Recent Publications Nano

Hard, transparent, sp3-containing 2D phase formed from few-layer graphene under compression

L. G. P. Martins, et al., “Hard, transparent, sp3-containing 2D phase formed from few-layer graphene under compression,” Carbon, 2020. Publisher's VersionAbstract
Despite several theoretically proposed two-dimensional (2D) diamond structures, experimental efforts to obtain such structures are in initial stage. Recent high-pressure experiments provided significant advancements in the field, however, expected properties of a 2D-like diamond such as sp3 content, transparency and hardness, have not been observed together in a compressed graphene system. Here, we compress few-layer graphene samples on SiO2/Si substrate in water and provide experimental evidence for the formation of a quenchable hard, transparent, sp3-containing 2D phase. Our Raman spectroscopy data indicates phase transition and a surprisingly similar critical pressure for two-, five-layer graphene and graphite in the 4-6 GPa range, as evidenced by changes in several Raman features, combined with a lack of evidence of significant pressure gradients or local non-hydrostatic stress components of the pressure medium up to ≈ 8 GPa. The new phase is transparent and hard, as evidenced from indentation marks on the SiO2 substrate, a material considerably harder than graphene systems. Furthermore, we report the lowest critical pressure (≈ 4 GPa) in graphite, which we attribute to the role of water in facilitating the phase transition. Theoretical calculations and experimental data indicate a novel, surface-to-bulk phase transition mechanism that gives hint of diamondene formation.
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Second harmonic generation microscopy as a cancer diagnosis tool

A. M. Garcia, et al., “Second harmonic generation microscopy as a cancer diagnosis tool,” in 2017 European Conference on Lasers and Electro-Optics and European Quantum Electronics Conference, 2017, pp. JSIII_1_3. Publisher's VersionAbstract
Optical microscopy is one of the most important tool for understanding biology processes. Recently with the advance of femtosecond laser all the nonlinear optical processes have been included into optical microscopy methods and Second Harmonic Generation (SHG) microscopy has emerged as a powerful new optical imaging tool with applications in disease diagnostics \[1-2\]. The ``gold standard'' in cancer diagnostics is still the traditional histology analysis where accuracy depends on the experience and interpretation skill of the pathologist. A major development would be to use the SHG microscopy as a quantitative tool to cancer diagnosis. Here we show SHG imaging results of the collagen fibers in prostate cancer tissue that can be directly correlated with the cancer malignancy diagnostic \[3\]. We performed SHG imaging in a back-scattering geometry on the histological slides from the same biopsies that were analyzed by the pathologist. We studied prostate from patients treated at the the Urology Center of UFMG Hospital, Belo Horizonte. A 1 mm diameter punch biopsy was extracted from multiple peripheral zone of the prostate showing normal tissue and cancer tissue with Gleason scores ranging from 3 to 5. The study was approved by the UFMG Institutional Review Board and the Brazilian National Health Committee on the use of humans as experimental subjects. Written informed consent was obtained from all participants before their biopsy procedures. Figure 1 shows SHG images for normal and cancer tissue. The SHG images show major differences on the collagen fiber alignment that changes with cancer progression. The average direction of the fibers in the image was calculated and we obtained a value for the fiber anisotropy \[4\]. The statistical analysis is presented in the boxplot in figure 1. Note that both the average values (crosses) and the median lines (black center lines) are well separated for the normal and cancer tissue.
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Labeling PLA-PEG nanocarriers with IR780: physical entrapment versus covalent attachment to polylactide

M. G. C. Machado, et al., “Labeling PLA-PEG nanocarriers with IR780: physical entrapment versus covalent attachment to polylactide,” Drug Delivery and Translational Research, 2020. Publisher's VersionAbstract
Near-infrared fluorescent dyes, such as IR780, are promising theranostics, acting as photosensitizers for photodynamic therapy and in vivo tracers in image-guided diagnosis. This work compared the uptake by macrophage-like cells of IR780 either physically associated or covalently attached to poly(D,L-lactide) (PLA) formulated as polymeric nanocapsules (NC) from a blend of PLA homopolymer and PLA-PEG block copolymer. The physicochemical characterization of both NC was conducted using asymmetric flow field-flow fractionation (AF4) analysis with static and dynamic light scattering and atomic force microscopy. The interaction of IR780 with serum proteins was evidenced by AF4 with fluorescence detection and flow cytometry in cell uptake studies. The average diameters of NC were around 120 nm and zeta potentials close to -40 mV for all NC. NC uptake by cells in different media and experimental conditions shows significantly lower fluorescence intensities for IR780 covalently linked to PLA and correspondingly low quantitative uptake. Different mechanisms of internalization were evidenced depending on the IR780 type of association to NC. Serum proteins mediate IR780 interaction with cells in a dose-dependent manner. Our results show that non-covalently linked IR780 was released from NC and accumulated in macrophage cells. Oppositely, IR780 conjugated to PLA provides stable association with NC, and its fluorescence is representative of cell uptake of the nanocarrier itself. This work strongly reinforces the importance of covalent attachment of a fluorescence dye such as IR780 to the nanocarrier to study their interaction with cells in vitro and to obtain reliable tracking in image-guided therapy.
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Soapstone reinforced hydroxyapatite coatings for biomedical applications

L. M. Mota, et al., “Soapstone reinforced hydroxyapatite coatings for biomedical applications,” Surface and Coatings Technology, vol. 397, pp. 126005, 2020. Publisher's VersionAbstract
Mechanical resistant bioactive materials are of high interest for biomedical applications. In this work, we address the improvement in mechanical properties of HA coatings by the addition of a cheap and widely available secondary phase material, the talc from soapstone. The composites hydroxyapatite/talc (HA/talc) were successfully obtained by pulsed electrodeposition and characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy, corrosion and wear resistance and biocompatibility tests. We found that the addition of talc greatly improves the mechanical properties of coatings (i. e., wear track and friction coefficient in wear tests were significantly diminished) without diminishing corrosion resistance and biocompatibility. Alamar Blue® tests, alkaline phosphatase activity, and collagen production indicate that the biocomposites are biocompatible and talc itself induce bone maturation.
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