Label-free super-resolution quantitative phase microscopy

Abstract

Quantitative phase microscopy (QPM) provides sensitive, label-free measurements of optical-path-length variations in transparent and weakly scattering specimens, offering valuable insights into biological structures without exogenous labels. However, its lateral resolution remains fundamentally constrained by optical diffraction, limiting the visualization of nanoscale phase features. Here we introduce HoloSIM, a holographic structured-illumination framework that enables super-resolution quantitative phase imaging. In HoloSIM, sample-induced phase information is first converted into a near-field holographic intensity pattern on an ultrathin fluorophore-coated SiN recording layer. The encoded hologram is then relayed through incoherent fluorescence emission and read out by structured illumination microscopy, allowing the hologram to be recovered with enhanced spatial bandwidth prior to four-step phase-shifting reconstruction of a super-resolved quantitative phase map. Near-field transfer analysis indicates that an effective sample-to-recording-plane separation of approximately 10 nm, corresponding to an ultrathin SiN-supported recording geometry, provides a favourable condition for preserving sub-diffraction phase information. Siemens-star simulations yielded an estimated effective full-pitch resolution of approximately 118 nm at 10% phase-modulation retention, while two-point phase-object simulations indicated distinguishable phase maxima at a centre-to-centre separation of 120 nm. These results demonstrate the potential of HoloSIM as a route toward label-free nanoscale quantitative phase microscopy beyond the conventional QPM diffraction limit.