Surface-Confined Ratiometric SERS Sensing Enables Quantitative Imaging of Cellular Malondialdehyde

) enables self-calibrated detection and effectively compensates for variations in laser excitation and nanoprobe distribution. Importantly, the probe demonstrates high chemical specificity toward MDA, showing negligible cross-reactivity with structurally related aldehydes, ketones, and common cellular biomolecules. The silica shell enhances structural stability and significantly reduces Ag-associated cytotoxicity, allowing reliable operation in biological environments. The developed probe exhibits a linear range (0.25-12.5 μM) and a detection limit of 0.5 nM for MDA. In cellular studies, the nanoprobe enables dose-dependent visualization of exogenous MDA and quantitative imaging of endogenous MDA generated during AAPH-induced lipid peroxidation. The ratiometric SERS imaging clearly differentiates oxidative stress levels among treatment groups. This ratiometric SERS platform provides a robust strategy for the mapping of cellular oxidative stress and offers a versatile tool for evaluating antioxidant interventions and neurodegenerative processes.