In situ synthesis within micron-sized hydrogel reactors created via programmable aerosol chemistry†

Recent progress in materials science and complex chemical systems has highlighted the critical role of containers in directing and modulating reactivity. Micron-sized reactors are especially attractive due to their significantly different surface/volume ratios compared to traditional laboratory glassware, while still providing high experimental throughput and being easily observable using optical microscopy. Despite their promise, there is a gap in adapting chemical synthesis protocols to work within microspheres. We demonstrate a programmable aerosol chemistry setup that automates the generation of calcium alginate microspheres and allows them to be used as micro-reactors for exploration of chemical reactivity. A range of reactions can be adapted for in situ synthesis within the forming microspheres by pre-loading the precursor solutions with solid and soluble reagents, exemplified by our preparation of Prussian blue and quinhydrone. The micro-reactors are permeable, allowing rapid uptake and release of small molecule reagents and products. Larger particles trapped within the calcium alginate matrix can also be released, triggered via rapid disassembly of the microspheres in response to calcium binders like EDTA. As our standard programmable apparatus is extensible to broad reagent types and reaction stoichiometries, we expect that its adoption will accelerate exploration of chemical reactivity and discovery within micro-reactors.