Manipulation Of Submicron Particles Research Articles

Electrokinetic oscillation, railing, and enrichment of submicron particles along 3D microelectrode tracks

We report on electrokinetic manipulation of submicron particles in a device with microfabricated Si electrodes featuring segmented sidewalls acting as tracks guiding particles under hydrodynamic drag. Electrohydrodynamic drag, both AC electroosmosis in low-conductive medium and electrothermal flow in high-conductive medium, gives rise to fluid rolls that deliver particles to tracks where they are held under the influence of dielectrophoretic forces. Particles are being railed along tracks under pressure-driven flow to a downstream junction where tracks act as bridges, keeping particles on course within the main channel causing their post-junction enrichment. This outcome, however, is strongly coupled to electrode sidewall contours as demonstrated here. We also report on particle oscillations under strong AC electroosmosis. Specifically, particles in deionized water can be seen bouncing off tracks or circulating with convective rolls in and out of space beneath tracks at an oscillation frequency and amplitude depending on the activation frequency. These results collectively draw attention to the functional use of electrode sidewall contours for continuous-flow manipulation of particles, which are rarely explored in microfluidics and yet could lead to more effective designs for particle separation and enrichment.

Stable, Free-space Optical Trapping and Manipulation of Sub-micron Particles in an Integrated Microfluidic Chip

We demonstrate stable, free-space optical trapping and manipulation in an integrated microfluidic chip using counter-propagating beams. An inverted ridge-type waveguide made of SU8 is cut across by an open trench. The design of the waveguide provides low propagation losses and small divergence of the trapping beam upon emergence from the facet, and the trench designed to be deeper and wider than the optical mode enables full utilization of the optical power with an automatic alignment for counter-propagating beams in a trap volume away from all surfaces. After integration with polydimethylsiloxane (PDMS) microfluidic channel for particle delivery, 0.65 μm and 1 μm diameter polystyrene beads were trapped in free space in the trench, and manipulated to an arbitrary position between the waveguides with a resolution of < 100 nm. Comparison with numerical simulations confirm stable trapping of sub-micron particles, with a 10 kBT threshold power of less than 1 mW and a stiffness that can be 1 order of magnitude larger than that of comparable fiber-based trapping methods.

A micromachined Stoneley acoustic wave system for continuous flow particle manipulation in microfluidic channels

Particle manipulation utilizing interface acoustic waves (IAWs) is proposed for the first time. An IAW-based manipulation system has been designed, micromachined and tested. This work addresses the issue of particle manipulation in microfluidic channels with particular emphasis on particles with submicron dimensions. The subject is of significant relevance for a range of bio-technological applications and in particular for lab-on-chip ones. Submicron particle manipulation in continuous flow has been demonstrated.

Sub-micron particle manipulation in an ultrasonic standing wave: applications in detection of clinically important biomolecules.

Separation of particles from the suspending phase is of interest, among others, to clinical analysts. A system that enables manipulation of sub-micron sized particles in suspensions of analytical scale volume (10-50 microl) using a non-cavitating ultrasonic standing wave is described. Particle suspensions, contained in glass capillary tubes of 1-2 mm internal dimension, are treated on the axis of a tubular transducer generating a radial standing wave field at 4.5 MHz. Microparticles (of average diameter range 0.3-10 microm) suspended in buffer are concentrated within seconds at preferred regions separated by submillimetre distances. Concentration of suspended latex particles was inhibited in solutions containing protein at levels similar to those occurring in clinical specimens when the suspensions were sonicated in capillaries of circular cross-section. This effect was associated with acoustic streaming of the suspending fluid. Silica microparticles (more dense and less compressible than latex) could be concentrated in the presence of streaming. Latex particles concentrated readily in square cross-section capillaries where no streaming was observed. With sub-micron particles, the geometry of the sample chamber, the suspending phase composition and the size, density and compressibility of the microparticles all influence particle manipulation. The radial standing wave system has been used to enhance agglutination of antibody-coated latex microparticles in the presence of antigen allowing rapid and highly sensitive detection of clinically important biomolecules. The sensitivity of conventional diagnostic tests for microbial antigen has been improved by application of ultrasound and clinical utility has been demonstrated, in particular, for detection of meningitis-causing bacteria.

Dielectrophoretic manipulation of rod-shaped viral particles

The dielectrophoretic manipulation of a rod-shaped virus, tobacco mosaic virus (TMV) by means of non-uniform AC electric fields is described. An expression is derived for the dielectrophoretic force on a homogeneous dielectric cylinder suspended in a liquid medium which shows that the dielectrophoretic force varies over a wide range of frequencies and medium conductivities. Measurements of the dielectrophoretic behaviour of TMV particles in microelectrode arrays have been made as a function of frequency and applied field strength. The results are shown to be in quantitative agreement with the derived expression for the dielectrophoretic force. By measuring the threshold field strength for the onset of dielectrophoresis, the force on a single TMV particle has been estimated. The results point to the potential use of dielectrophoresis for the collection and manipulation of sub-micron particles using microelectrode arrays.