In one form, one or more micropumps and optical micro-detectors are on a substrate, ideally many per square centimeter, each detecting fluid moved by its pump. A second form has many waveguides and, intersecting each, a fluid chamber controlling radiation in the guide; the device is best immersed in a fluid that moves in and out of chambers, intercepting radiation to yield position data-transmitted e.g. wirelessly for external reception. The device can be a chip in a live creature (e.g. implanted, or in blood); data go to a wireless receiver. Each guide ideally couples to a radiation source and detector. In a third form a membrane deflects a radiation-interacting fluid in a plenum; liquid moves between the plenum and a tube. The plenum cross-section is many times the tube's; radiation in the tube is monitored. Deflected liquid in the tube controls specimen movement to and from the tube.