A novel technique is presented which integrates the capacity of a laser tweezer to optically trap and manipulate objects in three-dimensions with the resolution-enhanced imaging capabilities of a solid immersion lens (SIL). Up to now, solid immersion lens imaging systems have relied upon cantilever-mounted SILs that are difficult to integrate into microfluidic systems and require an extra alignment step with external optics. As an alternative to the current
state-of-art, we introduce a device that consists of a free-floating SIL and a laser optical tweezer. In our design, the optical tweezer, created by focusing a laser beam through high numerical aperture microscope objective, acts in a two-fold manner: both as a trapping beam for the positioning and alignment of the SIL and as an near-field scanning beam to image the sample through the SIL. Combining the alignment, positioning, and imaging functions into a single device allows for the direct integration of a high resolution imaging system into microfluidic and biological environments.
An adaptive alignment technique is presented that provides precise control and active positioning of sub-millimeter-sized spherical lenses in two-dimensions through the application of electrophoretic forces in a microfluidic well. The device is comprised of a lithographically patterned microfluidic well and electrodes that can be addressed to position or align the spherical microlens to the corresponding beam source. The motion of the microlens is controlled using CMOS compatible voltages (3V - 1 (mu) A) that are applied to opposite electrodes in the microfluidic well, creating an electrical field in the solution. By applying voltages to opposite electrode pairs, we have demonstrated the movement of spherical microlenses with sizes ranging from 0.87 micrometers to 40 micrometers in directions parallel to the electrode surface. Under a bias of 3 volts, the microspheres had an experimentally measured electrophoretic velocities ranging from 13 to 16 micrometers /s. Optical alignment of the spherical or ball microlens can be accomplished using feedback from a photodetector to position the lens for maximum efficiency. Using this device, it is possible to actively align microlenses to optical fibers, VCSELs, LEDs, photodetectors, etc.