Near‐infrared light‐activated aptamer‐based nanoprobe for spatiotemporally resolved detection of L‐lactate in colorectal cancer

Intratumoral L‐lactate represents a valuable biomarker for both prognosis and therapy response, underscoring the importance of its accurate detection. However, traditional L‐lactate assays rely on indirect hydrogen peroxide readouts and often compromise the accuracy and specificity. Herein, we report an aptamer‐based nanoprobe (UCNP‐Apt‐Act) that allows direct L‐lactate detection. Aptamers offer high specificity for L‐lactate but suffer from poor cellular uptake and premature activation by extracellular L‐lactate. To overcome this, we introduced lanthanide‐doped upconversion nanoparticles (UCNPs) to enable spatially controlled unlocking by near‐infrared (NIR) light for intratumoral L‐lactate detection. The nanoprobe remains “locked” during delivery via an engineered actuator, preventing premature response to extracellular L‐lactate. Upon 980 nm excitation, UCNPs convert NIR to UV emission, photocleaving the actuator linker and unlocking the aptamer. Notably, the UCNP carriers enhanced cellular uptake by 41 times through overcoming membrane barriers. The unlocked nanoprobe shows a 46‐fold fluorescence enhancement in the presence of L‐lactate, with an exceptional selectivity against a broad range of molecules and biological ions and metabolites. It enables specific detection of L‐lactate in cancer cells, colorectal tumors, and diverse real samples, with excellent recoveries of 95.0%–110.0%. This strategy establishes a robust approach for endogenous small‐molecule sensing and provides a versatile platform for biomedical applications.