Bioinspired optical antennas: gold plant viruses

Abstract

The ability to capture the chemical signatures of biomolecules (i.e., electron-transfer dynamics) in living cells will provide an entirely new perspective on biology and medicine. This can be accomplished using nanoscale optical antennas that can collect, resonate and focus light from outside the cell and emit molecular spectra. Here, we describe biologically inspired nanoscale optical antennas that utilize the unique topologies of plant viruses (and thus, are called gold plant viruses) for molecular fingerprint detection. Our electromagnetic calculations for these gold viruses indicate that capsid morphologies permit high amplification of optical scattering energy compared to a smooth nanosphere. From experimental measurements of various gold viruses based on four different plant viruses, we observe highly enhanced optical cross-sections and the modulation of the resonance wavelength depending on the viral morphology. Additionally, in label-free molecular imaging, we successfully obtain higher sensitivity (by a factor of up to 106) than can be achieved using similar-sized nanospheres. By virtue of the inherent functionalities of capsids and the plasmonic characteristics of the gold layer, a gold virus-based antenna will enable cellular targeting, imaging and drug delivery. In an experimental and theoretical study, scientists in the United States illustrate the potential of gold nanoscale optical antennas based on viruses. Optical nanoantennas could be used as biomolecular sensors for exploring the interiors of cells. Gold nanospheres are promising for this purpose, but their smoothness restricts their sensitivity. Now, researchers at the University of California, Berkeley, CA, USA, perform electromagnetic calculations that show that gold nanoparticles having shapes based on the protective protein shells of plant viruses exhibit greatly enhanced scattering compared with smooth nanospheres. In experiments, they coated four different plant viruses with gold and observed increased optical cross-sections as well as a dependence of the resonance wavelength on the viral morphology. Furthermore, the team obtained up to a million-fold enhancement in label-free molecular imaging using the virus-shaped nanoparticles compared with their nanospherical counterparts.