Enhancement of resolution in microspherical nanoscopy by coupling of fluorescent objects to plasmonic metasurfaces

Abstract

The resolution of microsphere-based nanoscopy is studied using fluorescently labeled nanospheres and F-actin protein filaments with the emission coupled to the localized surface plasmon resonances in the underlying Au nanodisk arrays. Virtual imaging is performed through high-index microspheres embedded in plastic coverslips placed in contact with the nanoscale objects. For 150 and 200 nm periods of nanoplasmonic arrays, the imaging has a solid immersion lens-limited resolution, whereas for shorter periods of 80 and 100 nm, the resolution was found to increase up to ∼λ/7, where λ is the emission wavelength. The results cannot be interpreted within a framework of a regular localized plasmonic structured illumination microscopy since the array period was significantly shorter than the wavelength and postimaging processing was not used. It is hypothesized that the observed super-resolution is based on coupling of the emission of nanoscale objects to strongly localized near-field maxima in the adjacent plasmonic metasurfaces followed by evanescent coupling to high-index microspheres.

Optoplasmonic-Enhanced Imaging of Monolayer Polystyrene Nanoparticle Arrays by Barium Titanate Glass Microsphere-Assisted Microscopy: Implications for Nanoparticle Characterization

“…For optoplasmonic hybrid structures composed of BTG microspheres and BD substrates, the focused light from the microspheres effectively guides the incident light on plasmonic components (BD substrates). Through plasmonic–photonic interactions, the electric field at the gaps among nanoparticles and the contacting area between nanoparticles and BD substrates is enhanced. − Thus, the optoplasmonic structure serves as an intense near-field excitation source for the nanoparticles nearby. It has been demonstrated that the dielectric nanoparticles can be re-excited by the increased evanescent waves and it causes a new round of scattering to the far field, which provides more information in the far field .…”

“…23,25 By using optoplasmonic structures, Zhang and Lei observed fluorescent nanoparticles with a size of 100 nm, 24 and Brettin et al demonstrated that the resolution in imaging fluorescent objects could reach to ∼ λ/7. 25 For a fluorescent object, the absolute signals obtained in scattering and fluorescence modes under identical illumination and imaging conditions are quite different, and the scattering intensity is weaker than the fluorescence intensity for a small object. 26 While imaging nonfluorescent objects, only scattering mode signals are obtained.…”

“…The focused light or the evanescent field of WGMs will interact with the near fields associated with the surface plasmon polariton (SPP) modes in the metallic micro-/nano-structures. , This photonic–plasmonic interaction produces local electric field enhancements located between microspheres and metallic micro-/nano-structures. Enhanced electric fields can not only increase the fluorescence and intensity of surface-enhanced Raman spectroscopy signal of a sample placed between a metallic micro-/nano-structure and a dielectric microsphere but also improve the resolution of the microsphere in imaging fluorescent objects. , By using optoplasmonic structures, Zhang and Lei observed fluorescent nanoparticles with a size of 100 nm, and Brettin et al demonstrated that the resolution in imaging fluorescent objects could reach to ∼ λ/7 . For a fluorescent object, the absolute signals obtained in scattering and fluorescence modes under identical illumination and imaging conditions are quite different, and the scattering intensity is weaker than the fluorescence intensity for a small object .…”

Far‐Field Superresolution Imaging via Spatial Frequency Modulation

“…These include a possibility of excitation of LPs in nanostructured metals as well as SPPs in semiconductor and dielectric structures. [ 88,160–162 ] It was also shown that substrates play an important role in imaging magnification and resolution. Theoretical research shows the imaging resolution and the magnification factor are both relative to the refractive index of the substrate.…”

Microspherical nanoscopy: is it a reliable technique?

“…However, achieving of λ/6 − λ/8 resolution requires additional objects been involved, for example, plasmonic particles, wires and gratings [9][10][11]. Instead, labeling of small objects with fluorescent molecules can also greatly enhance resolution [12,13]. Some authors even claim resolution of minimal features down to λ/17.…”