Lior Turgeman

Bar Ilan University, Ramat Gan, Tel Aviv, Israel

Are you Lior Turgeman?

Claim your profile

Publications (10)22.89 Total impact

  • Dror Fixler, Lior Turgeman
    [Show abstract] [Hide abstract]
    ABSTRACT: In order to maximize the signal-to-noise ratio for a given temporal-resolution of typical photon counting single-molecule polarization-sensitive system, this talk suggests examining the rate of convergence and the variance of the time-averaged measured fluorescence intensity.
    Imaging Systems and Applications; 06/2013
  • Source
    Lior Turgeman, Dror Fixler
    [Show abstract] [Hide abstract]
    ABSTRACT: In fluorescence fluctuation polarization sensitive experiments, the limitations associated with detecting the rotational timescale are usually eliminated by applying fluorescence correlation spectroscopy analysis. In this paper, the variance of the time-averaged fluorescence intensity extracted from the second moment of the measured fluorescence intensity is analyzed in the short time limit, before fluctuations resulting from rotational diffusion average out. Since rotational correlation times of fluorescence molecules are typically much lower than the temporal resolution of the system, independently of the time bins used, averaging over an ensemble of time-averaged trajectories was performed in order to construct the time-averaged intensity distribution, thus improving the signal-to-noise ratio. Rotational correlation times of fluorescein molecules in different viscosities of the medium within the range of the anti-bunching time (1-10 ns) were then extracted using this method.
    Biomedical Optics Express 06/2013; 4(6):868-84. · 3.18 Impact Factor
  • Lior Turgeman, Dror Fixler
    [Show abstract] [Hide abstract]
    ABSTRACT: Recent developments in the field of fluorescence lifetime imaging microscopy (FLIM) techniques allow the use of high repetition rate light sources in live cell experiments. For light sources with a repetition rate of 20-100 MHz, the time-correlated single photon counting (TCSPC) FLIM systems suffer serious dead time related distortions, known as "inter-pulse pile-up". The objective of this paper is to present a new method to quantify the level of signal distortion in TCSPC FLIM experiments, in order to determine the most efficient laser repetition rate for different FLT ranges. Optimization of the F -value, which is the relation between the relative standard deviation (RSD) in the measured FLT to the RSD in the measured fluorescence intensity (FI), allows quantification of the level of FI signal distortion, as well as determination of the correct FLT of the measurement. It is shown that by using a very high repetition rate (80 MHz) for samples characterized by high real FLT's (4-5 ns), virtual short FLT components are added to the FLT histogram while a F -value that is higher than 1 is obtained. For samples characterized with short real FLT's, virtual long FLT components are added to the FLT histogram with the lower repetition rate (20-50 MHz), while by using a higher repetition rate (80 MHz) the "inter-pulse pile-up" is eliminated as the F -value is close to 1. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim).
    Journal of Biophotonics 05/2013; · 3.10 Impact Factor
  • L Turgeman, D Fixler
    [Show abstract] [Hide abstract]
    ABSTRACT: In time correlated single photon counting (TCSPC) systems the maximum signal throughput is limited by the occurrence of pile-up and other effects. In many biological applications that exhibit high levels of fluorescence intensity (FI), pile-up related distortions yields serious distortions in the fluorescence lifetime (FLT) calculation as well as significant decrease in the signal to noise ratio (SNR). Recent developments that allow the use of high repetition rate light sources (in the range of 50 to 100 MHz) in fluorescence lifetime imaging (FLIM) experiments enable minimization of classical pile-up related distortions. However, modern TCSPC configurations that use high-repetition-rate excitation sources for FLIM, suffer from dead time related distortions that cause unpredictable distortions of the FI signal. In this work, the loss of SNR described by F-value as it is typically done in FLIM systems. This F-value describes the relation of the relative standard deviation in the estimated FLT to the relative standard deviation in FI measurements. Optimization of the F-value allows minimization of signal distortion, as well as shortening of the acquisition time for certain samples. We applied this method for Fluorescein and Erythrosine fluorescent solutions that have different FLT values (4 nsec and 140 psec respectively).
    IEEE transactions on bio-medical engineering 01/2013; · 2.15 Impact Factor
  • Source
    Lior Turgeman, Dror Fixler
    [Show abstract] [Hide abstract]
    ABSTRACT: Recent developments in the field of single molecule orientation imaging have led us to devise a simple framework for analyzing fluorescence intensity fluctuations in single molecule polarization sensitive experiments. Based on the new framework, rotational dynamics of individual molecules are quantified, in this paper, from the short time behavior of the time averaged fluorescence intensity fluctuation trajectories. The suggested model can be applied in single molecule fluorescence fluctuations experiments to extract accurate expectation values of photon counts during very short integration time in which rotational diffusion is likely not to be averaged out.
    Optics Express 04/2012; 20(8):9276-83. · 3.55 Impact Factor
  • Lior Turgeman, Dror Fixler
    [Show abstract] [Hide abstract]
    ABSTRACT: A general framework to include fluctuations in the single molecule fluorescence intensity (FI) signal due to random changes in molecule dipole orientation was introduced at Optics Express (21, 2007). By assuming continuous changes in dipole orientation described by Brownian rotational diffusion, this research derives the probability density function (PDF) equation of FI fluctuations. Solution of the proposed equation for several limiting cases and different correlation times yields the short time behavior of FI fluctuations. Monte Carlo simulations results, in accordance with those found in theory will be presented during our talk.
    Proc SPIE 02/2012;
  • [Show abstract] [Hide abstract]
    ABSTRACT: In the present study we introduce a Whole-Object Fluorescence Life Time (wo-FLT) measurement approach for ease and a relatively inexpensive method of tracing alterations in intracellular fluorophore distribution and in the physical-chemical features of the microenvironments hosting the fluorophore. Two common fluorophores, Rhodamine 123 and Acridine Orange, were used to stain U937 cells which were incubated, with and without either Carbonyl cyanide 3-chlorphenylhydrazon or the apoptosis inducer H(2)O(2). The wo-FLT, which is a non-imaging quantitative measurement, was able to detect several fluorescence decay components and corresponding weights in a single cell resolution. Following cell treatment, both decay time and weight were altered. Results suggest that the prominent factor responsible for these alterations and in some cases to a shift in emission spectrum as well, is the intracellular fluorophore local concentration. In this study it was demonstrated that the proposed wo-FLT method is superior to color fluorescence based imaging in cases where the emission spectrum of a fluorophore remains unchanged during the investigated process. The proposed wo-FLT approach may be of particular importance when direct imaging is impossible.
    Journal of Fluorescence 01/2012; 22(3):875-82. · 1.79 Impact Factor
  • Source
    Shai Carmi, Lior Turgeman, Eli Barkai
    [Show abstract] [Hide abstract]
    ABSTRACT: We obtain an equation for the distribution of functionals of the path of a particle undergoing sub-diffusive continuous-time random-walk. Our equation is a fractional generalization of the Feynman-Kac equation for Brownian functionals and makes use of the substantial fractional derivative operator introduced by Friedrich and co-workers. We also derive a backward equation that depends on the initial position rather than the final one, and equations for a process with underlying Levy flights. As applications, we derive the PDFs of the occupation time in half-space, the first passage time, and the maximum of the walk; and calculate the average residence time in an interval, the survival probability if the interval is absorbing, and the moments of the area under the random walk curve. Comment: 24 pages, 4 figures
    04/2010;
  • Source
    Shai Carmi, Lior Turgeman, Eli Barkai
    [Show abstract] [Hide abstract]
    ABSTRACT: Functionals of Brownian motion have diverse applications in physics, mathematics, and other fields. The probability density function (PDF) of Brownian functionals satisfies the Feynman-Kac formula, which is a Schrödinger equation in imaginary time. In recent years there is a growing interest in particular functionals of non-Brownian motion, or anomalous diffusion, but no equation existed for their PDF. Here, we derive a fractional generalization of the Feynman-Kac equation for functionals of anomalous paths based on sub-diffusive continuous-time random walk. We also derive a backward equation and a generalization to Lévy flights. Solutions are presented for a wide number of applications including the occupation time in half space and in an interval, the first passage time, the maximal displacement, and the hitting probability. We briefly discuss other fractional Schrödinger equations that recently appeared in the literature. KeywordsContinuous-time random-walk-Anomalous diffusion-Feynman-Kac equation-Levy flights-Fractional calculus
    Journal of Statistical Physics 01/2010; 141(6):1071-1092. · 1.40 Impact Factor
  • Source
    Lior Turgeman, Shai Carmi, Eli Barkai
    [Show abstract] [Hide abstract]
    ABSTRACT: We derive backward and forward fractional Feynman-Kac equations for the distribution of functionals of the path of a particle undergoing anomalous diffusion. Fractional substantial derivatives introduced by Friedrich and co-workers [Phys. Rev. Lett. 96, 230601 (2006)10.1103/PhysRevLett.96.230601] provide the correct fractional framework for the problem. For applications, we calculate the distribution of occupation times in half space and show how the statistics of anomalous functionals is related to weak ergodicity breaking.
    Physical Review Letters 11/2009; 103(19):190201. · 7.73 Impact Factor