Molecularly Engineered Fluorescent Magnetic Microrobots for Sensing High‐Energy Nitroaromatic Explosives in Highly Acidic Aqueous Environments

Among various analytical sensing approaches currently in use, fluorescence sensing is known for its high sensitivity, rapid response, and applicability in monitoring a wide range of target molecules. Pairing an appropriate navigation system with a fluorescent molecule that can carry it to inaccessible or hard-to-reach environments can pave the way for remote and selective sensing applications. Herein, we design magnetic nanoparticles embedded with fluorescent material to form magneto-fluorescent, precisely navigable microrobots for sensing high-energy explosive compounds in acidic aqueous systems. Magnetic guidance via Helmholtz coils provides dynamic navigational control to direct the microrobots to specific regions of interest using externally applied magnetic fields. Upon specific interaction with picric acid, the sensing mechanism is triggered via fluorescence quenching ("on-off" switch). Materials characterization demonstrates that this quenching mechanism arises from the hydrogen bonding and charge-transfer interactions between ketenimine-functionalized probes and the hydroxyl group in picric acid, leading to the formation of water-soluble picrate complexes. Testing in microfluidic channels as proof-of-concept further validates the microrobot's ability for selective sensing of target analytes, emphasizing them as smart mobile sensors for environmental monitoring in harsh acidic conditions, confined spaces, hazardous material detection, and applications in the real world where conventional sensors face challenges.