Fast image reconstruction for fluorescence microscopy AIP Advances 2, 032174 (2012) Spectrally resolved fluorescence lifetime imaging microscope using tunable bandpass filters Rev. Sci. Instrum. 83, 093705 (2012) Holographic microrefractometer Appl. Phys. Lett. 101, 091102 (2012) Foucault imaging by using non-dedicated transmission electron microscope Appl. Phys. Lett. 101, 093101 (2012) Micro optical power meter for direct in situ measurement of light transmitted from microscopic systems and focused on micro-samples Rev. Sci. Instrum. 83, 083107 (2012) Additional information on Rev. Sci. Instrum.A microscope employing the characteristics of the reflection at the Brewster angle has been built for the study of first-order phase transitions in monolayers and the growth of two-dimensional domains without adding fluorescent impurities. It takes about 2.4 s to constitute an image.

Optical tweezers are used to apply calibrated forces to human erythrocytes, via small silica beads bound to their membrane. The shear modulus mu of the membrane is inferred from measurements of the cell deformation in the small strain linear regime. We find the same result mu = 2.5 +/- 0.4 microN/m for both discotic and nearly spherical swollen cells. This value is smaller than the one deduced from micropipettes experiments. However the two methods do not operate in the same deformation regime and are not expected to lead to the same result.

We compare and synthesize the results of two microrheological experiments on the cytoskeleton of single cells. In the first one, the creep function J(t) of a cell stretched between two glass plates is measured after applying a constant force step. In the second one, a microbead specifically bound to transmembrane receptors is driven by an oscillating optical trap, and the viscoelastic coefficient G e (ω) is retrieved. Both J(t) and G e (ω) exhibit power law

We compare the measurements of viscoelastic properties of adherent alveolar epithelial cells by two micromanipulation techniques: (i) magnetic twisting cytometry and (ii) optical tweezers, using microbeads of same size and similarly attached to F-actin. The values of equivalent Young modulus E, derived from linear viscoelasticity theory, become consistent when the degree of bead immersion in the cell is taken into account. E-values are smaller in (i) than in (ii): approximately 34-58 Pa vs approximately 29-258 Pa, probably because higher stress in (i) reinforces nonlinearity and cellular plasticity. Otherwise, similar relaxation time constants, around 2 s, suggest similar dissipative mechanisms.

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The area expansion and the shear moduli of the free spectrin skeleton, freshly extracted from the membrane of a human red blood cell (RBC), are measured by using optical tweezers micromanipulation. An RBC is trapped by three silica beads bound to its membrane. After extraction, the skeleton is deformed by applying calibrated forces to the beads. The area expansion modulus K(C) and shear modulus mu(C) of the two-dimensional spectrin network are inferred from the deformations measured as functions of the applied stress. In low hypotonic buffer (25 mOsm/kg), one finds K(C) = 4.8 +/- 2.7 microN/m, mu(C) = 2.4 +/- 0.7 microN/m, and K(C)/mu(C) = 1.9 +/- 1.0. In isotonic buffer, one measures higher values for K(C), mu(C), and K(C)/mu(C), partly because the skeleton collapses in a high-ionic-strength environment. Some data concerning the time evolution of the mechanical properties of the skeleton after extraction and the influence of ATP are also reported. In the Discussion, it is shown that the measured values are consistent with estimates deduced from experiments carried out on the intact membrane and agree with theoretical and numerical predictions concerning two-dimensional networks of entropic springs.

The formation of adsorbed films at the free surface of aqueous solutions of sodium hexadecanoate was observed by microscopy at the Brewster angle. A phase transition between a gas and a tilted phase occurs during these slow formations. The tilt of the molecules creates an observable optical anisotropy. We observed circular domains separated into regions of uniform tilt direction by straight defect lines, i.e., ‘‘star’’ textural defects very similar to those observed in freely suspended liquid crystal thin films and in Langmuir films of esters. The coalescence of domains leads to large regions of uniform tilt direction separated by straight or kink lines. A second transition towards a nontilted phase is observed. Quantitative information about the coefficients of the continuum elastic theory can be derived from our experiments.