Single-Cell Hyperthermia: Diamond Quantum Thermometry Reveals Thermal Control of Macrophage Polarization.

Fever elevates body temperature to enhance immune response; however, intracellular temperature can fluctuate by up to 15 °C, suggesting a previously unrecognized layer of thermal regulation. While hyperthermia has long been exploited in medicine, how localized temperature gradients influence cellular fate remains poorly understood. Here, a dual-function nanodiamond platform is introduced that integrates optically detected magnetic resonance (ODMR) thermometry with croconium-dye-based photothermal heating to precisely modulate temperature within endo-lysosomal compartments of macrophages. Controlled intracellular hyperthermia triggers oxidative stress, transcriptional reprogramming, and polarization toward a pro-inflammatory phenotype, as confirmed by immunofluorescence, flow cytometry, and transcriptomics. These findings reveal intracellular thermal gradients as active regulators of immune signaling and gene expression. By establishing a direct subcellular thermal trigger for immune activation, independent of the canonical heat-shock pathway. This work introduces a quantum-enabled strategy for probing and programming cellular thermodynamics at the nanoscale.