A complex droplet-based microfluidic platform for rapid immobilization of oligonucleotides on semiconductor quantum dots*

Quantum dot-oligonucleotide DNA (QD-DNA) has attracted significant interest due to its applications in analytical chemistry. A current solid phase method to achieve immobilization of oligonucleotides DNA onto QDs involves a two-step reaction and be performed in a batch-based setting. Lately, droplet microfluidics, as a capable tool, offers numerous advantages that are unavailable for batch processing. Herein, we introduce a platform for rapidly immobilizing DNA onto QDs. The reagents used in batches are now divided into separated aqueous droplets, carried by oil phase. Notably, the device encapsulates QDs and magnetic beads (MB) in droplets for the QD-MB conjugates as the first step of the reaction. The second step is to merge other droplets containing DNA with these droplets in a merger. The merged droplets are pumped through a serpentine micro-channel for better mixing, resulting in the QD-DNA conjugation. This platform presents several benefits such as a higher degree of control of the reaction conditions; exclusion of the external vortexing and pipetting; minimized cross-contamination and impurities; plus, reduced cost due to the less reagent consumption. To evaluate the conjugation, we perform the fluorescence transduction of nucleic acid hybridization off-chip.