Imaging of Biological Cells Using Luminescent Silver Nanoparticles.

The application of luminescent silver nanoparticles as imaging agents for neural stem and rat basophilic leukemia cells was demonstrated. The experimental size dependence of the extinction and emission spectra for silver nanoparticles were also studied. The nanoparticles were functionalized with fluorescent glycine dimers. Spectral position of the resonance extinction and photoluminescence emission for particles with average diameters ranging from 9 to 32 nm were examined. As the particle size increased, the spectral peaks for both extinction and the intrinsic emission of silver nanoparticles shifted to the red end of the spectrum. The intrinsic photoluminescence of the particles was orders of magnitude weaker and was spectrally separated from the photoluminescence of the glycine dimer ligands. The spectral position of the ligand emission was independent of the particle size; however, the quantum yield of the nanoparticle-ligand system was size-dependent. This was attributed to the enhancement of the ligand's emission caused by the local electric field strength's dependence on the particle size. The maximum quantum yield determined for the nanoparticle-ligand complex was (5.2 ± 0.1) %. The nanoparticles were able to penetrate cell membranes of rat basophilic leukemia and neural stem cells fixed with paraformaldehyde. Additionally, toxicity studies were performed. It was found that towards rat basophilic leukemia cells, luminescent silver nanoparticles had a toxic effect in the silver atom concentration range of 10-100 µM.

Surface plasmon as a probe for melting of silver nanoparticles.

The temperature dependence of the surface plasmon energy and bandwidth for silver nanoparticles in the size range 8-30 nm embedded in a silica matrix has been studied using diffuse reflection spectroscopy. The dependence shows a non-monotonic jump-like behaviour indicating a low-temperature size-dependent melting of silver nanoparticles. The melting point decreases with the decrease of the nanoparticle size. The hysteresis in the temperature dependence of the surface plasmon bandwidth has been observed, indicating the first-order phase transition.