Demonstration of a Hyperlens-integrated Microscope and Super-resolution Imaging

Summary

The use of a hyperlens has been regarded as a novel super-resolution imaging technique due to its advantages in real-time imaging and its simple implementation with conventional optics. Here, we present a protocol describing the fabrication and imaging applications of a spherical hyperlens.

Abstract

The use of super-resolution imaging to overcome the diffraction limit of conventional microscopy has attracted the interest of researchers in biology and nanotechnology. Although near-field scanning microscopy and superlenses have improved the resolution in the near-field region, far-field imaging in real-time remains a significant challenge. Recently, the hyperlens, which magnifies and converts evanescent waves into propagating waves, has emerged as a novel approach to far-field imaging. Here, we report the fabrication of a spherical hyperlens composed of alternating silver (Ag) and titanium oxide (TiO₂) thin layers. Unlike a conventional cylindrical hyperlens, the spherical hyperlens allows for two-dimensional magnification. Thus, incorporation into conventional microscopy is straightforward. A new optical system integrated with the hyperlens is proposed, allowing for a sub-wavelength image to be obtained in the far-field region in real time. In this study, the fabrication and imaging setup methods are explained in detail. This work also describes the accessibility and possibility of the hyperlens, as well as practical applications of real-time imaging in living cells, which can lead to a revolution in biology and nanotechnology.

Introduction

A desire to observe biomolecules in living cells led to the invention of microscopy, and the advent of microscopy propagated the revolution of various fields, such as biology, pathology, and material science, over last few centuries. However, further advancement of research has been restricted by diffraction, which limits the resolution of conventional microscopes to about half of the wavelength¹. Therefore, super-resolution imaging to overcome the diffraction limit has been an interesting research area in recent decades.

As the diffraction limit is attributed to the loss of the evanescent waves that contain sub-wave....

Protocol

1. Substrate Preparation

1. Obtain highly refined quartz wafer. For the fabrication reported here, use a wafer with a 500 µm thickness.
2. Spin-coat the quartz wafer with a positive photoresist at 2,000 rpm and bake for 60 s at 90 °C.
   NOTE: The positive photoresist layer is coated to prevent damage during the subsequent cutting step.
3. Use a dicing machine to cut the wafer with photoresist into small pieces 20 x 20 mm² in size.
4. Blow using a compressed nitrogen gun to remove particulates resulting from the cutting step.
5. Place it in an ultrasonic bath in de-ionized (DI) water for 5 min at 45 °C....

Results

The ability of the hyperlens device to resolve sub-diffraction features relies on its uniformity and on a high-quality fabrication. Here, a hyperlens is composed of a multilayer of Ag and TiO₂ deposited alternately. Figure 2a shows the SEM image of a well-made hyperlens¹⁷. The cross-sectional image shows that the multilayer of Ag and Ti₃O₅ thin film is deposited with uniform thickness on the hemispheric.......

Discussion

The fabrication of a hyperlens includes three major steps: defining hemispherical geometry into the quartz substrate through a wet-etching process, stacking the metal and dielectric multilayer using an electron beam evaporation system, and inscribing the object on the Cr layer. The most important step is the second, since it can significantly affect quality of the hyperlens. In the thin-film deposition process, there are two conditions that require special care for a clear super-resolved image. Stacking the multilayer co.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Focused Ion Beam milling machine	FEI	Helios Nanolab G3 CX
E-beam evaporation system	Korea Vacuum Tech	KVE-E4000
Scanning electron microscopy	Hitachi	SU6600
Inverted microscopy	Zeiss	Axiovert 200
Light source	EXCELITAS Technologies	X-Cite 110 LED
Band pass filter	Chroma	ET405/30M
Objective lens	Zeiss	Plan-Apochromat	NA=1.3, 100X
CCD camera	Andor	Zyla 4.2
Quartz wafer	CORNING	Fused Silica Corning 7980
Buffered oxide etchant	J.T Baker TM	J.T.Baker 5175
Photoresist	AZ electronic materials	GXR-601 PR
Chromium etchant	SIGMA-ALDRICH	651826
Aceton	J.T Baker TM	UN1090
Isopropyl alcohol	J.T Baker TM	UN1219
FEM simulation tool	COMSOL 5.1 Multiphysics