Biological properties of "naked" metal nanoparticles

Over the past few decades, inorganic nanoparticles, which exhibit significantly distinct physical, chemical and biological properties from their bulk counterpart's, have elicited much interest. Discoveries in the past decade have demonstrated that the electromagnetic, optical and catalytic properties of noble-metal nanoparticles such as gold, silver and platinum, are strongly influenced by shape and size. This has motivated an upsurge in research on the synthesis routes that allow better control of shape and size for various nano-biotechnological applications. Biomedical applications of metal nanoparticles have been dominated by the use of nanobioconjugates that started in 1971 after the discovery of immunogold labeling by Faulk and Taylor. Currently metal-based nanoconjugates are used in various biomedical applications such as probes for electron microscopy to visualize cellular components, drug delivery (vehicle for delivering drugs, proteins, peptides, plasmids, DNAs, etc), detection, diagnosis and therapy (targeted and non-targeted). However biological properties of bare-metal (naked) nanoparticles have remained largely unexplored. Therefore, in this review we discuss the novel biological properties and applications of three most widely used metal nanoparticles, namely, the nanoparticles of gold, silver and platinum. We describe the novel properties and use of these nanoparticles in angiogenesis and cancer related disorders.