Graphene Quantum Dots Decorated Cobalt–Hemin Metal–Organic Frameworks Mediated Fluorescent Sensor for Para-aminohippuric Acid Sensing

Para-aminohippuric acid (PAH) serves as a pivotal marker widely employed for accurately estimating effective renal plasma flow, playing a crucial role in the diagnosis and determination of various PAH-related diseases. Consequently, it arises a necessity to devise an advanced quantitative spectrofluorometric technique utilizing fluorescence detection methods for the precise detection of PAH. Therefore, the present work achieved the detection of PAH through a meticulously designed On-Off-On fluorescent nano-system, incorporating graphene quantum dots (CE-GQDs) into cobalt–hemin metal–organic frameworks (Co–hemin MOF). Briefly, the one-pot green synthesis of CE-GQDs was accomplished using the natural precursor derived from the Colocasia Esculenta stem through the hydrothermal method. Subsequently, the synthesized CE-GQD was encapsulated within the Co–hemin MOF, composed of cobalt nitrate hexahydrate as the metal and hemin as a linker. The outcome revealed a wide linear range (20–400 ng/mL) and the lowest detection limit (2.75 ng/mL). CE-GQD exhibited remarkable photoluminescence quenching kinetics towards the metal–organic framework and demonstrated recovery post-sensing. The amino group of PAH readily donates an electron pair to metal ions, facilitating the formation of a coordination bond between PAH and cobalt ions. Consequently, the interaction between carboxyl-enriched CE-GQDs within the designed Co–hemin MOF weakens upon the introduction of PAH. This weakening effect results in the recovery of the quenched fluorescence of CE-GQDs, termed fluorescence "Turn-On". In conclusion, the preference for CE-GQDs@Co–hemin MOF underscores its high sensitivity and stability for the detection of PAH. Looking ahead, the utilization of CE-GQDs@Co–hemin MOF holds promise for ushering in a new era in PAH sensing.