In situ experiments at SOLEIL under microfluidic conditions Analyzing samples in conditions relevant structures of these macromolecules alone and in complex with to their function is key to understand their drugs is the major goal of synchrotron-based X-ray diffraction experiments [2]. This technique is, however, performed under structure and behavior. Examples include cryogenic conditions (liquid nitrogen temperature) to mitigate the observation of living cells or proteins damaging the samples from an excessive X-ray dose. As a under physiological conditions (in vivo), consequence, the structural information obtained correspond nanoparticles during their synthesis (in to a specific « frozen state » of the protein, which may not be identical to what is actually happening under physiological situ) or catalysts under operating conditions conditions. Using a microfluidic chip containing channels and (operando). The manipulation of samples traps, microcrystals of proteins can be immobilized at pre- determined locations and then analyzed by diffraction at room to perform synchrotron-based analyses temperature or under physiological conditions. Data collected under these conditions is made possible by in this way provide information that are much more relevant to the precise control of fluids in micron-sized the actual functioning of the proteins in a living organism [3]. As a proof of principle of this approach, the PROXIMA-1 team has channels. The microfluidic laboratory of performed in situ diffraction experiments on lysozyme crystals SOLEIL provides the space, instruments trapped within dedicated microfluidic chips (Figure 1). Future and expertise to design and produce such experiments will involve the diffusion of a drug into the protein crystals, to observe the associated structural changes in situ. sample environments adapted to synchrotron techniques. FIGURE 1 When a fluid circulates in micron-sized channels, specific physical properties appear that are not accessible in systems of larger dimensions. The constraints imposed on fluid in these conditions lead to laminar flows, which allow the manipulation of liquids and of solid-liquid and liquid-liquid interfaces [1]. Controlling the behavior of fluids also provides a convenient tool to manipulate solutes or suspended objects, such as living cells, microcrystals, colloids or nanoparticles. In a synchrotron, such a tool is ideal to perform studies under physiological (biology), synthetic (chemistry) or catalytic (biology or chemistry) conditions. A microfluidic laboratory is now available at SOLEIL, which provides all the tools and know-how to design and use microfluidic systems adapted to synchrotron-based experiments. Selected examples are presented hereafter that showcase the potential use of these sample environments to perform X-ray diffraction, diffusion or absorption experiments. THEY FELL IN THE TRAP A current challenge in health research is to determine the detailed action of a drug on an organism, be it a pathogen or a healthy subject. Proteins are the main targets of drugs and as such, focus a lot of attention. Determining the three-dimensional 84