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We present a device that allows a user to trap a single nanoscale object in solution at ambient temperature, and then to position the trapped object with nanoscale resolution. This anti-Brownian electrophoretic trap (ABEL trap) works by monitoring the Brownian motion of the particle (via fluorescence microscopy), and then applying a feedback voltage to the solution so that the electrophoretic drift exactly cancels the Brownian motion. The ABEL trap works on any object that can be imaged optically and that acquires a charge in water. The ABEL trap is noninvasive, is gentle enough to handle biological molecules, and can trap objects far smaller than can be trapped with laser tweezers. Our proof-of-principle device can trap fluorescent polystyrene nanospheres with diameters down to 20nm.
Cohen et al. (2005) studied this question.