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Published online: 21 May 2008 | doi:10.1038/nchina.2008.113

Electrochemical DNA sensors: Turn on the signal

Anne Pichon

Introduction

© (2008) ACS

Electrochemical DNA (E-DNA) sensors are simple, efficient and inexpensive devices for genetic screening and detection. They work on the principle that the chemical interaction (hybridization) between DNA targets in solution and the probe layer — a layer of DNA fragments attached to an electrode — produces signal currents for electronic readout. Most E-DNA sensors today have limited sensitivity because of their 'signal-off' design, in which the hybridization produces low signal strengths. Chunhai Fan at the Chinese Academy of Sciences in Shanghai and co-workers¹ have prepared an enzyme-based, 'signal-on' E-DNA sensor with amplified signal currents, which can detect DNA targets at extremely low concentrations.

In the design, a probe layer of hairpin-shaped 'stem–loop' DNA fragments was used (see image). The researchers labelled one end of the DNA fragment with the vitamin biotin, and the other end with the steroid digoxigenin (DIG). The biotin end was attached to the electrode by a protein bridge. The DIG end was inaccessible to  the solution when the DNA fragment was in the 'loop' structure. On hybridization, the DNA fragment formed a duplex 'stem', which forced the DIG end away from the electrode.

Antibody-linked horseradish-peroxidase (HRP) enzymes were added to the solution of target DNA, which also contained some hydrogen peroxide. The antibody-linked HRP enzyme attached itself to the DIG-end, catalysed the reduction of hydrogen peroxide, and sent redox currents to the electrode. One HRP enzyme could catalyse thousands of reduction reactions, greatly amplifying signal currents.

The resulting E-DNA sensor had femtomolar sensitivity — excelling existing sensors by several orders of magnitude. It also displayed high differentiation ability and enabled the simultaneous detection of 16 different DNA targets in one array.

The authors of this work are from:
Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai, China; GeneFluidics, Monterey Park, California, USA.

Reference

1. Liu, G. et al. An enzyme-based E-DNA sensor for sequence-specific detection of femtomolar DNA targets. J. Am. Chem. Soc. doi: 10.1021/ja800554t (2008). | Article |