Label‐free multi‐parametric imaging of single cells: dual picosecond optoacoustic microscopy

Abstract

Advances in microscopy with new visualization possibilities often bring dramatic progress to our understanding of the intriguing cellular machinery. Picosecond optoacoustic micro‐spectroscopy is an optical technique based on ultrafast pump‐probe generation and detection of hypersound on time durations of picoseconds and length scales of nanometers. It is experiencing a renaissance as a versatile imaging tool for cell biology research after a plethora of applications in solid‐state physics. In this emerging context, this work reports on a dual‐probe architecture to carry out real‐time parallel detection of the hypersound propagation inside a cell that is cultured on a metallic substrate, and of the hypersound reflection at the metal/cell adhesion interface. Using this optoacoustic modality, several biophysical properties of the cell can be measured in a noncontact and label‐free manner. Its abilities are demonstrated with the multiple imaging of a mitotic macrophage‐like cell in a single run experiment.

The Mechanics of Mitotic Cell Rounding

“…Brillouin microscopy (Figure 1.8) relies on the effect of Brillouin scattering, which occurs due to the interaction of incident laser light with acoustic phonons, causing a frequency shift that can be related to the longitudinal modulus and therefore sample compressibility ( Scarcelli and Yun, 2008 , 2012 ; Prevedel et al, 2019 ). Both techniques have already been applied for the study of mitotic cells ( Pasternak et al, 2015 ; Liu et al, 2019 ).…”

“…In those cases, the sample is scanned by a laser beam and a frequency shift due to Brillouin scattering is detected which is related to the mechanical properties of the sample ( Scarcelli and Yun, 2008 , 2012 ). Thus far, in the context of mitosis, Brillouin microscopy was applied to single cells where differences in the Brillouin shift between interphase and mitosis were observed ( Liu et al, 2019 ; Figure 1.8), but the technique has not yet been used to study mitotic cells within complex tissues.…”

Picosecond ultrasounds as elasticity probes in neuron-like cells models

“…Since the BO frequency is related to the sound velocity and the decaying time is related to the viscosity, the time domain investigation of BO signature can be used to carry out an in-depth study of the elastic properties 29 . Recently, a multi parametric elastic mapping in mitotic macrophage cells has been reported 30 , illustrating how the various PA configurations can bring correlative information's to cell investigations.…”

“…In this case the short lifetimes are not directly related to viscosity but are mainly determined by the thickness of the probed biological material. Further development will be needed to obtain elastic information on specific areas using approaches described by Liu et al 30 . The BO associated to the nucleus is lasting longer than the BO associated to the cytoplasm.…”

Optical and mechanical properties of streptavidin-conjugated gold nanospheres through data mining techniques

“…Besides providing superior beam pointing stability (actually that of the laser cavity), the acquisition speed allowed for high rate sampling yielding unprecedented sensitivity in recent experiments, where relative transmissivity variations as low as where achieved 9 . Furthermore, the rapid acquisition of the time-resolved spectra over delay windows of tens of ns with sub-ps time resolution is well suited for investigating degradable and biological samples, such as imaging of cells structures on a single cell via photoacoustics microscopy 37 , 38 . The ASOSP technique allows avoiding sample exposure to high-intensity radiation, such as in-vivo photoacoustic imaging 39 , and collecting a statistically significant number of spectra where needed 27 .…”