Bright-field Nanoscopy: Visualizing Nano-structures with Localized Optical Contrast Using a Conventional Microscope

TL;DR

Bright-field Nanoscopy enables visualization of nanostructures down to a few nanometers using a standard microscope by exploiting thickness-dependent color changes in ultra-thin germanium on gold, without molecular tags.

Contribution

This work introduces a novel optical technique that visualizes nanoscale structures with a conventional microscope, bypassing the need for fluorescence or other molecular tags.

Findings

Visualized grain boundaries in graphene

Detected single 40 nm silver nanoparticles

Estimated a size detection limit of about 2 nm

Abstract

Most methods for optical visualization beyond the diffraction limit rely on fluorescence emission by molecular tags. Here, we report a method for visualization of nanostructures down to a few nanometers using a conventional bright-field microscope without requiring additional molecular tags such as fluorophores. The technique, Bright-field Nanoscopy, is based on the strong thickness dependent color of ultra-thin germanium on an optically thick gold film. We demonstrate the visualization of grain boundaries in chemical vapour deposited single layer graphene and the detection of single 40 nm Ag nanoparticles. We estimate a size detection limit of about 2 nm using this technique. In addition to visualizing nano-structures, this technique can be used to probe fluid phenomena at the nanoscale, such as transport through 2D membranes. We estimated the water transport rate through a 1 nm thick polymer film using this technique, as an illustration. Further, the technique can also be extended to study the transport of specific ions in the solution. It is anticipated that this technique will find use in applications ranging from single-nanoparticles resolved sensing to studying nanoscale fluid-solid interface phenomena.