Applications of Nano-materials inside cells

The application of various types of Nano-materials inside cells are on the research path. Nanotechnology refers to the research and technology development at atomic, molecular, and macromolecular scales, which leads to the controlled manipulation and study of structures and devices with length scales in the range of 1—100 nanometers. In the last two decades, the research of nanotechnology has grown explosively with over three hundred thousands publications in the field of nano-science according to Web of Science. Among these spectacular developments, a new emerging field that combines nanotechnology and biotechnology — nano biotechnology — is receiving increased attentions.

Nano-scale structures and materials (e.g., nano-particles, Nano-wires, nano-fibers, and nano-tubes) have been explored in many biological applications (e.g., bio-sensing, biological separation, molecular imaging, and/or anticancer therapy) because their novel properties and functions differ drastically from their bulk counterparts. Particularly, their high volume/surface ratio, surface tailor ability, improved solubility, and multifunctional open many new possibilities for biomedicine. Moreover, the intrinsic optical, magnetic, and biological properties of nano-materials offer remarkable opportunities to study and regulate complex biological processes for biomedical applications in an unprecedented manner. Since life itself, fundamentally, is a collective of processes at nano-scale within cells, it is unavoidable and necessary to understand the impacts of the presence of nano-materials inside the cells when one explores the advantages and promises of nano-materials for biomedical applications.

Obviously, the successful applications of the nano-materials in biology and medicine sometimes require them to enter cells. The entry of the nano-materials into the cell has to cross a major barrier, that is, the cell membrane that consists of a nanometer-thin lipid bilayer with embedded or peripherally attached proteins. Although it is not a trivial matter, nano-materials can enter cells via several known processes, including (i) non-specific uptake by endocytosis, where the nano-materials often end up in endocytic compartments; (ii) direct microinjection of nano-liter of dispersion of nano-materials, which is a tedious procedure and only applicable to a limited number of cells; (iii) electroporation, which uses charges to physically ‘‘push’’ nano-materials across the membrane;
and (iv) mediated/targeted uptake based on the surface functionalization of nano-materials by using known biological interactions or promoters. Among these processes, the last one holds the great promises and offers convenient flexibility because nano-materials themselves normally need a compatible surface to interact with the cells before realizing their own functionalities. Usually, the nano-materials should be compatible with biological systems, in addition to the required good water solubility. Although there are several developed strategies to coat the nano-materials for conferring good water solubility and desired functions, an ideal surface coating should satisfy the following basic requirements: (i) preventing the nano-materials from unwanted aggregation during the long-term storage; (ii) maintaining good water solubility; (iii) retaining the functionalities of the nano-materials; and (iv) ensuring the biocompatibility before the nano-materials interact with their targeted subjects.