Concept of a convex on-chip metalens as a miniature sensor of fluorescence of single molecules

Fluorescence spectroscopy of single molecules is of fundamental significance to determine a small amount of matter and to study molecular dynamic processes. However, the applications of this method in medicine require new solutions for the miniaturization of a sensor planform. The most promising direction in this area seems to be the development of photonic integrated circuits with a high molecule detection efficiency in a volume of about cubic micron. In this work, a concept of a dielectric metalens on a waveguide, which has a high efficiency of the focusing/collection of radiation from an aqueous solution, has been presented. The structure of the metalens with a numerical aperture of above 1.1 operating in the optical range near the fluorescence maximum of the Alexa Fluor 647 dye has been simulated. After the calculation of the molecule detection efficiency, diffusion autocorrelation functions of Alexa Fluor 647 molecules have been calculated to characterize the possibility of measuring the brightness, as well as the number and dynamics of single molecules in the focal volume of the metalens. This concept provides the foundation for the development of future sensors of single molecules as biomedical and environment screening tools.