Nanoparticle image velocimetry at topologically structured surfaces

Nanoparticle image velocimetry ͑nano-PIV͒, based on total internal reflection fluorescent microscopy, is very useful to investigate fluid flows within ϳ100 nm from a surface; but so far it has only been applied to flow over smooth surfaces. Here we show that it can also be applied to flow over a topologically structured surface, provided that the surface structures can be carefully configured not to disrupt the evanescent-wave illumination. We apply nano-PIV to quantify the flow velocity distribution over a polydimethylsiloxane surface, with a periodic gratinglike structure ͑with 215 nm height and 2 m period͒ fabricated using our customized multilevel lithography method. The measured tracer displacement data are in good agreement with the computed theoretical values. These results demonstrate new possibilities to study the interactions between fluid flow and topologically structured surfaces

Monitoring the orientation of rare-earth-doped nanorods for flow shear tomography

Rare-earth phosphors exhibit unique luminescence polarization features originating from the anisotropic symmetry of the emitter ion's chemical environment. However, to take advantage of this peculiar property, it is necessary to control and measure the ensemble orientation of the host particles with a high degree of precision. Here, we show a methodology to obtain the photoluminescence polarization of Eu-doped LaPO4 nano rods assembled in an electrically modulated liquid-crystalline phase. We measure Eu3+ emission spectra for the three main optimal configurations ({\sigma}, {\pi} and {\alpha}, depending on the direction of observation and the polarization axes) and use them as a reference for the nano rod orientation analysis. Based on the fact that flowing nano rods tend to orient along the shear strain profile, we use this orientation analysis to measure the local shear rate in a flowing liquid. The potential of this approach is then demonstrated through tomographic imaging of the shear rate distribution in a microfluidic system.Comment: 8 pages, 3 figures + supplementary files for experimental and numerical method

Optimization of multiplane μpIV for wall shear stress and wall topography characterization

Multiplane μPIV can be utilized to determine the wall shear stress and wall topology from the measured flow over a structured surface. A theoretical model was developed to predict the measurement error for the surface topography and shear stress, based on a theoretical analysis of the precision in PIV measurements. The main parameters that affect the accuracy of the measurement are identified. The effect of different parameter settings is studied by means of Monte Carlo simulations, and the results are compared with an experimental test case. The results are used to determine the recommended parameter settings for this measurement approach

Micro-Particle Image Velocimetry (PIV): Recent developments, applications, and guidelines

In this review we discuss the state of the art of the optical whole-field velocity measurement technique micro-scale Particle Image Velocimetry (PIV). PIV is a useful tool for fundamental research of microfluidics as well as for the detailed characterization and optimization of microfluidic applications in life science, lab-on-a-chip, biomedical research, micro chemical engineering, analytical chemistry and other related fields of research. An in depth description of the PIV method is presented and compared to other flow visualization and measurement methods. An overview of the most relevant applications is given on the topics of near-wall flow, electrokinetic flow, biological flow, mixing, two-phase flow, turbulence transition and complex fluid dynamic problems. Current trends and applications are critically reviewed. Guidelines for the implementation and application are also discussed. © 2009 The Royal Society of Chemistry

In vivo whole-field blood velocity measurement techniques

Mechanical, Maritime and Materials Engineerin

Tapered microfluidic chip for the study of biochemical and mechanical response at subcellular level of endothelial cells to shear flow

A lab-on-a-chip application for the investigation of biochemical and mechanical response of individual endothelial cells to different fluid dynamical conditions is presented. A microfluidic flow chamber design with a tapered geometry that creates a pre-defined, homogeneous shear stress gradient on the cell layer is described and characterized. A non-intrusive, non-tactile measurement method based on micro-PIV is used for the determination of the topography and shear stress distribution over individual cells with subcellular resolution. The cellular gene expression is measured simultaneously with the shape and shear stress distribution of the cell. With this set-up the response of the cells on different pre-defined shear stress levels is investigated without the influence of variations in repetitive experiments. Results are shown on cultured endothelial cells related to the promoter activity of the shear-responsive transcription factor KLF2 driving the marker gene for green fluorescent protein. © The Royal Society of Chemistry 2009