High-Density N-Vacancy-Induced Multipath Electrochemiluminescence Improvement of 3D g-C3N4 for Ultrasensitive MiRNA-222 Analysis

Using dissolved O2 as the cathodic co-reactant of three-dimensional (3D) g-C3N4 is a convenient method to improve the electrochemiluminescence (ECL) signal, but it still suffers the disadvantages of limited luminous efficiency of 3D g-C3N4 and low content, low reactivity, and instability of dissolved O2. Here, N vacancy with high density was first introduced into the structure of 3D g-C3N4 (3D g-C3N4-NV), which could conveniently realize multipath ECL improvement by simultaneously solving the above shortcomings effectively. Specifically, N vacancy could change the electronic structure of 3D g-C3N4 to broaden its band gap, increase fluorescence (FL) lifetime, and accelerate electron transfer rate, obviously improving the luminous efficiency of 3D g-C3N4. Meanwhile, N vacancy made the excitation potential of 3D g-C3N4-NV to shift from −1.3 to −0.6 V, effectively weakening the electrode passivation. Moreover, the adsorption capacity of 3D g-C3N4-NV was obviously enhanced, which could make the dissolved O2 enrich around 3D g-C3N4-NV. And massive active NV sites of 3D g-C3N4-NV could promote O2 to more efficiently convert to reactive oxygen species (ROS) that were key intermediates in ECL generation. Using the newly proposed 3D g-C3N4-NV-dissolved O2 system as an ECL emitter, an ultrasensitive target conversion biosensor was constructed for miRNA-222 detection. The fabricated ECL biosensor exhibited satisfactory analytical performance for miRNA-222 with a detection limit of 16.6 aM. The strategy achieved multipath ECL improvement by introducing high-density N vacancy simply in the 3D structure of g-C3N4 and could open a new horizon for developing a high-performance ECL system.