Construction of a novel xylan-based fluorescent probe for dual-responsive detection of pH and viscosity changes in cellular environments and in vivo

Intracellular viscosity typically reflects the state of the cellular microenvironment and is intrinsically linked to intracellular transport and metabolism. However, in pathological cellular microenvironments, factors that disturb normal physiological conditions are rarely isolated. The interplay between pH and viscosity is particularly significant, due to their mutual interactions within cells. To address these challenges, we developed a macromolecular fluorescent probe, AX-VpH, capable of simultaneously detecting pH and viscosity. Upon excitation at 371 nm, AX-VpH exhibits dual emission maxima at 465 nm and 570 nm. As the pH increased from 1.0 to 12.0, the emission intensity at 575 nm decreased by approximately 60%, accompanied by a blue shift to 465 nm, followed by a four-fold increase in emission intensity at 465 nm as pH continued to rise. Additionally, AX-VpH demonstrated a remarkable 30-fold enhancement in emission intensity at around 464 nm in response to increasing viscosity. Furthermore, AX-VpH had been successfully applied for viscosity imaging in live cells and zebrafish in vivo, highlighting its potential for studying microenvironmental changes within biological systems.