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Versatile Electrochemiluminescence and Electrochemical "On-Off" Assays of Methyltransferases and Aflatoxin B1 Based on a Novel Multifunctional DNA Nanotube.

Herein, a new multifunctional DNA nanotube (DNANT) was self-assembled and used to load Ru(phen)32+ and methylene blue (MB) as amplified signal probes for versatile electrochemiluminescence (ECL) and electrochemical (EC) "on-off" assays of Dam methylase (MTase) and aflatoxin B1 (AFB1). The DNA nanotube as a carrier could immobilize numerous MB or Ru(phen)32+ species in the double-stranded DNA (dsDNA) to significantly amplify signals, which enabled highly sensitive ECL and electrochemical detection of dual targets. The target Dam MTase first catalyzed the methylation of hairpin DNA (H1), and then the methylated DNA was cleaved by endonuclease DpnI to expose a single-strand DNA. After the Ru(phen)32+-DNANT or MB-DNANT signal probes were assembled to the electrode by hybridization, remarkable "signal on" states for amplified ECL or EC assays of MTase were obtained. Furthermore, in the presence of the target AFB1, the structure of DNANTs collapsed due to the specific binding of AFB1 to aptamer S2 in NTs, which led to the release of signal probes (Ru(phen)32+ or MB) from the electrode to achieve "signal off" state for dual detection of AFB1. Taking advantage of the multifunctional DNANT amplification signal probes, the versatile biosensors showed good analytical performance with very wide linear ranges (0.001-100 U mL-1 and 0.0001-100 ng mL-1 for MTase and AFB1 assay by DPV) and lower detection limits (2.1 × 10-4 U mL-1 and 0.018 pg mL-1 for MTase and AFB1 by DPV). This is the first time that ECL and EC "on-off" methods have been achieved separately for dual target assays, which opens a new avenue of DNANT-based signal amplification strategyies for the versatile design of biosensors in various biological detections.