A novel assay strategy based on isothermal amplification and cascade signal amplified electrochemical DNA sensor for sensitive detection of Helicobacter pylori

A novel and sensitive Helicobacter pylori assay strategy based on linear isothermal amplification reaction (LIAR) and DNAzymes catalyzed DNA sensor was developed. A 17 nt target DNA (tDNA) specific in the H. pylori genome was selected and used as primer in the LIAR. A template DNA was designed to produce an amplicon with Mg2+-dependent and RNA-cleaving DNAzyme (Md-Dz) activity. The amplicon (i.e. Md-Dz) was then detected with the DNA sensor. The DNA sensor was fabricated simply through immobilization of a hairpin DNA that contains both Md-Dz substrate and G-quadruplex DNAzyme (Gq-Dz), on gold electrodes. The Gq-Dz possesses peroxidase activity, catalyzing the electro-redox of the electrochemical signal probe hydroquinon. The LIAR, Md-Dz catalytic reaction, and DNA sensor fabrication and detection processes were characterized and optimized. The LIAR amplification efficiency is as high as ~5 × 105 fold, and the assay strategy is very sensitive, selective and repetitive. The differential pulse voltammetry (DPV) detection signals linearly correlate to the logarithmic tDNA concentration in the range of 0.1–10,000 fM, with a limit of detection (LOD) of 34 aM. The detection linear range for H. pylori genomic DNA is 2.1–67.2 pg, with an LOD of 1.3 pg. Muted DNA sequences and other pathogenic bacteria did not result in interferences. In addition, the DNA sensor is very stable in storage. More importantly, the DNA sensor and the assay strategy could be universally applicable to detect any biological sample and short DNA sequence of interests.