High‐Resolution Oil‐Free Imaging of Chromosomes Using Fourier Ptychographic Microscopy

ABSTRACT In conventional microscopic imaging of chromosomes, the use of high numerical aperture (NA) oil‐immersion objectives is essential. However, the use of oil‐immersion objectives poses a significant challenge to automated imaging systems because it increases the risk of sample contamination and instrumental damage. The shallow depth of field (DOF) of oil‐immersion objectives also demands more sophisticated mechanical focusing. Here, we introduce a chromosome oil‐free microscopic imaging system based on Fourier Ptychographic Microscopy (FPM) technology. The system employs a 100×, 0.8 NA dry objective to achieve a half‐pitch resolution of 194 nm at an incident wavelength of 524 nm. The reconstructed images of chromosomes surpassed the conventional imaging with a 100×, 1.25 NA oil‐immersion objective. We also utilized digital refocusing methods to extend the effective DOF to ±2.4 μm. This study preliminarily validates the possibility of developing a new generation of chromosome scanners without using an oil‐immersion objective.