An ultrasensitive electrochemical biosensor based on multifunctional hemin/G-quadruplex nanowires simultaneously served as bienzyme and direct electron mediator for detection of lead ion

Abstract

In this work, the multifunctional hemin/G-quadruplex nanowires formed by rolling circle amplification (RCA) was used to develop a direct electron transferred electrochemical biosensor with pseudo bienzyme cascade amplification for ultrasensitive lead ion (Pb2+) detection. Target Pb2+ would specifically identify and cleave the Pb2+-dependent DNAzyme to facilitate the capture of primers that further triggered RCA for amounts of long hemin/G-quadruplex nanowires generation in the presence of hemin. With the introduction of nicotinamide adenine dinucleotide (NADH) in electrolyte, the formed hemin/G-quadruplex nanowires could synchronously act as NADH oxidase and horseradish peroxidase (HRP)-mimicking DNAzyme to accelerate direct electron transfer of hemin to the electrode surface. By using multifunctional hemin/G-quadruplex nanowires to simultaneously serve as bienzyme and direct electron mediator, the proposed electrochemical biosensor exhibited improved convenience, ultrasensitivity and stability without addition of other proteases and electrochemical signal tags. Under optimal conditions, this proposed electrochemical biosensor showed enhanced selectivity to Pb2+ with a linear range from 10 fM to 200 nM and a low detection limit down to femtomolar level, which provided a potential platform for Pb2+ analysis in real sample.