Tracking Chemotherapy-Induced Oxidative Stressin Glioblastoma Cells Using NV-Based QuantumSensors

Temozolomide (TMZ) is the standard chemotherapeutic drug for glioblastoma (GBM) and is commonly administered in combination with radiation. However, despite its widespread use, the prognosis remains poor, underscoring the need for not just better treatments, but also better ways to understand how cells respond to them. Since TMZs efficacy is partly driven by the generation of reactive oxygen species (ROS), being able to track oxidative stress within cells can offer meaningful insights into treatment response and resistance. In this context, T1 relaxometry using nitrogen vacancy(NV) centers in nanodiamonds (NDs) offers a sensitive and reliable method to monitor intracellular changes, including ROS levels, with nanoscale precision. In this study, we used U87-MG GBM cells to investigate ROS generation following TMZ treatment at 250 {micro}M and 1000 {micro}M concentrations. Fixed cells were analyzed using T1 relaxometry of nitrogen vacancy (NV) centers in NDs as intracellular sensors, and the data were compared against untreated controls. A concentration-dependent decrease in T1 relaxation time was observed with increasing TMZ dose, indicating elevated radical production. These results affirm that NDs can robustly detect intracellular ROS in response to chemotherapeutic stress. Importantly, the study highlights a critical therapeutic insight: while TMZ typically induces ROS generation contributing to cell death, resistant cells often exhibit reduced ROS levels due to heightened antioxidant responses. Thus, in contexts where T1 times remain unchanged or increase post-treatment, the lack of ROS elevation may serve as an early indicator of drug resistance. Taken together, this work establishes ND based T1 relaxometry as a powerful tool to probe oxidative stress dynamics and assess drug responsiveness at the single-cell level, while also suggesting a framework for overcoming practical challenges in ND-based intracellular sensing.