Removing orientation-induced localization biases in single-molecule microscopy using a broadband metasurface mask

Nanoscale localization of single molecules is a crucial function in several advanced microscopy techniques, including single-molecule tracking and wide-field super-resolution imaging. Until now, a central consideration of such techniques is how to optimize the precision of molecular localization. However, as these methods continue to push towards the nanometre size scale, an increasingly important concern is the localization accuracy. In particular, single fluorescent molecules emit with an anisotropic radiation pattern of an oscillating electric dipole, which can cause significant localization biases using common estimators. Here we present the theory and experimental demonstration of a solution to this problem based on azimuthal filtering in the Fourier plane of the microscope. We do so using a high-efficiency dielectric metasurface polarization/phase device composed of nanoposts with subwavelength spacing. The method is demonstrated both on fluorophores embedded in a polymer matrix and in dL5 protein complexes that bind malachite green.