Paired-objectives photon enhancement (POPE) microscopy: enhanced photon collection for fluorescence imaging

Fluorescence microscopy is indispensable for visualizing biological structures and dynamics, yet its efficiency is limited-over half of emitted photons fall outside the objective's numerical aperture and go undetected. Here, we introduce Paired-Objectives Photon Enhancement (POPE) microscopy, which increases photon collection efficiency by up to two-fold using a single excitation source, single detector, and dual objectives. By integrating a 4f optical system with a reflective mirror positioned opposite the objective in an inverted microscope, POPE redirects a substantial portion of otherwise lost photons into the detection pathway. Compatible with super-resolution, confocal, epifluorescence, and autofluorescence modalities, POPE improves spatial resolution, acquisition speed, and signal-to-noise ratio, particularly under photon-limited conditions. It has been validated across fluorophore solutions, subcellular structures, live cells, and thick tissues, consistently enhancing imaging performance. As a modular and cost-effective upgrade for standard inverted microscopes, POPE extends access to high-sensitivity fluorescence imaging and enables new applications in cell biology, biophysics, and biomedical research.