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Recently, the coherent generation of GHz acoustic waves using ultrashort laser pulses has demonstrated the ability to probe the sound velocity in vegetal cells and in cell-mimicking soft micro-objects with micrometer resolution, opening tremendous potentialities for single-cell biology. However, manipulating biological media in physiological conditions is often a technical challenge when using a laser-based setup. In this article, we present a new opto-acoustic bio-transducer composed of a thin metal film sputtered on a transparent heat sink that allows reducing importantly the laser-induced cellular stresses, and offers a wide variety of optical configurations. In particular, by exploiting the acoustic reflection coefficient at the sample-transducer interface and the photoacoustic interaction inside the transparent sample, the density and compressibility of the sample can be probed simultaneously. Using an ad hoc signal analysis based on Hilbert and wavelet transforms, these quantities are measured accurately for a reference fluid. Similar analysis performed in a single vegetal cell also suggests high sensitivity to the state of the transducer-cell interface, and notably to the presence of the plasma membrane that encloses the cell vacuole. [ABSTRACT FROM AUTHOR]

An optical grating has been introduced in a picosecond ultrasonics experiment, in order to vary continuously the duration of the laser beam pulse from 0.1 to 150 ps. The evolution of the measured signal has been observed and analyzed through the comparison with a theoretical approach based on a two-temperature model. The latter allows matching the acoustic echoes together with the thermal background and the coincidence peak, for each pulse duration and at any time scale. The broadening of the acoustic echoes and the disappearing of its Brillouin component, along with the diminishing of the thermal coincidence peak, have been demonstrated when increasing the pulse duration. For a constant incident pulse energy, the efficiency of acoustic generation is optimum for the shortest pulses. Nevertheless, for longer pulses designed to obtain thermal conditions below the ablation threshold, acoustic generation could be enhanced. [ABSTRACT FROM AUTHOR]

Techniques that can probe the thermal properties of cells are used in many applications ranging from cryogenic preservation to hyperthermia therapy, and provide powerful tools to investigate diseased conditions. The structural complexity of cells, however, requires innovative modalities operating at a subcell scale. We developed a label-free, non-ionizing technique based on a thermoelastic lens. With this device, we captured images of single cells with a ~2 μm resolution based on thermal properties as the contrast mechanism. To investigate the thermorheological behaviour of cells, we present simultaneous acoustic imaging using an inverted opto-acoustic microscope. Acoustic impedances extracted from the acoustic images support the effusivity obtained from the thermal images. This technique should provide diagnostic tools at the single cell scale. [ABSTRACT FROM AUTHOR]

We present a time resolved spectroscopy for the picosecond ultrasonics technique. Detection of picosecond coherent phonons using a wavelength continuum generation in a photonic crystal fiber with femtosecond laser pulses is introduced. Measurements are performed on two samples made of tungsten and gallium arsenide for selected wavelengths of probe pulses within a bandwidth of 250 nm with an 825 nm center wavelength. Characteristic changes of the shape of the acoustic signal due to the selection of the probe wavelength are shown. [ABSTRACT FROM AUTHOR]

Cell mechanics play a key role in several fundamental biological processes, such as migration, proliferation, differentiation and tissue morphogenesis. In addition, many diseased conditions of the cell are correlated with altered cell mechanics, as in the case of cancer progression. For this there is much interest in methods that can map mechanical properties with a sub-cell resolution. Here, we demonstrate an inverted pulsed opto-acoustic microscope (iPOM) that operates in the 10 to 100 GHz range. These frequencies allow mapping quantitatively cell structures as thin as 10 nm and resolving the fibrillar details of cells. Using this non-invasive all-optical system, we produce high-resolution images based on mechanical properties as the contrast mechanisms, and we can observe the stiffness and adhesion of single migrating stem cells. The technique should allow transferring the diagnostic and imaging abilities of ultrasonic imaging to the single-cell scale, thus opening new avenues for cell biology and biomaterial sciences. [ABSTRACT FROM AUTHOR]