Quantitative assessment of cell viability based on flow cytometry and microscopy.

We compare flow cytometric and microscopic determination of cell viability by fluorescence labeling using calcein acetoxy-methyl-ester and ethidium homodimer-1 as live and dead stain, respectively. Peripheral blood monocytes served as model system and were accumulated applying density gradients. Subsequently, monocytes were further enriched by magnetic-activated or fluorescence-activated cell sorting (MACS, FACS) targeting the antigen CD14. Identical samples were used for flow cytometric and microscopic analysis to allow direct comparison of both analysis methods. More than 1,000 cells were measured for each sample to minimize the measurement uncertainty caused by counting statistics. We observed good agreement of flow cytometric and microscopic viability measurements. On average, the difference in viability measured by flow cytometry and microscopy amounted to (2.7 ± 1.4)% for live staining and (1.7 ± 1.2)% for dead staining. These deviations were similar to the uncertainty of measurement for cell viability, thus demonstrating that both methods delivered equal results. Besides monocytes, comparison of flow cytometric and microscopy viability for MACS enriched CD34-positive cells also showed consistent results.

Microfluidic structures for flow cytometric analysis of hydrodynamically focussed blood cells fabricated by ultraprecision micromachining.

We present three-dimensional microfluidic structures with integrated optical fibers, mirrors and electrodes for flow cytometric analysis of blood cells. Ultraprecision milling technique was used to fabricate different flow cells featuring single-stage and two-stage cascaded hydrodynamic focusing of particles by a sheath flow. Two dimensional focussing of the sample fluid was proven by fluorescence imaging in horizontal and vertical directions and found to agree satisfactorily with finite element calculations. Focussing of the sample stream down to 5 microm at a particle velocity of 3 m s(-1) is accessible while maintaining stable operation for sample flow rates of up to 20 microL min(-1). In addition to fluorescence imaging, the micro-flow cells were characterised by measurements of pulse shapes and pulse height distributions of monodisperse microspheres. We demonstrated practical use of the microstructures for cell differentiation employing light scatter to distinguish platelets and red blood cells. Furthermore, T-helper lymphocytes labelled by monoclonal antibodies were identified by measuring side scatter and fluorescence.

Evaluation of higher-order time-domain perturbation theory of photon diffusion on breast-equivalent phantoms and optical mammograms.

Time-domain perturbation theory of photon diffusion up to third order was evaluated for its accuracy in deducing optical properties of breast tumors using simulated and physical phantoms and by analyzing 141 projection mammograms of 87 patients with histology-validated tumors that had been recorded by scanning time-domain optical mammography. The slightly compressed breast was modeled as (partially) homogeneous diffusely scattering infinite slab containing a scattering and absorbing spherical heterogeneity representing the tumor. Photon flux densities were calculated from densities of transmitted photons, assuming extended boundary conditions. Explicit formulas are provided for second-order changes in transmitted photon density due to the presence of absorbers or scatterers. The results on phantoms obtained by perturbation theory carried up to third order were compared with measured temporal point spread functions, with numerical finite-element method (FEM) simulations of transmitted photon flux density, with results obtained from the diffraction of diffuse photon density waves, and from Padé approximants. The breakdown of first-, second-, and third-order perturbation theory is discussed for absorbers and a general expression was derived for the convergence of the Born series in this case. Taking tumor optical properties derived by the diffraction model as reference we conclude that estimates of tumor absorption coefficients by perturbation theory agree with reference values within +/-25% in only 65% (first order), 66% (second order), and 77% (third order) of all mammograms analyzed. In the remaining cases tumor absorption is generally underestimated due to the breakdown of perturbation theory. On average the empirical Padé approximants yield tumor absorption coefficients similar to third-order perturbation theory, yet at noticeable lower computational efforts.

In-vivo tissue optical properties derived by linear perturbation theory for edge-corrected time-domain mammograms.

A valuable method is described to analyze time-domain optical mammograms measured in the slab-like geometry of the slightly compressed female breast with a method based on linear perturbation theory including edge correction. Perturbations in scattering and absorption coefficients were mapped applying a computationally efficient point model.

Fluorescence of native and carotenoid-depleted LH2 from Chromatium minutissimum, originating from simultaneous two-photon absorption in the spectral range of the presumed (optically 'dark') S(1) state of carotenoids.

Native and carotenoid-depleted peripheral purple bacterial light-harvesting complex (LH2) were investigated by simultaneous two-photon excited (between 1300-1500 nm) fluorescence (TPF). TPF results from direct bacteriochlorophyll excitation in both samples. The spectral position of the 2A(g)(-) state of rhodopin [corrected] is indicated by a diminuition of the bacteriochlorophyll TPF in native LH2. In conclusion, comparison to carotenoid-depleted samples is a conditio sine qua non for unambiguous interpretation of similar experiments.

Acousto-optic mode locking of 3-microm Er lasers.

Er:YAG 2.94-microm lasers and Er:YLF 2.81-microm lasers were actively mode locked, with TeO(2) as the acousto-optic modulator. The Er:YLF crystal generated shorter and more stable pulses, whereas the Er:YAG had a higher slope efficiency of 0.8% in free-running operation. Mode-locked pulse durations of < 700 ps were obtained with Er: YLF by applying 4 W of electrical driving power to the LiNbO(3) transducer.

Spatially resolved small-angle noncollinear interferometric autocorrelation of ultrashort pulses with microaxicon arrays.

Small-angle, noncollinear, first- and second-order interferometric autocorrelation experiments with Ti:sapphire laser pulses of 9-80-fs duration have been performed with microaxicon arrays. Predictions of short-pulse spatial frequency effects were verified by comparison of interference patterns of single elements and matrices. An angular spectrum of Gaussian-shaped axicons was analyzed on the basis of linear refraction. Experimental data indicate contributions to autocorrelation by nonlinear refraction and travel-time differences. The influence of the spectral bandwidth was separated from the pulse-duration-dependent effects. Spatially resolved information about the coherence time was delivered by the multichannel structure.