Biofunctionalized Nanoparticles and Their Uses
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Nanoparticles and Their Uses
Melanie M. Tomczak, Joseph M. Slocik, Morley O. Stone, and Rajesh R. Naik Abstract Nanotechnology is revolutionizing the way that sensing, electronic, optical, and medical devices are designed because the properties of nanostructures are distinct from their bulk-material counterparts. The incorporation of nanomaterials into devices and sensors to exploit their unique properties has been a challenge because they must be functionalized in a manner that does not destroy their properties. Biological macromolecules can non-covalently or covalently bind to nanomaterials, resulting in the formation of biofunctionalized nanoparticles. These biofunctionalized nanoparticles are exemplified by the peptide-mediated suspension of carbon nanotubes in solution and the templating of bimetallic nanoparticles using multifunctional peptides.
Identification of Biomacromolecules with Affinity for Inorganics
Introduction The properties of nanomaterials are substantially different from those of bulk materials. Engineering of nanomaterials that exploits their intrinsic properties could lead to devices with unique attributes and superior performance (e.g., sensors that can monitor parts per billion or trillion). To achieve superior performance, biological macromolecules (or biomacromolecules) including proteins, peptides, and nucleic acids can be used to functionalize nanomaterials (Figure 1). Biomacromolecules that have a strong affinity for organic or inorganic targets of interest can be selected using combinatorial techniques such as phage display and then used to coat and stabilize the nanoparticles. Proteins and peptides have higherordered structures that can change when they interact with inorganics. For example, the peptide poly(L-lysine) changes from a random coil into an α-helical secondary structure during the formation of silica.1 Coiled-coil proteins can be used to coat carbon nanotubes (CNTs) to form a stable suspension of CNTs.2 In this case, not only is there a hydrophobic interaction between the CNTs and one side of the coiled-coils, but the coiled-coils interact with each other through electrostatic forces on the opposite sides of the coils. This results in what is thought to be a uni-
aqueous solutions in order to incorporate them into devices, circuits, and sensors. Examples include the use of sodium dodecyl sulfate (SDS) to solubilize CNTs,12,13 citrate to stabilize Au nanoparticles,14,15 and Brij surfactant to coat and facilitate selfassembly of silica nanoparticles.16,17 These surfactants function well to suspend the nanomaterials in solution, but they do not add any further functionality to the system. That is, the nanomaterials are simply suspended with no further affinity for a device platform or for a biological material. Through the use of biological macromolecules, a similar suspension can be achieved. However, biology can impart additional functionalities to the nanomaterial surface through the amino acid side group chemistries of peptides or through the amino or carboxy termini
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