Organic synthesis in soft wall-free microreactors: real-time monitoring of fluorogenic reactions.

A new approach of "laboratory on a chip" (LOC) devoted to organic synthesis based on electrically operated ionic liquid microdroplets used as air-stable "soft" microreactors was recently introduced. A number of challenging issues have yet to be addressed to allow standard macroscale organic chemistry to be directly transposed in these nonclassical microreactors. In particular, since standard (i.e., magnetical or mechanical) stirring methods are prohibited in such wall-free microreactors, effective alternatives have to be developed to circumvent mass-transfer limitations. With this aim in mind, a fluorogenic version of a click chemistry reaction was developed to evaluate the efficiency of alternative mixing methods on the reaction kinetics. We demonstrate that the combination of chaotic advection created by surface acoustic waves combined with a temperature increase (Marangoni effect) leads to the same kinetics regime as in standard macroscale conditions. This opens the route for application of the new generation of LOC to efficient organic synthesis in microscale.

DNA microarrays on silicon nanostructures: optimization of the multilayer stack for fluorescence detection.

To improve the sensitivity of fluorescence detection in DNA microarrays, the use of silicon nanostructures based on chemical vapor deposition (CVD) processes adopted for the growth of rough polycrystalline silicon was investigated. These substrates present advantages of two main properties which could lead to an enhancement of the fluorescence detection, i.e. (i) the increase of the available surface area in order to achieve a high loading capacity of biomolecules and (ii) the optimization of the stack of silicon nanostructures support. Indeed, the structures were elaborated on an initial thermal oxide layer and then covered with a silicon oxide layer, obtained by oxidation and allowing the functionalization for the subsequent grafting of DNA probes. Moreover, these oxide layers play a part in the fluorescence detection. The influence of the silicon oxide layer thickness above and below the silicon grains in close relation with the density of nanostructures on the emitted fluorescence was emphasized. This paper presents an experimental characterization of the fluorescence intensity and the optimization of the different layers that composed the substrate used for DNA microarrays. The performances of the microarrays were investigated by means of hybridization experiments using complementary fluorescent labeled-oligonucleotides targets. Our results indicate that an optimized substrate can be designed and that the use of oxidized silicon nanostructures for support of biochip could be a strategy for improving the sensitivity of fluorescence detection.