K-Doped Graphitic Carbon Nitride with Obvious Less Electrode Passivation for Highly Stable Electrochemiluminescence and Its Sensitive Sensing Analysis of MicroRNA

In this study, upon potassium (K) element doping, the electrochemiluminescence (ECL) excitation potential of graphitic carbon nitride (g-C3N4) obviously shifted from −1.57 to −0.74 V. Compared with other reported methods, this work was the first one that could reduce the ECL excitation potential of g-C3N4 to below the critical value of −0.9 V. It could more effectively overcome electrode passivation and significantly improve the ECL intensity and stability. Meanwhile, the lower excitation potential could significantly reduce other side reactions caused by high voltage, and the introduction of the K element could obviously increase the water solubility to shorten the preparation time. The apparent decrease of the excitation potential was due to the doping of the K element, which could reduce the band gap, increase the in-plane spacing, and expand π-conjugated systems. Furthermore, using K-doped g-C3N4 with highly stable electrochemiluminescence at lower potential as an emitter, a biosensor for microRNA-141 (miRNA-141) sensitive detection was constructed with the assistance of an innovative nicking enzyme-assisted strand displacement amplification (N-SDA). Compared to the traditional SDA, a nicking enzyme was introduced to obviously improve the utilization rate of the fuel chain and increase the number of cycles, finally resulting in higher signal amplification efficiency. Therefore, the constructed biosensor showed excellent performance in the ultrasensitive detection of miRNA-141 with the limit of detection (LOD) being 44.8 aM. This work gave a more effective means to obviously improve the ECL property of g-C3N4 caused by electrode passivation and provided a more efficient and convenient detection method for biochemical analysis.