High refractive index immersion liquid for superresolution 3D imaging using sapphire-based aplanatic numerical aperture increasing lens optics

Abstract

Optically transparent immersion liquids with refractive index (n∼1.77) to match the sapphire-based aplanatic numerical aperture increasing lens (aNAIL) are necessary for achieving deep 3D imaging with high spatial resolution. We report that antimony tribromide (SbBr₃) salt dissolved in liquid diiodomethane (CH₂I₂) provides a new high refractive index immersion liquid for optics applications. The refractive index is tunable from n=1.74 (pure) to n=1.873 (saturated), by adjusting either salt concentration or temperature; this allows it to match (or even exceed) the refractive index of sapphire. Importantly, the solution gives excellent light transmittance in the ultraviolet to near-infrared range, an improvement over commercially available immersion liquids. This refractive-index-matched immersion liquid formulation has enabled us to develop a sapphire-based aNAIL objective that has both high numerical aperture (NA=1.17) and long working distance (WD=12 mm). This opens up new possibilities for deep 3D imaging with high spatial resolution.

Projection Printing of Ultrathin Structures with Nanoscale Thickness Control

“…An indexmatched medium is used to couple the prism and the substrate. Diiodomethane (CH 2 I 2 ) is one of the liquids with the highest known refractive index (n = 1.74), 23 hence it is selected to be the index-matched medium in this work.…”

In situ printing of liquid superlenses for subdiffraction-limited color imaging of nanobiostructures in nature

“…Additionally, some water-immiscible liquids having high refractive indices may also be used for printing liquid lenses that may be used for water-immersion imaging applications. For example, the organic liquid diiodomethane (CH 2 I 2 ) ( n ~1.77) can increase its refractive index to 1.80 44 with dissolved antimony tribromide salts, although such compositions exhibit a high toxicity. More biocompatible liquids, such as silicone oil (a refractive index typically between 1.5 and 1.7) or other polymers, could be explored for superlens applications underwater using ink-jet printing or other dispensing methods.…”

Designing refractive index fluids using the Kramers–Kronig relations

“…While widely used in industrial applications, these immersion liquids are toxic and the rational design of novel liquids based on non-toxic materials would be useful. This is in particular relevant for biological and medical high-resolution imaging, such as total internal reflection fluorescence microscopy 7 , where high-index optics based on sapphire lenses facilitate super-resolution 8 .…”