  Throughout the evolution of biological species on Earth, cells and organs
have developed many complex structures and processes to ensure their
interactions with individual chemical molecules (small and macromolecular) and
nanoscale objects result in no harm. These evolutionary mechanisms complicate
our attempts to use modern nanoscale science to develop effective and efficient
treatments for disease or other biological dysfunctions. Here we describe the
complexity of biology on the nanoscale and the implications for the success of
recently-discovered nanoscience, which has resulted in an almost infinite
number of potential nanomaterials of unknown efficacy. We discuss how tools to
categorize nanomaterials on the basis of structure, properties and interactions
can provide insights on promising directions.
