Direct ultra-weak photon emission detection from mammalian cells using a photomultiplier tube-based system

Ultra-weak photon emission (UPE) refers to the spontaneous emission of extremely low-intensity light produced by cells as a by-product of metabolic activity. Unlike bioluminescence, which depends on specialised enzymatic pathways, or delayed luminescence (DL), a non-metabolic physical process arising from prior light exposure, UPE is thought to originate from oxidative metabolic reactions. Despite longstanding interest in its potential biological roles, including non-chemical signalling, experimental evidence of UPE in mammalian systems remains limited due to the low photon flux and conflation with DL. We used a custom-built dark-box detection system incorporating sensitive photomultiplier tubes to measure UPE from mammalian cell cultures. We demonstrate reproducible UPE detection from cultures compared to media in MCF7 cells (12,588.36 ± 176.59 counts vs. 12,121.51 ± 117.32 counts, p: 0.0012), A549 cells (12,646.78 ± 232.85 counts vs. 12,162.80 ± 89.43 counts, p: 0.0025) and in MCF10A cells (12,158.84 ± 52.49 counts vs. 12,004.37 ± 67.07 counts, p: 0.0037), with emissions distinguishable from DL. Distinct emission characteristics were observed across cell lines, with cancer-derived cells exhibiting higher average counts than non-transformed cells. Furthermore, induction of cellular stress via doxorubicin-mediated apoptosis significantly increased UPE intensity in MCF10A cells, indicating a relationship between emission magnitude and cellular stress. These findings establish a robust and accessible methodology for detecting UPE from mammalian cell lines and provide evidence that UPE intensity reflects metabolic and stress-related processes. This platform gears towards systematic investigation of UPE dynamics in health and disease and supports its potential utility as a label-free reporter of cellular oxidative status.