Synthesis and characterization of magnetic nanoparticles coated with polystyrene sulfonic acid for biomedical applications

The development of novel magnetic nanoparticles (MNPs) with satisfactory biocompatibility for biomedical applications has been the subject of extensive exploration over the past two decades. In this work, we synthesized superparamagnetic iron oxide MNPs coated with polystyrene sulfonic acid (PSS-MNPs) and with a conventional co-precipitation method. The core size and hydrodynamic diameter of the PSS-MNPs were determined as 8-18 nm and 50-200 nm with a transmission electron microscopy and dynamic light scattering, respectively. The saturation magnetization of the particles was measured as 60 emu g-1 with a superconducting quantum-interference-device magnetometer. The PSS content in the PSS-MNPs was 17% of the entire PSS-MNPs according to thermogravimetric analysis. Fourier-transform infrared spectra were recorded to detect the presence of SO3 - groups, which confirmed a successful PSS coating. The structural properties of the PSS-MNPs, including the crystalline lattice, composition and phases, were characterized with an X-ray powder diffractometer and 3D nanometer-scale Raman microspectrometer. MTT assay and Prussian-blue staining showed that, although PSS-MNPs caused no cytotoxicity in both NIH-3T3 mouse fibroblasts and SK-HEP1 human liver-cancer cells up to 1000 μg mL-1, SK-HEP1 cells exhibited significantly greater uptake of PSS-MNPs than NIH-3T3 cells. The low cytotoxicity and high biocompatibility of PSS-MNPs in human cancer cells demonstrated in the present work might have prospective applications for drug delivery.

Distinguishing Self-Assembled Pyrene Structures from Exfoliated Graphene

Sonication-assisted graphene production from graphite is a popular lab-scale approach in which ultrasound energy breaks down graphite sheets into graphene flakes in aqueous medium. Dispersants (surfactant molecules) are incorporated into the solution to prevent individual graphene flakes from reaggregating. However, in solution these dispersants self-assemble into various structures, which can interfere with the characterization of the graphene produced. In this study, we characterized graphene dispersions stabilized by a family of pyrene-based surfactants that facilitate a high exfoliation yield. These surfactants self-assembled to form flakes and ribbons-shapes very similar to those of graphene structures. The dispersant structures were present both in the graphene dispersion and in the precipitate after the solvent had been evaporated and could therefore have been mistakenly identified as graphene by electron microscopy techniques and other characterization techniques, such as Raman and X-ray photoelectron spectroscopy. Contrary to previous reports, we showed-by removing the dispersants by filtration and washing-that the surfactants did not affect the shape of the graphene prepared by sonication.