Digital optofluidics: LED-gated transport and fusion of microliter-sized organic droplets for chemical synthesis.

Microdroplet-based organic syntheses have been developed as a valuable alternative to traditional bulk-based methods. However, unlike their water counterparts, organic microdroplets can prove challenging to manipulate. Here, we describe the first optical manipulation of discrete, nanoliter- to microliter-sized apolar droplets floating on a liquid surface to induce on-demand droplet fusion for organic synthesis. We demonstrate droplet transport on centimeter-scale distances at speeds of 0.1 to 1 mm·s(-1) with well-programmable, sequential or parallel, fusion events. Because our strategy is compatible with most usual hydrocarbon solvents, such droplets can be used as microcompartments for reagents. Organic reactions readily occur upon droplet fusion, as demonstrated with an ene reaction. With an LED as the sole power source, and without any fabrication step, optical setup, pump or electrode implementation, our method provides a robust and versatile way to place digital organic chemistry under optical control.

Photosensitive polyamines for high-performance photocontrol of DNA higher-order structure.

Polyamines are small, ubiquitous, positively charged molecules that play an essential role in numerous biological processes such as DNA packaging, gene regulation, neuron activity, and cell proliferation. Here, we synthesize the first series of photosensitive polyamines (PPAs) and demonstrate their ability to photoreversibly control nanoscale DNA higher-order structure with high efficiency. We show with fluorescence microscopy imaging that the efficiency of the PPAs as DNA-compacting agents is directly correlated to their molecular charge. Micromolar concentration of the most efficient molecule described here, a PPA containing three charges at neutral pH, compacts DNA molecules from a few kilobase pairs to a few hundred kilobase pairs, while subsequent 3 min UV illuminations at 365 nm triggers complete unfolding of DNA molecules. Additional application of blue light (440 nm for 3 min) induces the refolding of DNA into the compact state. Atomic force microscopy reveals that the compaction involves a global folding of the whole DNA molecule, whereas UV-induced unfolding is a modification initiated from the periphery of the compacted DNA, resulting in the occurrence of intermediate flower-like structures prior to the fully unfolded state.

Cell-free preparation of functional and triggerable giant proteoliposomes.

Heat, we leak: We express a membrane protein outside well-defined giant liposomes obtained by gravity-transferred sucrose-in-oil droplets into a cell-free, reconstituted expression system. We show that the presence of the liposome is necessary during expression for efficient protein insertion into the membrane and that temperature can trigger the resulting membrane function.

Microfluidic mixing triggered by an external LED illumination.

The mixing of confined liquids is a central yet challenging operation in miniaturized devices. Microfluidic mixing is usually achieved with passive mixers that are robust but poorly flexible, or active mixers that offer dynamic control but mainly rely on electrical or mechanical transducers, which increase the fragility, cost, and complexity of the device. Here, we describe the first remote and reversible control of microfluidic mixing triggered by a light illumination simply provided by an external LED illumination device. The approach is based on the light-induced generation of water microdroplets acting as reversible stirrers of two continuous oil phase flows containing samples to be mixed. We demonstrate many cycles of reversible photoinduced transitions between a nonmixing behavior and full homogenization of the two oil phases. The method is cheap, portable, and adaptable to many device configurations, thus constituting an essential brick for the generation of future all-optofluidic chip.

Modification-free photocontrol of ß-lactam conversion with spatiotemporal resolution.

ß-Lactams can be converted into ß-amino acids by ß-lactamase, a bacterial enzyme, leading to significant change in the biological function of the substrate molecules. Here we describe a method for photocontrol of ß-lactam conversion without gene nor enzyme modification. This is achieved by the addition of a cationic photosensitive surfactant, AzoTAB, to a gene expression medium containing DNA coding for ß-lactamase, the enzyme capable of the desired conversion. In the absence of UV (365 nm) or after illumination by blue light (480 nm) for 4 min, conversion of ß-lactam is strongly reduced while the application of UV for 4 min results in a strong enhancement of substrate conversion. Several cycles of activation/inhibition are obtained upon successive UV/blue light illuminations. When both reconstituted photoresponsive gene expression medium and ß-lactamase substrate are encapsulated in independent microfluidic chambers, selective UV illumination results in spatially resolved activation of substrate conversion.

A rational design of catechol-based compounds: an experimental and theoretical study of optical properties.

The synthesis and optical properties of 4,5-disubstituted (tert-butyldimethylsilyloxy)-protected catechol derivatives are reported. One or two carbon-carbon triple bond functions were introduced through the Sonogashira cross-coupling reaction. The effects on the optical properties of monosubstitution at the 4-position or disubstitution at the 4- and 5-positions of these catechol derivatives with electron-withdrawing or -donating substituents have been investigated. The experimental chemical-structure-polarisability relationship has been studied by using the Lippert-Mataga correlation and compared with the results of a theoretical study carried out with DFT calculations. These compounds are promising candidates for the fine-tuning of internal charge transfer, but also as potential non-linear chromophores and ligands within multifunctional coordination complexes.