Aggregation-induced emission of DNA fluorescence as a novel pan-marker of cell death, senescence and sepsis <i>in vitro</i> and <i>in vivo</i>

<b>Background and Aim:</b> Effective monitoring of cell death and senescence is critical across biology and medicine, yet a universal <i>in situ</i> fluorescent marker has remained elusive. This study aimed to identify and characterize a novel, endogenous optical signal arising from cellular stress and to evaluate its potential as a universal, label-free biomarker for visualizing cellular fate in diverse physiological and pathological contexts. <b>Material and Methods:</b> Autofluorescence was characterized in human cell lines, <i>C. elegans</i>, a mouse sepsis model, and human plasma samples using two-photon and fluorescence lifetime imaging microscopy. The molecular origin of the signal was investigated through lysosome isolation, high-throughput DNA sequencing, gel electrophoresis, and photophysical experiments with synthetic nucleic acid oligonucleotides. The underlying routes to lysosomal accumulation were probed using shRNA-mediated knockdown and dominant-negative protein expression. <b>Results:</b> We discovered that cytosolic DNA fragments, sequestered into lysosomes via ESCRT-mediated microautophagy, aggregate and exhibit strong aggregation-induced emission (AIE) with a distinct peak at ~600 nm. This signal originates from excimer formation in single-stranded DNA, with mitochondrial DNA being a primary source during cell death. This label-free fluorescence allowed for the differentiation of cell death types <i>in vitro</i> and its intensity correlated with the progression of aging in <i>C. elegans</i> and sepsis in both mice and a human pilot study. <b>Conclusions:</b> Aggregated nucleic acids within lysosomes represent a novel, universal, and label-free endogenous biomarker for cell death and senescence. This AIE-based optical signal provides a powerful tool for real-time <i>in situ</i> visualization and dynamic tracking of cellular fate, holding significant potential for applications in basic research, diagnostics, and therapeutic monitoring.