Intracellular accumulation and dissolution of silver nanoparticles in L-929 fibroblast cells using live cell time-lapse microscopy.

Cytotoxicity assessments of nanomaterials, such as silver nanoparticles, are challenging due to interferences with test reagents and indicators as well uncertainties in dosing as a result of the complex nature of nanoparticle intracellular accumulation. Furthermore, current theories suggest that silver nanoparticle cytotoxicity is a result of silver nanoparticle dissolution and subsequent ion release. This study introduces a novel technique, nanoparticle associated cytotoxicity microscopy analysis (NACMA), which combines fluorescence microscopy detection using ethidium homodimer-1, a cell permeability marker that binds to DNA after a cell membrane is compromised (a classical dead-cell indicator dye), with live cell time-lapse microscopy and image analysis to simultaneously investigate silver nanoparticle accumulation and cytotoxicity in L-929 fibroblast cells. Results of this method are consistent with traditional methods of assessing cytotoxicity and nanoparticle accumulation. Studies conducted on 10, 50, 100 and 200 nm silver nanoparticles reveal size dependent cytotoxicity with particularly high cytotoxicity from 10 nm particles. In addition, NACMA results, when combined with transmission electron microscopy imaging, reveal direct evidence of intracellular silver ion dissolution and possible nanoparticle reformation within cells for all silver nanoparticle sizes.

Electrochemical release of fluorescently labeled thiols from patterned gold surfaces.

Reductive desorption of alkanethiols is a tool for spatially and temporally controlled release of small molecules or particles from individually addressable gold electrodes. Here we report on the dynamics of release using fluorophore-terminated C6 or C11 thiols. We show that the release kinetics for C6 thiols are determined solely by diffusive transport, whereas for C11 thiols the release kinetics are attenuated by the low solubility that limits the rate at which the desorbed thiols can diffuse away from the surface. The release of multiple different molecules from the same electrode is demonstrated using red- and green-emitting fluorophores. The fraction of the monolayer released is dependent on the electrode potential.