Programmable Assembly of Nanoarchitectures Using Genetically Engineered Viruses
by Yu Huang, Chung-Yi Chiang, Soo Kwan Lee, Yan Gao, Evelyn L. Hu, James De Yoreo, and Angela M. Belcher
This article is possibly the most interesting piece of literature that I have read during this semester, therefore I wish to share with others. The paper is connected to soft matters because it focused on discussing the interaction of viruses with nanostructure, which is indeed an emerging field of research. All in all, biological systems possess inherent molecular recognition and self-assembly capabilities and therefore are attractive templates for constructing complex material structures. In the articles, the authors utilized highly engineered M13 bacteriophage as templates to assemble various nanoachitectures including nanoparticle arrays, heteronanoparticle architectures, and nanowires. According to the authors, the genome of M13 phage can be engineered to produce viral particles with distinct peptides, providing a generic template for programmable assembly of complex nanostructures. Phage clones with gold-binding motifs on the capsid and streptavidin-binding motifs at one end are created to assemble Au and CdSe nanocrytals into ordered one-dimensional arrays and more complex geometries.
In (A) of figure 1, the scheme for engineering the type 8-3 phage is shown. The genome of the engineered bacteriophage bears insertions in gVIII and gIII, which leads to motif expressions on pVIII and pIII proteins. Gene insertions and the correspondingly expressed motifs are highlighted in yellow and red in the picture above. This engineered phage can be used to template assembly of a variety of nanoarchitectures. Part (B) and (C) of the picture above are presented to give experimental proofs of expressed peptide motifs on clone #9s1. Picture (B) shown the ELISA plate result of the interactions between the s1 motif and the streptavidin-coated wells. The green color indicates positive interaction. The intensity of the green color represents the amount of the bound phage in the well. Serial dilutions (50%, 2-fold) of each phage clone were carried out in a row of ELISA plate wells. Picture (C) illustrates the mass spectra of wild-type, which is the M13KE bateriophage from New England Biolabs, and #9s1 clones.
Figure 2 shows the gold-binding experiments and corresponding TEM images. Picture (A) shows different clones mixed with Au nanoparticles. Only sample p8#9 shows visible precipitate, highlighted by the arrow. All the other solutions remain clear. Picture (B) shows only Au nanoparticles. Picture (C) shows wild-type phage mixed with Au nanoparticles, stained with 2% uranyl acetate. Picture (D) shows sample p8#17 mixed with Au nanoparticles, stained with 2% uranyl acetate. Picture (E) importantly shows wirelike structures in the mixture of sample p8#9 and Au particles. The authors show that the inset shows Au particles self-assembled into 1D arrays on the virus.
Figure 3 shows the TEM images of various nanoarchitectures templated by clone #9s1. Gold nanoparticles (approximately 5 nm) bind to pVIII proteins along the virus axis and form 1D arrays, while s1 motif on pIII protein simultaneously binds to streptavidin-coated nanoparticles. Arrows highlight the streptavidin-conjugated gold nanoparticles (approximately 15 nm) and CdSe quantum dots bound on pIII proteins. The authors use the insets to show the assembly schemes of observed structures. White represents the virus structure, yellow dots represent gold nanoparticles, the green dot represents a CdSe quantum dot, and red represents the streptavidin coating around gold or CdSe particles.
Figure 4 shows the TEM images of the progressive growth of continuous gold nanowires templated by gold nanoparticle arrays on pVIII proteins. Picture (A) shows before electroless deposition, picture (B) shows 3-min deposition, and picture (C) shows 5-min deposition. Picture (D) shows the TEM image of gold nanowires obtained via direct nucleation of gold from solution. The authors use the inset to show an enlarged view of a nucleated gold wire. Picture (E) shows a three-dimensional plot of an atomic force microscopy (AFM) image of a two-terminal device based on a single viral gold nanowire as described in part (C). Last but not least, picture (F) shows the two-terminal I-V behavior of a nanowire measured at room temperature.
Through these experiments, the authors demonstrated that type 8-3 engineered phage can be used as templates to assemble nanoarchitectures of various geometries and materials. The authors insist that the results obtained suggest a generic assembly approach that can be extended to program the assembly of various material systems with nanometric precision. The authors believe that this work demonstrates the great possiblity of different bottom-up assembly method and opens up new directions and opportunities in nanoscale science and biotechnology.