Combined acoustic and optical trapping

Abstract

Combining several methods for contact free micro-manipulation of small particles such as cells or micro-organisms provides the advantages of each method in a single setup. Optical tweezers, which employ focused laser beams, offer very precise and selective handling of single particles. On the other hand, acoustic trapping with wavelengths of about 1 mm allows the simultaneous trapping of many, comparatively large particles. With conventional approaches it is difficult to fully employ the strengths of each method due to the different experimental requirements. Here we present the combined optical and acoustic trapping of motile micro-organisms in a microfluidic environment, utilizing optical macro-tweezers, which offer a large field of view and working distance of several millimeters and therefore match the typical range of acoustic trapping. We characterize the acoustic trapping forces with the help of optically trapped particles and present several applications of the combined optical and acoustic trapping, such as manipulation of large (75 μm) particles and active particle sorting.

Rapid 3D fluorescence imaging of individual optically trapped living immune cells

“…Earlier studies typically imaged only in 2D or released the object of interest from the trap prior to 3D imaging [10,20], allowing it to change its position or orientation relative to other objects, and frequently to wander out of the field of view. Alternatively, the focal plane of the trapping beam can be adjusted independently from the imaging plane through the use of additional lenses [21] or by adjusting the SLM pattern [22]. HOT have previously been used to image in 3D by positioning trapped cells relative to the imaging plane [23].…”

Acoustofluidics 23: acoustic manipulation combined with other force fields

“…Optical traps, with a wavelength of the order of 1 µm are able to manipulate single small particles with a very high degree of precision, while acoustic radiation forces are able to handle a large number of particles simultaneously and can levitate relatively large, dense particles efficiently. Thalhammer et al 53 use a combination of acoustical and optical techniques to undertake a variety of manipulation tasks. The ultrasonic field is set up in a square capillary which is held between a glass slide and an optical mirror backed with a PZT transducer, as shown schematically in Figure 9.…”

Microexplosions polysterene microparticles on substrate covered by aluminum

“…At the same time, the micro-objects with sizes up to 100 microns are still quite small for a mechanical movement. There is another complicate combined method of micro-objects grasping with the usage of light and ultrasound [5]. But here is another [6] described simpler method of moving micro-objects by means of the microexplosions of polystyrene microparticles in a beam of an ultraviolet laser with a wavelength of 355 nm.…”