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Bionanoparticles are naturally produced entities that are of nanometer dimension. For aeons, nature has been an avid and extremely sophisticated exponent of nanoscience. Viruses and other protein assemblies such as the iron storage protein ferritin are examples of naturally occurring nanoparticles. The branch of bionanotechnology in which naturally occurring nanoparticles are modified and manipulated for various applications is a rich and newly emerging field of research. The current research in this area can be broadly classified as host–guest chemistry (including biomineralization) and the bioconjugate chemistry of bionanoparticles. Because bionanoparticles have marvelous and complex structures which are important in understanding their chemical applications, a separate section is devoted in this review for each nanoparticle.
In the first portion of the review, the host–guest chemistry based on bionanoparticles is discussed. Three systems—ferritin, cowpea chlorotic mottle virus (CCMV), and tobacco mosaic virus (TMV)—have recently been used to package hard and conducting inorganic materials. The hybrid conducting quantum nanodots can be selectively patterned on two-dimensional substrates by engineering recognition elements on the biomaterial component to recognize specific sites on the two-dimensional substrate. This is one of the most promising approaches for developing nanoelectronic devices. Some recent work using filamentous bacteriophage M13 to bind and align nanocrystals in an ordered array is described in the following section. In the later portion of the review, the bioconjugation of bionanoparticles, especially of the cowpea mosaic virus (CPMV) system, is covered. These have potential applications in both the areas of materials science and biomedical research. Several decades ago, Paul Ehrlich pioneered the “magic bullet concept,” where he proposed that a drug could be targeted with the help of ligands having defined affinity for specific cells. His predictions have been practically realized recently by using ligand-decorated bionanoparticles, which can selectively target the receptors present on specific cell types, to package and deliver therapeutic genes/drugs to target cells. The last section of this review covers the recent development of using bionanoparticles, especially adenoviruses, for gene delivery.
The practical examples discussed in this review serve as a tribute to the accuracy of many of Richard Feynman's predictions in his classic talk titled “There is plenty of room at the bottom” on December 29, 1959, at the annual meeting of the American Physical Society at Caltech.