Creating a so-called "lab on a chip"—with microfluidic channels and integrated photonics that sort cells in a fluid stream in real time using fluorescence as a criterion—is the goal of numerous research projects in biophotonics. Now, scientists at the National University of Singapore have created a noninvasive microfluidic particle-switching chip with integrated optical microstructures that reaches a switching efficiency of close to 100%. The big advantage of the chip is that it achieves the switching without the need for a bulky and costly external microscope.
Fabricated in polydimethylsiloxane using soft lithography, the device was tested using 10 μm diameter polystyrene spheres for particles. The 532 nm laser beam that sorts the spheres is coupled to the chip via an optical fiber and passes through an integrated concave cylindrical microlens; adjusting the lateral position of the beam with an alignment stage allows varying of the beam's angle anywhere between -20° and +20° for sorting in five zones within the microfluidic channel. The beam power was about 100 mW at the fiber tip, and the main channel was 100 μm wide and 35 μm high. Including fibers that measure fluorescence would allow sorting of particles based on their emission properties.
Contact Andrew A. Bettiol at [email protected].