Multifunctional core–shell particles composed of magnetic particles covered with a gold nanoshell can be induced to align into conducting lines upon application of a magnetic field (see Figure). The formation of Au clusters and “streaky” gold nanoparticles on the surface of the PS beads is demonstrated and the preparation, characterization, and applications of magnetic and polystyrene beads featuring a gold shell are addressed.

We developed a novel surface plasmon resonance (SPR) method, based on Fourier transform infrared (FTIR) spectroscopy, as a label-free technique for studying dynamic processes occurring within living cells in real time. With this method, the long (micrometer) infrared wavelength produced by the FTIR generates an evanescent wave that penetrates deep into the sample. In this way, it enables increased depth of sensing changes, covering significant portions of the cell-height volumes. HeLa cells cultivated on a gold-coated prism were subjected to acute cholesterol enrichment or depletion using cyclodextrins. Cholesterol insertion into the cell plasma membrane resulted in an exponential shift of the SPR signal toward longer wavelengths over time, whereas cholesterol depletion caused a shift in the opposite direction. Upon application of the inactive analog alpha-cyclodextrin (alpha-CD), the effects were minimal. A similar trend in the SPR signal shifts was observed on a model membrane system. Our data suggest that FTIR-SPR can be implemented as a sensitive technique for monitoring in real time dynamic changes taking place in living cells.

We discuss the Surface-Plasmon-Resonance (SPR) technique based on Fourier -Transform -In-fraRed (FTIR) spectrometry. We explore the potential of the infrared surface plasmon resonance technique for biological studies in aqueous solutions and compare it to the conventional surface plasmon technique operating in the visible range. We demonstrate that the sensitivity of the SPR technique in the infrared range is not lower and in fact is even higher. We show several examples of applying FTIR-SPR for biological studies: (i) monitoring D-glucose concentration in solution, and (ii) measuring D-glucose uptake by erythrocytes in suspension. We emphasize the advantages of infrared SPR for studying living cell cultures and show how this technique can be used for characterization of (i) cholesterol penetration into plasma membrane, and (ii) transferrin-induced clathrin-mediated endocytosis. * electronic address: golos@vms.huji.ac.il

The development of novel technologies capable of monitoring the dynamics of cell-cell and cell-substrate interactions in real time and a label-free manner is vital for gaining deeper insights into these most fundamental cellular processes. However, the label-free technologies available today provide only limited information on these processes. Here, we report a new (to our knowledge) infrared surface plasmon resonance (SPR)-based methodology that can resolve distinct phases of cell-cell and cell-substrate adhesion of polarized Madin Darby canine kidney epithelial cells. Due to the extended penetration depth of the infrared SP wave, the dynamics of cell adhesion can be detected with high accuracy and high temporal resolution. Analysis of the temporal variation of the SPR reflectivity spectrum revealed the existence of multiple phases in epithelial cell adhesion: initial contact of the cells with the substrate (cell deposition), cell spreading, formation of intercellular contacts, and subsequent generation of cell clusters. The final formation of a continuous cell monolayer could also be sensed. The SPR measurements were validated by optical microscopy imaging. However, in contrast to the SPR method, the optical analyses were laborious and less quantitative, and hence provided only limited information on the dynamics and phases of cell adhesion.

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