Visualized detection of single-base difference in multiplexed loop-mediated isothermal amplification amplicons by invasive reaction coupled with oligonucleotide probe-modified gold nanoparticles.

Loop-mediated isothermal amplification (LAMP) is a well-developed DNA amplification method with an ultra-high sensitivity, but it is difficult to recognize a single-base difference (like genotyping) in target-specific amplicons by conventional detection ways, such as the intercalation of dyes into dsDNA amplicons or the increase of solution turbidity along with the polymerization process. To allow genotyping based on LAMP suitable for POCT (point-of-care testing) or on-site testing, here we proposed a highly specific and cost-effective method for detecting a single-base difference in LAMP amplicons. The method includes three key steps, sequence amplifier to amplify multiple fragments containing the single nucleotide polymorphisms (SNPs) of interest, allele identifier to recognize a targeted base in the amplicons by invasive reaction, and signal generator to yield signals by hybridization-induced assembly of oligonucleotide probe-modified gold nanoparticles. Because the allele identifier is sensitive to one base difference, it is possible to use multiplexed LAMP (mLAMP) to generate amplicon mixtures for multiple SNP typing. Genotyping of 3 different SNPs (CYP2C19*2, CYP2C19*3 and MDR1-C3435T) for guiding the dosage of clopidogrel is successfully carried out in a 3-plex LAMP on real clinical samples. As our method relies on the naked-eye detection and constant-temperature reaction, no expensive instrument is required for both target amplification and sequence identification, thus much suitable for inexpensive gene-guided personalized medicine in source-limited regions.

Application of multiplex PCR combined with invasive reaction and chromogenic reaction catalyzed by gold nanoparticles in detection of encephalitis and meningitis virus / 中国人兽共患病学报

We developed a method for detecting encephalitis and meningitis virus by using multiplex PCR combined with invasive reaction and a chromogenic reaction catalyzed by gold nanoparticles.Primers were designed based on the conservative regions of encephalitis and meningitis virus (Eastern equine encephalitis virus,EEEV;Western equine encephalomyelitis virus,WEEV;West Nile virus,WNV;Nipah virus,NiPA;Japanese encephalitis virus,JEV).Multiplex PCR system,invasive reaction and a chromogenic reaction catalyzed by gold nanoparticles were established to detect different encephalitis and meningitis virus in one reaction.Tick-borne encephalitis virus (TBEV),St Louis encephalitis virus (StLEV),Chikungunya virus (CHIKV) and Dengue virus(DV) were used to test its specificity.Quantitative RNA transcribed in vitro and PCR fragments were used to assess its sensitivity.Clinical specimens collected from JEV patients were detected by this method.A method for detecting encephalitis and meningitis virus by using multiplex PCR,invasive reaction and a chromogenic reaction catalyzed by gold nanoparticles were successfully established.This method can detect targeted pathogens specifically,and it has no cross reaction with TBEV,StLEV,CHIKV and DV.The detecting limitation for different targets was 103 copies/μL.Clinical samples were positive for JEV nucleic acids for above assay.The method presented here has characteristic of high specificity,sensitivity and throughput.The results can be observed by visual inspection.This method has broad application prospects in pathogen detection.

Ultra-sensitive quantification of the colorectal cancer-specific NDRG4 gene methylation levels in stool / 医学研究生学报

Objective The NDRG4 gene methylation in stool is a candidate biomarker for non?invasive diagnosis of colorectal cancer. However, the traditional methods for methylation detection could not be well applied to stool samples due to the low sensitivity and low specificity. The aim of this study was to develop a highly sensitive and specific method for quantifying the methylated NDRG4 gene in stools. Methods Forty one stool samples were collected from 12 colorectal cancer patients, 4 adenoma patients and 25 nor?mal persons. The invasive reaction was combined with real?time PCR and the relative quantification was performed by 2-ΔCT method to develop the highly sensitive and specific methylated DNA detection method, which was used for detecting NDRG4 methylation levels in 41 of stool samples. Results The sensitivity of the method was as low as 10 copies of methylated NDRG4 gene fragments. The specificity was high enough to distinguish 0.01% of methylated fragments from un?methylated fragments and 105 copies of unmethylated NDRG4 fragments gave noamplification signals. The detection results from 41 of stool samples showed that detection rate of the NDRG4 gene in stool from adenoma and colorectal cancer groups had a significant difference comparing to that from the normal group. Conclusion The 2-ΔCT method could accurately quantify the methylation levels of the NDRG4 gene in stool samples, and provide an efficient tool for non?invasive colorectal cancer detection.

Sensitive and specific colorimetric DNA detection by invasive reaction coupled with nicking endonuclease-assisted nanoparticles amplification.

Colorimetric DNA detection is preferable to methods in clinical molecular diagnostics, because no expensive equipment is required. Although many gold nanoparticle-based colorimetric DNA detection strategies have been developed to analyze DNA sequences of interest, few of them can detect somatic mutations due to their insufficient specificity. In this study, we proposed a colorimetric DNA detection method by coupling invasive reaction with nicking endonuclease-assisted nanoparticles amplification (IR-NEANA). A target DNA firstly produces many flaps by invasive reaction. Then the flaps are converted to targets of nicking reaction-assisted nanoparticles amplification by ligation reaction to produce the color change of AuNPs, which can be observed by naked eyes. The detection limit of IR-NEANA was determined as 1pM. Most importantly, the specificity of the method is high enough to pick up as low as 1% mutant from a large amount of wild-type DNA backgrounds. The EGFR gene mutated at c.2573 T>G in 9 tissue samples from non-small cell lung cancer patients were successfully detected by using IR-NEANA, suggesting that our proposed method can be used to detect somatic mutations in biological samples.