Anielle Christine Almeida Silva

Effect of Fe2O3 concentration on the structure of the SiO2-Na2O-Al2O3-B2O3 glass system.

The structural properties of the glass matrix 40SiO(2)·30Na(2)O·1Al(2)O(3)·(29-x)B(2)O(3)·xFe(2)O(3) (mol%), 0.0≤x≤29.0 were studied by X-ray diffraction (XRD), differential thermal analysis (DTA) and Raman and infrared spectroscopy (FT-IR). XRD demonstrated Fe(3)O(4) crystal formation for Fe(2)O(3) concentrations of 29.0 mol%. DTA showed that glass transition and crystallization temperatures changed as a function of Fe(2)O(3) concentration and that these alterations were related to structural change in the glass system. Interesting aspects of Raman and FT-IR spectra were found, and this gives information about of the structure changes in Si-O-Si units of these glasses as a function of Fe(2)O(3) concentration.

Shell Thickness Modulation in Ultrasmall CdSe/CdSxSe1–x/CdS Core/Shell Quantum Dots via 1-Thioglycerol

In this study, we report on the synthesis of CdSe/CdS core-shell ultrasmall quantum dots (CS-USQDs) using an aqueous-based wet chemistry protocol. The proposed chemical route uses increasing concentration of 1-thioglycerol to grow the CdS shell on top of the as-precipitated CdSe core in a controllable way. We found that lower concentration of 1-thioglycerol (3 mmol) added into the reaction medium limits the growth of the CdSe core, and higher and increasing concentration (5-11 mmol) of 1-thioglycerol promotes the growth of CdS shell on top of the CdSe core in a very controllable way, with an increase from 0.50 to 1.25 nm in shell thickness. The growth of CS-USQDs of CdSe/CdS was confirmed by using different experimental techniques, such as optical absorption (OA) spectroscopy, fluorescence spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and Raman spectroscopy. Data collected from OA were used to obtain the average values of the CdSe core diameter, whereas Raman data were used to assess the average values of the CdSe core diameter and CdS shell thicknesses.

Controlling the cytotoxicity of CdSe magic-sized quantum dots as a function of surface defect density.

Quantum dots are potentially very useful as fluorescent probes in biological systems. However, they are inherently cytotoxic because of their constituents. We controlled the cytotoxicity of CdSe magic-sized quantum dots (MSQDs) as a function of surface defect density by altering selenium (Se) concentration during synthesis. Higher Se concentrations reduced the cytotoxicity of the CdSe MSQDs and diminished mRNA expression of methallothionein because of the low cadmium ions (Cd(2+)) concentration adsorbed on the surface of the MSQDs. These results agree with luminescence spectra, which show that higher Se concentrations decrease the density of surface defects. Therefore, our results describe for the first time a simple way of controlling the cytotoxicity of CdSe MSQDs and making them safer to use as fluorescence probes in biological systems.

Assessment of the genotoxic potential of two zinc oxide sources (amorphous and nanoparticles) using the in vitro micronucleus test and the in vivo wing somatic mutation and recombination test

In this study, we evaluated the toxic and genotoxic potential of zinc oxide nanoparticles (ZnO NPs) of 20 nm and the mutagenic potential of these ZnO NPs as well as that of an amorphous ZnO. Toxicity was assessed by XTT colorimetric assay. ZnO NPs were toxic at concentrations equal to or higher than 240.0 μM. Genotoxicity was assessed by in vitro Cytokinesis Block Micronucleus Assay (CBMN) in V79 cells. ZnO NPs were genotoxic at 120.0 μM. The mutagenic potential of amorphous ZnO and the ZnO NPs was assayed using the wing Somatic Mutation and Recombination Test (SMART) of Drosophila melanogaster. In the Standard cross, the amorphous ZnO and ZnO NPs were not mutagenic. Nevertheless, Marker trans-heterozygous individuals from the High bioactivation cross treated with amorphous ZnO (6.25 mM) and ZnO NPs (12.50 mM) displayed a significant increased number of mutant spots when compared with the negative control. In conclusion, the results were not dose related and indicate that only higher concentrations of ZnO NPs were toxic and able to induce genotoxicity in V79 cells. The increase in mutant spots observed in D. melanogaster was generated due to mitotic recombination, rather than mutational events.

Photothermal Spectroscopic Characterization in CdSe/ZnS and CdSe/CdS Quantum Dots: A Review and New Applications

Nanostructured semiconductors or Quantum Dots (QDs) are materials in continuous development that hold potential for a variety of new applications, including uses in fluorescent labels for biomedical science, photonic devices and sensor materials (Bruchez et al., 1998; Prasad, 2004; Sounderya & Zhang, 2008). In biomedical applications, several nanodiagnostic assays have been developed that use QDs. They have been applied to diagnostics, the treatment of diseases, bioimaging, drug delivery, engineered tissues and biomarkers (Sounderya & Zhang, 2008). For example, CdSe/ZnS dendron nanocrystals have been used as biosensor systems for detection of pathogens such as Escherichia Coli and Hepatitis B (Liu, 2007). CdSe/ZnS core-shell nanocrystals have been shown to be useful for tailoring the fluorescence of dental resin composites (Alves et al., 2010). Core-shell quantum dots (CS) have been used as heteronanocrystals, structures that allow optical amplification because of their stimulated emission of single-exciton states (Klimov et al., 2007), and highquality CdSe/ZnS doped titania and zirconia optical waveguides have been prepared (Jasieniak et al., 2007).

Cd1−xMnxTe ultrasmall quantum dots growth in a silicate glass matrix by the fusion method

In this study, we synthesized Cd1−xMnxTe ultrasmall quantum dots (USQDs) in SiO2-Na2CO3-Al2O3-B2O3 glass system using the fusion method. Growth of these Cd1−xMnxTe USQDs was confirmed by optical absorption, atomic force microscopy (AFM), magnetic force microscopy (MFM), scanning transmission electron microscopy (TEM), and electron paramagnetic resonance (EPR) measurements. The blueshift of absorption transition with increasing manganese concentration gives evidence of incorporation of manganese ions (Mn2+) in CdTe USQDs. AFM, TEM, and MFM confirmed, respectively, the formation of high quality Cd1−xMnxTe USQDs with uniformly distributed size and magnetic phases. Furthermore, EPR spectra showed six lines associated to the S = 5/2 spin half-filled d-state, characteristic of Mn2+, and confirmed that Mn2+ are located in the sites core and surface of the CdTe USQD. Therefore, synthesis of high quality Cd1−xMnxTe USQDs may allow the control of optical and magnetic properties.

Biological analysis and imaging applications of CdSe/CdSxSe1-x/CdS core-shell magic-sized quantum dot.

Although colloidal magic-sized quantum dots present great promise for biological applications due to their high stability and strong luminescence, nanotoxicological analyses are scarcely reported and biomedical applications have not been demonstrated. This is the first report on biological effects of CdSe/CdSxSe1-x/CdS core-shell magic-sized quantum dot (CS-MSQD) with specific application in breast cancer cell detection. The 2-nm CS-MSQD presents a broad bandwidth emission from 450 to 750nm, low toxicity, non-immunogenicity and biocompatibility. The CS-MSQD was conjugated to a breast cancer-specific Fab antibody, and passively diffused into cells for in vitro detection of a breast cancer cell line, demonstrating to be an unprecedented tool for biomedical applications.

Nanofilm of ZnO nanocrystals/carbon nanotubes as biocompatible layer for enzymatic biosensors in capacitive field-effect devices

The incorporation of nanomaterials that are biocompatible with different types of biological compounds has allowed the development of a new generation of biosensors applied especially in the biomedical field. In particular, the integration of film-based nanomaterials employed in field-effect devices can be interesting to develop biosensors with enhanced properties. In this paper, we studied the fabrication of sensitive nanofilms combining ZnO nanocrystals and carbon nanotubes (CNTs), prepared by means of the layer-by-layer (LbL) technique, in a capacitive electrolyte-insulator-semiconductor (EIS) structure for detecting glucose and urea. The ZnO nanocrystals were incorporated in a polymeric matrix of poly(allylamine) hydrochloride (PAH), and arranged with multi-walled CNTs in a LbL PAH-ZnO/CNTs film architecture onto EIS chips. The electrochemical characterizations were performed by capacitance–voltage and constant capacitance measurements, while the morphology of the films was characterized by atomic force microscopy. The enzymes glucose oxidase and urease were immobilized on film’s surface for detection of glucose and urea, respectively. In order to obtain glucose and urea biosensors with optimized amount of sensitive films, we investigated the ideal number of bilayers for each detection system. The glucose biosensor showed better sensitivity and output signal for an LbL PAH-ZnO/CNTs nanofilm with 10 bilayers. On the other hand, the urea biosensor presented enhanced properties even for the first bilayer, exhibiting high sensitivity and output signal. The presence of the LbL PAH-ZnO/CNTs films led to biosensors with better sensitivity and enhanced response signal, demonstrating that the adequate use of nanostructured films is feasible for proof-of-concept biosensors with improved properties that may be employed for biomedical applications.

CdSe magic-sized quantum dots incorporated in biomembrane models at the air-water interface composed of components of tumorigenic and non-tumorigenic cells

Cadmium selenide (CdSe) magic-sized quantum dots (MSQDs) are semiconductor nanocrystals with stable luminescence that are feasible for biomedical applications, especially for in vivo and in vitro imaging of tumor cells. In this work, we investigated the specific interaction of CdSe MSQDs with tumorigenic and non-tumorigenic cells using Langmuir monolayers and Langmuir-Blodgett (LB) films of lipids as membrane models for diagnosis of cancerous cells. Surface pressure-area isotherms and polarization modulation reflection-absorption spectroscopy (PM-IRRAS) showed an intrinsic interaction between the quantum dots, inserted in the aqueous subphase, and Langmuir monolayers constituted either of selected lipids or of tumorigenic and non-tumorigenic cell extracts. The films were transferred to solid supports to obtain microscopic images, providing information on their morphology. Similarity between films with different compositions representing cell membranes, with or without the quantum dots, was evaluated by atomic force microscopy (AFM) and confocal microscopy. This study demonstrates that the affinity of quantum dots for models representing cancer cells permits the use of these systems as devices for cancer diagnosis.

Study of the nonlinear optical properties of CdS quantum dots in phosphate glass

The aim of this work is the use of the Z-scan technique to determine the nonlinear refraction and nonlinear absorption of phosphate glass doped with CdS. This glass matrix, termed as PANK (P2O5-Al2O3-Na2O-K2O), was doped with 1, 2 and 3 % of CdS concentration. The quantum dots (QDs) are materials extensively investigated in the last years for their special physical properties associated to discrete energetic levels.