Showing papers by "Pietro Ferraro published in 2013"

Digital holography as a method for 3D imaging and estimating the biovolume of motile cells

Abstract: Sperm morphology is regarded as a significant prognostic factor for fertilization, as abnormal sperm structure is one of the most common factors in male infertility. Furthermore, obtaining accurate morphological information is an important issue with strong implications in zoo-technical industries, for example to perform sorting of species X from species Y. A challenging step forward would be the availability of a fast, high-throughput and label-free system for the measurement of physical parameters and visualization of the 3D shape of such biological specimens. Here we show a quantitative imaging approach to estimate simply and quickly the biovolume of sperm cells, combining the optical tweezers technique with digital holography, in a single and integrated set-up for a biotechnology assay process on the lab-on-a-chip scale. This approach can open the way for fast and high-throughput analysis in label-free microfluidic based “cytofluorimeters” and prognostic examination based on sperm morphology, thus allowing advancements in reproductive science.

Imaging live humans through smoke and flames using far-infrared digital holography

Abstract: The ability to see behind flames is a key challenge for the industrial field and particularly for the safety field. Development of new technologies to detect live people through smoke and flames in fire scenes is an extremely desirable goal since it can save human lives. The latest technologies, including equipment adopted by fire departments, use infrared bolometers for infrared digital cameras that allow users to see through smoke. However, such detectors are blinded by flame-emitted radiation. Here we show a completely different approach that makes use of lensless digital holography technology in the infrared range for successful imaging through smoke and flames. Notably, we demonstrate that digital holography with a cw laser allows the recording of dynamic human-size targets. In this work, easy detection of live, moving people is achieved through both smoke and flames, thus demonstrating the capability of digital holography at 10.6 μm.

Random resampling masks: a non-Bayesian one-shot strategy for noise reduction in digital holography

Abstract: Holographic imaging may become severely degraded by a mixture of speckle and incoherent additive noise. Bayesian approaches reduce the incoherent noise, but prior information is needed on the noise statistics. With no prior knowledge, one-shot reduction of noise is a highly desirable goal, as the recording process is simplified and made faster. Indeed, neither multiple acquisitions nor a complex setup are needed. So far, this result has been achieved at the cost of a deterministic resolution loss. Here we propose a fast non-Bayesian denoising method that avoids this trade-off by means of a numerical synthesis of a moving diffuser. In this way, only one single hologram is required as multiple uncorrelated reconstructions are provided by random complementary resampling masks. Experiments show a significant incoherent noise reduction, close to the theoretical improvement bound, resulting in image-contrast improvement. At the same time, we preserve the resolution of the unprocessed image.

Imaging through scattering microfluidic channels by digital holography for information recovery in lab on chip

Abstract: We tackle the problem of information recovery and imaging through scattering microfluidic chips by means of digital holography (DH) In many cases the chip can become opalescent due to residual deposits settling down the inner channel faces, biofilm formation, scattering particle uptake by the channel cladding or its damaging by corrosive substances, or even by condensing effect on the exterior channels walls In these cases white-light imaging is severely degraded and no information is obtainable at all about the flowing samples Here we investigate the problem of counting and estimating velocity of cells flowing inside a scattering chip Moreover we propose and test a method based on the recording of multiple digital holograms to retrieve improved phase-contrast images despite the strong scattering effect This method helps, thanks to DH, to recover information which, otherwise, would be completely lost

Quantitative phase maps denoising of long holographic sequences by using SPADEDH algorithm

Abstract: We propose a denoising method for digital holography mod 2π wrapped phase map by using an adaptation of the SPArsity DEnoising of Digital Holograms (SPADEDH) algorithm. SPADEDH is a l(1) minimization algorithm able to suppress the noise components on digital holograms without any prior knowledge or estimation about the statistics of noise. We test our algorithm with either general numerical simulated wrapped phase, quantifying the performance with different efficiency parameters and comparing it with two popular denoising strategies, i.e., median and Gaussian filters, and specific experimental tests, by focusing our attention on long-sequence wrapped quantitative phase maps (QPMs) of in vitro cells, which aim to have uncorrupted QPMs. In addition, we prove that the proposed algorithm can be used as a helper for the typical local phase unwrapping algorithms.

Graded-size microlens array by the pyro-electrohydrodynamic continuous printing method.

Abstract: In the present work, the pyro-electrohydrodynamic technique was used for the realization of tunable-size microlens arrays. Poly(methyl methacrylate) dissolved in different solvent mixtures was used as the polymeric material for the realization of the microstructures. By controlling the experimental parameters and in particular, the volume of the drop reservoir, graded-size square arrays of tens of microlenses with focal length in the range 1.5–3 mm were produced. Moreover, the optical quality and geometrical features were investigated by profilometric and interferometric analysis.

Spontaneous assembly of carbon-based chains in polymer matrixes through surface charge templates.

Abstract: Stable chains of carbon-based nanoparticles were formed directly in polymer matrixes through an electrode-free approach. Spontaneous surface charges were generated pyroelectrically onto functionalized ferroelectric crystals, enabling the formation of electric field gradients that triggered the dipole−dipole interactions responsible for the alignment of the particles, while embedded in the polymer solution. The phenomenon is similar to the dielectrophoretic alignment of carbon nanotubes reported in the literature. However, here the electric fields are generated spontaneously by a simple heat treatment that, simultaneously, aligns the particles and provides the energy necessary for curing the host polymer. The result is a polymer sheet reinforced with well-aligned chains of carbon-based particles, avoiding the invasive implementation of appropriate electrodes and circuits. Because polymers with anisotropic features are of great interest for enhancing the thermal and/or the electrical conductivity, the electrode-free nature of this technique would improve the scaling down and the versatility of those interconnections that find applications in many fields, such as electronics, sensors, and biomedicine. Theoretical simulations of the interactions between the particles and the charge templates were implemented and appear in good agreement with the experimental results. The chain formation was characterized by controlling different parameters, including surface charge configuration, particle concentration, and polymer viscosity, thus demonstrating the reliability of the technique. Moreover, micro-Raman spectroscopy and scanning electron microscopy were used for a thorough inspection of the assembled chains.

Enhancing depth of focus in tilted microfluidics channels by digital holography.

Abstract: In this Letter we propose a method to enhance the limited depth of field (DOF) in optical imaging systems, through digital holography. The proposed approach is based on the introduction of a cubic phase plate into the diffraction integral, analogous to what occurs in white-light imaging systems. By this approach we show that it is possible to improve the DOF and to recover the extended focus image of a tilted object in a single reconstruction step. Moreover, we demonstrate the possibility of obtaining well-focused biological cells flowing into a tilted microfluidic channel.

Plasmon resonance of gold nanorods for all-optical drawing of liquid droplets

Abstract: We present a laser-assisted system for dispensing liquid micro-droplets by near infrared illumination of a pyroelectric crystal functionalized with gold nanorods embedded into polyvinyl alcohol. The non-invasive near infrared source resonates with the plasmon oscillations of the gold nanorods, providing a controlled thermal stimulus able to generate the pyroelectric effect. The resulting electric field interacts electro-hydrodynamically with a liquid reservoir leading to precise drawing of micro-litre droplets. This laser-assisted electro-hydrodynamic technique may open the way to the development of more compact and non-invasive nano-dispensing devices.

Milking liquid nano-droplets by an IR laser: a new modality for the visualization of electric field lines

Abstract: Liquid handling at micron- and nano-scale is of paramount importance in many fields of application such as biotechnology and biochemistry. In fact, the microfluidics technologies play an important role in lab-on-a-chip devices and, in particular, the dispensing of liquid droplets is a required functionality. Different approaches have been developed for manipulating, dispensing and controlling nano-droplets under a wide variety of configurations. Here we demonstrate that nano-droplets can be drawn from liquid drop or film reservoirs through a sort of milking effect achieved by the absorption of IR laser radiation into a pyroelectric crystal. The generation of the pyroelectric field induced by the IR laser is calculated numerically and a specific experiment has been designed to visualize the electric field stream lines that are responsible for the liquid milking effect. The experiments performed are expected to open a new route for the visualization, measure and characterization procedures in the case of electrohydrodynamic applications.

Automatic Digital Hologram Denoising by Spatiotemporal Analysis of Pixel-Wise Statistics

Abstract: In this paper, a new technique to reduce the noise in a reconstructed hologram image is proposed Unlike all the techniques in the literature, the proposed approach not only takes into account spatial information but also temporal statistics associated with the pixels This innovative solution enables, at first, the automatic detection of the areas of the image containing the objects (foreground) This way, all the pixels not belonging to any objects are directly cleaned up and the contrast between objects and background is consistently increased The remaining pixels are then processed with a spatio-temporal filtering which cancels out the effects of speckle noise, while preserving the structural details of the objects The proposed approach has been compared with other common speckle denoising techniques and it is found to give better both visual and quantitative results

Manipulation of Nematic Liquid Crystal Microdroplets by Pyroelectric Effect

Abstract: We present experimental results concerning liquid crystals microdroplets behavior onto functionalized lithium niobate substrates covered with Polydimethylsiloxane (PDMS) polymer. Droplets are fragmented, driven, and reassembled by electric fields generated by pyroelectric effect. We analyze the dynamics of the observed phenomena and suggest possible technological applications.

Investigation on 3D morphological changes of in vitro cells through digital holographic microscopy

Abstract: We report the investigation of the identification and measurement of region of interest (ROI) in quantitative phase-contrast maps (QPMs) of biological cells by digital holographic microscopy (DHM), with the aim to analyze the 3D positions and 3D morphology together. We consider as test case for our tool the in vitro bull sperm head morphometry analysis. Extraction and measurement of various morphological parameters are performed by using two methods: the anisotropic diffusion filter, that is based on the Gaussian diffusivity function which allows more accuracy of the edge position, and the simple thresholding filter. In particular we consider the calculation of area, ellipticity, perimeter, major axis, minor axis and shape factor as a morphological parameter, instead, for the estimation of 3D position, we compute the centroid, the weighted centroid and the maximum phase values. A statistical analysis on a data set composed by N = 14 holograms relative to bovine spermatozoa and its reference holograms is reported.

Non-Bayesian noise reduction in digital holography by random resampling masks

Abstract: Images from coherent laser sources are severely degraded by a mixture of speckle and incoherent additive noise. In digital holography, Bayesian approaches reduce the incoherent noise, but prior information are needed about the noise statistics. On the other hand, non-Bayesian techniques presents the shortcomings of resolution loss or very complex acquisition systems, required to record multiple uncorrelated holograms to be averaged. Here we propose a fast non- Bayesian method which performs a numerical synthesis of a moving diffuser in order to reduce the noise. The method does not depend on prior knowledge of the noise statistics and the proposed technique is one-shot, as only one single hologram capture is required. Indeed, starting from a single acquisition multiple uncorrelated reconstructions are provided by random sparse resampling masks, which can be incoherently averaged. Experiments show a significant improvement, close to the theoretical bound. Noteworthy, this is achieved while preserving the resolution of the unprocessed image.

Pyroelectric manipulation of liquid crystal droplets

Abstract: Very interesting effects can be observed in maneuvering nematic liquid crystal (NLC) droplets onto functionalized polar lithium niobate (LN) crystal surfaces, covered with thin films of Polydimethylsiloxane (PDMS). It has been discovered that pyroelectric effect is able to drive a reversible fragmentation process in liquid crystal drops, starting from nanoliter drops and obtaining pico/femtoliter droplets. These small droplets are patterned according to the geometry of the substrate and aligned along the electric field lines. This novel approach for manipulating different classes of liquids by exploiting the pyroelectric effect, where the strong electric fields generated allow to manipulate liquids in 2D on a substrate or even in 3D, has been recently discovered and exploited for different purposes. In particular, manipulation of liquid crystals by a thermal stimulus could be suitable for applications such as spatial modulation of the wettability (i.e. wettability patterning), or, in principle, a dynamical optical element able to switch from a diffuser (fragmentation) state to a microlens array. Moreover, the biocompatibility of some kinds of nematic or cholesteric liquid crystals makes them suitable as biomaterials for applications in biology and tissue engineering.

Reconstruction of an image of an object at least partially hidden by a flame

Abstract: It is disclosed a system for reconstructing an image of an object hidden by a flame The system comprises a laser source emitting an infrared radiation and a lensless, off-axis interferometric arrangement that divides the infrared radiation into an object beam and a reference beam The object beam is enlarged and then irradiates the object, that scatters it The reference beam is enlarged and then interferes with the scattered object beam, so as to create a hologram The system comprises an infrared detector which detects the hologram and a processing unit which reconstructs the image of the object by numerically processing the hologram The system therefore provides the object image based on digital holography at infrared wavelengths Differently from known thermographic acquisition techniques, even if large portions of the object are hidden by the flame, the system allows to reconstruct an image of the whole object, with no blind areas

Lensless Digital Holography Improves Fire Safety

Abstract: House fires cause thousands of deaths every year. Firefighters and first responders are called on to work in these hostile environments where their vision is impaired due to curtains of smoke and walls of flames.

Synthesis and 3D display of multi-wavelengths digital holograms through adaptive transformation

Abstract: We propose a reconstructing method of digital color holograms based on the stretching techniques. With a simple affine transformation on the Fresnel reconstructions, we are able to manage the focus of the digital color reconstructions of the same object in order to obtain a synthetic single digital hologram in which three different colors are multiplexed. In addition, a 3D scene is synthesized combining multiple optically recorded digital color holograms of different objects. Numerical analysis and display tests are used to evaluate the effectiveness of the proposed method.

Digital holographic microscopy for the evaluation of human sperm structure

Abstract: The morphology of the sperm head has often been correlated with the outcome of in vitro fertilization (IVF), and has been shown to be the sole parameter in semen of value in predicting the success of intracytoplasmic sperm injection (ICSI) and intracytoplasmic morphologically selected sperm injection (IMSI). In this paper, we have studied whether Digital Holographic (DH) microscopy may be useful to obtain quantitative data on human sperm head structure and compared this technique to high power digitally enhanced Nomarski microscope. The main advantage of DH is that a high resolution 3-D quantitative sample imaging may be obtained thorugh numerical refocusing at different object planes without any mechanical scanning. We show that DH can furnish useful information on the dimensions and structure of human spermatozoo, that cannot be revealed by conventional phase contrast microscopy. In fact, in this paper DH has been used to evaluate volume and indicate precise location of vacuoles, thus suggesting its use as an additional useful prognostic quantitative tool in assisted reproduction technology (ART).

Tilted objects EFI in digital holography by two different numerical approaches

Abstract: Limited depth of field (DOF) is one of the main shortage for many optical imaging systems. This is a limitation that precludes to get in focus, in a single plane, objects that are located at different distances, but that fall in the same field of view. Furthermore, the depth of field is reduced as much as greater is the requirement for a high magnification and to obtain an extended focus image (EFI) of these objects remains one of the major challenges. In this work we propose and compare two different approaches to build the EFI of holograms recorded on a tilted plane. In the first case, a simplified three-dimensional (3D) formulation of the angular spectrum method (ASM) is proposed. It allows to generate the entire stack of propagated images in a single shot. In the second approach, a numerical cubic phase plate (CPP) is included into the reconstruction process of digital holograms with the aim to enhancing DOF of optical imaging system. Theoretical formulations of the two approaches are supported by experimental evidences. The obtained results show that the proposed strategies allow to reconstruct effectively an EFI from holograms recorded on an inclined plane.

Self-assembling of liquid crystal droplets on lithium niobate substrates driven by pyroelectric effect

Abstract: It is known that one of the major attractive feature of liquid crystals (LCs) lies in the fact that their optical properties can be modulated by electric, optical or magnetic fields. Recently, it was discovered that liquid crystal droplets, in particular conditions, can be driven in desired locations following electric field lines. The pyroelectric properties of the periodically poled lithium niobate (PPLN) crystal are exploited and PPLN crystal is used as substrate. In fact, heating and/or cooling this material, it has already been demonstrated that surface charges can appear, by pyroelectric effect, leading to very interesting phenomena. Then, being a polar LC molecule, it undergoes a force due to the existing fields, able to move the material. Results show that fragmented droplets coalesce to form bigger droplets in fixed locations, on a longer time scale. In some cases, one single drop can be observed onto each hexagonal domain. These drops behave as microlenses and the whole sample could be viewed as a dynamical optical micro-element able to switch from a diffuser state (fragmentation state) to a microlens array (coalescence state), without the need of an external voltage. Moreover, the birefringent properties of liquid crystals can make such microlenses also tunable.

Cell mechanics investigation by digital holographic microscopy

Abstract: In biology and biomedical research fields one of the main topic is the understanding of morphology and mechanics of cells and microorganisms. Biological samples present low amplitude contrast that limits the information that can be retrieved through optical bright-field microscope measurements. Optical transparency is overcame for fixed specimen by means of staining techniques but such well-established methods present the issue to be invasive and not applicable on live cells. Study of microorganism in their natural environment without perturbing their equilibrium is challenging in biology. The main effect on light propagating in such objects is in phase, indeed it is altered respect to the phase of the beam propagating in the surrounding medium. This is known as phase-retardation or phase-shift. Objects are visible by Phase Contrast Imaging (PCI) due to interferometric processes able to transform tiny phase variation in amplitude modulation so that any small differences in the beam optical path can be visualized. Digital Holography (DH) in microscopy present as a powerful tool to overcome all these issues. The main characteristic is the possibility to discern between intensity and phase information performing quantitative mapping of the Optical Path Length. Up to now, DH has been considered as an innovative and alternative approach in microscopy and it’s a good candidate for complete specimen analysis in the framework of no invasive microscopy. In this paper, the flexibility of DH is employed to analyze in a completely and no-invasive way the cell mechanics of live and unstained cell subjected to appropriate stimuli. The potentialities of DH are employed to measure all the parameters useful to understand the deformations induced by external and controlled stress in living cells.

New method of holographic three-dimensional tracking of living cells exploiting their morphological properties

Abstract: We propose a new strategy of three-dimensional (3D) tracking of living cells by digital holography microscopy based on the morphological changes of cells during the migration. A comparison with other 3D tracking methods is accomplished.

Charge-driven dispensing of picolitre drops for biomolecules microarrays by Pyro-Electro-hydrodynamic system

Abstract: At present, most microfluidic technologies consist of microchannels where liquids are manipulated by changing pressures or electrode voltages but such systems suffer from different drawbacks such as complex fabrication, sample cross-contamination, high voltage or pressure requirements. Our work represents instead a new and simple system where the liquid actuation and dispensing has been achieved through electrode-free configurations using polar dielectric crystals such as lithium niobate (LN) and by exploiting the pyroelectric effect. This novel `Pyro-Electro-hydrodynamic' manipulation system could be used as a pioneering portable instrument for detecting in-situ even low concentrated analytes not detectable by traditional methods.

New method of 3D tracking of in vitro cells by digital holographic microscopy

Abstract: We propose a new strategy of three-dimensional (3D) tracking of living cells by digital holographic microscopy based on the morphological changes of cells during the migration. The typical strategy adopted in digital holography for the tracking of living cells consists into compute the 3D position dividing the calculation process into two parts: the estimation of the focal plane on the amplitude reconstruction of the digital holograms and the estimation of the transverse coordinates by the phase reconstruction of digital holograms computed at distance equal to the estimated focal plane. We propose to use an approximation of the Tamura coefficient, as image contrast measure, fo r the estimation of the focal plane and a new morphological operator, that is called minimum boundary filter (MBF), from which we compute the transverse coordinates. A comparison with other 3D tracking methods is accomplished. Keywords: Digital holographic microscopy, 3D tracking. 1. INTRODUCTION Many studies report on the ability of digital holography [1-8] to track particle, microorganism and cells [9-14] and there are several methodology to obtain the 3D positions. The typical strategy adopted in digital holography for the tracking of living cells consists into estimate the 3D position dividing the calculation process into two parts: the estimation of the focal plane (i.e. the Z coordinate along the optical axis of the imaging systems) on the amplitude reconstruction of the digital holograms [15,16], and the estimation of the transverse coordinates by the phase reconstruction of digital holograms computed at distance d equal to the estimated focal plane. About the estimation of the focal plane, several autofocus approaches were developed in digital holography for pure phase objects for live-cell imaging. These techniques are based on a suitable image contrast coefficients and perform a numer ical scanning of the focus. Instead the localization in the plane can be computed through different image segmentation methods. We propose a new strategy for both focal plane estimation and image segmentation. In particular, we propose to use an approximation of the Tamura coefficient, as image contrast measure, for the estimation of the in-focus distance. This metric has been applied successfully for the amplitude reconstructi on of digital holograms of macroscopic s cattering objects [17]. Instead, for the estimation of the transverse coordinates, we introduce a new morphological operator that we have called minimum boundary filter (MBF) [11]. This operator is robust with resp ect both noise and morphological variations of cells. In fact, the most popular image segmentation techniques used in th e holographic tracking methods introduce position estimation errors caused by these two aforementioned issues. Instead the MBF is built specifically to take into account the morphological changes during the cells migration. We test the proposed method in a typical situation for which extensive changes in cells morphology are associated to cells motion and we perform a comparison between other popular strategies.

A new 3D tracking method exploiting the capabilities of digital holography in microscopy

Abstract: A method for 3D tracking has been developed exploiting Digital Holographic Microscopy (DHM) features. In the framework of self-consistent platform for manipulation and measurement of biological specimen we use DHM for quantitative and completely label free analysis of specimen with low amplitude contrast. Tracking capability extend the potentiality of DHM allowing to monitor the motion of appropriate probes and correlate it with sample properties. Complete 3D tracking has been obtained for the probes avoiding the issue of amplitude refocusing in traditional tracking processing. Our technique belongs to the video tracking methods that, conversely from Quadrant Photo-Diode method, opens the possibility to track multiples probes. All the common used video tracking algorithms are based on the numerical analysis of amplitude images in the focus plane and the shift of the maxima in the image plane are measured after the application of an appropriate threshold. Our approach for video tracking uses different theoretical basis. A set of interferograms is recorded and the complex wavefields are managed numerically to obtain three dimensional displacements of the probes. The procedure works properly on an higher number of probes and independently from their size. This method overcomes the traditional video tracking issues as the inability to measure the axial movement and the choice of suitable threshold mask. The novel configuration allows 3D tracking of micro-particles and simultaneously can furnish Quantitative Phase-contrast maps of tracked micro-objects by interference microscopy, without changing the configuration. In this paper, we show a new concept for a compact interferometric microscope that can ensure the multifunctionality, accomplishing accurate 3D tracking and quantitative phase-contrast analysis. Experimental results are presented and discussed for in vitro cells. Through a very simple and compact optical arrangement we show how two different functionalities can be accomplished by the same optical setup, i.e. 3D tracking of micro-object and quantitative phase contrast imaging.

Adaptive transformations for color hologram display

Abstract: The advent of digital holography (whereby the interference pattern that constitutes the hologram is recorded using a digital detector array, rather than analog photographic media) has opened up new possibilities for developing spectacular 3D imaging and display systems.1, 2 Making these a reality requires capturing all the details of an object by recording three monochromatic digital holograms with different wavelengths (red, green, blue) that correspond to the primary colors of light.3, 4 These single-color holograms can then be numerically reconstructed and combined to display a fully detailed image of the object. However, achieving good-quality results requires a strategy for correctly superimposing the reconstructed hologram images,5–10 which may differ in scale or be spatially shifted relative to each other. To address this, we have recently developed a simple method based on adaptive affine transformations of holograms that allows full control over the object’s position and size within a 3D volume.11–13 This method ensures adaptive compensation of the three constituent color holograms, which are subsequently superimposed using a correlation-matching procedure. The final step is to create a synthetic hologram, incorporating information from all the different-colored holograms recorded of the same object, using the NTSC (National Television Systems Committee) coefficients. The resulting hologram can be optically reconstructed by a spatial light modulator (SLM) at a single wavelength to display the image in 3D with all its original color features. To illustrate the steps in our proposed method, we can consider the numerical reconstructions of two digital holograms of the same object, recorded at two different wavelengths, red and green. The red and green reconstructions will have Figure 1. Reconstruction of color holograms of a matryoshka doll (a), recorded with wavelengths red D 632:8nm and green D 532nm. The reconstructions of the red (b) and green (c) holograms do not perfectly coincide spatially, producing loss of detail in their superimposition (d).

3D lithography of polymers for micro-photonic applications

Abstract: New techniques for manipulating surface wettability have been recently presented and a wide variety of techniques have been developed for fabricating 3D structures of interest in the optics, photonics and nanotechnology fields. The so called soft lithography is able to transfer microscale patterns to a substrate by using an elastomeric stamp or mold, typically made of polydimethylsiloxane (PDMS). This technique allows one to develop biocompatible lab-on-chip devices for a wide variety of applications ranging from organic LED to cell and tissue engineering and biomolecular analysis.

Cell-material interaction investigated by Digital Holographic microscopy

Abstract: In this paper, the flexibility of DH is employed to analyse in a completely and no-invasive way the cell mechanics of live and unstained cell subjected to appropriate stimuli. The potentialities of DH are employed to measure all the parameters useful to understand the deformations induced by external and controlled stress in living cells.