Wiktionary
a. Smaller than microscopic; too small to be seen even with a microscope.
Usage examples of "submicroscopic".
All the action took place in the walls separating the tanks, which were not really walls but nearly infinite grids of submicroscopic wheels, ever-rotating and many-spoked.
Conceptually, the universe had been a reasonably comfortable place to live in, in primitive atomic theory which offered the assurance that everything, earth, air, fire or water, steel and oranges, man or star, was ultimately composed of submicroscopic vortices called protons and electrons leavened a little with neutrons and neutrinos which had no charge, and bound together by a disorderly but homely family of mesons.
Using laser technology developed for the alignment of submicroscopic harddisk computer assemblies, Wolfe and his team aligned old brain stem and young spine so precisely that the identical matrixes of their fibers were butted together, bridged by Beatrice's bonding material.
They were twenty million klicks off target, a submicroscopic jump.
He indeed was visited by dreams in which he had shrunk to submicroscopic size and entered a brain, strolling in through some forehead's pore and into the cul-de-sac of a sweat gland.