Super-Resolution Real Imaging in Microsphere-Assisted Microscopy.

Hok Sum Sam Lai,Wen Jung Li,Feifei Wang,Yi Li,Boliang Jia,Lianqing Liu,Thomas Abraham

doi:10.1371/journal.pone.0165194

Abstract

Microsphere-assisted microscopy has received a lot of attention recently due to its simplicity and its capability to surpass the diffraction limit. However, to date, sub-diffraction-limit features have only been observed in virtual images formed through the microspheres. We show that it is possible to form real, super-resolution images using high-refractive index microspheres. Also, we report on how changes to a microsphere’s refractive index and size affect image formation and planes. The relationship between the focus position and the additional magnification factor is also investigated using experimental and theoretical methods. We demonstrate that such a real imaging mode, combined with the use of larger microspheres, can enlarge sub-diffraction-limit features up to 10 times that of wide-field microscopy’s magnification with a field-of-view diameter of up to 9 μm.

Highlights

It has been presumed in the past that even the best optical microscopes in the world would be subjected to a limit in resolution due to the diffractive nature of light
According to the literature [8,15,16,17], a Blu-ray disc has a gap between its tracks that ranges from 100 to 120 nm [8,16,17]. This separation is below the diffraction limit, making it unobservable using normal microscopes and suitable for the super-resolution tests performed in this study
While being comparable to virtual imaging modes in terms of resolution, this new mode lowers the limit on the working distance of an objective lens and provides flexibility for additions that may have been previously hindered by this working distance

Summary

Introduction

It has been presumed in the past that even the best optical microscopes in the world would be subjected to a limit in resolution due to the diffractive nature of light. Nobel-Prize-winning fluorescence-based techniques like stimulated emission depletion microscopy (STED) [2] and photo-activated localized microscopy (PALM) [3] are good examples of such methods that can attain live-cell imaging with resolution beyond the diffraction limit. Spatially modulated illumination (SMI) can increase the resolution of fluorescence microscopes by constructing a standing wave and reducing the 3D point-spread function of illumination [4]. Because the intrusive nature of fluorescence microscopy is generally deleterious, developing super-resolution techniques that do not use fluorescence is important. A current trend towards super-resolution images involves developing metamaterials or designing unique lenses that can break the diffraction barrier [5].

Methods

Results

Conclusion