The µPIVOT: an integrated particle image velocimeter and optical tweezers instrument for microenvironment investigations

Abstract

A novel instrument to manipulate and characterize the mechanical environment in and around microscale objects in a fluidic environment has been developed by integrating two laser-based techniques: micron-resolution particle image velocimetry (μPIV) and optical tweezers (OT). This instrument, the μPIVOT, enables a new realm of microscale studies, yet still maintains the individual capabilities of each optical technique. This was demonstrated with individual measurements of optical trap stiffness (∼70 pN μm −1 for a 20 μm polystyrene sphere and a linear relationship between trap stiffness and laser power) and fluid velocities within 436 nm of a microchannel wall. The integrated device was validated by comparing computational flow predictions to the measured velocity profile around a trapped particle in either a uniform flow or an imposed, gravity-driven microchannel flow (R 2 = 0.988, RMS error = 13.04 μm s −1 ). Interaction between both techniques is shown to be negligible for 15 μm to 35 μm diameter trapped particles subjected to fluid velocities from 50 μm s −1 to 500 μm s −1 even at the highest laser power (1.45 W). The integrated techniques will provide a unique perspective toward understanding microscale phenomena including single-cell biomechanics, non-Newtonian fluid mechanics and single particle or particle-particle hydrodynamics.

Mechanical Stress Analysis of Microfluidic Environments Designed for Isolated Biological Cell Investigations

“…Through fluid mechanics, flow-based mechanical test sequences (including shear and extensional loading) may provide control of unique microenvironments when coupled with single cell suspension techniques. The µPIVOT (micron resolution particle image velocimetry combined with optical tweezers) was recently developed to apply controlled multiaxial stresses to single cells suspended with optical tweezers within custom channel designs [16,17]. …”

Optical manipulation for single‐cell studies

“…Eight years later Ozkan et al [44] showed various types of optical manipulation in a microfluidic flow system. More recently, Nè ve et al [45] demonstrated the combination of micrometerresolution particle image velocimetry (mPIV) and optical tweezers in order to manipulate and characterize the mechanical environment in and around microscale objects. They predicted that with this setup, fluid-particle interactions, full field measurements of direct particle-particle interactions, as well as the stress fields around deformed elastic and viscoelastic bodies such as biological cells can be explored.…”

“…Mejia et al [149] performed thermal probing of E. coli RNA polymerase off-pathway mechanisms. The kinetic mechanism of RNA polymerase (RNAP) revealed a pause-free transcription velocity in the temperature range between 7 to 45 C that was force independent. They suggest that pause entry seems to be a thermally accessible process that presents a maximum at 21 C and conclude that arrest could play a regulatory role in vivo.…”

Advances and applications on microfluidic velocimetry techniques

“…Simultaneous lPIV and impedance measurements enable simultaneous fluid characterization and real-time monitoring of biological species. The combination of lPIV and optical tweezers (called lPIVOT) was proposed to measure the velocity profile around a trapped suspended particle, which would provide clues toward a better understanding of biological cells suspended in a fluid medium (Neve et al 2008). It was reported that when the trapped particle with diameter between 15 and 35 lm was exposed to fluid flow from 50 lm s -1 to 500 lm s -1 , the influence of optical tweezers acting on the tracer particles can be neglected.…”