Cell Membrane-Anchored MXene@Au SERS Nanoprobe for Precise Cell Surface pH Monitoring Upon a Cerebral Ischemia 3D Cell Model

Precise extracellular pH (pH_e) monitoring is crucial for investigating cellular physiology and pH-related therapeutic mechanisms, while the pH_e distribution is heterogeneous and increases with distance from the plasma membrane. Therefore, direct pH detection at the cell surface is crucial for precise monitoring of extracellular pH changes. Herein, a simple yet multifunctional cell membrane-anchored surface-enhanced Raman spectroscopy (SERS) nanoprobe (TAM) for cell surface pH monitoring is fabricated by assembling pH-responsive 4-mercaptopyridine (4-Mpy)-functionalized Au nanoparticles (Au NPs) onto large-scale MXene (Ti₃C₂) nanosheets. The TAM nanoprobe exhibits a sensitive and reversible pH response over a wide range (pH 3.00-9.02), covering both physiological and pathological extracellular conditions. Owing to its ideal nanoscale dimensions, strong electrostatic affinity for the membrane, and high SERS enhancement capability, the TAM nanoprobe readily anchors to the cell surface and produces intense SERS signals. By leveraging these properties, we can achieve sensitive pH detection of the cell surface on different cells by SERS. Furthermore, real-time monitoring of hypoxia-induced cell surface acidification is accomplished. Notably, the dynamic changes of cell surface pH upon cerebral ischemia are successfully evaluated using both 2D and 3D cellular models, highlighting the applicability of the TAM nanoprobe in complex biological systems. This work not only establishes a new paradigm for the design of cell membrane-anchored SERS nanoprobes but also enhances our understanding of the role of cell surface pH in related pathological processes.