Embedment of quantum dots and biomolecules in an in-situ formed dipeptide hydrogel using microfluidics.

As low-molecular-weight hydrogelators, dipeptide hydrogel materials are suited for embedding multiple organic molecules and inorganic nanoparticles. Herein, a simple but precisely controllable method is presented that enables the fabrication of dipeptide-based hydrogels via supramolecular assembly inside microfluidic channels. Water-soluble quantum dots (QDs) as well as premixed porphyrins and a dipeptide in dimethyl sulfoxide (DMSO) are injected into a Y-shaped microfluidic junction. At the DMSO/water interface the confined fabrication of a dipeptide-based hydrogel is initiated. Thereafter, the as-formed hydrogel flows along the meandered-shaped microfluidics channel in a continuous fashion, gradually completing gelation and QD entrapment. Compared to hydrogelation in conventional test tubes, microfluidically controlled hydrogelation leads to a tailored dipeptide hydrogel regarding material morphology and nanoparticle distribution.  Changing compositions, concentrations, and flow rates leads to a diverse range of hydrogel nanostructures and properties. By stopping the hydrogel flow and removing the microchannel-bearing part of the microfluidic device, the dynamic assembly and gradual entrapment of QDs can be captured at individual positions inside the microfluidic device. By further analysis, we confirm that QDs are entrapped outside of nanofibers composed by dipeptides and porphyrins inside the hydrogels in a non-covalent fashion, and can achieve organic/inorganic energy transfer inside hydrogels. The unique combination of "bottom-up" self-assembly of supramolecular peptide building blocks and "top-down" microfluidic control over hydrogel morphology and nanoparticle embedability provides the basis to implement tailored flow-through matrices for multiple molecules integrated in one coordinated system with stable and uniform entrapment of compounds of interest.