Abstract
Mechanical imaging and characterisation of biological cells has been a subject of interest for the last twenty years. Ultrasonic imaging based on the scanning acoustic microscope (SAM) and mechanical probing have been extensively reported. Large acoustic attenuation at high frequencies and the use of conventional piezo-electric transducers limit the operational frequency of a SAM. This limitation results in lower resolution compared to an optical microscope. Direct mechanical probing in the form of applied stress by contacting probes causes stress to cells and exhibits poor depth resolution. More recently, laser ultrasound has been reported to detect ultrasound in the GHz range via Brillouin oscillations on biological cells. This technique offers a promising new high resolution acoustic cell imaging technique. In this work, we propose, design and apply a thin-film based opto-acoustic transducer for the detection in transmission of Brillouin oscillations on cells. The transducer is used to generate acoustic waves, protect the cells from laser radiation and enhance signal-to-noise ratio (SNR). Experimental traces are presented in water films as well as images of the Brillouin frequency of phantom and fixed 3T3 fibroblast cells.
Highlights
Mechanical characterisation of biological cells is of great interest, as their properties are mostly unknown and can be the basis for mechanical modelling
It provides an alternative mechanism for contrast which could provide new insights into cell biology. This kind of characterisation can be performed on a cell by applying stress and measure the deformations directly, with for example, an atomic force microscope (AFM) tip [1], by optical trapping [3] or micropipette aspiration [4]
This opens the opportunity to measure the speed of sound and to obtain the profile of the sample provided that the penetration depth of the acoustic wave is large enough to reach the boundary of a given object
Summary
Mechanical characterisation of biological cells is of great interest, as their properties (like stiffness or elasticity) are mostly unknown and can be the basis for mechanical modelling. It provides an alternative mechanism for contrast which could provide new insights into cell biology This kind of characterisation can be performed on a cell by applying stress and measure the deformations directly, with for example, an atomic force microscope (AFM) tip [1], by optical trapping [3] or micropipette aspiration [4]. Those approaches have the advantage that measurements are obtained directly. The SAM output depends on two or more parameters meaning that the quantitative measurements are not obtained directly and its resolution is typically lower than that of optical systems
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