Synthesis and Characterization of Silver Nanoparticle-Multiwalled Carbon Nanotube Composites

Multiwalled carbon nanotubes (MWCNTs) grown by spray pyrolysis have been decorated with silver nanoparticles prepared via the silver mirror reaction. Good dispersion of silver nanostructures was obtained on the surface of MWCNTs, resulting in an efficient and simple wet chemistry method for increasing the reactivity of the carbon nanotubes surfaces. High-resolution transmission electron microscopy showed the orientations of the crystallography planes of the anchored silver nanoparticles and revealed their size distribution. Raman spectroscopy results confirm that the composite material preserves the integrity of the MWCNTs. Scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were also employed for sample characterization

Luminescence imaging and toxicity assessment of graphene quantum dots using in vitro models

Graphene quantum dots (GQDs) have been of high interest due to their size and optical characteristics, which improves when functional groups are added to their borders and defects. In this work, the in vitro toxicity of aqueous dispersion of GQDs (w/wo amino-functionalization) was investigated in two different cellular models (S. cerevisiae and H9c2 cell line). Results in yeast suggest that when at up to 25 % volume concentration, the effect of all tested GQDs was only inhibitory, and, in both cellular models, the toxic effect is rigorously dose-dependent. The comparison of IC50 values of all the tested GQDs reveals no significant variations among them, pointing to non-carbonized citric acid as the more toxic precursor. The obtained data suggest that functionalization makes GQDs less toxic, being the one functionalized with thioacetamide slightly more toxic, followed by the ones functionalized with thiourea and glutathione, respectively. Results confirm that their toxicity is characteristics as a whole, and not as the sum of the toxicity of the precursors. In both models, concentrations up to 2 % showed no significant toxicity. Finally, fluorescence microscopy images suggest that GQDs interact with the cellular membrane and enter in the cell, manifesting fluorescent properties

Comparison of Gold Nanoparticles Prepared Using Monobasic Sodium Citrate or Sodium Borohydride for Neomycin Determination in Saliva after Solid-Phase Extraction (SPE) on a Molecularly Imprinted Polymer (MIP)

Two distinct spherical gold nanoparticles (AuNPs) were compared for the spectrophotometric determination of neomycin in saliva. The AuNPs were produced using AuCl3 and monobasic sodium citrate (in water bath at 100 °C) under magnetic stirring (AuNPs-citrate) and using HAuCl4 and NaBH4, at room-temperature under mechanical agitation in a commercial reactor (AuNPs-H). Both AuNPs were spherical with diameters of 7.7 nm (AuNPs-H) and 26.1 nm (AuNPs-citrate) and the maximum wavelength of the localized surface plasmon resonance (LSPR) bands were at 511 nm (AuNPs-H) and 529 nm (AuNPs-citrate). Equivalent spectral extinctions were found despite the fact the large difference in concentrations of AuNPs in dispersions: 4.2 × 10−9 mol L−1 for the AuNPs-H and 8.7 × 10−11 mol L−1 for the AuNPs-citrate. Both AuNPs interacted with aminoglycosides (AMG), affecting intensity of the LSPR band as the concentration of AMG increased. The response of the AuNPs-H was more sensitive toward AMG covering the following ranges: 0.6–600 µg L−1 (gentamicin), 7.3–550 µg L−1 (neomycin) and 14–520 µg L−1 (kanamycin). AuNPs-H optical response was more robust in function of the pH with AuNPs-citrate response only observed in acid solution, favoring electrostatic interaction with AMG. Catalytic activity of AuNPs-H, in reducing the 4-phenolate ion, presented a higher rate constant (4.3 × 10−3 s−1) and was used as analytical probe to determine neomycin in saliva after solid phase extraction with a commercially available AMG imprinted polymer enabling quantification to 0.36 μg of the analyte.</p