Prentiss has constructed a simple and functional optical tweezer setup that is integrated with microfluidic devices. It traps particles using light transported by two optical fibers. A microfabricated structure automatically aligns the two fibers so that the light leaving the fibers counterpropagates along the same axis. The image above shows the two optical fibers that form the trap on opposite sides of a microfluidic channel that allows the chemical environment of the particle to be changed while it remains trapped. The bright spot is an optically trapped microsphere. The system can be used on unaltered optical microscope, and is a robust and simple way to couple laser tweezers to microfluidic devices.