Dual-emission europium metal-organic frameworks for ratiometric fluorescence and colorimetric detection of methylglyoxal.

Abstract

The reliable on-site detection of methylglyoxal (MGO) is increasingly acknowledged as a clinically relevant indicator of carbonyl stress and the risk of diabetes-related complications. However, this remains challenging due to matrix effects, structurally related interferents, and the absence of reaction-based, self-calibrated sensing platforms. This work presents a dual-emission europium metal-organic framework (Eu-DADP/DPA) engineered with 5,6-diamino-1,10-phenanthroline (DADP) and dipicolinic acid (DPA) as ligands for the sensitive and selective dual-mode detection of MGO. DPA can sensitize Eu3+ for emission due to its antenna effect, while DADP cannot. Consequently, the MOF displayed dual emission at 409 and 632 nm from DADP and Eu3+ ions, respectively, with excitation at 280 nm. Upon addition of MGO, the two amino groups of DADP undergo cyclization to form a 2-methylquinoxaline-like structure, which suppresses photoinduced electron transfer (PET) and enhances ligand conjugation, resulting in a gradual increase of the 409 nm emission and slight attenuation of the Eu3+ emission. This response enables ratiometric fluorescence detection of MGO at 0-10 μM with a detection limit of 84 nM. Simultaneously, the MOF acts as a peroxidase-like nanozyme, catalyzing the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to a blue product; this activity is inhibited by MGO, providing a convenient colorimetric method for visual or semi-quantitative screening at relatively higher MGO concentrations. The sensor demonstrates selectivity against the tested interferents and satisfactory recoveries in spiked serum samples, with smartphone-based RGB recoveries ranging from 98.2% to 111.3%. This dual-mode Eu-MOF platform combines ratiometric fluorescence sensing with colorimetric detection, providing an analytical approach for MGO measurement with potential for portable readout.