Detecting Mitochondrial Free Radicals with Quantum Sensors: From Organelles to a D. melanogaster Model of Neurodegeneration

This study identifies a distinct free radical signature in a D. melanogaster model of Parkinsons Disease, successfully differentiating Pink1-deficient flies from wild-type controls. This insight was achieved using a robust quantum sensing methodology for the selective detection of free radicals in biological systems. Our approach utilizes optically detected magnetic resonance (ODMR) and magnetic modulation (MM) protocols with nanodiamond nitrogen-vacancy (NV) centres. Selective identification is achieved using the spin probe TEMPOL, a cell-permeable superoxide dismutase 2 (SOD2) mimic that initially quenches the photoluminescence signal. Upon scavenging free radicals like hydroxyl and superoxide, TEMPOL is converted to a diamagnetic adduct, restoring the contrast and thus enabling quantitative detection. The approach was first validated in a chemical system with radical generation confirmed by electron paramagnetic resonance (EPR) spectroscopy. It was then demonstrated across biological scales, from isolated mitochondria and whole glioblastoma cells to the Drosophila model. In these studies, high-resolution respirometry revealed distinct free radical signatures, and findings were compared with NV T1 relaxometry. This work provides new biophysical insight into mitochondrial dysfunction, demonstrating a distinct free radical signature in a neurodegeneration model and connecting it to specific metabolic states.