A silver(I) doped bud-like DNA nanostructure as a dual-functional nanolabel for voltammetric discrimination of methylated from unmethylated genes.

Abstract

A small DNA structure, referred to as DNA nanobud (NB), was used for the first time to design a dual-functional nanolabel in order to recognize a particular oligonucleotide sequence, generate and amplify the electrochemical analytical signal. NBs containing numerous repetitive desired sequences were prepared through self-assembly of 8-h rolling circle amplification. Then, redox-active silver ions were loaded onto the NBs by over-night incubation with a solution of AgNO3. The incorporation of Ag+ into NBs was confirmed by field emission scanning electron microscopy, dynamic light scattering, UV-Vis spectroscopy, zeta potential measurements, and energy-dispersive X-ray spectroscopy. A DNA sandwich complex was created after hybridization of Ag+-NB with target sequence, which was captured by immobilized probe on a gold electrode. Cyclic voltammetry was applied to measure the redox signal of silver ions produced typically at a potential around 0.02V vs. Ag/AgCl. The label can specifically discriminate fully methylated BMP3 gene from fully unmethylated bisulfate-converted part of the gene. The electrochemical signal produced by DNA sandwich complex of gold/probe/BMP3/Ag+-NB was linear toward BMP3 concentration from 100 pM to 100nM. The method has a 100 pM BMP3 detection limit. Conceivably, this nanolabel can be designed and modified such that it may also be used to detect other sequences with lower detection limits. Graphical abstract Ag+-NB as a new nanolabel for genosensing was formed by loading Ag+ on a spherical DNA nanostructure, nanobud (NB), synthesized by rolling circle amplification process. By using a gold electrode (AuE), Ag+-NB with numerous electroactive cations and binding sites can detect targets and generate amplified electrochemical signals.