A novel self-enhancement NCNDs-BPEI-Ru nanocomposite with highly efficient electrochemiluminescence as signal probe for ultrasensitive detection of MTB

Herein, a novel self-enhanced Ru(II)-based nanocomposite (NCNDs-BPEI-Ru), synthesized by covalently connecting nitrogen-doped carbon nanodots (NCNDs) and tris (4,4'-dicarboxylicacid-2,2'-bipyridyl) ruthenium (II) dichloride (Ru(dcbpy)(3)Cl-2) through branched polyethyleneimine (BPEI), could be used as an electrochemiluminescence (ECL) signal probe for ultrasensitive detection of mycobacterium tuberculosis (MTB) DNA fragment. Without any extraneous coreactants, NCNDs-BPEI-Ru could generate an ultra-strong initial ECL signal on the glassy carbon electrode (GCE) (signal-on) due to the coreaction from BPEI and NCNDs to Ru(dcbpy)(3)Cl-2. Then, self-assembled DNA nanotubes embedding methylene blue molecules (MB-DNANTs) were modified on the nanocomposite to effectively quench the ECL intensity of NCNDs-BPEI-Ru owing to the quenching effect of MB for Ru(dcbpy)(3)Cl-2 (signal-off). Finally, the 3D DNA nanomachine, formed by a DNA-functionalized magnetic beads (DNA-MBs) could transform trace target MTB into massive output DNA, and the MB-DNANTs could be disintegrated to get ECL signal recovery (signal-on) due to hybridization of output DNA and the 52 in DNANTs. Therefore, the proposed biosensor exhibited predominant performance for the detection of MTB DNA fragment with a low detection limit of 1.4 aM, which showed great application value in the detection of biomarkers in clinical diagnosis.