Electrostatic assembly of nanoparticles

There is much excitement in the study of nanoscale matter with respect to their fundamental properties, organization to form superstructures and applications. The unusual physicochemical and optoelectronic properties of nanoparticles are primarily due to confinement of electrons within particles of dimensions smaller than the bulk electron delocalization length, this process being termed quantum confinement.1–3 The exotic properties of nanoparticles have been considered in applications such as optoelectronics, 4 catalysis, 5 reprography, 6 single-electron transistors (SETs) and light emitters, 7 non-linear optical devices8 and photoelectrochemical applications.9 Magnetic nanoparticles are being viewed with interest from a fundamental point of view (superparamagnetism in the nanoparticles)10 as well as in applications such as magnetic memory storage devices, 11 magnetic resonance image enhancement12 and magnetic refrigeration.13 The ability to tune the optical absorption/emission properties of semiconductor nanoparticles (the so-called “quantum dots”) by simple variation in nanoparticle size is particularly attractive in the facile band-gap engineering of materials14 and the growth of quantum dot lasers.15 More recently, nanoscale matter has been looked at with interest for potential application in nanocomputers, synthesis of advanced materials, energy storage devices, electronic and optical displays, chemical and biosensors as well as biomedical devices.16 It is expected that some of the more immediate applications of nanoparticles will be in medical diagnosis and therapeutics. Exciting examples include detection of genetic disorders using gold nanoparticles, 17,18 color-coded fluorescent labeling of cells using semiconductor quantum dots19,20 and cell transfection for gene therapy and drug delivery.21