Quantum chemical-guided design of a near-infrared probe for simultaneous monitoring of SO₂ derivatives and viscosity for mitochondrial in apoptotic cells.

The cellular sulfur dioxide levels and viscosity significantly affect cellular functions, especially apoptosis, driving the need for real-time monitoring via fluorescence imaging. However, near-infrared fluorescence probes capable of simultaneously tracking these dynamic changes during apoptosis are rare. In this study, we introduce AXC-C, a versatile near-infrared fluorescent probe designed using density functional theory (DFT) approaches to monitor sulfur dioxide derivatives and viscosity in the mitochondria of apoptotic cells. We showed that AXC-C distinguishes between sulfur dioxide and viscosity through distinct emission channels, exhibiting high selectivity and sensitivity. Excited-state calculations confirmed that the twisted intramolecular charge transfer (TICT) process governs its viscosity response. At the same time, observations of electrostatic potential and local electron affinity energy identified the sulfur dioxide interaction site. AXC-C demonstrated versatility by effectively visualizing mitochondrial viscosity changes and sulfur dioxide generation during apoptosis, establishing it as a multifunctional detection platform. Additionally, smartphone-based colorimetric analysis enabled rapid, precise, and cost-effective sulfur dioxide detection in real food samples, offering practical solutions for environmental and food safety applications. This study highlights how quantum chemical strategies can revolutionize fluorescent probe design, offering new avenues for real-time cellular imaging and practical detection platforms.