Pierre Lidon

Terbium(III) Luminescent Complexes as Millisecond-Scale Viscosity Probes for Lifetime Imaging

Fluorescent probes that are able to directly measure viscosity are attractive candidates for the study of intracellular environments. We report a new class of luminescent rotors, based on the sensitized emission of a terbium(III) complex. A 4-fold increase in both quantum yield and luminescence lifetime was observed in viscous media for the studied complexes, with a lifetime ranging from 0.23 to 0.89 ms over a broad range of viscosities (0.6-1200 cP). The presented approach, relying on the millisecond-scale luminescence lifetime of the lanthanide ions, was applied to fixed T24 cancer cells using temporal sampling lifetime imaging microscopy.

Phase characterization of the reflection on an extreme UV multilayer: comparison between attosecond metrology and standing wave measurements.

We characterize the phase shift induced by reflection on a multilayer mirror in the extreme UV range (80-93 eV) using two techniques: one based on high order harmonic generation and attosecond metrology (reconstruction of attosecond beating by interference of two-photon transitions), and a second based on synchrotron radiation and measurements of standing waves (total electron yield). We find an excellent agreement between the results from the two measurements and a flat group delay shift (±40 as) over the main reflectivity peak of the mirror.

Power-law creep and residual stresses in a carbopol gel

We report on the interplay between creep and residual stresses in a carbopol microgel. When a constant shear stress σ is applied below the yield stress σy, the strain is shown to increase as a power law of time, γ(t) = γ0 + (t/τ)α, with an exponent α = 0.39 ± 0.04 that is strongly reminiscent of Andrade creep in hard solids. For applied shear stresses lower than some typical value σc ≃ 0.2σy, the microgel experiences a more complex, anomalous creep behavior, characterized by an initial decrease of the strain, that we attribute to the existence of residual stresses of the order of σc that persist after a rest time under a zero shear rate following preshear. The influence of gel concentration on creep and residual stresses are investigated as well as possible aging effects. We discuss our results in light of previous works on colloidal glasses and other soft glassy systems.

Measurement of the acoustic radiation force on a sphere embedded in a soft solid

The acoustic radiation force exerted on a small sphere located at the focus of an ultrasonic beam is measured in a soft gel. It is proved to evolve quadratically with the local amplitude of the acoustic field. Strong oscillations of the local pressure are observed and attributed to an acoustic Fabry-Perot effect between the ultrasonic emitter and the sphere. Taking this effect into account with a simple model, a quantitative link between the radiation force and the acoustic pressure is proposed and compared to theoretical predictions in the absence of dissipation. The discrepancy between experiment and theory suggests that dissipative effects should be taken into account for fully modeling the observations.

Correction to “Terbium(iii) Luminescent Complexes as Millisecond-Scale Viscosity Probes for Lifetime Imaging”

T influence of dissolved oxygen in the photophysical measurements presented in this Communication was underestimated. Following a recent publication by Williams, Parker, and co-workers, luminescence measurements of compound [TbL] were carried out in air-equilibrated and degassed methanol and glycerol solutions. In methanol, very strong enhancement of luminescence properties was observed as oxygen concentration decreased; specifically, the luminescence lifetime increased significantly from 0.22 ms in airequilibrated medium to 1.26 ms in degassed methanol. In contrast, a modest increase was observed in glycerol upon degassing, from 0.86 to 1.00 ms. The comparable lifetimes measured for [TbL] in degassed methanol and degassed glycerol suggest that viscosity does not play the major role. On the other hand, in air-equilibrated solvents the difference in luminescence lifetimes can be correlated in a first approximation to the large difference of oxygen solubility, varying from 4.15 × 10−4 in methanol to 4.8 × 10−6−5.5 × 10−6 in glycerol, expressed as mole fractions at 298 K and 101.3 kPa. While the lifetime measurements performed in various airequilibrated methanol−glycerol mixtures are valid (Figure 2a), their interpretation as a function of the medium viscosity (Figure 2b) is incorrect. Instead, the results should be read as a function of oxygen concentration, which decreases as glycerol content increases.