Bond-selective transient phase imaging via sensing of the infrared photothermal effect

Delong Zhang,Lu Lan,Ji-Xin Cheng,Hassaan Majeed,Gabriel Popescu,Mikhail E Kandel,Yeran Bai

doi:10.1038/s41377-019-0224-0

Abstract

Phase-contrast microscopy converts the phase shift of light passing through a transparent specimen, e.g., a biological cell, into brightness variations in an image. This ability to observe structures without destructive fixation or staining has been widely utilized for applications in materials and life sciences. Despite these advantages, phase-contrast microscopy lacks the ability to reveal molecular information. To address this gap, we developed a bond-selective transient phase (BSTP) imaging technique that excites molecular vibrations by infrared light, resulting in a transient change in phase shift that can be detected by a diffraction phase microscope. By developing a time-gated pump–probe camera system, we demonstrate BSTP imaging of live cells at a 50 Hz frame rate with high spectral fidelity, sub-microsecond temporal resolution, and sub-micron spatial resolution. Our approach paves a new way for spectroscopic imaging investigation in biology and materials science.

Highlights

Introduction Since Antony vanLeuwenhoek’s single lens microscope in the 18th century[1], optical bright field microscopy has relied on absorption as the main contrast mechanism in an intensity image
The optical phase shift φ can be described with regard to the refractive index n and the thickness l of an object in air[28], as φ
By detecting the optical phase of photons passing through biological samples, phase-contrast microscopy and quantitative phase imaging have become powerful label-free imaging tools to understand biological samples

Summary

Introduction

Leuwenhoek’s single lens microscope in the 18th century[1], optical bright field microscopy has relied on absorption as the main contrast mechanism in an intensity image. Samples with low absorption or scattering, such as biological cells, generate weak intensity modulation and low-contrast images. Transparent samples change the probing light significantly in terms of optical phase delay. By introducing an additional quadrature phase shift between the incident and scattered light, Frits Zernike converted the sample’s phase shift into brightness variation, which allowed the investigation of transparent, unlabeled specimens[2]. Holography was proposed as an approach to convert phase information into intensity via interference between photons passing through a sample and a reference field[3,4]. Holography has since advanced significantly as digital

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