In mammalian cells three closely related cavin proteins cooperate with the scaffolding protein caveolin to form membrane invaginations known as caveolae. Here we have developed a novel single-molecule fluorescence approach to directly observe interactions and stoichiometries in protein complexes from cell extracts and from in vitro synthesized components. We show that up to 50 cavins associate on a caveola. However, rather than forming a single coat complex containing the three cavin family members, single-molecule analysis reveals an exquisite specificity of interactions between cavin1, cavin2 and cavin3. Changes in membrane tension can flatten the caveolae, causing the release of the cavin coat and its disassembly into separate cavin1-cavin2 and cavin1-cavin3 subcomplexes. Each of these subcomplexes contain 9 ± 2 cavin molecules and appear to be the building blocks of the caveolar coat. High resolution immunoelectron microscopy suggests a remarkable nanoscale organization of these separate subcomplexes, forming individual striations on the surface of caveolae.DOI:
http://dx.doi.org/10.7554/eLife.01434.001
Nanopore sensors detect individual species passing through a nanoscale pore. This experimental paradigm suffers from long analysis times at low analyte concentration and non-specific signals in complex media. These limit effectiveness of nanopore sensors for quantitative analysis. Here, we address these challenges using antibody-modified magnetic nanoparticles ((anti-PSA)-MNPs) that diffuse at zero magnetic field to capture the analyte, prostate-specific antigen (PSA). The (anti-PSA)-MNPs are magnetically driven to block an array of nanopores rather than translocate through the nanopore. Specificity is obtained by modifying nanopores with anti-PSA antibodies such that PSA molecules captured by (anti-PSA)-MNPs form an immunosandwich in the nanopore. Reversing the magnetic field removes (anti-PSA)-MNPs that have not captured PSA, limiting non-specific effects. The combined features allow detecting PSA in whole blood with a 0.8 fM detection limit. Our ‘magnetic nanoparticle, nanopore blockade’ concept points towards a strategy to improving nanopore biosensors for quantitative analysis of various protein and nucleic acid species.
For
the fabrication of perovskite solar cells (PSCs) using a solution
process, it is essential to understand the characteristics of the
perovskite precursor solution to achieve high performance and reproducibility.
The colloids (iodoplumbates) in the perovskite precursors under various
conditions were investigated by UV–visible absorption, dynamic
light scattering, photoluminescence, and total internal reflection
fluorescence microscopy techniques. Their local structure was examined
by in situ X-ray absorption fine structure studies. Perovskite thin
films on a substrate with precursor solutions were characterized by
transmission electron microscopy, X-ray diffraction analysis, space-charge-limited
current, and Kelvin probe force microscopy. The colloidal properties
of the perovskite precursor solutions were found to be directly correlated
with the defect concentration and crystallinity of the perovskite
film. This work provides guidelines for controlling perovskite films
by varying the precursor solution, making it possible to use colloid-engineered
lead halide perovskite layers to fabricate efficient PSCs.
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