The ability to manipulate micrometer to nanometer scale particles in a parallel and dynamic fashion is of prime importance in the fields of cellular biology, micro/nano assembly, and microfluidics. So far it has not been implemented in microbeam systems. All microbeam systems (including our own) rely on irradiation of cells adhered to a substrate and moved mechanically to the microbeam. This does not allow for easy manipulation of single cells or groups of cells.
On the other hand, Optoelectronic Tweezers (OET), initially developed by our collaborators at Berkeley, have been proven to be a powerful tool for parallel manipulation of multiple cell-sized objects. An OET system, integrated into the microbeam endstation, will allow real-time manipulation of single cells before, during and after irradiation, of specific interest to many of our users. This design will allow for a new class of bystander experiments, where cells are irradiated and then brought into contact with other (irradiated or non-irradiated) cells for controlled time periods and then sorted out into subgroups for separate analysis based on location in the irradiation dish or based on morphology.
Our goal is to be able to load cells into a microfluidic channel, place them in prescribed locations within the Point-and-Shoot field of fire, irradiate specific cells and then dispense single cells or groups of cells, into separate vials, keeping track of which cell is which.
To date, we have created a set of OET electrodes with the guidance of our Berkeley collaborators in the cleanroom at Columbia University. As a preliminary test, we manufactured the devices on 1mm thick glass slides. Future work will focus on reducing the thickness of the bottom substrate to allow charged particles to easily pass through.
The OET consists of two parallel plate Indium Tin Oxide (ITO) electrodes. One electrode is covered with a 1 μm thick layer of hydrogenated amorphous silicon (a-Si:H), a thin film semiconductor that acts as a photoconductive layer. When light is focused on the surface of the a-Si:H, its conductivity increases by several orders of magnitude. By patterning a dynamic image with a computer and a projector, a reconfigurable virtual electrode is created. In order to prevent evaporation of the fluid and to easily control the spacing between the parallel plates, a rubber gasket was placed between the electrodes, and a plastic clamp was used to hold the two plates together, as shown above in figure 1. Initial tests to manipulate a 19 μm diameter bead by projecting a red square pattern outline in the OET device found a maximum velocity of approximately 50 μm/s.
Trials on live cells are commencing.