Reconfigurable label-free shape-sieving of submicron particles in paired chalcogenide waveguides

Up-to-date particle sieving schemes face formidable challenges for sieving label-free submicron molecules with similar sizes and dielectric constants but diverse shapes. Herein, optical sorting of polystyrene particles with various shapes is illustrated in optofluidic nanophotonic paired waveguide (ONPW) composed of chalcogenide semiconductor Sb2Se3. The Sb2Se3-ONPW creates the coupling length (C-L) between the neighboring hot spots that can be actively modulated via the transition of Sb2Se3 between amorphous (AM) and crystalline (CR) phases. Submicron particles interfere with the coupled hotspots, which can exert various optical torques on the particles according to their profiles. In the model system, spherical (diameter of 0.5 mu m) and rod-shaped (diameter of 0.5 mu m, length of 1.5 mu m) polystyrene particles were employed to mimic two types of bacteria, namely, Staphylococcus aureus and rod-shaped Escherichia coli, respectively. For the AM state, the C-L value is similar to 7.0 mu m, enabling the structure to trap the sphere stably in the hot spots. For the CR state, the C-L value becomes similar to 25 mu m, leading to stable trapping of the rod-shaped particle. In this work, the working wavelength was fixed at 1.55 mu m at which both AM- and CR-Sb2Se3 are transparent. Our scheme may offer a paradigm shift in shape-selective sieving of biomolecules and fulfill the requirements of the new-generation lab-on-chip techniques, where the integrated manipulation system must be much more multifunctional and flexible.

Automated summary

This study presents an optical sorting method for polystyrene particles using optofluidic nanophotonic paired waveguide (ONPW) composed of chalcogenide semiconductor Sb2Se3. The coupling length between hot spots in the ONPW can be modulated by changing the state of Sb2Se3, allowing for the trapping and sorting of particles with different shapes. This scheme may provide a new approach for shape-selective sieving of biomolecules and meet the requirements of new-generation lab-on-chip techniques.