Tailored optical vector fields for ultrashort-pulse laser induced complex surface plasmon structuring.

Precise tailoring of optical vector beams is demonstrated, shaping their focal electric fields and used to create complex laser micro-patterning on a metal surface. A Spatial Light Modulator (SLM) and a micro-structured S-waveplate were integrated with a picosecond laser system and employed to structure the vector fields into radial and azimuthal polarizations with and without a vortex phase wavefront as well as superposition states. Imprinting Laser Induced Periodic Surface Structures (LIPSS) elucidates the detailed vector fields around the focal region. In addition to clear azimuthal and radial plasmon surface structures, unique, variable logarithmic spiral micro-structures with a pitch Λ âˆ¼1µm, not observed previously, were imprinted on the surface, confirming unambiguously the complex 2D focal electric fields. We show clearly also how the Orbital Angular Momentum(OAM) associated with a helical wavefront induces rotation of vector fields along the optic axis of a focusing lens and confirmed by the observed surface micro-structures.

Dynamic modulation of spatially structured polarization fields for real-time control of ultrafast laser-material interactions.

The polarization state of an ultrafast laser is dynamically controlled using two Spatial Light Modulators and additional waveplates. Consequently, four states of polarization, linear horizontal and vertical, radial and azimuthal, all with a ring intensity distribution, were dynamically switched at a frequency ν = 12.5 Hz while synchronized with a motion control system. This technique, demonstrated here for the first time, enables a remarkable level of real-time control of the properties of light waves and applied to real-time surface patterning, shows that highly controlled nanostructuring is possible. Laser ablation of Induced Periodic Surface Structures is used to directly verify the state of polarization at the focal plane.

Complete wavefront and polarization control for ultrashort-pulse laser microprocessing.

We report on new developments in wavefront and polarization control for ultrashort-pulse laser microprocessing. We use two Spatial Light Modulators in combination to structure the optical fields of a picosecond-pulse laser beam, producing vortex wavefronts and radial or azimuthal polarization states. We also carry out the first demonstration of multiple first-order beams with vortex wavefronts and radial or azimuthal polarization states, produced using Computer Generated Holograms. The beams produced are used to nano-structure a highly polished metal surface. Laser Induced Periodic Surface Structures are observed and used to directly verify the state of polarization in the focal plane and help to characterize the optical properties of the setup.

Microfluidic reactor for the radiosynthesis of PET radiotracers.

Here we show the first application of a microfabricated reaction system to PET radiochemistry, we term "microfluidic PET". The short half-life of the positron emitting isotopes and the trace chemical quantities used in radiolabelling make PET radiochemistry amenable to miniaturisation. Microfluidic technologies are capable of controlling and transferring tiny quantities of liquids which allow chemical and biochemical assays to be integrated and carried out on a small scale. Such technologies provide distinct advantages over current methods of PET radiochemical synthesis. To demonstrate "proof of principle" we have investigated the radiohalogenation of small and large molecular weight molecules using the microfluidic device. These reactions involved the direct radioiodination of the apoptosis marker Annexin V using iodine-124, the indirect radioiodination of the anti-cancer drug doxorubicin from a tin-butyl precursor and the radiosynthesis of 2-[(18)F]FDG from a mannose triflate precursor and fluorine-18 and hence provide a test bed for microfluidic reactions. We demonstrate the rapid radioiodination of the protein Annexin V (40% radiochemical yield within 1 min) and the rapid radiofluorination of 2-[(18)F]FDG (60% radiochemical yield within 4s) using a polymer microreactor chip. Chromatographic analysis showed that the labelling efficiency of the unoptimised microfluidic chip is comparable to conventional PET radiolabelling reactions.

Changes in the myelinated axons of femoral nerve in amyotrophic lateral sclerosis.

Myelinated fibres in femoral nerves removed from amyotrophic lateral sclerosis (ALS) cases at post mortem were compared with age matched controls. A technique for processing whole transverse sections of the nerves for osmication and subsequent morphometric analysis is described. Although areas depleted in myelinated fibres were seen in the nerves from the ALS group, no statistically significant difference was shown due to wide variations in the controls. However, the ALS nerves showed a degree of disruption in the myelin which was not apparent in the controls. The most obvious effect was widespread "wrinkling" of the myelin in both large and small fibres from the ALS nerves. This phenomenon is the initial stage of a process which eventually results in uneven myelin thickness and nodal swellings and finally myelin ovoids and balls. We illustrate the steps in the progression of this degeneration with teased nerve studies and electron microscopy and propose that there are qualitative changes in the myelin of peripheral nerve in ALS. It seems likely that these are secondary effects resulting from axonal degeneration caused by deterioration and loss of anterior horn cells in the spinal cord.

Electrophoretic separation of myosin isoenzymes. Implications for the histochemical demonstration of fibre types in biopsy specimens of human skeletal muscle.

Myosin, the protein responsible for ATPase activity and hence the conversion of chemical into mechanical energy by muscle, is known to exist in polymorphic forms. A correlation exists between the myosin type present in a muscle as demonstrated by gel electrophoresis and the staining of sections of that muscle for ATPase activity. It is still possible to determine the major fibre type in a muscle electrophoretically even when pathological changes make interpretation of histochemical staining of sections difficult. The refinement of the electrophoretic technique in the present study has separated myosin from some specimens of muscle into three isoenzyme forms. The density of staining of the three myosin bands corresponds to the numbers of muscle fibres staining dark, pale or intermediate grey for ATPase activity after preincubation at pH 4.6. As other workers have noted, some specimens of muscle show a continuum or wide range of intermediate staining fibres after preincubation at pH 4.6. However, this is not reflected in the electrophoretic patterns which show only the three isoenzyme forms of myosin rather than a large range of these molecules. A particular myosin molecule would appear to be specific for each of the histochemical fibre types 1, 2A and 2B.

The correlation of light and electron microscope observations.

A technique is described to allow electron microscopic investigation of a specific feature of a section on a glass slide. A section on a glass slide (previously treated with a silicone release agent) is processed as required for light microscopy. The section is then impregnated with Araldite and cured with an epoxy resin block on top of it. The section and block are removed from the slide and viewed with a light microscope. The selected area for ultrastructural study remains under continuous observation while the block is trimmed. Semi-thin (1 micron) sections retain the original staining for light microscopy and ultra-thin sections are stained with heavy metals in the normal manner. We show how an inflammatory lesion in a large area of muscle in a case of polymyositis may be quickly located and studied at the ultrastructural level.

A phosphorylated light-chain component of myosin from skeletal muscle.

1. The low-molecular-weight components of myosin from rabbit skeletal muscle migrated as four bands on polyacrylamide-gel electrophoresis in 8m-urea but only as three in systems containing sodium dodecyl sulphate. The two bands of intermediate mobility in 8m-urea (Ml(2) and Ml(3)) had identical mobilities in sodium dodecyl sulphate. 2. The isolation of pure samples of all four low-molecular-weight components by DEAE-Sephadex chromatography is described. 3. The amino acid compositions of components Ml(2) and Ml(3) were identical. Further analyses showed the presence of 1 mol of phosphate/18500g of component Ml(2) and less than 10% of this amount in component Ml(3). Neither light component contained ribose. 4. Alkaline phosphatase from Escherichia coli converted component Ml(2) into Ml(3). Incubation with crude preparations of phosphorylase b kinase or protein kinase in the presence of ATP converted component Ml(3) into Ml(2). 5. Phosphorylation of component Ml(3) with the kinases isolated from skeletal muscle and [gamma-(32)P]ATP gave incorporation of (32)P only into component Ml(2) whether whole myosin or separated low-molecular-weight components were used. 6. High-voltage electrophoresis at pH6.5 and pH1.8 of a chymotryptic digest of (32)P-labelled component Ml(2) yielded one major radioactive peptide containing serine phosphate. 7. The amino acid sequence of this peptide was shown to be: Arg-Ala-Ala-Ala-Glu-Gly-Gly-(Ser,Ser(P))-Asn-Val-Phe. This sequence shows no obvious similarity to the site phosphorylated in the conversion of phosphorylase b into phosphorylase a by phosphorylase b kinase. 8. Evidence suggests that in vivo all the 18500-molecular-weight light chain is in the phosphorylated form. The extent of dephosphorylation that occurred during myosin extraction depended on the conditions employed.

An electrophoretic study of the low-molecular-weight components of myosin.

1. The low-molecular-weight components of myosin freshly prepared by the standard procedure from adult rabbit skeletal muscle migrated as four main bands Ml(1), Ml(2), Ml(3) and Ml(4) on polyacrylamide-gel electrophoresis in 8m-urea. 2. The number of bands increased on storage. This change was accelerated by increasing the temperature and pH. 3. None of the bands had electrophoretic mobilities identical with those of the well-characterized proteins of the myofibril or with the sarcoplasmic proteins. 4. By varying the ionic conditions and concentration of muscle mince used for the initial extraction it was possible to change the relative proportions of the two electrophoretic bands of intermediate mobility, Ml(2) and Ml(3). 5. The four-band picture similar to that obtained with rabbit was observed with myosin isolated from skeletal muscle of the rat, mouse, hamster, pigeon and chicken. 6. Rabbit cardiac myosin gave only two bands on electrophoresis. Myosin from rabbit red muscle gave a pattern intermediate between cardiac and white-skeletal-muscle myosin, i.e. the two fastest bands were present in decreased relative amounts. 7. It is suggested that the differences in the low-molecular-weight components of myosin from different types of muscle are a consequence of differences in the isoenzyme composition of the myosins.