Optical tweezers for trapping in a microfluidic environment

Optical tweezers use the force from a light beam to implement a precise gripping tool. Based purely on an optical principle, it works without any bodily contact with the object. In this paper we describe an optical tweezers that targets an application within the framework of nuclear magnetic resonance (NMR) spectroscopy of small objects, which are embedded inside a microfluidic channel that will be integrated in a micro-NMR detector. In the project's final stages, the whole system will be installed within the wide bore of a superconducting magnet. The aim is to precisely maintain the position of the object to be measured, without the use of susceptibility disturbing materials or geometries. In this contribution we focus on the design and construction of the tweezers. For the optical force simulation of the system we used a geometrical optics approach, which we combined with a ray fan description of the output beam of an optical system. By embedding both techniques within an iterative design process, we were able to design efficient optical tweezers that met the numerous constraints. Based on details of the constraints and requirements given by the application, different system concepts were derived and studied. Next, a highly adapted and efficient optical trapping system was designed and manufactured. After the components were characterized using vertical scanning interferometry, the system was assembled to achieve a monolithic optical component. The proper function of the optical tweezers was successfully tested by optical trapping of fused silica particles.

Optical system for trapping particles in air

An innovative optical system for trapping particles in air is presented. We demonstrate an optical system specifically optimized for high precision positioning of objects with a size of several micrometers within a nanopositioning and nanomeasuring machine (NPMM). Based on a specification sheet, an initial system design was calculated and optimized in an iterative design process. By combining optical design software with optical force simulation tools, a highly efficient optical system was developed. Both components of the system, which include a refractive double axicon and a parabolic ring mirror, were fabricated by ultra-precision turning. The characterization of the optical elements and the whole system, especially the force simulations based on caustic measurements, represent an important interim result for the subsequently performed trapping experiments. The caustic of the trapping beam produced by the system was visualized with the help of image processing techniques. Finally, we demonstrated the unique efficiency of the configuration by reproducibly trapping fused silica spheres with a diameter of 10 μm at a distance of 2.05 mm from the final optical surface.

Precipitation Kinetics in Metastable Solid Solutions – Theoretical Considerations and Application to Cu-Ti Alloys

Cu-2.9 at.% Ti single crystals were homogenized at various temperatures (780 °C ≤ TH ≤ 960°C) and quenched. Subsequent isothermal aging at 350 °C led to phase separation, the kinetics of which have been followed by employing small-angle neutron scattering (SANS). According to comple-mentary transmission electron and analytical field ion microscopy studies, the resulting transformation products of this first order phase transition are stoichiometrically ordered ellipsoidal Cu4Ti particles, the aspect ratio of which changes with aging time (t) as revealed by two-dimensional SANS-detection. In the early stages of phase separation, the decomposition kinet-ics are strongly influenced by the quenching rate via quenched-in excess vacancies. During aging the structure factor S(K,t) develops a maximum, the height (Sm) of which increases and the position (Km) of which decreases with t. Neither Sm(t) nor Km(t) follow a power law as predicted by several recent theories on spinodal decomposition. On the other hand, the time evolution of the mean Ti-rich cluster size (R), their number density (Nv), and the supersaturation (Δc) as inferred from the SANS-data and the diffuse Laue-scattering, are well predicted by a precipitation model which describes nucleation, growth and coarsening as competing processes.

New sources and instrumentation for neutrons in biology

Neutron radiation offers significant advantages for the study of biological molecular structure and dynamics. A broad and significant effort towards instrumental and methodological development to facilitate biology experiments at neutron sources worldwide is reviewed.

Electrocardiographic signs of hypertrophy in fabry disease-associated hypertrophic cardiomyopathy

AIMS

Fabry disease results from deficient activity of the lysosomal enzyme alpha-galactosidase A. Progressive accumulation of the major substrates leads, in both men and women, to progressive hypertrophic cardiomyopathy. We aimed to evaluate the utility of different electrocardiographic (ECG) parameters for assessing the degree and severity of hypertrophic cardiomyopathy in patients with Fabry disease.

METHODS

A total of 166 ECGs of 94 hemi- and heterozygous patients with Fabry disease were analysed and compared with echocardiographic-estimated left ventricular mass (LVM).

RESULTS

There was a significant (p < 0.0001) correlation between QRS duration (R2 = 0.59), 12-lead amplitude/duration product (R2 = 0.61), Sokolow-Lyon voltage/duration product (R2 = 0.52) and LVM. Analysis of receiver operating characteristics revealed that the 12-lead amplitude/duration product had the highest sensitivity-specificity relationship (p < 0.01 compared with the Cornell index).

CONCLUSION

In general, ECG signs of left ventricular hypertrophy correlated well with LVM as revealed by echocardiography. Of the parameters studied, the 12-lead amplitude/duration product was the most successful at describing the severity of cardiac involvement in Fabry disease. These data suggest that ECG parameters have potential for use as a simple and cost-effective means of screening for hypertrophic cardiomyopathy in patients with Fabry disease.