Dual-Wavelength On-Chip Integrated Metalens for Epi-Fluorescence Single-Molecule Sensing.

Area of Science:

• Nanophotonics
• Spectroscopy
• Biomedical Engineering

Background:

• Single-molecule fluorescence spectroscopy enables sensitive detection but requires miniaturization for point-of-care applications.
• Lab-on-a-chip devices are crucial for portable diagnostics and real-time molecular analysis.

Purpose of the Study:

• To numerically design achromatic on-chip metalenses for sensitive single-molecule detection.
• To enable lab-on-a-chip fluorescence spectroscopy for diagnostics and molecular dynamics studies.

Main Methods:

• Numerical design of silicon nitride metalenses on waveguides with high numerical aperture (NA=1.1).
• Selective focusing of guided light into aqueous solutions at specific wavelengths (500-780 nm).
• Demonstration of overlapping focal volumes for efficient epi-fluorescence collection.

Main Results:

• Metalenses achieved high molecule detection efficiencies, collecting thousands of photons per second per molecule.
• Demonstrated reliable diffusion fluorescence correlation spectroscopy for nanomolar concentration and diffusion analysis.
• Segmented metalenses compensated for chromatic focal shift, ensuring overlapping focal volumes.

Conclusions:

• Achromatic on-chip metalenses are suitable for ultra-compact and sensitive single-molecule detection.
• This technology advances precision medicine and environmental monitoring through point-of-care diagnostics.
• Metalenses facilitate lab-on-a-chip fluorescence spectroscopy for probing molecular dynamics.