This study presents a novel dielectric metalens device that enables single-molecule fluorescence detection without the need for an objective lens. The metalens, made of hydrogen-doped amorphous silicon (aSiH), features a high numerical aperture (NA) of 0.6, high focusing efficiency, and dual-wavelength operation at 635 nm and 670 nm. This design allows for the implementation of fluorescence correlation spectroscopy (FCS) with a single Alexa 647 molecule in the focal volume. The metalens also enables real-time monitoring of individual fluorescent nanoparticle transitions and identification of hydrodynamic diameters ranging from a few to hundreds of nanometers. The device's compact size and high sensitivity make it suitable for portable single-molecule sensors, particularly in applications such as precision medicine and environmental monitoring. The study demonstrates the metalens's performance through FCS experiments, showing that it can detect 1.7 Alexa 647 molecules in the detection volume, comparable to conventional objective lenses but with a significantly smaller size. Additionally, the metalens can distinguish different sizes of nanoparticles, providing insights into their diffusion times and brightness. The results highlight the potential of metalenses in advancing single-molecule sensing technologies.This study presents a novel dielectric metalens device that enables single-molecule fluorescence detection without the need for an objective lens. The metalens, made of hydrogen-doped amorphous silicon (aSiH), features a high numerical aperture (NA) of 0.6, high focusing efficiency, and dual-wavelength operation at 635 nm and 670 nm. This design allows for the implementation of fluorescence correlation spectroscopy (FCS) with a single Alexa 647 molecule in the focal volume. The metalens also enables real-time monitoring of individual fluorescent nanoparticle transitions and identification of hydrodynamic diameters ranging from a few to hundreds of nanometers. The device's compact size and high sensitivity make it suitable for portable single-molecule sensors, particularly in applications such as precision medicine and environmental monitoring. The study demonstrates the metalens's performance through FCS experiments, showing that it can detect 1.7 Alexa 647 molecules in the detection volume, comparable to conventional objective lenses but with a significantly smaller size. Additionally, the metalens can distinguish different sizes of nanoparticles, providing insights into their diffusion times and brightness. The results highlight the potential of metalenses in advancing single-molecule sensing technologies.