Spatially selective manipulation of cells with single-beam acoustical tweezers.

Acoustical tweezers open major prospects in microbiology for cells and microorganisms contactless manipulation, organization and mechanical properties testing since they are biocompatible, label-free and have the potential to exert forces several orders of magnitude larger than their optical counterpart at equivalent power. Yet, these perspectives have so far been hindered by the absence of spatial selectivity of existing acoustical tweezers - i.e., the ability to select and move objects individually - and/or their limited resolution restricting their use to large particle manipulation only and/or finally the limited forces that they could apply. Here, we report precise selective manipulation and positioning of individual human cells in a standard microscopy environment with trapping forces up to ~200 pN without altering their viability. These results are obtained with miniaturized acoustical tweezers combining holography with active materials to synthesize specific wavefields called focused acoustical vortices designed to produce stiff localized traps with reduced acoustic power.

A minimal titration model of the mammalian dynamical heat shock response.

Environmental stress, such as oxidative or heat stress, induces the activation of the heat shock response (HSR) and leads to an increase in the heat shock proteins (HSPs) level. These HSPs act as molecular chaperones to maintain cellular proteostasis. Controlled by highly intricate regulatory mechanisms, having stress-induced activation and feedback regulations with multiple partners, the HSR is still incompletely understood. In this context, we propose a minimal molecular model for the gene regulatory network of the HSR that reproduces quantitatively different heat shock experiments both on heat shock factor 1 (HSF1) and HSPs activities. This model, which is based on chemical kinetics laws, is kept with a low dimensionality without altering the biological interpretation of the model dynamics. This simplistic model highlights the titration of HSF1 by chaperones as the guiding line of the network. Moreover, by a steady states analysis of the network, three different temperature stress regimes appear: normal, acute, and chronic, where normal stress corresponds to pseudo thermal adaption. The protein triage that governs the fate of damaged proteins or the different stress regimes are consequences of the titration mechanism. The simplicity of the present model is of interest in order to study detailed modelling of cross regulation between the HSR and other major genetic networks like the cell cycle or the circadian clock.

A high-power tunable Raman fiber ring laser for the investigation of singlet oxygen production from direct laser excitation around 1270 nm.

We report on the development of a tunable Raman fiber ring laser especially designed for the investigation of the 3Σ(-)(g) →1 Δg transition of molecular oxygen. Singlet oxygen (1Δg) is a reactive species of importance in the fields of biology, photochemistry, and phototherapy. Tunability of the Raman fiber ring laser is achieved without the use of an intracavity tunable bandpass filter and the laser thus achieves a slope efficiency only obtained up to now in Perot-Fabry cavities. A measurement of the action spectrum of a singlet oxygen trap is made in air-saturated ethanol and acetone to demonstrate the practical application of the tunable Raman fiber ring laser for the investigation of the 3Σ(-)(g) →1 Δg transition of molecular oxygen.