Hyperbolic material enhanced scattering nanoscopy for label-free super-resolution imaging

Abstract

Fluorescence super-resolution microscopy has, over the last two decades, been extensively developed to access deep-subwavelength nanoscales optically. Label-free super-resolution technologies however have only achieved a slight improvement compared to the diffraction limit. In this context, we demonstrate a label-free imaging method, i.e., hyperbolic material enhanced scattering (HMES) nanoscopy, which breaks the diffraction limit by tailoring the light-matter interaction between the specimens and a hyperbolic material substrate. By exciting the highly confined evanescent hyperbolic polariton modes with dark-field detection, HMES nanoscopy successfully shows a high-contrast scattering image with a spatial resolution around 80 nm. Considering the wavelength at 532 nm and detection optics with a 0.6 numerical aperture (NA) objective lens, this value represents a 5.5-fold resolution improvement beyond the diffraction limit. HMES provides capabilities for super-resolution imaging where fluorescence is not available or challenging to apply.

Label-free incoherent super-resolution optical microscopy

“…Fluorescence based algorithms have been previously applied to coherently scattering specimens [36,55]. However, the reconstructed images generated must be interpreted with caution with regards to resolution beyond the diffraction-limit as coherence of the scattered light cannot be neglected [13,29].…”

“…This could be attributed to the ease of utilizing/manipulating the photo-kinetics of nano-sized fluorescent molecules to gain information beyond the diffraction-limit. The different approaches developed for label-free super-resolution microscopy, albeit with their respective experimental challenges especially for life sciences applications, includes near-field scanning optical microscopy [31], super-lens [32], micro-sphere assisted super-resolution imaging [33], super-resolution via scattering [33,34], optical super-oscillation techniques [35], hyperbolic materials for super-resolution imaging [36], utilizing the intrinsic autofluorescence of biological specimens in tandem with fluorescence-based superresolution algorithms [37,38] etc.…”

Far-Field Super-Resolution Microscopy Using Evanescent Illumination: A Review

“…In 2012, a blind SIM method has been demonstrated by E. Mudry et al [48], which exploited the statistical properties of speckle patterns and does not require precise knowledge of the illuminating intensity patterns. Thus, the resolution of traditional optical microscopes can be doubled through random speckle illumination, which inspires researchers to develop more speckle-based SR microscopy [49,76,[82][83][84].…”

“…Subsequently, Liu's group further optimized the processing of the HMM and fabricated a single-layer 2.5 nm thick Ag and MgO ultra-thin hyperbolic meta-surface, which further pushed the resolution down to 24 nm [84,86]. In addition, a label-free SR imaging method using plasmonic material, called hyperbolic material enhanced scattering (HMES) nanoscopy, was first demonstrated by Liu et al [83], who introduced a hyperbolic material as the substrate to not only enhance the scattering intensities of small objects but also control the illumination/scattered field distributions at deep subwavelength scales, as shown in Figure 10a-c. Ag nanoparticles in Figure 10e are used to enhance the back scattering illumination.…”

Nondestructive inspection of surface nanostructuring using label-free optical super-resolution imaging

“…Some indirect optical imaging methods has been implemented to characterize periodic surfaces by observing the diffraction pattern caused by the back-scattered light. But artifacts may arise when the periodicity breaks or the initial structure orientation is changed 23 , 24 . Structured illumination have been used as an alternative to increase the modulation transfer function of the microscope and thus the image contrast on non-fluorescent periodic samples.…”