photoelectrochemical immunosensor was able to detect PSA at different concentrations in human serum samples, and presented the lowest detection limit ever reported in the literature for devices of this type, according to the authors of the article. “The high sensitivity and selectivity of the immunosensor can be attributed to the heterojunction between Ni-gC3N4 and TiO2”, explains Bott-Neto.
The work makes a fundamental contribution to taking photoelectrochemical detection technology, which is characterized by low cost and high levels of sensitivity and selectivity, to applications that require portability, such as point-of-care tests.
Paper reference: Photocatalysis of TiO2 Sensitized with Graphitic Carbon Nitride and Electrodeposited Aryl Diazonium on Screen-Printed Electrodes to Detect Prostate Specific Antigen under Visible Light. José L Bott-Neto, Thiago S Martins, Lorenzo A Buscaglia, Sergio A S Machado, and Osvaldo N Oliveira Jr. ACS Applied Materials & Interfaces 2022, 14, 19, 22114–22121. https://doi.org/10.1021/acsami.2c03106
Corresponding author contact: joseluiz.bott@gmail.com
(Português) Carta da SBPMat à presidente da CAPES sobre o acesso às revistas da RSC.
Sorry, this entry is only available in Brazilian Portuguese.
B-MRS Newsletter. Year 9, issue 7.
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B-MRS Newsletter. Year 9, issue 6.
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Featured article: New natural insulator for ultrathin devices.
A team of researchers from Brazilian institutions took the first steps towards the use of phlogopite, a mineral abundant in Brazil, as a natural source of ultrathin insulating layers that could be used in optoelectronic devices of the future. “Our work presents the insertion of this natural mineral in materials research and its possible use in different areas of nanotechnology”, says scientist Alisson R. Cadore, corresponding author of the article recently published in the journal 2D Materials.
The work is part of the search for two-dimensional materials (one or a few atoms thick) at low cost. In this search, the scientific community has investigated the so-called “lamellar materials”, which are formed by stacked ultrathin layers, joined together by the so-called “van der Waals forces”. Because they are relatively weak, these physical forces allow the lamellae separation to be performed using several methods. One of the best-known examples of this group is graphite, which is the source of graphene. Another example is that of micas, a family of minerals that includes phlogopite, which had never been studied in its two-dimensional form before the work of the Brazilian team.
In this work, the researchers used macroscopic phlogopite crystals mined in Itabira (state of Minas Gerais, Brazil) to generate two-dimensional layers by mechanical exfoliation. This extremely simple technique gained fame for having led to the first successful production of graphene, which earned Andre Geim and Konstantin Novoselov the Nobel Prize in Physics in 2010. In this method, a common adhesive tape is used to separate flakes from the material, by sticking them to the tape. The procedure is repeated until reaching the thinnest possible layer, the monolayer.
Using this method, the authors of the paper obtained monolayers and few-layers flakes of phlogopite. With them, they carried out a robust characterization that involved several experimental techniques in laboratories at Universidade Presbiteriana Mackenzie (UPM), at the National Laboratory of Synchrotron Light (LNLS) and at the Federal University of Minas Gerais (UFMG). Some results were confirmed with computer simulations carried out by the authors of the Federal University of Lavras (UFLA).
“In this work, we theoretically and experimentally identified the chemical and structural composition of phlogopite and demonstrated that this natural and abundant insulator can be exfoliated to the limit of a single layer, maintaining its physical characteristics”, summarizes Cadore, who is currently a researcher at the National Laboratory of Nanotechnology (LNNano), but carried out the work at UPM, where he was a Professor. One of the main findings of the study was the fact that the ultrathin phlogopite is stable when subjected to thermal processing, as well as when exposed to the environment (the samples were left for 13 months in ambient conditions without showing degradation).
In addition, the work compared the characteristics of phlogopite with those of the synthetic insulator most used as a substrate in nanodevices, hexagonal boron nitride. For this, the Brazilian team developed a collaboration with the National Institute of Materials Science (NIMS, Japan), where the material with the best physical properties is produced. The Japanese group supplied the synthetic crystals.
According to the authors, given that two-dimensional phlogopite is an excellent electrical and thermal insulator, in addition to being naturally abundant and easy to extract, it can be used as a low-cost material in devices that are still little explored at the nano scale, such as transistors, capacitors and photodetectors. These applications become even more promising given the possibility of using two-dimensional phlogopite in structures with unique properties called “van der Waals heterostructures”, which are formed by stacking ultrathin layers of different materials, joined by van der Waals forces. Therefore, the authors of the article assembled phlogopite and tungsten disulfide heterostructures and studied some of their properties. “We emphasize that two-dimensional phlogopite is a stable insulator under ambient conditions and can be easily combined with other 2D materials, creating ultrathin hybrid heterostructures, which expands the application of this nanomaterial in new future optoelectronic devices”, says Cadore.
Carried out as part of Raphaela de Oliveira’s doctorate, the work on the two-dimensional phlogopite is part of a research line begun in the Physics Department at UFMG. “Our studies have always involved different national and international researchers in obtaining and characterizing different natural 2D materials and their application in nanodevices and nanophotonics”, says Cadore, whose PhD in Physics at UFMG was on two-dimensional graphene heterostructures. The objective of these works is to find materials with the ideal characteristics for these applications, in order to replace the synthetic materials, which are expensive.
The work developed with phlogopite was inspired by studies carried out with soapstone, started at UFMG in 2015. Studies with this mineral continued at LNLS – CNPEM conducted by researcher Ingrid Barcelos, who also completed her PhD in Physics at UFMG with research on van der Waals heterostructures. In 2021, Ingrid won, for her work with soapstone, one of the For Women in Science awards, granted by L’Oréal Brasil in partnership with UNESCO and the Brazilian Academy of Sciences (ABC).
The research on two-dimensional phlogopite was funded by CAPES, CNPq, Mackenzie Research and Innovation Fund, FAPESP, FAPEMIG and the L’OREAL-UNESCO-ABC Award for Women in Science.
Paper reference: Exploring the structural and optoelectronic properties of natural insulating phlogopite in van der Waals heterostructures. Alisson R Cadore, Raphaela de Oliveira, Raphael Longuinhos, Verônica de C Teixeira, Danilo A Nagaoka, Vinicius T Alvarenga, Jenaina Ribeiro-Soares, Kenji Watanabe, Takashi Taniguchi, Roberto M Paniago, Angelo Malachias, Klaus Krambrock, Ingrid D Barcelos and Christiano JS de Matos. 2022 2D Mater. 9 035007. https://doi.org/10.1088/2053-1583/ac6cf4.
Corresponding author contact: alissoncadore@
B-MRS Newsletter. Year 9, issue 5.
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Featured article: Biosensor of conducting polymer and nanoparticles in the fight against the pandemic.
A team of researchers from the Brazilian Federal University of Paraná (UFPR) has developed a low-cost biosensor capable of detecting Covid-19 antibodies in about 30 minutes and with high sensitivity. The system has shown promise for producing handheld, disposable devices that could be used to diagnose coronavirus infection or to confirm antibody production after vaccination using just a few drops of blood.
Biosensors are systems that have a biological element (in this case, the N protein of the SARS-CoV-2 virus) responsible for chemically interacting with what you want to detect (in this case, the specific antibody for that antigen). When the interaction takes place, the chemical reaction is transformed in the device into an interpretable signal.
The biosensor developed at UFPR is based on a stainless steel mesh coated with a hybrid material which is formed by a polymer that conducts electricity (polypyrrole) and gold nanoparticles. In these nanoparticles, virus proteins are immobilized, so that antibodies from blood samples, if any, come into contact with their antigens, spontaneously react with them and become detectable.
Facing the pandemic
The idea of the research emerged at the beginning of the Covid-19 pandemic, when society needed to have systems for the detection of the virus and the antibodies generated by the infection. At that moment, Professors Dênio Souto and Marcio Vidotti, from UFPR, decided to gather their expertises in sensors and related topics and be part of the global efforts.
“We already knew from the beginning that the urgency and multidisciplinary nature of the subject would increase our challenge”, says Bruna M. Hryniewicz, first author of the article that reports this research in the journal Materials Today Chemistry. Bruna took part in the research during her PhD, still in progress, under the guidance of Professor Vidotti, both from the Research Group on Macromolecules and Interfaces at UFPR.
A detection system was built based on the doctoral thesis of Ana Leticia Soares, which has just been defended by UFPR. With the guidance of professors Marcio Vidotti and Luis Fernando Marches, the work resulted in a platform formed by a conductive polymer modified with gold nanoparticles that showed promising responses when joined to several pairs of antigens and antibodies.
More sensitivity and selectivity
Starting from this platform, the team investigated some issues that could improve the sensitivity and selectivity of the biosensor – parameters that allow reducing the amount of false positives and negatives in the detection results, even in small amounts of sample.
In this sense, the authors synthesized and characterized two polypyrrole morphologies to produce the hybrid material, the globular and the nanotubular, and found that the polymeric nanotube biosensor had a sensitivity eight times higher to detect antibodies than the globular polypyrrole system.
Another important point was the choice of the method of immobilization of the N protein in the nanoparticles. The researchers chose to promote a covalent bond (chemical bond based on the sharing of electron pairs between the atoms involved), which brings more stability and sensitivity to the system. In fact, this methodology positions the antigen in an orientation in which the sites of interaction with the antibody are available – an interaction that is further encouraged by the favorable chemical environment provided by polypyrrole. “All these characteristics allow the biosensor to present satisfactory sensitivity and selectivity responses”, says Jaqueline Volpe, also the first author of the article, who participated in the research during her master’s degree, under the guidance of Professor Dênio Souto, both from the Spectrometry, Sensors and Biosensors.
In addition to the participation of professors, post-docs and students from the Graduate Program in Chemistry at UFPR, the collaboration of researchers and physicians from UFPR and Hospital Erasto Gaertner, in Curitiba, was fundamental in the research. These collaborators quickly provided the SARS-CoV-2 N protein. They also obtained blood samples from people with and without Covid-19 who had had PCR tests (the diagnostic methodology considered the most accurate), which were used to test the performance of the biosensor.
“Taking into account that the work was carried out during the height of the pandemic, the challenges were numerous, from access to laboratories, to the exploration of a highly relevant topic, which generates greater pressure in the development of research”, comments Larissa Bach Toledo, co-author of the article.
According to the authors, the biosensor developed is promising for use on a large scale in the diagnosis of infected people and in the monitoring of antibodies due to the simple and scalable method of manufacturing the electrodes (batch synthesis), added to the low cost of the stainless steel matrix, and the high sensitivity of the system. However, to produce it commercially, it would be necessary to do many more validation tests with real samples, as well as transforming the system into a simple, miniaturized and easy to use device, in which the detection results could be interpreted by anyone.
This research was funded by the German foundation Alexander von Humboldt, UFPR through Proind 2020 and the Brazilian agencies CAPES and CNPq. The work also received support from INCTBio, of which Professor Marcio Vidotti is a member.
Reference of the paper: Development of polypyrrole (nano)structures decorated with gold nanoparticles toward immunosensing for COVID-19 serological diagnosis. B. M. Hryniewicz, J. Volpe, L. Bach-Toledo, K. C. Kurpel, A. E. Deller, A. L. Soares, J. M. Nardin, L. F. Marchesi, F. F. Simas, C. C. Oliveira, L. Huergo, D. E. P. Souto, M. Vidotti. Materials Today Chemistry. Volume 24, June 2022, 100817. https://doi.org/10.1016/j.mtchem.2022.100817.
Contact of the corresponding authors: denio.souto@ufpr.br and mvidotti@ufpr.br.
B-MRS Newsletter. Year 9, issue 4.
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Featured article: Catalysts for the sustainable production of hydrogen peroxide.
Hydrogen peroxide (H2O2) is a compound widely used, especially as a bleach or antiseptic in the production of pulp and paper, in cleaning, pharmacy and beauty products and in the treatment of wastewater, among other applications. With a large and growing market, the production of hydrogen peroxide has the challenge of becoming more sustainable, using methods that are environmentally friendly and allow the compound to be obtained in the same place where it will be used, reducing risks, costs and the environmental impact of transport. In this scenario, producing hydrogen peroxide in electrochemical generators using basically water, air and electricity is a promising path, which some companies are already treading. However, the success of this process largely depends on having efficient, stable and low-cost catalysts.
In a recently published scientific article, a team made up of researchers from the Brazilian Federal University of Mato Grosso do Sul (UFMS), Federal University of Grande Dourados (UFGD), and the São Carlos Institute of Chemistry (IQSC-USP) made a contribution in this regard. They developed catalysts based on graphene nanoribbons and metallic nanoparticles and studied in detail their performance in the electrochemical production of hydrogen peroxide. In addition to showing that these catalysts significantly improve reaction efficiency, equating to the best conventional catalysts in some aspects, the study advanced the understanding of fundamental phenomena that open possibilities to continue optimizing the electrocatalytic production of hydrogen peroxide.
“We proposed the synthesis of catalysts with a low content of noble metal (≤6.4% by mass), with high catalytic efficiency and high durability for the electrochemical production of H2O2”, says Professor Gilberto Maia (UFMS), co-author of the article. Indeed, noble metals such as gold and palladium are known for their catalytic properties but have the disadvantage of cost. “Our catalysts were built from oxides of molybdenum, gold and palladium, which together form nanoparticles anchored on the surface of graphene nanoribbons”, describes Maia.
The team tested the efficiency of the catalysts in terms of generating hydrogen peroxide through the two-electron oxygen reduction reaction (ORR-2e– ), in which one molecule of oxygen, two hydrogen cations and two electrons form one molecule of hydrogen peroxide. Mainly, the researchers tested, with very positive results, the activity of the catalyst (its ability to increase the rate of reaction), its selectivity (its ability to direct the reaction towards a certain product, in this case, hydrogen peroxide) and its stability (the ability to maintain its properties over time).
“The results we obtained showed that the improved catalytic activity for ORR-2e– was promoted by a combination of factors including geometry, palladium content, interparticle distance and active site blocking effects, while the electrochemical stability of the catalysts may have been enhanced by the presence of molybdenum”, says Professor Maia.
The work was developed within a collaboration between researchers from the Institute of Chemistry at UFMS and the Environmental Electrochemistry Research Group at IQSC-USP, who have been working together on the synthesis, characterization and application of electrocatalytic materials. According to the authors, the main idea and the first combinations of synthesis emerged as an offshoot of the doctoral thesis by Guilherme Fortunato, which was supervised by Professor Gilberto Maia and was defended in UFMS in 2019. The work continued and finalized within the postdoctoral research of Fortunato, carried out at IQSC under the supervision of Professor Marcos Lanza.
The research was funded by Brazilian federal and state agencies Capes, CNPq, FAPESP and FUNDECT-MS.
Paper reference: Using Palladium and Gold Palladium Nanoparticles Decorated with Molybdenum Oxide for Versatile Hydrogen Peroxide Electroproduction on Graphene Nanoribbons. Guilherme V. Fortunato, Leticia S. Bezerra, Eduardo S. F. Cardoso, Matheus S. Kronka, Alexsandro J. Santos, Anderson S. Greco, Jorge L. R. Júnior, Marcos R. V. Lanza, and Gilberto Maia. ACS Applied Materials & Interfaces 2022 14 (5), 6777-6793. DOI: 10.1021/acsami.1c22362.
Corresponding authors contact: g.fortunato@usp.br and gilberto.maia@ufms.br.