Preparation of biofunctionalized quantum dots using microfluidic chips for bioimaging

Biofunctionalized quantum dots (QDs), especially protein-coated QDs, are known to be useful targeted fluorescent labels for cellular and deep-tissue imaging. These nanoparticles can also serve as efficient energy donors in fluorescence resonance energy transfer (FRET) binding assays for the multiplexed sensing of tumor markers. However, current preparation processes for protein-functionalized QDs are laborious and require multiple synthesis steps (e.g. preparing them in high temperature, making them dispersible in water, and functionalizing them with surface ligands) to obtain a high quality and quantity of QD formulations, significantly impeding the progress of employing QDs for clinical diagnostics use such as a QD-based immunohistofluorescence assay. Herein, we demonstrate a one-step synthesis approach for preparing protein-functionalized QDs using a microfluidic (MF) chip setup. Using bovine serum albumin (BSA) molecules as the surface ligand model, we first studied and optimized the MF reaction synthesis parameters (e.g. reaction temperature, and channel width and length) for making protein-functionalized QDs using COMSOL simulation modeling, followed by experimental verification. Moreover, in comparison with the BSA-functionalized QDs synthesized using the conventional bench-top method, BSA-QDs prepared using the MF approach exhibit a significantly higher protein-functionalization efficiency, photostability and colloidal stability. The proposed one-step MF synthesis approach provides a rapid, cost effective, and a small-scale production of nanocrystals platform for developing new QD formulations in applications ranging from cell labeling to biomolecular sensing. Most importantly, this approach will considerably reduce the amount of chemical waste generated during the trial-and-error stage of developing and perfecting the desired physical and optical properties of new QD materials.