We introduce a method for optically imaging intracellular proteins at nanometer spatial resolution. Numerous sparse subsets of photoactivatable fluorescent protein molecules were activated, localized (to approximately 2 to 25 nanometers), and then bleached. The aggregate position information from all subsets was then assembled into a superresolution image. We used this method--termed photoactivated localization microscopy--to image specific target proteins in thin sections of lysosomes and mitochondria; in fixed whole cells, we imaged vinculin at focal adhesions, actin within a lamellipodium, and the distribution of the retroviral protein Gag at the plasma membrane.

/pdf/imaging-intracellular-fluorescent-proteins-at-nanometer-3hryxg5982.pdf

Imaging intracellular fluorescent proteins at nanometer resolution.

We have developed a high-resolution fluorescence microscopy method based on high-accuracy localization of photoswitchable fluorophores. In each imaging cycle, only a fraction of the fluorophores were turned on, allowing their positions to be determined with nanometer accuracy. The fluorophore positions obtained from a series of imaging cycles were used to reconstruct the overall image. We demonstrated an imaging resolution of 20 nm. This technique can, in principle, reach molecular-scale resolution.

/pdf/sub-diffraction-limit-imaging-by-stochastic-optical-52u8r6g2lp.pdf

Sub-diffraction-limit imaging by stochastic optical reconstruction microscopy (STORM).

A brief history and review of geopolymer technology is presented with the aim of introducing the technology and the vast categories of materials that may be synthesized by alkali-activation of aluminosilicates. The fundamental chemical and structural characteristics of geopolymers derived from metakaolin, fly ash and slag are explored in terms of the effects of raw material selection on the properties of geopolymer composites. It is shown that the raw materials and processing conditions are critical in determining the setting behavior, workability and chemical and physical properties of geopolymeric products. The structural and chemical characteristics that are common to all geopolymeric materials are presented, as well as those that are determined by the specific interactions occurring in different systems, providing the ability for tailored design of geopolymers to specific applications in terms of both technical and commercial requirements.

Geopolymer technology: the current state of the art

In 1873, Ernst Abbe discovered what was to become a well-known paradigm: the inability of a lens-based optical microscope to discern details that are closer together than half of the wavelength of light. However, for its most popular imaging mode, fluorescence microscopy, the diffraction barrier is crumbling. Here, I discuss the physical concepts that have pushed fluorescence microscopy to the nanoscale, once the prerogative of electron and scanning probe microscopes. Initial applications indicate that emergent far-field optical nanoscopy will have a strong impact in the life sciences and in other areas benefiting from nanoscale visualization.

/pdf/far-field-optical-nanoscopy-3qevt2g1wp.pdf

Far-Field Optical Nanoscopy

The Role of Inorganic Polymer Technology in the Development of ‘Green Concrete’

Conventional light microscopy is limited in its resolving power by the Rayleigh limit to length scales on the order of 200 nm. On the other hand, spectroscopic techniques such as fluorescence resonance energy transfer cannot be used to measure distances >10 nm, leaving a "gap" in the ability of optical techniques to measure distances on the 10- to 100-nm scale. We have previously demonstrated the ability to localize single dye molecules to a precision of 1.5 nm with subsecond time resolution. Here we locate the position of two dyes and determine their separation with 5-nm precision, using the quantal photobleaching behavior of single fluorescent dye molecules. By fitting images both before and after photobleaching of one of the dyes, we may localize both dyes simultaneously and compute their separation. Hence, we have circumvented the Rayleigh limit and achieved nanometer-scale resolution. Specifically, we demonstrate the technique by measuring the distance between single fluorophores separated by 10-20 nm via attachment to the ends of double-stranded DNA molecules immobilized on a surface. In addition to bridging the gap in optical resolution, this technique may be useful for biophysical or genomic applications, including the generation of super-high-density maps of single-nucleotide polymorphisms.

/pdf/single-molecule-high-resolution-imaging-with-photobleaching-2wo9htnny9.pdf

Single-molecule high-resolution imaging with photobleaching

Microstructure and microchemistry of fully-reacted geopolymers and geopolymer matrix composites

Geopolymer cements (GPs) possess the ability to form high-strength, thermally-stable, and near-net shape structures at room temperature. It has been found that GPs can also be used to bond both metals and ceramics. Unlikeorganics, geopolymers can be heated to elevated temperatures and are easier to apply as compared to refractory adhesives. Many refractory adhesives require at least one, if not multiple curing steps, at elevated temperatures before they can be used in service. Geopolymers, however, need only be cured once at relatively low temperatures (40 - 80°C) to complete their curing process. Geopolymers contain no organic carriers often found in refractory adhesives, and can be processed from inexpensive and relatively non-toxic materials, i.e. watetglass and calcined aluminosilicate clays. This study details how geopolymer cements can be used to bond 6061-T6 aluminum alloy, 1008/1010 steel, alumina, and borosilicate glass at both ambient and elevated temperatures (25 - 430°C). Shear strength values of various samples were determined according to ASTM D1002-01 (single) and ASTM D3528-96 (double) shear lap tests. The microstructure and chemical composition of the geopolymer bond as well as interface were studied with scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) in the SEM.

Use of Geopolymeric Cements as a Refractory Adhesive for Metal and Ceramic Joins

Comparison of Naturally and Synthetically‐Derived, Potassiumbased Geopolymers

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

Geopolymers: Nanoparticulate, Nanoporous Ceramics Made Under Ambient Conditions

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