Fig. 1.

(a) A micropipette applies a small volume of fluid to the focusing and sample inlets. These inlets possess a higher internal pressure than the large reservoir drop. Due to this pressure gradient, fluid moves downstream towards the reservoir until the pressures equilibrate. Particles suspended in the sample fluid traverse the pore as they move downstream. The electrical resistance of the device is briefly changed while a particle is in the pore, yielding a detectable voltage pulse. (b) Focusing channels are used to align the particles before they traverse the pore, resulting in a more consistent signal. To minimize leaking, electrodes were fabricated lengthwise down the channel, stopping a short distance (100μm) on either side of the pore.