Polymer Backbone Engineering Regulates Fluorescence Turn-On Sensing of α-Ketoglutaric Acid from Paper Devices to Live Cells

Chitosan, a biocompatible polymer derived from crab shells, is an attractive platform for biosensing applications. Detection of ketoglutaric acid (KGA), an important metabolic biomarker associated with metabolic disorders, remains analytically challenging. Herein, we report two naphthalimide-grafted polymeric probes based on hydrophobic chitosan (NH–CS) and hydrophilic poly(allylamine) (NH-PAA) for selective KGA detection. Owing to differences in backbone polarity, the probes exhibit distinct photophysical behaviors.The NH–CS probe is showing a significantly higher fluorescence turn-on response (∼6.7-fold) with KGA than NH-PAA (∼2.6-fold). The sensing mechanism involves selective imine formation between the hydrazine unit and the carbonyl group of KGA, which suppresses the PET process and enhances fluorescence. The NH–CS probe exhibits high sensitivity in aqueous media with a limit of detection of 0.12 μM. Again, the probe enables practical detection of KGA through a paper-based device and successful quantification in spiked urine samples. Additionally, the NH–CS probe shows concentration-dependent fluorescence enhancement in live cells, indicating its potential for intracellular imaging and metabolic monitoring.