Abstract
We theoretically investigate light scattering from a bi-sphere system consisting of a gold nanosphere and a lossless dielectric microsphere illuminated at a resonant optical wavelength of the microsphere. Using generalized multisphere Mie theory, we find that a gold nanosphere 100 times smaller than the dielectric microsphere can be detected with a subdiffraction resolution as fine as one-third wavelength in the background medium when the microsphere is illuminated at a Mie resonance. Otherwise, off-resonance, the spatial resolution reverts to that of the nonresonant nanojet, approximately one-half wavelength in the background medium. An important potential biophotonics application is the detection of antibody-conjugated gold nanoparticles attached to the membranes of living cells in an aqueous environment.
Highlights
Scattering by a bi-sphere system, which has potential applications to biomedical, atmospheric and ocean optics, has been investigated extensively over the last forty years, as for example [1,2,3,4,5,6,7,8]
Using generalized multisphere Mie theory, we find that a gold nanosphere 100 times smaller than the dielectric microsphere can be detected with a subdiffraction resolution as fine as one-third wavelength in the background medium when the microsphere is illuminated at a Mie resonance
We show via generalized multisphere Mie theory (GMM) solutions that, in this scenario, the location of the metal nanoparticle can be determined with subdiffraction λbackground/2m resolution, where m is the refractive index contrast of the dielectric microsphere relative to its background medium
Summary
Scattering by a bi-sphere system, which has potential applications to biomedical, atmospheric and ocean optics, has been investigated extensively over the last forty years, as for example [1,2,3,4,5,6,7,8]. Since the thickness of cellular membranes is approximately 10nm for most cells, i.e., essentially negligible, a reasonably good model is a bi-sphere system in an infinite water background medium, whether the metal nanoparticle is positioned on the exterior or interior surface of the membrane Such a system can be analyzed with generalized multisphere Mie theory (GMM) [15]. We have previously reported that FDTD simulations of plane-wave light scattering from a lossless dielectric spheroid reveal the presence of subdiffraction optical nanospots near the surface of the spheroid which are formed via near-field interference [22]. These nanospots extend a short distance outward from the spheroid’s surface into the background medium. A spheroid generates a large number of approximately equal-amplitude nanospots distributed about its surface [22], and the location of the nanoparticle cannot be unambiguously determined
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