Abstract
A limitation of standard brightfield microscopy is its low contrast images, especially for thin specimens of weak absorption, and biological species with refractive indices very close in value to that of their surroundings. We demonstrate, using a planar photonic chip with tailored angular transmission as the sample substrate, a standard brightfield microscopy can provide both darkfield and total internal reflection (TIR) microscopy images with one experimental configuration. The image contrast is enhanced without altering the specimens and the microscope configurations. This planar chip consists of several multilayer sections with designed photonic band gaps and a central region with dielectric nanoparticles, which does not require top-down nanofabrication and can be fabricated in a larger scale. The photonic chip eliminates the need for a bulky condenser or special objective to realize darkfield or TIR illumination. Thus, it can work as a miniaturized high-contrast-imaging device for the developments of versatile and compact microscopes.
Highlights
A limitation of standard brightfield microscopy is its low contrast images, especially for thin specimens of weak absorption, and biological species with refractive indices very close in value to that of their surroundings
We demonstrate that after the attachment of a planar photonic chip to the substrate of a standard brightfield microscopy (BFM), both darkfield and total internal reflection (TIR) imaging can be realized in one experimental set-up without the use of a bulky darkfield condenser (DFC) and other specialized components
The new microscopes can be named as chip-based darkfield microscopy (C-Darkfield microscopy (DFM)) and chip-based total internal reflection microscopy (C-TIRM)
Summary
A limitation of standard brightfield microscopy is its low contrast images, especially for thin specimens of weak absorption, and biological species with refractive indices very close in value to that of their surroundings. The photonic chip eliminates the need for a bulky condenser or special objective to realize darkfield or TIR illumination It can work as a miniaturized high-contrast-imaging device for the developments of versatile and compact microscopes. These specialized techniques need additional optical or mechanical components, complicating the configuration of the microscope and increasing the complexities in operations Another widely used approach is darkfield illumination, which is suitable for specimens that display little or no absorption and/or weakly absorbing biological samples. The C-DFM and C-TIRM have the merits of large illumination area, high imaging contrast, simple configuration and easy for optical-alignment Both DFM and TIRM emphasize the high-spatial-frequency components associated with small features in the specimen morphology and in some imaging scenarios, can even provide resolution beyond the diffraction limit[16,17]. It is ideally suited to analyze the localization and dynamics of molecules and events occurring near the interface, such as the plasma membranes and surface-bound single molecules
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