Competitive substitution in europium metal–organic gel for signal-on electrochemiluminescence detection of dipicolinic acid

Metal–organic gels (MOGs) emerged as an attractive luminescent soft material for electrochemiluminescence (ECL). In this work, a cathodic ECL-activated europium metal–organic gel (Eu-MOG) has been synthesized by a facile mixing of Eu 3+ with 4′-(4-carboxyphenyl)-2,2′:6′,2′′-terpyridine (Hcptpy) under mild conditions. The prepared Eu-MOG is highly mesoporous for co-reactant permeation to produce an ultra-stable and high-efficient ECL, based on the antenna effect of Eu 3+ coordinating with Hcptpy. Moreover, dipicolinic acid (DPA) can competitively coordinate with Eu 3+ instead of water molecules, producing an enhanced ECL signal. Therefore, an ECL enhancement assay was developed for DPA detection. There was a linear relationship between the ECL intensity and the logarithmic concentration of DPA in the 0.01–1 μM range, and the detection limit is 7.35 nM. This work displays the promising application of Eu-MOG in the ECL field, opening a broad inspection for seeking a new generation of ECL luminophores. Graphical Abstract