This technique combines the enhanced lateral and vertical resolution characteristic of AFM with simultaneous measurements of topographic and optical signals. SNOM can achieve a spatial resolution beyond the diffraction limit by scanning a sub-wavelength-sized aperture, confining the excitation beam to the close proximity of the sample. The resolution depends on the size of the aperture and the distance between the probe and the sample, rather than on the wavelength. The most commonly used SNOM probe is an aluminum-coated tapered optical fiber with an aperture <100 nm, positioned very close to the surface (~10nm). The position of the probe is controlled by a piezo-electric stand, and the light emitted by the sample is collected either by an objective or through the same optical fiber. SNOM can simultaneously map topographic and optical properties with high spatial resolution, has single molecule sensitivity, and is relatively noninvasive. In addition, by using fluorescent labels it can provide a high level of molecular specificity SNOM detected a highly patchy distribution of some fluorescent lipid analogues reflecting a lipid domain structure in fixed, dried cells . The sizes of these patches were consistent with the sizes of domains implied by measurements of lateral diffusion with fluorescence photobleaching recovery. SNOM was also used to observe clustering of fluorescently labeled membrane receptors; clusters of platelet-derived growth factor (PDGF) receptors down to 80-100 nm diameter were observed on glioblastoma cells , and activation-dependent clustering of ErbB2 was revealed on breast tumor cells .
150 | 7 Role of Lipid Microdomains in the Formation of Supramolecular Protein Complexes 7.3
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.