Photophoretic velocimetry--a new way for the in situ determination of particle size distribution and refractive index of hydrocolloids.

The migration of particles induced by the forces of light is known as photophoresis. The photophoretic velocity of particles under the influence of a strong light source, e.g. a laser beam, is recorded and measured by means of digital image processing which is called photophoretic velocimetry (PPV). The photophoretic velocity depends on the particle size as well as on its refractive index. By applying PPV, we show the determination of the intrinsic properties of polystyrene (PS), melamine resin (MF) and SiO(2) particles, deduced from velocity distributions of both monodisperse as well as polydisperse suspensions. Especially the continuous determination of the refractive index of single hydrocolloids is of great interest for quality assurance and the discrimination of polydisperse biological or inorganic samples. Also, PPV is not restricted to in water dispersed samples only.

Summary of the ISEV workshop on extracellular vesicles as disease biomarkers, held in Birmingham, UK, during December 2017.

This report summarises the presentations and activities of the ISEV Workshop on extracellular vesicle biomarkers held in Birmingham, UK during December 2017. Among the key messages was broad agreement about the importance of biospecimen science. Much greater attention needs to be paid towards the provenance of collected samples. The workshop also highlighted clear gaps in our knowledge about pre-analytical factors that alter extracellular vesicles (EVs). The future utility of certified standards for credentialing of instruments and software, to analyse EV and for tracking the influence of isolation steps on the structure and content of EVs were also discussed. Several example studies were presented, demonstrating the potential utility for EVs in disease diagnosis, prognosis, longitudinal serial testing and stratification of patients. The conclusion of the workshop was that more effort focused on pre-analytical issues and benchmarking of isolation methods is needed to strengthen collaborations and advance more effective biomarkers.

Methods to Analyze EVs.

Research in the field of extracellular vesicles (EVs) is challenged by the small size of the nano-sized particles. Apart from the use of transmission and scanning electron microscopy, established technical platforms to visualize, quantify, and characterize nano-sized EVs were lacking. Recently, methodologies to characterize nano-sized EVs have been developed. This chapter aims to summarize physical principles of novel and conventional technologies to be used in the EV field and to discuss advantages and limitations.

Photophoretic velocimetry for colloid characterization and separation in a cross-flow setup.

We introduce photophoretic velocimetry as a new technique for characterization of particulate matter on the basis of optical particle properties. Complementary to well-established techniques, we could show that, by measuring the photophoretic velocity of the single particles, it is possible to distinguish particles of different sizes as well as particles of one size but different refractive indices. The difference in photophoretic migration of particles can be applied to the separation of particles. Polystyrene, melamine, and SiO2 microparticles (0.3-10 mum) suspended in purified water were used as test samples for validation of a cross-flow setup. The particles were pushed perpendicular to a uniform, pulsation-free fluid flow by a focused He-Ne laser (lambda = 633 nm, P = 47 mW, I(max) = 14.0 kW cm(-2)) providing a well-defined Gaussian-shaped flux distribution. The migration behavior was observed by means of a video camera system, and the velocities and displacements were calculated by using an adapted particle imaging velocimetry code as an approach to automatic characterization. The photophoretic displacement depends on both flow conditions and particle properties and can be applied for separation means.