Intrinsic dark-field Fourier ptychographic diffraction tomography under non-matched illumination
Published 26 January, 2026
Observing living cells in their natural, three-dimensional state within standard laboratory dishes is crucial for biomedical research. However, it poses a challenge for high-resolution microscopes. The geometry of common multi-well plates restricts the lighting angles, leading to blurry and low-contrast images.
Now, researchers from Nanjing University of Science and Technology have turned this problem into a solution. Their new method, called dark-field Fourier ptychographic diffraction tomography (DF-FPDT), cleverly uses the same restricted lighting to selectively enhance the fine details of a cell while suppressing the blurry background.
“Instead of fighting the physical constraints of the culture dish, our method embraces them,” says Professor Chao Zuo, corresponding author of the study. “We use an algorithm to tell the reconstruction process to ignore the missing 'fuzzy' information and only piece together the sharp, high-frequency details that are naturally encoded in the images.”
The result is a 3D image with much clearer contrast, similar to that from a more complex dark-field microscope.
The team validated DF-FPDT by imaging live cells and other samples. “The results showed dramatically improved visibility of intracellular structures like mitochondria, which are often hard to see with standard label-free methods under these conditions,” adds Zuo.
The technique also successfully captured dynamic processes, such as mitochondria fusing and dividing over time.
“This innovation provides biologists with a powerful, label-free tool for long-term 3D observation of cells in their most common and practical growing environment,” says Zuo. “It requires no special sample preparation, fluorescent dyes, or hardware modifications to standard microscopes, making it readily accessible for labs.”
Professor Chao Zuo
Contact author
Chao Zuo, Professor, Nanjing University of Science and Technology, He obtained his Bachelor of Science degree from Zijin College, Nanjing University of Science and Technology. Subsequently, he served as a research assistant at the Centre for Optical and Laser Engineering (COLE), Nanyang Technological University (NTU), Singapore, from 2012 to 2013. In 2014, he obtained his Ph.D. from NJUST. He was exceptionally promoted to associate professor and professor at NJUST in 2014 and 2016 respectively. He currently leads the Smart Computational Imaging Laboratory (SCILab: http://www.scilaboratory.com) at NJUST, where his research centres on computational bio-imaging, non-interferometric phase retrieval, optical information processing, and high-speed 3D optical sensing. He has published over 180 peer-reviewed journal articles, garnering more than 10,000 citations according to Google Scholar. He holds membership in several professional organisations and serves as a reviewer for numerous prestigious peer-reviewed journals (>30) within optical sciences-related fields.
Funder: This work was supported by the National Natural Science Foundation of China, National Key Research and Development Program of China, Biomedical Competition Foundation of Jiangsu Province, and others as listed in the paper.
Conflict of interest: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
See the article: Habib Ullah, Shun Zhou, Kaiyu Du, Zhidong Bai, Xingyu Huang, Linpeng Lu, Qian Chen, Chao Zuo. Intrinsic dark-field Fourier ptychographic diffraction tomography under non-matched illumination. iOptics (2025): 100006. https://doi.org/10.1016/j.iopt.2025.100006