Continuous optical sorting of nanoscale biomolecules in integrated microfluidic-nanophotonic chips

Optical sorting holds great potential in precise biomolecule separation. However, the current approaches still face challenges to separate nanoscale biomolecules in a continuous manner. Here we report an integrated microfluidic-nanophotonic platform, named SWANS (Silicon Waveguide-pair Array-based Nanophotonic Sorting), for continuous sorting of nanoscale biomolecules. The platform leveraged the back-and-forth light coupling in waveguide-pair arrays to create a near-field optical lattice. Particles in the near-field lattice experienced recurring trapping and deflection events and eventually established distinct trajectories. The sorting mechanism was studied through theoretical analysis and the trajectory experiment of individual 200-nm and 500-nm particles. To validate the SWANS platform, the mixture of 200-nm, 300-nm and 500-nm particles, as well as the mixture of S. aureus and 100-nm particle was separated massively. The results confirmed sorting efficiency of 95.4 % and 85.7 % for 500-nm particles and S. aureus, respectively. The SWANS platform provides new avenues for continuous biomolecule separation and is anticipated to facilitate broad biomedical applications.