The sensitive and selective detection of nucleic acids is of vital importance to clinical diagnosis, mutational analysis, gene therapy, biological studies and biodefense applications. An increasing number of research groups and companies are interested in this field and have obtained promising results. However, in addition to sensitivity and selectivity, there are a lot of problems existing in most available technologies such as high cost, tedious operation and time-consuming need to be resolved urgently.

Prof. TANG Zhuo’s group from Chengdu Institute of Biology, Chinese Academy of Sciences, working on organic chemistry, nucleic acid chemistry and chemical biology. One core work of them is to develop biosensors for nucleic acid detection (especially for clinical diagnosis) based on DNAzyme. Recently, they again reported a new nucleic acid detection method “GQ-HCR” after their last contribution “Colorimetric Detection of PCR Product with DNAzymes Induced by 5′-Nuclease Activity of DNA Polymerases” in 2011.

The new method “GQ-HCR” is mainly based on G-quadruplex (GQ) and hybridization chain reaction (HCR). The authors integrated GQ into HCR hairpin DNA probes so that only two simple hairpin DNA probes were enough for a sample testing, including target recognization, signal amplification and signal report. Furthermore, the amplified signals could be reported in various forms such as color signals could be observed by naked eyes directly, chemiluminiscence signals as well as fluorescence signals when react with different signal substrate, ABTS, DAB, luminol, ZnPPIX, tyramine·HCl and so on.

In the work, they not only realized the detection of ssDNA and RNA detection to obtain a detection limit at several nanomolar concentration, but also overcame the limitation of HCR’s application in dsDNA detection and got a detection limit as low as several copies of target genes in combination with PCR. In addition, they have tried to make GQ-HCR to be a visible chip technology with which the analysts only need to add pre-treated samples on a chip pre-fixed with GQ-HCR probes, then a visible dectection result could be obtained within one hour at room temperature. Experiments on the visible chip displayed satisfactory reproducibility and also demonstrated GQ-HCR has good selectivity that noly one mutation could be differentiated.

In conclusion, GQ-HCR is a time and money-saving, easy-to-use, portable and high-throughput assay promising nucleic acid detection method due to its inherent merits: 1) Two simple hairpin DNA probes without any chemical modifications are enough for sample testing; 2) The detection process needs only 0.5~1h and can work at room temperature; 3) Comparing with most existing technologies, GQ-HCR is independent of expensive and fragile protein enzyme and instruments. However, the authors think that much remains to be done to improve the sensitivity of this new method and a much easier way for dsDNA detection need to be put forward.

Now, the GQ-HCR method have been applied successfully in the identification of medicinal materials in Chinese patent medicines. And, a patent have been applied for while a paper entitled " Amplified detection of nucleic acid by G-quadruplex based hybridization chain reaction" was published online in Biosensors and Bioelectronics (2012,38, 258–263).