Fig. 1
From: Waveguide-PAINT offers an open platform for large field-of-view super-resolution imaging
Optimized waveguide design enables a uniform and large TIRF illumination. a Classical objective TIRF and waveguide TIRF approaches. With objective TIRF, the illumination (red) field size is limited by the objective lens size and magnification and by a roll-off in intensity away from the central axis. In waveguide TIRF, the light (red) undergoes total internal reflection at the interface between the core and the aqueous solution, producing an optical sectioning illumination over the entire waveguide surface (up to 2000 μm in our chips). b The chip design includes an inverted nanotaper with a 150 nm input width ws, a 15 mm length L, and an expansion rate α = 0.006 (yellow box). The waveguide input facet is offset from the substrate etching site (orange box). (See also Supplementary Fig. 2). The waveguide structures appear in reflectance as light-grey stripes on the chip surface (photograph, top left). c Scanning electron microscopy of the input facet shows that deep-etching the silicon (Si) substrate after the Si3N4/SiO2 layer without the two-step-etching leads to a rough facet (c top). Si deep-etching after further lithographic steps—to offset the two etching sites—provides a smooth input facet (c bottom). d Scattered light from the top waveguide surface in the absence of a taper (left) is less uniform than that with a nanotaper with expansion angle alpha (right). e Line profiles (magenta, without taper; cyan, with taper) show modulation depth > 20% and < 12%, respectively. f Low magnification (×4) imaging of about 50 COS-7 cells labelled with cholera toxin B conjugated to Alexa 647. Scale bars: 1 µm (c), 10 µm (d), and 200 µm (f)
