Label-free and immobilization-free electrochemiluminescent sensing platform for highly sensitive detection of As(III) by combining target-induced strand displacement amplification with polydopamine nanospheres

Abstract

Strand displacement amplification (SDA) is a classic isothermal amplification technique, which usually requires one primer and one template. Here, we integrated the primer and the template to design a hairpin DNA. Using polydopamine nanospheres (PDANS) as a reversible and nonspecific inhibitor, an immobilization-free and label-free ECL sensor was fabricated. Without As(III), hairpin DNA is constrained by PDANS, and SDA process is inhibited. Ru(phen)32+, as ECL probe, can diffuse to the negatively charged ITO electrode surface to bring strong ECL response. While the presence of As(III) released the hairpin DNA, and triggered the SDA process with the help of polymerase and nicking endonuclease to generate lots of dsDNA, which interacted with Ru(phen)32+ to form the complex of dsDNA-Ru(phen)32+. The complex is difficult to approach the ITO electrode surface owing to the electrostatic repulsion, resulting in low ECL response. As a consequence, the detection limit of 1.2 × 10−3 ppb for As(III) can be achieved. Meanwhile, it is also applied to assay As(III) in flos sophorae. This strategy not only avoided the adjustment of primer-template ratio and improved amplification efficiency, but also reduced the treatment of the electrode and the immobilization of probe on the electrode. It is hopeful that this method was applied to assay food contaminants, environmental pollutions.