Protein nanoarchitectonics at liquid-related interfaces: physicochemical communications with biological processes

Building functional material structures that resemble living systems from atoms and molecules is a highly challenging process. However, a sophisticated yet expeditious approach can be formulated by utilizing biological materials characterized by meticulously regulated nanostructures that function as fundamental units. Proteins are regarded as the most promising candidates. The nanoarchitectonics of proteins in interfacial environments involving liquids such as water is a highly attractive and feasible approach. In this feature review article, we introduce systems that can be regarded as protein nanoarchitectonics at each of the following interface types: gas-liquid, solid-liquid and liquid-liquid (oil-water and water-water). The air-water interface is an ideal medium for organising water-soluble proteins into ultrathin films and also serves as a simple model system. Research into protein nanoarchitectonics at solid-liquid interfaces appears to be evolving to a higher level, with a focus on solving problems and revealing new functions of proteins. The oil-water interface also presents opportunities for the organization of biological materials, and various fundamental characterization studies of its interfaces have been conducted. The water-water interface is considered the optimal environment in which to apply knowledge gained from model systems such as the air-liquid and solid-liquid interfaces to more realistic biological systems. Furthermore, physicochemical communication between interfaces has been shown to regulate complex processes, including cell differentiation and coupling biochemical reactions with device functions. Pursuing such methodologies may facilitate the creation of functional systems that exhibit characteristics analogous to those of living organisms.