Defocus-integration Interferometric Scattering Microscopy for Speckle Suppression and Enhancing Nanoparticle Detection on Substrate

TL;DR

This paper introduces a defocus-integration interferometric scattering microscopy method that suppresses speckle noise caused by substrate surface undulations, significantly improving nanoparticle detection sensitivity on flat substrates.

Contribution

The study reveals symmetry properties of scattering phases and develops a defocus-integration technique to suppress speckles, enhancing nanoparticle imaging in iSCAT microscopy.

Findings

Achieved 6.9 dB signal-to-noise ratio enhancement.

Demonstrated applicability to various nanoparticle materials and substrates.

Effectively suppresses speckle noise from substrate surface undulations.

Abstract

Direct optical detection and imaging of single nanoparticles on substrate in wide field underpin vast applications across different research fields. However, the speckles originating from the unavoidable random surface undulations of the substrate ultimately limit the size of the decipherable nanoparticles by the current optical techniques, including the ultrasensitive interferometric scattering microscopy (iSCAT). Here we report a defocus-integration iSCAT to suppress the speckle noise and to enhance the detection and imaging of single nanoparticles on ultra-flat glass substrate and silicon wafer. In particular, we discover distinct symmetry properties of the scattering phase between the nanoparticle and the surface undulations that cause the speckles. Consequently, we develop the defocus-integration technique to suppress the speckles.We experimentally achieve an enhancement of the signal to noise ratio by 6.9 dB for the nanoparticle detection. We demonstrate that the technique is generally applicable for nanoparticles of various materials and for both low and high refractive-index substrates.