Marie Abboud

Imaging gold nanoparticles in living cell environments using heterodyne digital holographic microscopy

This paper describes an imaging microscopic technique based on heterodyne digital holography where subwavelength-sized gold colloids can be imaged in cell environments. Surface cellular receptors of 3T3 mouse fibroblasts are labeled with 40 nm gold nanoparticles, and the biological specimen is imaged in a total internal reflection configuration with holographic microscopy. Due to a higher scattering efficiency of the gold nanoparticles versus that of cellular structures, accurate localization of a gold marker is obtained within a 3D mapping of the entire samples scattered field, with a lateral precision of 5 nm and 100 nm in the x,y and in the z directions respectively, demonstrating the ability of holographic microscopy to locate nanoparticles in living cell environments.

Scattering through fruits during ripening: laser speckle technique correlated to biochemical and fluorescence measurements

This paper reports monitoring fruits maturation using speckle technique. Performed measurements aim the assessing of biological inner fruit variation effect on the speckle image. We show that the speckle grain size is both affected by the glucose level inside the fruits and by the chlorophyll content. Moreover, the determination of circular polarization degree and circular grain size indicate that a Rayleigh diffusion regime gradually becomes predominant in fruits. Principal component analysis is used to highlight high correlation between results and strengthen the establishment of speckle as a novel non invasive method to monitor fruits ripening.

Detection of Golden apples’ climacteric peak by laser biospeckle measurements

In this paper, we report a study in which a laser biospeckle technique is used to detect the climacteric peak indicating the optimal ripeness of fruits. We monitor two batches of harvested Golden apples going through the ripening phase in low- and room-temperature environments, determine speckle parameters, and measure the emitted ethylene concentration using gas chromatography as reference method. Speckle results are then correlated to the emitted ethylene concentration by a principal component analysis. From a practical point of view, this approach allows us to validate biospeckle as a noninvasive and alternative method to respiration rate and ethylene production for climacteric peak detection as a ripening index.

Retrieving controlled motion parameters using two speckle pattern analysis techniques: spatiotemporal correlation and the temporal history speckle pattern

This paper presents simulation of speckle activity through controlling a moving plate. We present two procedures to extract the initial movement frequency and amplitude, either through correlation calculus or through processing the temporal history of the speckle pattern. We compare and discuss these two methods in terms of efficiency and the ability to retrieve motion parameters. The correlation technique seems to be more suitable for monitoring biospeckle activity as it provides more reliable parameter estimation than the temporal history of the speckle pattern. The evolution of temporal history of the speckle pattern parameters and their response sensibility with amplitude and frequency variations have been studied and quantified. Briers contrast appears to depend only on movement amplitude, whereas inertia moment varies with amplitude and frequency.

Influence of size, proportion, and absorption coefficient of spherical scatterers on the degree of light polarization and the grain size of speckle pattern

In this paper, we present the evolution of speckle pattern polarimetric parameters in response to controlled changes in scatterer sizes, proportions, and the absorption coefficient in media. The experimental study was performed on mixtures of polystyrene microspheres with dye in order to ensure biological medium-like properties. The speckle grain sizes and degrees of polarization for linear and circular light were monitored. We observed helicity flipping in the degree of circular polarization for small scatterer proportion around 25%. Furthermore, linear depolarization decreased slightly for media containing more small particles. Good agreement was shown with numerical results computed using a Monte Carlo simulation of polarized light taking into account our experimental configuration. Speckle grain size also evolves with the increase of small scatterers as well as the media absorption coefficient. Such variations of properties are encountered during fruit maturation, in tissues in precancerous stages, and any transformation that causes a modification in particle proportions and absorption coefficient in biological media. The computed parameters proved to be sensitive to these changes.

Early diagnosis of teeth erosion using polarized laser speckle imaging

Abstract. Dental erosion starts with a chemical attack on dental tissue causing tooth demineralization, altering the tooth structure and making it more sensitive to mechanical erosion. Medical diagnosis of dental erosion is commonly achieved through a visual inspection by the dentist during dental checkups and is therefore highly dependent on the operator’s experience. The detection of this disease at preliminary stages is important since, once the damage is done, cares become more complicated. We investigate the difference in light-scattering properties between healthy and eroded teeth. A change in light-scattering properties is observed and a transition from volume to surface backscattering is detected by means of polarized laser speckle imaging as teeth undergo acid etching, suggesting an increase in enamel surface roughness.

Evaluation of low viscosity variations in fluids using temporal and spatial analysis of the speckle pattern

The noninvasive detection of a materials viscoelasticity is of great importance in the medical field. In fact, certain diseases cause changes in tissue structure and biological fluid viscosity; tracking those changes allows for detection of these diseases. Rheological measurements are also imperative in the industrial field, where it is necessary to characterize a materials viscoelasticity for manufacturing purposes. In this Letter, we present a noncontact, noninvasive, and low cost method for determining low viscosity values and variations in fluids. Laser speckle and viscometric measurements are performed on test samples having low scattering coefficients and low viscosities. The speckle spatial analysis proved to be as accurate as the speckle temporal correlation method reported in previous studies. Very low viscosities of the order of 1 mPa.s were retrieved for the first time using speckle images with either a frame rate of 1950 fps or a single acquired image.

Characterization of Bacillus thuringiensis parasporal crystals using laser speckle technique: effect of crystal concentration and dimension

In this paper, we report experimental results where laser speckle grain size and degree of light polarization are used to distinguish different sizes of Bacillus thuringiensis spherical crystals and different concentration within fermentation products. Three strains of Bacillus thuringiensis, isolated from the Lebanese soil, are selected. After fermentation, crystals and spores are separated using a technique based on flotation in order to obtain large quantities of relatively pure crystals. Crystals are then embedded in an agarose matrix gel and illuminated by a laser. Speckle patterns are recorded and analyzed. Results show that when crystal concentrations increase in the sample, the values of the degree of light linear polarization and speckle grain size decrease, and the negative values of light circular polarization degree increase. A transition from a Rayleigh scattering regime to a Mie regime is also observed. Furthermore, when the diameter of spherical crystals increases, the normalized value of the light linear polarization degree and the grain size diminish drastically for a given concentration of crystals in the matrix, whereas the normalized value of light circular polarization degree increases. This optical characterization constitutes an unambiguous signature of spherical crystals produced by fermentations of different Bacillus thuringiensis strains and shows that speckle may potentially be used at an industrial scale as a low-cost and noninvasive technique in order to characterize crystal geometry and to evaluate the yield of crystal production within fermentation.

Laser speckle dynamic for monitoring fruits maturation

Our study is based on using a non-invasive technique, the bio-speckle technique, in order to follow the ripening of fruits during different stages: before and after the climacteric stage. To assess the impact of the ripening of fruits on their optical properties, speckle grain is measured and the variation of its dimensions is evaluated. In addition, and in order to correlate this observation with the degradation of chlorophylls, both a physical approach based on recording the fluorescence spectrum of chlorophylls, and a biochemical approach based on a pigmentation analysis, are used. We therefore show the efficiency of biospeckle metrology for monitoring fruit maturation.

Speckle imaging for monitoring the growth kinetics of Bacillus thuringiensis

This paper presents an application of laser speckle imaging method to characterize the kinetic growth of Bacillus thuringiensis (Bt). Numbers of parameters, such as speckle grain size and spatial contrast, are considered in order to characterize the culture medium and to monitor in real time the fermentation process. We show that the grain size and the contrast of the speckle image decrease with the increase of the cells concentration. The correlation of speckle results with optical density measurements shows the effectiveness of dynamic speckle for real-time monitoring of Bt cells growth kinetics.