Organic Hyperbolic Material Assisted Illumination Nanoscopy

Abstract

Resolution capability of the linear structured illumination microscopy (SIM) plays a key role in its applications in physics, medicine, biology, and life science. Many advanced methodologies have been developed to extend the resolution of structured illumination by using subdiffraction‐limited optical excitation patterns. However, obtaining SIM images with a resolution beyond 40 nm at visible frequency remains as an insurmountable obstacle due to the intrinsic limitation of spatial frequency bandwidth of the involved materials and the complexity of the illumination system. Here, a low‐loss natural organic hyperbolic material (OHM) that can support record high spatial‐frequency modes beyond 50 k 0 , i.e., effective refractive index larger than 50, at visible frequencies is reported. OHM‐based speckle structured illumination microscopy demonstrates imaging resolution at 30 nm scales with enhanced fluorophore photostability, biocompatibility, easy to use and low cost. This study will open up a new route in super‐resolution microscopy by utilizing OHM films for various applications including bioimaging and sensing.

Ultrathin Layered Hyperbolic Metamaterial-Assisted Illumination Nanoscopy

“…According to the theory of super-resolution fluorescence imaging with structured illumination, the resolution enhancement is 1 + k cutoff / k 0 at the emission (detection) wavelength; therefore, the k cutoff of 12 k 0 at the excitation wavelength results in a resolution enhancement around 13 at the emission wavelength. It is worth noting that such a great improvement of the resolution can only be achieved within the optical near fields where the electric field intensity decreases exponentially with distance from the HMM substrate; as a result, the ULH-HMM demonstrated here is a powerful near-field imaging technique with a depth limitation, as discussed in our previous studies. , …”

“…These HMM multilayers are treated as a uniaxial layer. Note that the effective medium approximation (EMA) is widely used in the theoretical model to obtain an effective permittivity of alternating multilayers from permittivities of the respective bulk metals and dielectrics of a composite HMM; however, it is no longer accurate for the ultrathin metal layered HMM used in this work due to the nonlocal or quantum size effect in the ultrathin metals. ,, The permittivity of the ultrathin layered HMMs was obtained by performing ellipsometry measurement of the entire multilayers, instead of using EMA, which requires the permittivity of each layer. By applying the transfer matrix method with the SE measurement data, a good agreement between the measured reflection R , transmission T , and absorption A = 1– R – T spectra and the calculated spectra is obtained (Figure c).…”

“…In this context, metamaterial-assisted illumination nanoscopy (MAIN) − has been proposed to address the issue. With the MAIN, super-resolution imaging with a 7-fold resolution improvement has been demonstrated , based on the well-developed linear structured illumination strategy by using hyperbolic metamaterials (HMMs) for providing a structured illumination beyond the diffraction limit.…”

“…In this context, metamaterial-assisted illumination nanoscopy (MAIN) − has been proposed to address the issue. With the MAIN, super-resolution imaging with a 7-fold resolution improvement has been demonstrated , based on the well-developed linear structured illumination strategy by using hyperbolic metamaterials (HMMs) for providing a structured illumination beyond the diffraction limit. To this end, a planar HMM substrate is generally made by alternating dielectric and metal thin layers with the resultant principal components of permittivity tensor having opposite signs; as a result, surface plasmon polaritons are activated at these dielectric–metal interfaces and evanescently coupled such that structured illumination patterns carrying deep subwavelength information are creased at the top surface of the planar HMM substrate and then used for super-resolution imaging. , The imaging resolution of such a composite HMM-based MAIN is limited by the HMM’s optical loss and metal layer thickness. , While ultrathin continuous metal films have recently been produced, such as copper seed Au and Ag thin-films and metallic quantum-well TiN thin-film, their optical loss is severe at the visible frequency so that they cannot be used for MAIN.…”

“…8,14 The imaging resolution of such a composite HMMbased MAIN is limited by the HMM's optical loss and metal layer thickness. 9,15 While ultrathin continuous metal films have recently been produced, such as copper seed Au 16 and Ag 17 thin-films and metallic quantum-well TiN thin-film, 18 their optical loss is severe at the visible frequency so that they cannot be used for MAIN. Therefore, the lack of a low-loss HMM system with ultrathin metal layers has been a major roadblock challenging the attainability of further resolution improvement of the MAIN.…”