Mapping flows in vivo is essential for the investigation of cardiovascular pathologies in animal models. The limitation of optical-based methods, such as space-time cross correlation, is the scattering of light by the connective and fat components and the direct wave front distortion by large inhomogeneities in the tissue. Nonlinear excitation of the sample fluorescence helps us by reducing light scattering in excitation. However, there is still a limitation on the signal-background due to the wave front distortion. We develop a diffractive optical microscope based on a single spatial light modulator (SLM) with no movable parts. We combine the correction of wave front distortions to the cross-correlation analysis of the flow dynamics. We use the SLM to shine arbitrary patterns of spots on the sample, to correct their optical aberrations, to shift the aberration corrected spot array on the sample for the collection of fluorescence images, and to measure flow velocities from the cross-correlation functions computed between couples of spots. The setup and the algorithms are tested on various microfluidic devices. By applying the adaptive optics correction algorithm, it is possible to increase up to 5 times the signal-to-background ratio and to reduce approximately of the same ratio the uncertainty of the flow speed measurement. By working on grids of spots, we can correct different aberrations in different portions of the field of view, a feature that allows for anisoplanatic aberrations correction. Finally, being more efficient in the excitation, we increase the accuracy of the speed measurement by employing a larger number of spots in the grid despite the fact that the two-photon excitation efficiency scales as the fourth power of this number: we achieve a twofold decrease of the uncertainty and a threefold increase of the accuracy in the evaluation of the flow speed.
Ramification of blood circulation is relevant in a number of physiological and pathological conditions. The oxygen exchange occurs largely in the capillary bed, and the cancer progression is closely linked to the angiogenesis around the tumor mass. Optical microscopy has made impressive improvements in in vivo imaging and dynamic studies based on correlation analysis of time stacks of images. Here, we develop and test advanced methods that allow mapping the flow fields in branched vessel networks at the resolution of 10 to 20 μm. The methods, based on the application of spatiotemporal image correlation spectroscopy and its extension to cross-correlation analysis, are applied here to the case of early stage embryos of zebrafish.
Optical Microscopy has been applied to life science from its birth and reached widespread application due to its major advantages: limited perturbation of the biological tissue and the easy accessibility of the light sources. However, as the spatial and time resolution requirements and the time stability of the microscopes increase, researchers are struggling against some of its limitations: limited transparency and the refractivity of the living tissue to light and the field perturbations induced by the path in the tissue. We have developed a compact stand-alone, completely scan-less, optical setup that allows to acquire non-linear excitation images and to measure the sample dynamics simultaneously on an ensemble of arbitrary chosen regions of interests. The image is obtained by shining a square array of spots on the sample obtained by a spatial light modulator and by shifting it (10 ms refresh time) on the sample. The final image is computed from the superposition of (100-1000) images. Filtering procedures can be applied to the raw images of the excitation array before building the image. We discuss results that show how this setup can be used for the correction of wave front aberrations induced by turbid samples (such as living tissues) and for the computation of space-time cross-correlations in complex networks.
Gold nanocages (AuNCs) have been shown to be a useful tool both for imaging and hyperthermia therapy of cancer, thanks to their outstanding optical properties, low toxicity and facile functionalization with targeting molecules, including peptides and antibodies. In particular, hyperthermia is a minimally invasive therapy which takes advantage of the peculiar properties of gold nanoparticles to efficiently convert the absorbed light into heat. Here, we use AuNCs for the selective targeting and imaging of prostate cancer cells. Moreover, we report the hyperthermic effect characterization of the AuNCs both in solution and internalized in cells. Prostate cancer cells were irradiated at different exposure times, with a pulsed near infrared laser, and the cellular viability was evaluated by confocal microscopy.
Microcirculation plays a key role in the maintenance and hemodynamics of tissues and organs also due to its extensive interaction with the immune system. A critical limitation of state-of-the-art clinical techniques to characterize the blood flow is their lack of the spatial resolution required to scale down to individual capillaries. On the other hand the study of the blood flow through auto- or cross-correlation methods fail to correlate the flow speed values with the morphological details required to describe an intricate network of capillaries. Here we propose to use a newly developed technique (FLICS, FLow Image Correlation Spectroscopy) that, by employing a single raster-scanned xy-image acquired in vivo by confocal or multi-photon excitation fluorescence microscopy, allows the quantitative measurement of the blood flow velocity in the whole vessel pattern within the field of view, while simultaneously maintaining the morphological information on the immobile structures of the explored circulatory system. Fluorescent flowing objects produce diagonal lines in the raster-scanned image superimposed to static morphological details. The flow velocity is obtained by computing the Cross Correlation Function (CCF) of the intensity fluctuations detected in pairs of columns of the image. The whole analytical dependence of the CCFs on the flow speed amplitude and the flow direction has been reported recently. We report here the derivation of approximated analytical relations that allows to use the CCF peak lag time and the corresponding CCF value, to directly estimate the flow speed amplitude and the flow direction. The validation has been performed on Zebrafish embryos for which the flow direction was changed systematically by rotating the embryos on the microscope stage. The results indicate that also from the CCF peak lag time it is possible to recover the flow speed amplitude within 13% of uncertainty (overestimation) in a wide range of angles between the flow and the image scanning direction.
We have previously addressed experimentally blood fluidodynamics in microcapillaries by coupling optical microscopy to pixelated detection. By computing the Cross-Correlation Function (CCF) of signals coming from pixels at a distance along the flow we obtained information on the flow speed and direction. The extension of these experiments to more complex systems with high branching of capillaries and/or inverted flows needs a theoretical investigation that we present here. We focus first on straight capillaries and harmonic flows between a minimum Vmin ≠ 0 and a maximum Vmax flow speed. The CCF shows multiple peaks at lag times that correspond closely to the maximum and minimum flow speeds. The general analytical expression of the CCF is given, the position of its maxima are discussed by means of geometrical considerations and numerical analysis and an experimental validation are presented. The second case that we study is the flow in the branches of a y-shaped junction in a microcapillary. By simply modeling the branching in laminar flow (low Reynold numbers) and assuming a smooth transition of speeds along the branches we derive a simple numerical model to compute the trajectories of micro-beads. We estimate the flow speed in the branches by computing the CCFs between linear regions of interest set perpendicular to the axes of the branches.
Biomedical issues in vasculogenesis and cardiogenesis require methods to follow hemodynamics with high spatial (micrometers) and time (milliseconds) resolution. At the same time, we need to follow relevant morphogenetic processes on large fields of view. Fluorescence cross-correlation spectroscopy coupled to scanning or wide-field microscopy meets these needs but has limited flexibility in the excitation pattern. To overcome this limitation, we develop here a two-photon two-spots setup coupled to an all-reflective near-infrared (NIR) optimized scanning system and to an electron multiplying charge-coupled device. Two NIR laser spots are spaced at adjustable micron-size distances (1 to 50 μm) by means of a Twyman-Green interferometer and repeatedly scanned on the sample, allowing acquisition of information on flows at 4 ms–3 μm time-space resolution in parallel on an extended field of view. We analyze the effect of nonhomogeneous and variable flow on the cross-correlation function by numerical simulations and show exemplary application of this setup in studies of blood flow in zebrafish embryos in vivo. By coupling the interferometer with the scanning mirrors and by computing the cross-correlation function of fluorescent red blood cells, we are able to map speed patterns in embryos’ vessels.
The vascular system of Zebrafish embryos is studied by means of Fluorescence Correlation and Image Correlation Spectroscopy. The long term project addresses biologically relevant issues concerning vasculogenesis and cardiogenesis and in particular mechanical interaction between blood flow and endothelial cells. To this purpose we use Zebrafish as a model system since the transparency of its embryos facilitates morphological observation of internal organs in-vivo. The correlation analysis provides quantitative characterization of fluxes in blood vessels in vivo. We have pursued and compared two complementary routes. In a first one we developed a two-spots two-photon setup in which the spots are spaced at adjustable micron-size distances (1-40 μm) along a vessel and the endogenous (autofluorescence) or exogenous (dsRed transgenic erythrocytes) signal is captured with an EM-CCD and cross-correlated. In this way we are able to follow the morphology of the Zebrafish embryo, simultaneously measure the heart pulsation, the velocity of red cells and of small plasma proteins. These data are compared to those obtained by image correlations on Zebrafish vessels. The two methods allows to characterize the motion of plasma fluids and erythrocytes in healthy Zebrafish embryos to be compared in the future to pathogenic ones.
P53 is a tumor suppressor used as marker for early cancer diagnosis and prognosis. We have studied constructs based on
gold nanoparticles (NPs) decorated with specific anti-p53 antibodies and with a fluoresceine derivative, FITC. The
interaction of gold surface plasmons with fluorophores bound within few nanometers from the surface, likely induces
changes in the fluorophore excited state lifetime. Indeed we found previously that this parameter follows linearly the p53
concentration in solutions (in vitro conditions) up to 200-400 pM, depending on the size of the NP, with a 5 pM
uncertainty. We have evaluated here the nanosensor specificity for p53 by testing it in-vitro against bovine serum
albumine, beta-lactolglobulin and lysozyme. Moreover, the titration of total cell extracts from p53+/+ or p53-/- cells with
the p53antibody decorated gold NPs, indicates that this construct can also be used to detect the presence of p53 in total
cell extracts and it will be therefore a valuable tool also for in vivo screening.
Recent studies have demonstrated that dendritic cells (DCs) play a crucial role in the activation of Natural Killer cells
(NKs) that are responsible for anti-tumor innate immune responses. The focus of this report is on the role of pathogen
associated molecular pattern (PAMP) activated-DCs in inducing NK
cell-mediated anti-tumor responses.
Mice transplanted sub-cute (s.c.) with AK7 cells, a mesothelioma cell line sensitive to NK cell responses, are injected
with fluorescent NK cells and DC activation is then induced by s.c. injection of Lipopolysaccharide (LPS). Using 4
dimensional tracking we follow the kinetic behavior of NK cells at the Draining Lymph-Node (DLN). As control, noninflammatory
conditions are also evaluated.
Our data suggest that NK cells are recruited to the DLN where they can interact with activated-DCs with a peculiar
kinetic behavior: short lived interactions interleaved by rarer longer ones. We also found that the changes in the NK
dynamic behavior in inflammatory conditions clearly affect relevant motility parameters such as the instantaneous and
average velocity and the effective diffusion coefficient. This observation suggests that NK cells and activated-DCs might
efficiently interact in the DLN, where cells could be activated. Therefore the interaction between activated-DCs and NK
cells in DLN is not only a reality but it may be also crucial for the start of the immune response of the NKs.