But as you said, there are going to be those that have no record and cannot be detected in that capacity so that is why you have to have other layers of security. ↗
Small bodies, about half a micron in diameter, and later referred to under the name of 'mitochondria' were detected under the light microscope as early as 1894. ↗
The postdoc explained to me how to distinguish different sorts of particles on the basis of the amounts of energy they deposited in various sorts of detectors, spark chambers, calorimeters, what have you. ↗