Widefield two-photon random illumination microscopy (2P-RIM)

TL;DR

The paper introduces 2P-RIM, a widefield two-photon microscopy technique that enables fast, low-damage, high-resolution imaging over large areas with effective axial sectioning, surpassing traditional methods in speed and safety.

Contribution

It presents a novel widefield two-photon microscopy method using speckled illumination and an image standard deviation algorithm for large FOV, high resolution, and low photo-damage imaging.

Findings

Achieves micrometric axial sectioning of 2 μm.

Provides lateral resolution of 220 nm.

Uses excitation powers 10 times lower than focused laser scanning.

Abstract

Biological and biomedical samples are routinely examined using focused two-photon (2P) fluorescence microscopy due to its intrinsic axial sectioning and reduced out-of-focus bleaching. However, 2P imaging often requires excitation intensities that can damage samples through ionization and radical formation. Additionally, the lateral resolution of 2P microscopy is lower compared to linear one-photon (1P) fluorescence microscopy. Widefield 2P microscopy, using cameras, holds promise for reducing photo-toxicity while maintaining high image acquisition rates. Widefield imaging trades the high power and short integration times of sequential single point scanning for the low power and extended integration times of parallel detection across millions of pixels. However, generating effective axial sectioning over arbitrarily large fields of view (FOVs) has remained a challenge. In this work, we introduce 2P Random Illumination Microscopy (2P-RIM), an easy-to-implement 2P widefield technique, that achieves low photo-damage, fast imaging, micrometric axial sectioning, and enhanced lateral resolution for arbitrarily large FOVs. By using widefield speckled illuminations in conjunction with an image standard deviation matching algorithm, 2P-RIM demonstrated multicolor imaging over FOVs greater than 200 um, lateral resolution 220 nm, axial sectioning 2 um, and peak excitation powers about 10 times lower than those used in focused laser scanning microscopy.