Nanodiamond‐Based Quantum Sensing Reveals Changes in Endo‐Lysosomal Activity of Stimulated Cardiac Fibroblasts in a Cellular Fibrosis Model

ABSTRACT Despite a growing recognition of endo‐lysosomes as key regulators of cellular homeostasis, our understanding of their functional dynamics during cellular senescence, particularly in cardiac fibrosis, remains limited. Senescent cells exhibit profound changes in endo‐lysosomal redox status and iron dynamics, yet tracking these alterations in real time within living cells poses significant challenges. Conventional biochemical assays often lack spatial resolution and temporal sensitivity, while fluorescent probes can be hampered by photobleaching or interference from the complex endo‐lysosomal microenvironment. This has created a need for non‐invasive, high‐resolution tools. In this context, nanodiamonds containing nitrogen‐vacancy (NV) centers offer a promising solution for in vitro cell culture models. These quantum sensors are biocompatible, photostable, and capable of detecting changes in redox and iron dynamics at the nanoscale during the progression of senescence and fibrosis. In this work, we have shown that fluorescent nanodiamonds with NV centers could open new avenues for understanding how endo‐lysosomal activity changes during cardiac fibroblasts transdifferentiation to senescent myofibroblasts upon mechanical and biochemical stimulation.