Highly sensitive biosensor based on target induced dual signal amplification to electrochemiluminescent nanoneedles of Ru(II) complex.

Here, electrochemiluminescent nanoneedles of Ru(II) complex were synthesized to fabricate an "off-on" electrochemiluminescence (ECL) biosensor in assistance with target Pb2+ induced dual signal amplification. Firstly, new needle-like nanostructures of luminous Ru(II) complex (RuNDs) different from the previous ones were prepared through solvent evaporation induced self-assembly on the electrode, which processed high ECL efficiency due to massive Ru(II) complexes in those structures, giving a strong initial ECL signal. To further improve the stability of the RuNDs film, silver nanowires (AgNWs) with excellent electric-conductivity dispersed in Nafion solution were modified by film formation, which was also convenient for subsequent modification. Through Ag-S bond, the DNA duplex formed by ssDNA with -SH (S1) and ssDNA modified with ferrocene (S2-Fc) was immobilized, leading to an obvious decrease of the ECL signal because of the effective quenching effect of Fc (off state). With the presence of target Pb2+, G-quadruplex structure was formed owing to the high specific affinity between S1 and Pb2+, making S2-Fc fall off from the electrode. Interestingly, the ECL signal not only could be recovered due to the abscission of Fc, but also improved by the generation of Pb2+-G-quadruplex (on state). Based on the effective dual signal amplification, a sensitive ECL biosensor was constructed for Pb2+determination with a low estimated detection limit down to 0.33 pM. The strategy using luminous Ru(II) complex as precursor to directly prepare needle-like nanostructure was a convenient and effective way to enhance the ECL efficiency. Meanwhile, the simple and efficient target Pb2+ induced dual signal amplification would provide new thought for signal enhancement in the fabrication of biosensors.