Ferritin array

There are some unique examples of organic-inorganic hybrids in natural systems. Some kinds of protein possess inorganic components at their interior. Because such bio-originated hybrid structures have discrete size and composition, they can be used for preparation of fine mesoscopic structures. For example, ferritin, which is composed of 24 self-assembled peptide subunits and capable of including iron oxide, is a good candidate to fulfill this demand. Yamashita demonstrated use of a ferritin array for preparation of a mesoscopic nanodot array (Fig. 2.11 ).47 A Langmuir... 

Traditional methods for fabricating nano-scaled arrays are usually based on lithographic techniques. Alternative new approaches rely on the use of self-organizing templates. Due to their intrinsic ability to adopt complex and flexible conformations, proteins have been used to control the size and shape, and also to form ordered two-dimensional arrays of nanopartides. The following examples focus on the use of helical protein templates, such as gelatin and collagen, and protein cages such as ferritin-based molecules. 

To prepare an antibody protein array, a monolayer of protein A, which was compressed at a surface pressure of 11 mN m l was transferred to a compartment containing anti-ferritin antibody in 10 mM pH 7.0 phosphate buffer. The antibody molecules were self assembled onto the protein A layer. The protein A/antibody molecular membrane was transfered to a compartment containing ultrapure water for rinsing, and was then transfered onto the surface of an HOPG plate by the horizontal method. AFM measurements were made in a pH 7.0 of 10 mM phosphate buffer solution. 

The antibody array was soaked in different concentrations of ferritin solutions for 1 h, and was assayed for AFM imaging in solution. Ferritin molecules were recognized and fixed by the antibody array. The ferritin concentration was 10 ng ml l. Individual ferritin molecules on the antibody array were selectivity quantitated by AFM imaging. 

Figure 2.11 Monolayer array of ferritin and conversion into a nanodot array.

Fig. 24 (a-c) TEM images top row) of diffiaent width ferritin ID arrays in polyelectrolyte tubular nanostructures, formed by adjusting the concentration of the polymer solution. The illustrations bottom row) indicate the different widths of the foritin ID arrays and polymer tubular nanostructures. Reprinted with permission from [184]. Copyright (2008) Wiley... 

Kim MS, Shin KM, Kim SI, Spinks GM, Kim SJ (2008) Controlled array of ferritin in tubular nanostructure. Macromol Rapid Commun 29 552-556... 

Other sensor platforms have also been explored, such as surface plasmon resonance, field-effect transistors, other optical/spectrophotometric methods, for example, Raman spectroscopy and chemiluminescence, and electrochemical techniques. Very recently, Cai et al. have demonstrated that arrays of carbon-nanotube tips with an imprinted nonconducting polymer coating can recognize proteins below the picograms per liter level, using electrochemical impedance spectroscopy. Devices for the specific recognition of human ferritin and human papillomavirus-derived E7 protein were described (Figure 34). 

For example, two-dimensional iron-oxide nanoparticle array can be prepared using ordered ferritin molecules as the template. Au and CdSe — ZnS quantum dots can assemble into ordered arrays using a chaperonin protein template, which was modified with thiol groups to bind the nanoparticles via metal-ligand interactions. Au nano-... 

Yamashita demonstrated the use of a biomolecular array for structure transcription (Fig. 17). A Langmuir monolayer of ferritin, which is composed of 24 self-assembled peptide subunits and is capable of including iron oxide. 

FIGURE 17. Preparation of iron particles arrays from a Langmuir monolayer of ferritin. Polymer, lipid, protein, etc. 

Membrane-associated proteins such as bacteriorhodopsins, phycobiliproteins, photosynthetic reaction centers (PRCs), and ferritins are unique in tiliat they can self-assemble into 2D crystals in the presence of membrane fragments or surfactants [36-38,43-51]. However, the aqueous solubility and nonamphiphilic nature of most proteins does not lend them to LB/LS film formation per se, due to their unfavorable partitioning behavior, and their unfolding and denaturation at the air-water interface [36-38,43-45]. However, soluble proteins can be assembled into bidimensional arrays using several approaches ... 

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