Romain Grossier

Generating nanoliter to femtoliter microdroplets with ease

In this letter, we present a simply constructed and easy-to-use fluidic device that generates arrayed aqueous phase microdroplets in oil of controlled size with volumes ranging from nanoliter to femtoliter without surfactant. This can be applicable with a range of materials, allowing production and storage of monodisperse microdroplets. We illustrate the potential of our methodology in the field of nanoparticle generation

Practical Physics Behind Growing Crystals of Biological Macromolecules

The aim of this review is to provide biocrystallographers who intend to tackle protein-crystallization with theory and practical examples. Crystallization involves two separate processes, nucleation and growth, which are rarely completely unconnected. Here we give theoretical background and concrete examples illustrating protein crystallization. We describe the nucleation of a new phase, solid or liquid, and the growth and transformation of existing crystals obtained by primary or secondary nucleation or by seeding. Above all, we believe that a thorough knowledge of the phase diagram is vital to the selection of starting position and path for any crystallization experiment.

Monitoring picoliter sessile microdroplet dynamics shows that size does not matter.

We monitor the dissolution of arrayed picoliter-size sessile microdroplets of the aqueous phase in oil, generated using a recently developed fluidic device. Initial pinning of the microdroplet perimeter leads to a nearly constant contact diameter, thus contraction proceeds via microdroplet (micrometer-diameter) height and contact angle reductions. This confirms that picoliter microdroplets contraction or dissolution due to the selective diffusion of water in oil has comparable dynamics with microliter droplet evaporation in air. We observe a constant microdroplet dissolution rate in different aqueous solutions. The application of this simple model to solvent-diffusion-driven crystallization experiments in confined volumes, for instance, would allow us to determine precisely the concentration in the microdroplet during an experiment and particularly at nucleation.

Nanotechnologies dedicated to nucleation control

This paper highlights the work of our group on the control and the observation of nucleation with techniques using nanotechnologies. This control is performed either by triggering nucleation in time with an external field or by localising it spatially in a microdroplet. Localisation in time using light irradiation induces nucleation by forming radicals; the use of electric field acts locally on the density of the solution. Localisation in space with a microfluidic device produces hundreds of nanovolume crystallisers where concentration and temperature are easily monitored. Thus, accurate statistical studies lead to the nucleation parameters (metastable zone, nucleation rate and polymorphism). Lastly, confinement with a microdroplet generator permits to reach very high supersaturations in fL to pL volumes allowing nucleation of a single crystal per microdroplet. All these methods clearly enhance nucleation in the metastable zone. Finally, they use small quantities of products offering potentialities for the screening of crystallisation conditions and phases (polymorphism).

Crystallization via tubing microfluidics permits both in situ and ex situ X-ray diffraction

A microfluidic platform was used to address the problems of obtaining diffraction-quality crystals and crystal handling during transfer to the X-ray diffractometer. Crystallization conditions of a protein of pharmaceutical interest were optimized and X-ray data were collected both in situ and ex situ.

Addressing the Stochasticity of Nucleation: Practical Approaches

This chapter presents different practical ways to address nucleation stochasticity. The methods use either statistical studies on spontaneous nucleation or local control of nucleation. Techniques developed in our laboratory are described: droplet-based microfluidics, microinjectors in oil, and external electrical or mechanical fields in confined systems. Results of nucleation kinetics obtained on various molecules are presented in terms of metastable zone, critical supersaturation, nucleation rate, induction time, interfacial energy of the critical nucleus, polymorphism, and detection of the critical nucleus. These practical approaches show considerable potential to increase understanding and control of the nucleation mechanism.