LinkNotes: particles

2009-12-15

'Micro-ants' -- Moving tiny particles using magnetic fields

‘Micro-ants’: Tiny conveyor belts for the 21st century

A new kind of micro-mobility: Moving tiny particles using magnetic fields (w/ Video)

Alfredo Alexander-Katz, the Toyota Career Development Assistant Professor of Materials Science and Engineering, and his doctoral student Charles Sing and other researchers, devised a system that uses tiny beads made of polymers with specks of magnetic material in them. With these beads suspended in a liquid, they applied a rotating magnetic field, which caused the beads to spontaneously form short chains which began spinning, creating currents that could then carry along surrounding particles — even particles as much as 100 times larger than the beads themselves.

clipped from web.mit.edu

Chains of superparamagnetic colloidal particles rotate to produce flows on length scales much larger than the chain dimensions, allowing them to behave like "micro-ants" that can move large particles.
Photo - Image: Charles Sing

clipped from web.mit.edu

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2009-09-19

Optoelectronic Tweezers for Dynamic Cell Manipulation

Clipped from: 07.20.2005 - Engineers create optoelectronic tweezers to round up cells, microparticles

Engineers create optoelectronic tweezers to round up cells, microparticles

BERKELEY – Rounding up wayward cells and particles on a microscope slide can be as difficult as corralling wild horses on the range, particularly if there's a need to separate a single individual from the group.

But now, a new device developed by University of California, Berkeley, engineers, and dubbed an "optoelectronic tweezer," will enable researchers to easily manipulate large numbers of single cells and particles using optical images projected on a glass slide coated with photoconductive materials.

Clipped from: IPL: Integrated Photonics Laboratory

The working principle behind optoelectronic tweezers is light-induced dielectrophoresis. A photosensitive device layer forms "virtual electrodes" upon exposure to light, creating non-uniformities in an applied electric field (Fig. 1). The non-uniform electric field gives rise to a force known as dielectrophoresis: micro- and nanoparticles move as a result of the non-uniformities in the electric field imparting unequal forces on the induced dipole of the particle.

Figure 1:Device structure used in optoelectronic tweezers (OET).

Clipped from: Lab on a Chip Articles

Phototransistor-based optoelectronic tweezers for dynamic cell manipulation in cell culture media

Hsan-yin Hsu, Aaron T. Ohta, Pei-Yu Chiou, Arash Jamshidi, Steven L. Neale and Ming C. Wu

Clipped from: Phototransistor-based optoelectronic tweezers for dynamic cell manipulation in ..... (DOI: 10.1039/b906593h)

Optoelectronic tweezers (OET), based on light-induced dielectrophoresis, has been shown as a versatile tool for parallel manipulation of micro-particles and cells [...] However, the conventional OET device cannot operate in cell culture media or other high-conductivity physiological buffers [...] In this paper, we report a new phototransistor-based OET (Ph-OET). Consisting of single-crystalline bipolar junction transistors, the Ph-OET has more than 500× higher photoconductivity than amorphous silicon.[...]

Fig. 6 Schematic of the Ph-OET device. Samples are placed in between an ITO-coated glass and the Ph-OET. AC electric field bias is applied between the top ITO electrode and bottom silicon substrate. Optical access is provided through the ITO glass.

Fig. 13 Spatial control of two cells. (a) Initially, two cells in close proximity are trapped in a single optical box. (b) Separation of the two adjacent cells. (c) Joining of two separated cells. (d–e) Stacking of 2 cells vertically in one single trap.

Clipped from: YouTube - Phototransistor-based optoelectronic tweezers for dynamic cell manipulation in cell culture media

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