Miniature Achromatic Metalens Integrated With Optical Fiber (AMOF) for Remote Single-Nanoparticle Fluorescence Probing

초록

Single-nanoparticle and single-molecule fluorescence detection delivers unparalleled capabilities for quantifying concentrations, hydrodynamic sizes, and molecular dynamics for biosensing assays or environmental monitoring. Metalenses offer a promising route to miniaturizing high-NA objective lenses, but their use in fiber-integrated probes for quantitative single-particle analysis remains largely unexplored. In this work, we introduce an achromatic metalens integrated with a solid-core optical fiber (AMOF) as a compact sensing head that enables remote epi-fluorescence correlation spectroscopy (FCS) in aqueous solutions. We achieve remote epi-fluorescence monitoring of polystyrene nanoparticles of sizes from 110 nm to 4 & micro;m and streptavidin biomolecules in the far-red spectral range within a defined focal volume. By systematically varying the optical fiber core diameters, we reveal and quantify a design trade-off between single-nanoparticle sensitivity and detection volume, enabling accurate determination of particle concentration and size down to low picomolar-femtomolar regimes through remote FCS. The robust operation of the AMOF head over meter-scale fiber lengths without complicated alignment demonstrates that high numerical aperture (NA) achromatic metalenses can be effectively combined with optical fibers for remote single-particle fluorescence analysis. This approach opens promising opportunities for in situ diagnostics, environmental nanoparticle monitoring, and remote emitter characterization.

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