Charge transport in nanoparticle assemblies

NP assemblies exhibit bulk properties that are controllable from the bottom up. NPs with a variety of optical, chemical, and electronic functionalities can be prepared by chemical synthetic methods. Molecules - either as capping ligands or cross - linkers - can confer additional functionalities (such as chemical or biorecognition), control inter-NP separations, and influence the rate of charge transfer between NPs. Properties of assemblies can be further controlled via assembly procedure. Assemblies can be organized into ID, 2D, and 3D arrays of various length scales with controllable degrees of order/disorder. They can exhibit unusual architectural features such as large porosity and surface area at can be desirable depending on application. The controlled functionality afforded by NP assemblies combined with the ability of NPs to serve as charge relays has enabled a host of new opportunities, both fundamental and applied. Assemblies have enabled systematic studies of phenomena ranging from single-electron charging to metal - insulator transitions. In terms of applications, there has been particular interest in exploiting functionality of NP assemblies for electronic chemical and biological sensing. A number of proof-of-principle devices, such as vapor-, electrochemical-, chemical-, and biosensors, have already been demonstrated. Further studies are required to explore more fully the large range of material properties and applications enabled by the large choice of assembly components (including mixtures of NPs) and architectures. In view of the desirable features of electronics (such as low cost, scalability, integrability, etc.), this area will likely continue to represent a significant target of opportunity for future studies. © 2008 American Chemical Society.