Selective detection of an antibiotic using hydrogen-bonded organic frameworks (HOFs): insights from DFT mechanistic analysis

The development of non-toxic, cost-effective and high fluorescent sensing materials has earned significant interest in the last decade. In this work, a simple synthesis technique of mesoporous hydrogen-bonded organic frameworks (HOFs) suitable for the ultrasensitive detection of a commonly used antibiotic, enrofloxacin (ENR), has been reported. The fluorescence of the HOF is completely quenched after the formation of a HOF–Cu²⁺ complex as a turn off sensor which undergoes a turn-on mechanism in the presence of ENR. The competitive binding of ENR displaces Cu²⁺ ions, thereby restoring the fluorescence of the free HOF. The quenching effect of the fluorescence of the HOF in the presence of Cu²⁺ ions was quantitatively analysed, establishing a limit of detection (LOD) of 57 nM. The formation of a Cu²⁺–ENR conjugate upon ENR addition leads to the recovery of fluorescence intensity. The mechanism of competitive binding was validated by kinetic studies and computational studies based on density functional theory (DFT). The sensor demonstrated a linear response for ENR detection between 0.01 and 1.0 μM, with a limit of detection (LOD) of 70 nM, and a wider non-linear detection range extending to 50 μM. Furthermore, successful recovery tests in spiked buffer, diluted human serum, commercial milk, and river water samples confirmed the robustness of the sensing platform in complex biological and environmental matrices. The high sensitivity with excellent selectivity towards the antibiotic in the presence of other interferences and the successful recovery in spiked sample analysis highlight the potential applications of this sensing platform.