Supplemental Information for
Bioinspired Optical Antennas: Gold Plant Viruses
Supplementary Discussions
1. Optical resonance of the hemi-shell metallic layer on a smooth nanosphere and a viral
capsid.
As demonstrated in ref (S1) a hemi-shell metallic layers on a smooth nanosphere
(called nanocrescent) shows a single resonance in the range of 400 to 1000 nm, while
our gold-virus particles uphold multiple resonances in the range of wavelength as shown
in Fig. S2. It can be explained by the existence of multiple plasmonic poles on the metal
layer. Moreover, the resonance wavelengths can be varied by capsid morphology as
shown in Figure 3 in the main text. The multiple resonances support the sensitivity of the
gold viruses in molecular fingerprint detection.
2. Optical properties change by the thickness of the gold layer on viruses
The thickness of the gold layer on viruses permits the change of optical properties (Fig.
S3). Although changing metal thickness can be a strategy for a modulation of optical
property, yet, a thick metal deposition may lose sharp tips or generate a continuous metal
layer, which can cause the decrease of local-field enhancement. In experiments, the 10nm gold CPMV did not generate a clear Raman spectrum even with a resonance closed
to the excitation wavelength, 785 nm. Therefore, in order to vary resonance wavelengths
for applications, a proper set of viral capsid and gold thickness is required, which is
another on-going study of ours
References
S1 B. M. Ross, L. P. Lee, Nanotechnology 19, (Jul 9, 2008).
Supplementary Figures
Fig S1. Optical setup for (A) plasmon resonance energy transfer (PRET) and (B) surfaceenhanced Raman scattering (SERS) experiments.
Fig S2. Scattering spectra of gold-virus (A) and gold-bead (B) via dark-field imaging. More
resonance peaks were shown in the gold virus due to its capsid morphology than the smooth
particle.
Fig S3. Optical resonance modulation by gold thickness. The spectra were measured on monodispersed CPMVs conjugated with the gold layer of (A) 2 nm, (B) 5 nm, and (C) 10 nm thickness.
Fig. S4. Schematics for Au-viruses conjugation process. (A) After viral particles were attached on
a glass substrate through a drop casting method, (B) a thin gold layer was deposited by using an
electron-beam evaporator. (C) For mono-dispersed particles, gold-virus particles were chemically
attached on a modified substrate by using thiol-gold bond.
Fig. S5. Electron microscope images of gold virus. (A) SEM image of gold deposited closed
packed CPMVs on a glass slide. (B) SEM image of monodispersed 5-nm gold CPMVs on a glass
slide. (C) TEM image of 5-nm gold CPMVs. All scale bars are 100 nm except one of the close-up
images in (C) is 20 nm.
Fig. S6. Viral morphology and biochemical activity before and after the engineering process.
Schematic structure of original virus (A) and gold virus (D). TEM images were taken before (B)
and after metal layer deposition (E). The scale bars in the TEM images are 10 nm. The infectivity
of wt-CPMV (C) and CPMV after metal deposition (F) was evaluated by a local lesion assay five
days after mechanical inoculation of Cowpea (Vigna unguiculata) cv. Chinese x Iron plants. The
red arrows indicate the local lesions and, which are illustrated at higher resolution in the exploded
panels to the right. Taken together, the original structure as well as inherent infection function can
still be maintained.
Fig. S7. Dark-field scattering from nanoparticles of intact virus, 30-nm gold nanosphere, and gold
virus. (A) CCD images of dark-field scatterings. (B) Intensity profiles along the dot lines marked
on (A).
Fig. S8. Comparison of SERS signal from gold virus, 30 nm-AuNP aggregation and 785 nmresonance Aurod. Each of the lowest concentrations were denoted. While the AuNP aggregation
showed a comparable SERS signal at 1pM, the signal variation among aggregates was too high
to be reliable in sensing applications. The Aurod showed a similar signal intensity as the goldcoated nanosphere shown in Fig. 4d.