Publications
Dive into the wealth of knowledge and insights available in this section. Access our latest research findings, scientific papers, and scholarly articles that contribute to the advancement of graphene and carbon materials science. Stay informed about our ongoing research initiatives and explore the frontiers of nanotechnology
Potentiality graphene oxides-functionalized magnetic nanomaterials for RNA extraction from rabies and SARS-CoV-2 viruses.
Nucleic acid extraction technologies are fundamental tools in studying pathogenic agents. In this work, we report the use of magnetic materials functionalized with graphene oxide (GO) to enhance the isolation of viral RNA in biological suspensions. Graphene oxides with different synthesis parameters were used as additives and support to potentiate the extraction and purification of RNA. As additives, graphene oxides with varying degrees of oxidation were synthesized and added to a commercial nucleic acid extraction kit......
Investigation of Rabies virus in wild mammals of the atlantic forest in Rio de Janeiro, Brazil
M. Cocchi, C. M. Barboza, J. G. Garcia, R. M. Zamudio, A. Champi, R. L. M. Novaes, S. F. Costa-Neto, R. Moratelli & H. B. C. R. Batista
With the successful control of rabies transmitted by dogs in Brazil, wild animals have played a relevant epidemiological role in the transmission of rabies virus (RABV). Bats, non-human primates and wild canines are the main wild animals that transmit RABV in the country. It is worth highlighting the possibility of synanthropic action of these species, when they become adapted to urban areas, causing infections in domestic animals and eventually in humans. This work aimed to evaluate the circulation of RABV in the Pedra Branca Forest, an Atlantic Forest area, located in the state of Rio de Janeiro, Southeast Brazil. Saliva and blood samples were obtained from 60 individuals of eight species of bats, captured with mist nets, and 13 individuals of callitrichid primates, captured with tomahawk traps. Saliva samples were subjected to Reverse Transcription Polymerase Chain Reaction (RT-PCR), targeting the RABV N gene, with all samples being negative. Blood samples of all animals were submitted to the Rapid Fluorescent Focus Inhibition Test (RFFIT) to detect neutralizing antibodies (Ab) for RABV. Six bat samples (8%) were seropositive for RABV with antibody titers greater than or equal to 0.1 IU/mL. The detection of Ab but not viral RNA indicates exposure rather than current RABV transmission in the analyzed populations. The results presented here reinforce the importance of serological studies in wildlife to access RABV circulation in a region.
Feature engineering and machine learning for electrochemical detection of rabies virus in graphene-based biosensors
Ronaldo Challhua, Ronaldo Prati, Ana Champi
Electrochemical biosensors are small analytical devices that convert a biological response into a processable signal with high sensitivity, ease of operation, cost-effectiveness, and miniaturization capability. The current study proposes enhancing the reliability of the electrochemical detection of enveloped viruses, such as the rabies virus using feature engineering and machine learning. Portable detection was achieved using a graphene-based microfluidic sensor and the current was recorded from electrochemical experiments using a portable potentiostat. After data mining and feature engineering, a dataset obtained from staircase cyclic voltammetry was used in different machine learning models. The features from the voltammogram were extracted following theoretic aspects to build a dataset with uncovering patterns and valuable information. Correlation-based and recursive feature elimination algorithms were used for feature engineering. Our analysis showed that the best F-measure score a model trained was obtained through a support vector machine with 0.9830 for the diagnostic tasks following the proposed feature engineering pipeline.
Lyophilized and sonicated graphene oxide and its nanoecotoxicity applications
Josefina Schmuck, Wilfredo Rondan c, Ulises Reno, Jaime Vasquez, Luciana Regal, Ana Maria Gagneten, Ana Champi (2024)
The present work aimed to perform an exhaustive structural and chemical characterization of Lyophilized-Sonicated Graphene Oxide (L-SGO) and its nanoecotoxicological applications using Chlorella vulgaris and Lactuca sativa as biological models, exposed to 0.1, 1, 10 and 100 mg L−1 of L-SGO. In addition, both exposed and unexposed organisms to L-SGO were analyzed by optical and stereoscopic microscopy, scanning electronic microscopy (SEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and spectrofluorimetry. The 96 h-EC50 obtained for C. vulgaris was 37.52 mg L−1, and growth inhibition at the highest concentration tested (100 mg L−1) was 62.18 %. In L. sativa, germination (%) showed a significant difference between the control and the 100 mg L−1 treatment, while root elongation showed no differences between the treatments.
Influence of multilayers Bernal and Rhombohedral graphene obtained by green chemistry on the acceleration in the germination process of tomato seeds
Wilfredo Rondan, Roberta Albino dos Reis, José Javier Sáez Acuña, Amedea Barozzi Seabra, Ana Champi (2024)
The environmental ramifications stemming from the application of graphene-based materials have sparked significant interest in recent years. This study delved into assessing the influence of multilayer graphene, specifically focusing on the Bernal (2H) and Rhombohedral (3R) phases, on the germination process of tomato (Solanum lycopersicum) seeds. Multilayers Bernal-Rhombohedral Graphene (MBRG) were synthesized employing green chemistry principles, utilizing the ultrasonication technique operating at 40 kHz within a deionized water solution. Systematic characterization of the phases was conducted via X-ray diffraction, Raman Spectroscopy, TEM, and conductivity measurements. Subsequent administration of MBRG at concentrations ranging from 10 to 500 mgL−1 on tomato seeds revealed an expedited germination process, achieving completion within 3 days.
Portable reduced graphene oxide biosensor for detection of rabies virus in bats using nasopharyngeal swab samples
Challhua, R., Akashi, L., Zuñiga, J., Batista, H. B. D. C. R., Moratelli, R., & Champi, A. (2023)
We developed a portable biosensor for fast detection of rabies virus (RABV) in bat swab samples. The biosensor's reduced graphene oxide (rGO) electrode, coated with complementary DNA (cDNA), showed high sensitivity and specificity. Testing with RNA and bat samples demonstrated accurate detection within a wide concentration range (0.145–25.39 ng/μL) and a low detection limit (0.104 ng/μL). The biosensor's rapid response time outperformed conventional methods. This innovation holds promise for on-site RABV detection, with potential applications for other RNA viruses.
Low-cost synthesis of titanium dioxide nanotubes/reduced graphene oxide heterostructure for pH sensor applications
Albertin, K. F., Akashi, L., Challhua, R., Zúñiga, J., Rivera, M., Rondan, W., ... & Champi, A. (2023)
This study investigates depositing Graphene Oxide (GO) films onto Titanium Dioxide nanotubes (TiO2NTs) for pH sensing applications. TiO2NTs were obtained through electrochemical anodization, while GO was synthesized via a modified Hummer's method and deposited using dip coating at room temperature. Thermal treatment of the TiO2NTs/GO structure reduced the GO film. pH electrode characterization showed a linear response of the TiO2NTs/GO system at 57 mV/pH with no hysteresis effect.
Synthesis and Characterization of Core@shell β-NaYF4 to Yb3+/Ho3+@SiO2 with Different Ratios of Fluorine to Yttrium
Rondan, W., Rivera, M., Acosta, D., Puga, R., Loro, H., Eyzaguirre, C., & Champi, A. (2022)
Fluorescent β-NaYF4 to Yb3+/Ho3+@SiO2 nanoparticles were synthesized with varying fluorine-to-yttrium ratios using the solvothermal method followed by SiO2 coating. Characterization revealed higher luminescence intensity at a 20:1 ratio, but SiO2 coating reduced it. These findings advance research in biomedical applications for stable nanoparticles with silica coating.
Synthesis of lysozyme-reduced graphene oxide films for biosensor applications
Zuñiga, J., Akashi, L., Pinheiro, T., Rivera, M., Barreto, L., Albertin, K. F., & Champi, A. (2022)
We synthesized dispersed reduced graphene oxide (Ly-RGO) using Lysozyme as a dispersant, showing potential for biosensor applications. Characterization of the fabrication process was conducted using XPS, XRD, and Raman Spectroscopy. Ly-RGO electrodes demonstrated significant electrical signal transduction in voltammograms. Calibration with human saliva and SARS-CoV-2 RNA samples in cyclic voltammetry and chronoamperometry measurements indicates Ly-RGO's promise for biosensor devices.
Hints of granular superconductivity in natural graphite verified by trapped flux transport measurements
Champi, A., Precker, C. E., & Esquinazi, P. D. (2023)
This study explores electrical transport in natural graphite, suggesting superconductivity with Tc ≈ 350 K. Conducted within 300-450 K and B ≤ 400 mT, resistance measurements reveal trapped flux, stable for ~30 minutes before vanishing at ~330 K. This transition coincides with enhanced magnetoresistance at T < Tc. Raman measurements confirm rhombohedral stacking, indicating potential for high-temperature superconductivity.
Deconvolution of photoluminescence spectra and electronic transition in carbon dots nanoparticles from microcrystalline cellulose
Balanta, M., da Silva Filho, W., Souza, M., De Assunção, R., Champi, A., & Cuevas, R. (2023).
This study explores the photoluminescence properties of carbon dots (CDs) derived from microcrystalline cellulose (MCC), crucial for optoelectronic and biomedical applications. Analysis of PL, PLE, and absorption spectra reveals insights into fluorescence spectrum emission and bandwidth. Gaussian deconvolution identifies emission bandwidths for core and surface states, challenging previous assumptions and enhancing our understanding of CDs' electronic transitions for luminescent applications.
Interaction of Silver Nanoparticles with Bilayer Graphene:
A Raman Study
Akashi, L., Ferreira, H., Villanueva, J., Yactayo, M., Landauro, C. V., ... & Champi, A. (2022)
In this work, we investigate the interaction of silver with micromechanical exfoliated bilayer graphene (BLG) using Raman spectroscopy. We evaluate the behavior of the most characteristic Raman BLG bands as a function of the laser energy. The Ag presence on BLG leads to the appearance of the D band, and the behavior of the 2D and G bands shows that the presence of the silver leads to graphene doping.
Simultaneous carbonization and sulfonation of microcrystalline cellulose to obtain solid acid catalyst and carbon quantum dots
Souza, M., Batista, A., Cuevas, R., da Silva Filho, W., Balanta, M., Champi, A., & de Assunção, R. (2022).
This study demonstrates a one-step method for producing solid acid catalysts (SACs) from Microcrystalline Cellulose (MCC) and concentrated sulfuric acid. The resulting SACs exhibit high ionic exchange capacity (1.3 mmol g−1) and catalytic activity, achieving up to 80% conversion in oleic acid esterification with methanol. Additionally, the process generates carbon dots (CD) in the supernatant, indicating potential applications in various physicochemical processes.
Multiple-excitation study of the double-resonance Raman bands in rhombohedral graphite
Ramos, S. L., Pimenta, M. A., & Champi, A. (2021).
This study compares the double-resonance (DR) Raman process in rhombohedral graphite with Bernal graphite. Rhombohedral graphite exhibits a richer DR Raman spectrum, attributed to its larger Brillouin zone (BZ) volume. Results show broader and more complex bands, especially in the 2D and intervalley TO-LA bands, suggesting greater phonon dispersion diversity.
Simultaneous carbonization and sulfonation of microcrystalline cellulose to obtain solid acid catalyst and carbon quantum dots
M.C.G. Souza, A.C.F. Batista, R.F. Cuevas, W.J.F. da Silva Filho, M.A.G. Balanta, A. Champi, R.M.N. de Assunção (2022)
Lignocellulosic materials have been successfully used in the production of solid acid catalysts (SACs), generally prepared in two steps: Biomass thermal or hydrothermal carbonization followed by sulfonation. The process' supernatant is usually discarded; however, this liquid fraction may contain potentially important substances. In this work, the production of SACs was carried out by simultaneous carbonization/sulfonation of Microcrystalline Cellulose (MCC) by direct reaction with concentrated sulfuric acid. The obtained catalyst have excellent characteristics, with an ionic exchange capacity of 1.3 mmol g−1. The SAC's catalytic activity was evaluated in oleic acid esterification with methanol in a molar ratio of 1:20, yielding up to 80 % conversion in 6 h of reaction at 65 °C. The supernatant showed the presence of carbon dots (CD) characterized by solution UV/Vis spectra pattern and Fluorimetry assays. Thus, the presented process allows obtaining SACs and CDs that can act as catalysts in a series of physicochemical processes.