Amplified and selective detection of Ag+ ions based on electrically contacted enzymes on duplex-like DNA scaffolds

In the present study, ultrasensitive detection of Ag+ is demonstrated by a biocatalytic signal amplification system which is realized by only one DNA sequence based electrical contacted enzyme structure and the Au nanoparticles/Carbon nanodots (AuNPs/C-dots) composite immobilization platform. In the presence of Ag+, with the interaction of cytosine-Ag+-cytosine (C-Ag+-C), cytosine-rich DNA sequence labeled with methylene blue (MB) molecules near 5′ end and Glucose Oxidase (GOx) at 3′ end, has a self-hybridization and then forms a duplex-like structure which makes MB and GOx approach the AuNPs/C-dots modified electrode. MB units can then act as a relay that electrically contacts GOx with the AuNPs/C-dots modified electrode and activate the bioelectrocatalyzed oxidation of glucose to glucose acid. In consequence, based on the bioelectrocatalyzed signal amplification on the AuNPs/C-dots platform, Ag+ could be quantitatively detected in the range of 10−11-10−5 M with a low detection limit of 3 pM. Also, there is an excellent selectivity against other interferential metal ions. The detection of Ag+ ions was realized by Ag+ self-induced conformational change of DNA scaffold which involved only one oligonucleotide showing its convenience and availability.