Auto-cleaning paper-based electrochemiluminescence biosensor coupled with binary catalysis of cubic Cu2O-Au and polyethyleneimine for quantification of Ni2+ and Hg2+

Inspired by the pop-up greeting cards, a 3D collapsible auto-cleaning paper-based electrochemiluminescence (ECL) biosensor (CAPEB) with different functions of signal collection and residual multiple cleaning, is developed for sensitive detection of Ni2+ and Hg2+ by simply regulating its 3D configurations. The multiple fluidic paths and the hollow-channel structure were firstly integrated into the paper substrate, realizing simultaneously repetitive auto-cleaning of the two working electrodes. For achieving ultrasensitive Ni2+ and Hg2+ monitoring, binary catalysis consisting of the intermolecular co-reaction (H2O2 and N-(4-Aminobutyl)-N-ethylisoluminol (ABEI)) and intramolecular catalysis (polyethyleneimine (PEI)-ABEI) was introduced. Specifically, silver nano-spheres with a large specific surface area and excellent conductivity were grown on the paper working electrode and served as the sensor substrate for fixing PEI-ABEI and Ni2+-specific DNAzyme. With the assistance of DNAzyme, Cu2O-Au and ferrocene (Fc) labeled strand S2 were immobilized on electrode surface through the hybridization reaction, and catalyzed H2O2 to generate reactive oxygen species, promoting the luminescence of ABEI. In the existence of Ni2+, DNAzyme was activated followed by cleavage of strand S2 to induce the release of Fc, which quenched the ECL signal of ABEI, eventually realizing the detection of Ni2+. Similarly, for sensitive quantification of Hg2+, full thymine (T) bases strand S3 was modified on surface of Cu2O-Au and anchored Hg2+ by T-Hg2+-T pairing interaction. The ECL intensity was decreased along with increasing of Hg2+ due to the quenching effect of Hg2+ on ECL emission of ABEI. Based on this ingenious system, the detection of Ni2+ and Hg2+ had high sensitivity, wide linear ranges, and low detection limits. The results indicated that the integration of a multi-channel structure into a paper device chips opened new opportunities for designing promising paper-based devices for metal ions diagnosis.