Properties of in situ generated gold nanoparticles in the cellular context.

Gold nanostructures that serve as probes for nanospectroscopic analysis of eukaryotic cell cultures can be obtained by the in situ reduction of tetrachloroauric acid (HAuCl4). To understand the formation process of such intracellularly grown particles depending on the incubation medium, the reaction was carried out with 3T3 fibroblast cells in three different incubation media, phosphate buffer, Dulbecco's Modified Eagle Medium (DMEM), and standard cell culture medium (DMEM with fetal calf serum). The size, the optical properties, the biomolecular corona, and the localization of the gold nanoparticles formed in situ vary for the different conditions. The combination of surface-enhanced Raman scattering (SERS) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) microscopic mapping and transmission electron microscopy (TEM) provides complementary perspectives on plasmonic nanoparticles and non-plasmonic gold compounds inside the cells. While for the incubation with HAuCl4 in PBS, gold particles provide optical signals from the nucleus, the incubation in standard cell culture medium leads to scavenging of the toxic molecules and the formation of spots of high gold concentration in the cytoplasm without formation of SERS-active particles inside the cells. The biomolecular corona of nanoparticles formed in situ after incubation in buffer and DMEM differs, suggesting that different intracellular molecular species serve for reduction and stabilization. Comparison with data obtained from ready-made gold nanoparticles suggests complementary application of in situ and ex situ generated nanostructures for optical probing.

Scrapie-infected cells, isolated prions, and recombinant prion protein: a comparative study.

Fourier -transform infrared microscopic spectra of scrapie-infected nervous tissue measured at high spatial resolution (approximately 6 microm) were compared with those obtained from the purified, partly proteinase K digested scrapie isoform of the prion protein isolated from nervous tissue of hamsters infected with the same scrapie strain (263K) to elucidate similarities/dissimilarities between prion structure investigated in situ and ex vivo. A further comparison is drawn to the recombinant Syrian hamster prion protein SHaPrP(90-232) after in vitro conformational transition from the predominantly alpha-helical isoform to beta-sheet-rich structures. It is shown that prion protein structure can be investigated within tissue and that detectability of regions with elevated beta-sheet content as observed in microspectra of prion-infected tissue strongly depends on spatial resolution of the experiment.

Detection of pathological molecular alterations in scrapie-infected hamster brain by Fourier transform infrared (FT-IR) spectroscopy.

In this report a new approach for the identification of pathological changes in scrapie-infected Syrian hamster brains using Fourier transform infrared microspectroscopy is discussed. Using computer-based pattern recognition techniques and imaging, infrared maps with high structural contrast were obtained. This strategy permitted comparison of spectroscopic data from identical anatomical structures in scrapie-infected and control brains. Consistent alterations in membrane state-of-order, protein composition, carbohydrate and nucleic acid constituents were detected in scrapie-infected tissues. Cluster analysis performed on spectra of homogenized medulla oblongata and pons samples also reliably separated uninfected from infected specimens. This method provides a useful tool not only for the exploration of the disease process but also for the development of rapid diagnostic and screening techniques of transmissible spongiform encephalopathies.