Design of Smart Polymeric Sensor Based on Poly(n-Isopropylacrylamide) and Anthrapyrazolone Derived Fluorescent Crosslinker for the Detection of Nitroaromatics in Aqueous Medium

Explosive detection in aqueous medium using fluorometric titrations is of paramount importance for security and safety, as it offers a susceptible and rapid method to identify potential threats in water sources or aqueous environments, ensuring the protection of critical infrastructure and public safety. Previously, we have investigated fluorescence-based explosive detection via pi-electron-rich anthrapyrazolone-derived fluorophore moiety (dye) as an effective sensor in an organic medium. However, the dye's solubility in water makes it difficult to identify nitroaromatics (NACs) in aqueous media. In the current study, thermoresponsive crosslinked polymer (TCP) with dye [DHBBI(MA)2] added as a crosslinker between the polymer chains is synthesised by straightforward and easy free radical polymerization. The emission intensity of TCP is significantly reduced with interaction with NACs like TNP, ATNP, DNP, and PNP, primarily through static quenching attributed to a photoinduced electron transfer (PET) process. TNP exhibited the most efficient quenching, with a Ksv value of 10.7 x 102 M-1 for TCP and 6.189 x 102 M-1 for DHBBI(MA)2. The limit of detection (LOD) was 0.12 nM for TCP and 0.135 nM for DHBBI(MA)2. TCP proved to be approximately 1.72 and 1.12 times more efficient in TNP detection than DHBBI (MA)2 in terms of Ksv value and LOD. At higher temperatures beyond the LCST of the polymer, TCP exhibits additional fluorescence quenching, making it effective for NAC detection. This switch in fluorescence quenching near the cloud point temperature (TCP) of PNIPAM in aqueous media indicates TCP's potential for real-world applications, including rapid detection and identification of nitroaromatics and environmental monitoring in soil and water.