Nanomaterials, such as metal or semiconductor nanoparticles and nanorods, exhibit similar dimensions to those of biomolecules, such as proteins (enzymes, antigens, antibodies) or DNA. The integration of nanoparticles, which exhibit unique electronic, photonic, and catalytic properties, with biomaterials, which display unique recognition, catalytic, and inhibition properties, yields novel hybrid nanobiomaterials of synergetic properties and functions. This review describes recent advances in the synthesis of biomolecule-nanoparticle/nanorod hybrid systems and the application of such assemblies in the generation of 2D and 3D ordered structures in solutions and on surfaces. Particular emphasis is directed to the use of biomolecule-nanoparticle (metallic or semiconductive) assemblies for bioanalytical applications and for the fabrication of bioelectronic devices.

Integrated Nanoparticle–Biomolecule Hybrid Systems: Synthesis, Properties, and Applications

An overview of the wide range of nanoreactors that have been constructed from synthetic and biological building blocks using both covalent and noncovalent approaches is given. Focus is on self-assembled systems, varying in size from a few nanometers to tens of micrometers. The review is divided into several sections that cover the development of tailor-made nanoreactors, starting from small organic molecular containers expanding to large compartment-containing assemblies. First, the construction of capsules from low molecular weight compounds by means of covalent synthesis and self-assembly by highly directive and pre-designed interactions is discussed. Second, nanocapsules based on micellar and vesicular assemblies that are built up frow low molecular weight molecules are described. Finally, the construction of nanoreactors from macromolecular building blocks, as well as recent developments in the use of viruses as nanocontainers and reactors are outlined.

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Self-Assembled Nanoreactors

Discrete catalytic nanoparticles with diameters in the range of 1−2 nm and 3−5 nm respectively are obtained by placing controllable numbers of metal atoms into the cores of apoferritin, and used for growth of single-walled carbon nanotube (SWNTs) on substrates by chemical vapor deposition (CVD). Atomic force microscopy (AFM), transmission electron microscopy (TEM), and micro-Raman spectroscopy are used to characterize isolated nanotubes grown from the discrete nanoparticles. The characterizations, carried out at single-tube and single-particle level, obtain clear evidence that the diameters of nanotubes are determined by the diameters of catalytic nanoparticles. With nanoparticles placed on ultrathin alumina membranes, isolated SWNTs are grown and directly examined by transmission electron microscopy. For the first time, both ends of an as-grown single-walled nanotube are imaged by TEM, leading to a microscopic picture of nanotube growth mechanism. It is shown that controlling the structures of catalytic ...

Growth of Single-Walled Carbon Nanotubes from Discrete Catalytic Nanoparticles of Various Sizes

Materials scientists increasingly draw inspiration from the study of how biological systems fabricate materials under mild synthetic conditions by using self-assembled macromolecular templates. Containerlike protein architectures such as viral capsids and ferritin are examples of such biological templates. These protein cages have three distinct interfaces that can be synthetically exploited: the interior, the exterior, and the interface between subunits. The subunits that comprise the building blocks of these structures can be modified both chemically and genetically in order to impart designed functionality to different surfaces of the cage. Therefore, the cages possess a great deal of synthetic flexibility, which allows for the introduction of multifunctionality in a single cage. In addition, hierarchical assembly of the functionalized cages paves the way for development of a new class of materials with a wide range of applications from electronics to biomedicine.

Biological Containers: Protein Cages as Multifunctional Nanoplatforms

Protein-based nanomedicine platforms for drug delivery comprise naturally self-assembled protein subunits of the same protein or a combination of proteins making up a complete system. They are ideal for drug-delivery platforms due to their biocompatibility and biodegradability coupled with low toxicity. A variety of proteins have been used and characterized for drug-delivery systems, including the ferritin/apoferritin protein cage, plant-derived viral capsids, the small Heat shock protein (sHsp) cage, albumin, soy and whey protein, collagen, and gelatin. There are many different types and shapes that have been prepared to deliver drug molecules using protein-based platforms, including various protein cages, microspheres, nanoparticles, hydrogels, films, minirods, and minipellets. The protein cage is the most newly developed biomaterial for drug delivery and therapeutic applications. The uniform size, multifunctionality, and biodegradability push it to the frontier of drug delivery. In this Review, the recent strategic development of drug delivery is discussed with emphasis on polymer-based, especially protein-based, nanomedicine platforms for drug delivery. The advantages and disadvantages are also discussed for each type of protein-based drug-delivery system.

Protein‐Based Nanomedicine Platforms for Drug Delivery

The empty protein cage of ferritin has been used to synthesize and entrap nanoscale particles of a green cobalt oxide via oxidative hydrolysis of Co(II) by H2O2. The resulting composite material retains the properties of the protein while incorporating the characteristics of the encapsulated mineral. The visible absorption spectrum has a broad band at 350 nm and the IR spectrum shows a band at 587 cm-1 characteristic of the cobalt oxyhydroxide Co(O)OH.

Victoria T. Stark

Papers

Nanophase cobalt oxyhydroxide mineral synthesized within the protein cage of ferritin.