It's micro-, nano-, picoliters, and so on. A milliliter is a unit of volume equal to one thousandth (0.001) of a liter. To discuss even smaller volumes, we can use:
microliters (0.000 0001 of a liter),
nanoliters (0.000 000 001 of a liter), or
picoliters (0.000 000 000 001 of a liter).
Smaller than picoliters are femtoliters, attoliters, zeptoliters, and yoctoliters. Read more