The lack of specifiability of our modules was a key challenge to commercialization. Specification will require detailed basic investigations of the properties and chemistry of nanoparticle materials in biological systems. In addition, we will have to establish analytical tools and quantitative descriptors to detail the distribution of properties present in a population of nanoparticles. This is categorically different from specification for organic molecules and proteins, in which properties can be effectively described by an average. In nanomaterials, performance properties may be dominated by a relatively small population of particles, so averaging cannot always be used.