"Subcellular level" refers to a very small scale within a cell, like zooming in to see the tiny structures and processes that happen inside it. Full definition
To see what mensacarcin was doing to melanoma on a subcellular level, Loesgen and her team synthesized a fluorescent mensacarcin probe. (sciencedaily.com)
Paintings gave me the opportunity to hint at rapid movement using brushstrokes, while choice of colour remained entirely subjective in the absence of colour at the subcellular level. (sciencemag.org)
Biology at the subcellular level can be likened to a dance: Proteins, lipids, sugars and other molecules follow specific steps to sustain the energy needs, respiration and reproduction of life. (scientificamerican.com)