Sequence of physical changes to the cell membrane during glucocorticoid-induced apoptosis in S49 lymphoma cells.

During apoptosis, physical changes in the plasma membrane prepare the cell for clearance by phagocytes and hydrolysis by secretory phospholipase A(2) (sPLA(2)). The relationships among these changes have not been adequately established, especially for hormone-stimulated apoptosis. This study addresses these issues for glucocorticoid-induced apoptosis in S49 lymphoma cells. Flow cytometry, microscopy, and fluorescence spectroscopy were used to assess merocyanine 540 emission, laurdan generalized polarization, phosphatidylserine exposure, caspase activation, and membrane permeability to propidium iodide in the absence and presence of sPLA(2). The earliest event observed was activation of cellular caspases. Results with membrane probes suggest that interlipid spacing also increases early during apoptosis and precedes transbilayer migration of phosphatidylserine, DNA fragmentation, and a general increase in lipid order associated with blebbing and dissolution of the cells. The activity of sPLA(2) appeared to be linked more to lipid spacing than to loss of membrane asymmetry. The early nature of some of these events and their ability to promote activity of a proinflammatory enzyme suggests the possibility of an inflammatory response during T-lymphocyte apoptosis.

Single-step plasma synthesis of carbon-coated silicon nanoparticles.

We have developed a novel single-step technique based on nonthermal, radio frequency (rf) plasmas to synthesize sub-10 nm, core-shell, carbon-coated crystalline Si (c-Si) nanoparticles (NPs) for potential application in Li(+) batteries and as fluorescent markers. Hydrogen-terminated c-Si NPs nucleate and grow in a SiH4-containing, low-temperature plasma in the upstream section of a tubular quartz reactor. The c-Si NPs are then transported downstream by gas flow, and are coated with amorphous carbon (a-C) in a second C2H2-containing plasma. X-ray diffraction (XRD), X-ray photoelectron spectroscopy, and in situ attenuated total reflection Fourier transform infrared spectroscopy show that a thin, < 1 nm, 3C-SiC layer forms at the c-Si/a-C interface. By varying the downstream C2H2 plasma rf power, we can alter the nature of the a-C coating as well as the thickness of the interfacial 3C-SiC layer. The transmission electron microscopy (TEM) analysis is in agreement with the Si NP core size determined by Raman spectroscopy, photoluminescence spectroscopy, and XRD analysis. The size of the c-Si NP core, and the corresponding light emission from these NPs, was directly controlled by varying the thickness of the interfacial 3C-SiC layer. This size tunable emission thus also demonstrates the versatility of this technique for synthesizing c-Si NPs for potential applications in light emitting diodes, biological markers, and nanocrystal inks.