1985年美国科学家Kary Mullis发明PCR方法以后,PCR已经成为生命科学研究领域中最常规的实验方法之一。PCR是用于放大扩增特定的DNA片段的分子生物学技术,可看作是生物体外的特殊DNA复制。PCR的最大特点,是能将微量DNA大量扩增。 最传统的一代PCR采用琼脂糖电泳的方式对PCR产物进行分析,操作繁琐、难于做定量分析。为使PCR技术能对基因水平进行定量分析,1992年开发了荧光实时定量PCR(二代PCR)。实时定量PCR(qPCR)通常在DNA扩增时对反应体系中的荧光信号进行实时收集,通过三个参数间(荧光信号-Cq值(罗氏公司)或Ct值(ABI公司)-靶基因的起始浓度)的关系,能以相对定量的方式确定靶基因的拷贝数或推断基因表达水平。由于荧光定量PCR的分析是相对定量的方式,这也是目前荧光定量PCR的最大技术缺点。在低拷贝靶分子、模板浓度差异的条件下,其检测灵敏度、精确度都受到了限制。 1999年霍普金斯大学的Vogelstein教授首先提出了第三代的Digital PCR(数字PCR)的概念。此后数字PCR技术得到迅速的发展。数字PCR是一种核酸检测和绝对定量的新方法。同传统PCR相比,数字PCR增加了一步分隔(partitioning)的操作,将几十微升的反应体系分隔成了众多微小独立反应体系。核酸模板在这种分割过程中被充分稀释,理想状态下每个微反应体系中至多含有1个分子的核酸模板。和qPCR不同,数字PCR不对扩增过程进行实时监测,而是检测end-point的荧光信号。扩增完成后所有液滴的荧光将逐个被识别并进行计数,不需要构建标准曲线,就可以得到绝对定量的结果。 目前数字PCR的主要产品有: 1. QX200 QX200目前已经是Bio-Rad的产品。Bio-Rad的技术主要来源于QuantaLife公司,QuantaLife 利用油包水微滴生成技术开发了微滴式数字ddPCR,这是最早出现的相对成熟的数字PCR平台,在运行成本和实验结果稳定性方面都基本达到了商品化的标准。 2011年QuantaLife 公司被Bio-Rad公司收购,其微滴式数字PCR仪产品更名为QX100,继续在市场上销售,2013年该公司又推出了升级型号QX200。 2. Raindrop Raindrop数字PCR是美国RainDance Technologies公司于2012年推出的产品。能够提供更高的检测范围,适用于处理更大浓度差异的不同样品,这个设备将其原有的二代测序文库制备平台技术也整合进入数字PCR技术平台,在高压气体驱动下,将每个标准反应体系分割成100万至1000万个P升级微滴反应乳液,这种超高的微滴数目可以为用户“提供更高的检测动态范围,适用于处理更大浓度差异的不同样品。在2017年Bio-Rad完成了对RainDance公司的收购。 3. Quant Studio 3D Applied Biosystems公司2013年也推出了Quant Studio 3D数字PCR系统,是目前数字PCR市场上新型号产品之一。采用高密度流控芯片技术,使样本均匀分配至20,000个单独的反应孔中。在整个测定流程中,样本之间保持完全隔离,防止样品交叉污染。移液过程和操作步骤减少。芯片式设计避免了微滴式系统可能出现的管路堵塞问题。Applied Biosystems在OpenArray芯片平台之外推出的全新的芯片式数字PCR系统,这个全新系统在设计上综合考虑了系统稳定性与运行成本因素。 2013年Thermo Fisher公司收购了Applied Biosystems。 Quant Studio 3D 数字PCR可用于分子标准品定量;原体检测和定量测定;罕见癌症基因突变检测;拷贝数变异分析;GMO检测和污染评估;mRNA 和miRNA表达低倍变化的确定等。 4. Naica TM crystal Naica ™ crystal数字PCR系统是由法国Stilla Technologies公司推出的产品。将微滴均匀性和芯片可视化以及相同PCR反应条件创新性集成在同一系统中,使用微流体创新型Sapphire芯片,样品通过毛细通道网格以30,000个Crystal微滴的形式进入发布在2D芯片中。 这种方法在满足实验室对数据精准性、重复性要求的同时,让数字PCR分子检测变得更加简单快捷。PCR扩增过程在芯片上实现。最终对阳性微滴计数从而得到精准的核酸绝对数量。作为首款三个荧光通道检测的数字PCR平台,Naica ™ crystal数字PCR系统可在2小时内实现多达36个目标基因的检测。Naica ™ Crystal系统由Geode微滴生成;扩增仪和Prism3微滴阅读分析系统组成,仅需唯一耗材——Sapphire芯片,即可完成从加样、微滴生成和扩增,直到采集数据获得结果。 Naica ™ crystal数字PCR可用于:基因表达差异检测;拷贝数变异(CNV);低丰度及稀有序列的精确定量;甲基化含量鉴定;肿瘤治疗的伴随诊断;无创产前筛查;病原微生物的检测(病毒、细菌等);二代测序辅助建库;肿瘤治疗的实时监控 (ctDNA检测)等。 ReaserchGate 论坛对digital PCR不同品牌比较的讨论: David Otaegui Biodonostia Institute 6th Jun, 2014 :Digital PCR, Qx200 vs Quantstudio 3D; Which one you think is the best? Eric Ouellet University of British Columbia – Vancouver 7th Jul, 2014:Hi David, Our lab uses a QX100 ddPCR platform from Bio-Rad (now QX200). At the time it was the only available option. However, I can offer some advice on its usability. As you may know, bio-rad uses droplets to perform ddPCR, a process on which they are continuously improving upon. The new cartridge designs can, in our experience, reliably and reproducibly partition samples. Although the process is more labor-intensive (and to some extent, more prone to user error), we did welcome the added flexibility of using such a system. The Quantstudio 3D instrument is a bit reminiscent of the platform pioneered by Fluidigm. In these case, the partition is done geographically. In many cases, the yes/no readouts are sufficient, but in cases where samples would need to be recovered, these platforms would have great difficulty in achieving this, compared to emulsion-based systems. However, for most clinical applications, these instruments are often very useful. Raindance is also another promising company that is currently trying to enter the market of droplet-based digital PCR detection, although they currently offer fee-per-service options rather than instruments themselves. However, according to their documentation, they can achieve partition levels that dwarf the other platforms, providing there is a need for such high levels. The other aspects to consider are not only the capabilities of these various systems, but perhaps more importantly, the cost of the consumables and reagents, especially when compared to NGS platforms that are constantly becoming more affordable. Ultimately, the balance between flexibility and ease-of-use would have to be weighed for any particular application. In our case, we required the flexibility, albeit a steeper learning curve. Giovanni Lopez Universidad Peruana Cayetano Heredia 2nd Feb, 2015:Here in South America QX200 this $180456....Includes only: A reader Droplet oil (1863004), a droplet generation oil (186305),Buffer 2X Control Kit (1863052),ddPCR Supermix 2X (1863010). What is it that more is spent? Rupesh Deshmukh Laval University 12th Dec, 2016:Can anyone provide me cost comparison between QX200 and Quantstudio 3D.Thanks Kevin Kelly Thermo Fisher Scientific 7th Jul, 2017:Hi Rupesh, The QS3D costs around half of what the Bio-Rad system costs. If you'd like more info send me a message at kevin.f.kelly@thermofisher.com, and I'd be happy to connect you with your local sales rep for additional information. Thanks, Kevin David Dobnik Nacionalni inštitut za biologijo 9th Sept, 2017:Hi David, In our lab we have two Bio-Rad's machines (QX100 and 200) a Fluidigm Biomark HD and have also had the chance to test Quantstudio 3D and Stilla's Naica platform. Overall, regarding the usability and throughput, the Bio-Rad's system is the one I prefer. We have tested duplex assays on QX100 and QS3D side by side and separation of clusters on QS3D was rather poor. However, if you do not plan to run a lot of samples per run, even QS3D might be a good choice looking from the cost perspective. Oliver Schultz Stilla Technologies 4th Apr, 2018:Dear network, if you′re interested in an innovative new approach to digital droplet PCR, please check out the NAICA system from STILLA Technologies. It′s the fastest system on the market, including a 3-color detection and the capability of recovering the droplets after read-out for downstream applications. Learn more at www.stillatechnologies.com Best wishes, Oliver Minka Kova č Omega 8th Aug, 2018:Dear all, in our lab we have a Quantstudio3D. We know also other platforms like BioRad, Stilla, Fluidigm and QuantStudio 12 Flex with Open Array. Honestly speaking if you have a small number of samples per day, less than 96 per day the platform for you is QST3D. Price performance for small amount of samples is strongly on QST3d side (price of the instrument, price per reaction). Second majority of assay's from ABI now Thermo Fisher Scientific works well with no additional optimization, like 90 -95 %. But yes, sometimes for some assays additional optimization is a MUST. So regarding the Quality of the data from results between QST3D and BioRad (others as well) I have to say that data is dependent on the fine optimization. You can even find the scientific articles which showed that systems on the digital market are more or less comparable. The entering price of the QST3D instrument is more than half lower compared to the BioRad droplet platform. If you have more than 96 samples per day or ca 10000 samples yearly you have to think about bigger systems (Stilla, BioRad, OpenArray) Best wishes, Minka
iNature :对于全球最高引的前100篇文章,篇均引用量是 34834.92 次;这100篇文章主要聚集在 生物化学及分子生物学领域;这100篇文章中, 发表在PHYSICAL REVIEW B杂志及JBC杂志都是发表了7篇文章;对于这100篇文章,产出率最高的机构是加州大学;总的来说,这100篇文章主要是聚集在基础研究, 如蛋白质的定量,蛋白质的分析,实时定量PCR技术,BLAST的诞生,DNA测序,同源序列比对等方面。 iNature编辑组的统计时间是2017年11月26日。 1 引用量最高的10000篇文章分析 我们以Web of Science为基础,通过相关的检索,从1874-2018年,总共检索到 120611782条记录( 图.1 )。 图.1 总文章数 我们对于所有的文章进行了分类归档,发现引用次数大于10万次,为第一档,有3篇文章;第二档的引用量是5-10万次,有9篇文章;第三档的引用量是1-5万次,有238篇文章;第四档的引用量是5000-1万次,有748篇文章;第五档的引用量是1000-5000次,有22994篇文章;第六档的引用量是500-1000次,有68509篇文章; 第七档的引用量是小于500次,有120519371篇文章 ( 图.2 ) 。 文章分档 引用次数 文章数 累加文章数 I 10万 3 II 5-10万 9 12 III 1-5万 238 250 IV 5000-1万 748 998 V 1000-5000 22994 23902 VI 500-1000 68509 92411 VII 500 120519371 120611782 图.2 所有文章的归档分类 之后我们根据引用量从高到底,进行排序,我们筛选了10000条记录(因为Web of Science最多只能一次分析10000条记录),进行相应的统计分析。 我们发现每篇文章的平均引用次数是3173.14次,总引用次数是31731393次,施引文献是14692585 ( 图.3 ) 。另外,我们发现,最高引用文章大部分都聚集在1990-2010年之间,达到了40%以上。 图.3 10000篇文章引用分析 之后,我们看了一下不同时间段,对于这些文章的引用次数分析,发现绝大部分引用都是聚集在1990-2016年之间( 图.4 )。 图.4 10000篇文章不同时间段引用分析 由于分析10000篇文章,工作量太大,我们就直接分析前100篇文章,发现前100篇文章的平均引用量是34834.92次,总引用次数是3483492次,施引文献达到2627346篇。这100篇文章,占前10000篇的总引用的10.98%,但是总文章数是1.00%,故我们主要分析这100篇文章 ( 图.5 ) 。 图.5 100篇文章引用分析 2 引用量最高的100篇文章分析 对于这100文章发表的时间进行分析,我们发现在1950年以前只有4篇,1950-1960年之间,有10篇;1961-1970年,有9篇;1971-2010年,总共有74篇,占了绝大部分;2010年以后,只有3篇文章( 图.6 ),这三篇文章分别是遗传进化( MEGA5: Molecular Evolutionary Genetics Analysis Using Maximum Likelihood, Evolutionary Distance, and Maximum Parsimony Methods,2011年),癌症综述( Hallmarks of Cancer: The Next Generation,2011年 ),全球癌症统计( Global Cancer Statistics,2011年 ) 。 图.6 100篇文章发表时间分析 其次我们对这100篇文章的种类进行了基本分析,发现生物化学及分子生物学方面有35篇,物理学有15篇,化学有14篇,数学11篇 ( 图.7 ) 。 图.7 100篇文章方向分析 我们再次对这100篇文章发表的杂志进行分析(3篇),发表在PHYSICAL REVIEW B杂志及JBC杂志都是7篇文章;ANALYTICAL BIOCHEMISTRY,JOURNAL OF CHEMICAL PHYSICS,NATURE,NUCLEIC ACIDS RESEARCH都是发表了4篇文章,总的来说,这高引用的100篇文章,大部分都是生物,物理,生物化学及化学方面的文章。另外这9个杂志占了39篇文章 ( 图.8 ) 。 图.8 100篇文章杂志分析 我们再次统计了国家,发现美国有44篇,占了绝大部分,其次是英国,达到9篇;德国有6篇,很遗憾,没有发现有中国参与的文章 ( 图.9 ) 。 图.9 100篇文章国家分布 我们对研究机构统计了一下,发现加州大学系统占的比例最大,达到了7篇,其次是宾夕法尼亚州立大学,达到了4篇 ( 图.10 ) 。 图.10 100篇文章的大学或研究所分析 3 引用量最高的100篇文章列表 对于这100篇文章,主要是技术的变革及基础研究,如蛋白质的定量,蛋白质的分析,实时定量PCR技术,BLAST的诞生,DNA测序,同源序列比对等,这些东西都是非常的基础,故这也注定了它们的高引用量 ( 图.11 ) 。 标题 总引用次数 年均引用 1 PROTEIN MEASUREMENT WITH THE FOLIN PHENOL REAGENT 335844 5012.6 2 CLEAVAGE OF STRUCTURAL PROTEINS DURING ASSEMBLY OF HEAD OF BACTERIOPHAGE-T4 244785 5099.69 3 RAPID AND SENSITIVE METHOD FOR QUANTITATION OF MICROGRAM QUANTITIES OF PROTEIN UTILIZING PRINCIPLE OF PROTEIN-DYE BINDING 201313 4793.17 4 DNA SEQUENCING WITH CHAIN-TERMINATING INHIBITORS 66790 1629.02 5 DENSITY-FUNCTIONAL THERMOCHEMISTRY .3. THE ROLE OF EXACT EXCHANGE 65244 2609.76 6 Generalized gradient approximation made simple 63484 2885.64 7 SINGLE-STEP METHOD OF RNA ISOLATION BY ACID GUANIDINIUM THIOCYANATE PHENOL CHLOROFORM EXTRACTION 63161 2037.45 8 DEVELOPMENT OF THE COLLE-SALVETTI CORRELATION-ENERGY FORMULA INTO A FUNCTIONAL OF THE ELECTRON-DENSITY 61406 2046.87 9 A short history of SHELX 58640 5864 10 Analysis of relative gene expression data using real-time quantitative PCR and the 2(T)(-Delta Delta C) method 58159 3421.12 11 ELECTROPHORETIC TRANSFER OF PROTEINS FROM POLYACRYLAMIDE GELS TO NITROCELLULOSE SHEETS - PROCEDURE AND SOME APPLICATIONS 55121 1413.36 12 A SIMPLE METHOD FOR THE ISOLATION AND PURIFICATION OF TOTAL LIPIDES FROM ANIMAL TISSUES 51444 843.34 13 BASIC LOCAL ALIGNMENT SEARCH TOOL 49116 1754.14 14 CLUSTAL-W - IMPROVING THE SENSITIVITY OF PROGRESSIVE MULTIPLE SEQUENCE ALIGNMENT THROUGH SEQUENCE WEIGHTING, POSITION-SPECIFIC GAP PENALTIES AND WEIGHT MATRIX CHOICE 47444 1976.83 15 Gapped BLAST and PSI-BLAST: a new generation of protein database search programs 45557 2169.38 16 NONPARAMETRIC-ESTIMATION FROM INCOMPLETE OBSERVATIONS 44604 743.4 17 MINI-MENTAL STATE - PRACTICAL METHOD FOR GRADING COGNITIVE STATE OF PATIENTS FOR CLINICIAN 43637 1014.81 18 A REVISED MEDIUM FOR RAPID GROWTH AND BIO ASSAYS WITH TOBACCO TISSUE CULTURES 41340 738.21 19 THE NEIGHBOR-JOINING METHOD - A NEW METHOD FOR RECONSTRUCTING PHYLOGENETIC TREES 38735 1249.52 20 A RAPID METHOD OF TOTAL LIPID EXTRACTION AND PURIFICATION 37927 642.83 21 REVISED EFFECTIVE IONIC-RADII AND SYSTEMATIC STUDIES OF INTERATOMIC DISTANCES IN HALIDES AND CHALCOGENIDES 37143 884.36 22 DENSITY-FUNCTIONAL EXCHANGE-ENERGY APPROXIMATION WITH CORRECT ASYMPTOTIC-BEHAVIOR 34065 1135.5 23 SELF-CONSISTENT EQUATIONS INCLUDING EXCHANGE AND CORRELATION EFFECTS 33872 639.09 24 Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set 33658 1529.91 25 The moderator-mediator variable distinction in social psychological research: conceptual, strategic, and statistical considerations. 33191 1037.22 26 Processing of X-ray diffraction data collected in oscillation mode 32667 1555.57 27 The status, quality, and expansion of the NIH full-length cDNA project: The Mammalian Gene Collection (MGC) 32391 2313.64 28 DETECTION OF SPECIFIC SEQUENCES AMONG DNA FRAGMENTS SEPARATED BY GEL-ELECTROPHORESIS 32239 749.74 29 REGRESSION MODELS AND LIFE-TABLES 32022 696.13 30 COLORIMETRIC METHOD FOR DETERMINATION OF SUGARS AND RELATED SUBSTANCES 31882 514.23 31 RAPID COLORIMETRIC ASSAY FOR CELLULAR GROWTH AND SURVIVAL - APPLICATION TO PROLIFERATION AND CYTO-TOXICITY ASSAYS 31292 894.06 32 The CLUSTAL_X windows interface: flexible strategies for multiple sequence alignment aided by quality analysis tools 30770 1465.24 33 HELICAL MICROTUBULES OF GRAPHITIC CARBON 30386 1125.41 34 STATISTICAL METHODS FOR ASSESSING AGREEMENT BETWEEN TWO METHODS OF CLINICAL MEASUREMENT 29847 932.72 35 FUZZY SETS 29740 561.13 36 CONTROLLING THE FALSE DISCOVERY RATE - A PRACTICAL AND POWERFUL APPROACH TO MULTIPLE TESTING 29691 1290.91 37 Electric field effect in atomically thin carbon films 28520 2037.14 38 INHOMOGENEOUS ELECTRON GAS 27972 518 39 CONFIDENCE-LIMITS ON PHYLOGENIES - AN APPROACH USING THE BOOTSTRAP 27721 840.03 40 SPECIAL POINTS FOR BRILLOUIN-ZONE INTEGRATIONS 27045 643.93 41 MEGA5: Molecular Evolutionary Genetics Analysis Using Maximum Likelihood, Evolutionary Distance, and Maximum Parsimony Methods 26581 3797.29 42 USE OF LEAD CITRATE AT HIGH PH AS AN ELECTRON-OPAQUE STAIN IN ELECTRON MICROSCOPY 25405 461.91 43 From ultrasoft pseudopotentials to the projector augmented-wave method 25057 1318.79 44 MEASUREMENT OF OBSERVER AGREEMENT FOR CATEGORICAL DATA 25005 609.88 45 PROJECTOR AUGMENTED-WAVE METHOD 24314 1013.08 46 MEGA4: Molecular evolutionary genetics analysis (MEGA) software version 4.0 24066 2187.82 47 RELIABILITY OF MOLECULAR WEIGHT DETERMINATIONS BY DODECYL SULFATE-POLYACRYLAMIDE GEL ELECTROPHORESIS 23835 486.43 48 THE ATTRACTIONS OF PROTEINS FOR SMALL MOLECULES AND IONS 23763 344.39 49 ISOLATION OF BIOLOGICALLY-ACTIVE RIBONUCLEIC-ACID FROM SOURCES ENRICHED IN RIBONUCLEASE 23574 604.46 50 The colorimetric determination of phosphorus 23420 251.83 51 Cutoff Criteria for Fit Indexes in Covariance Structure Analysis: Conventional Criteria Versus New Alternatives 22755 1197.63 52 Particle swarm optimization 22586 982 53 DISC ELECTROPHORESIS .2. METHOD AND APPLICATION TO HUMAN SERUM PROTEINS 22463 415.98 54 MAXIMUM LIKELIHOOD FROM INCOMPLETE DATA VIA EM ALGORITHM 22259 542.9 55 A TECHNIQUE FOR RADIOLABELING DNA RESTRICTION ENDONUCLEASE FRAGMENTS TO HIGH SPECIFIC ACTIVITY 21557 615.91 56 Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set 21539 979.05 57 NEW LOOK AT STATISTICAL-MODEL IDENTIFICATION 21172 481.18 58 Global Cancer Statistics 20983 2997.57 59 A NEW GENERATION OF CA-2+ INDICATORS WITH GREATLY IMPROVED FLUORESCENCE PROPERTIES 20677 626.58 60 CLINICAL-DIAGNOSIS OF ALZHEIMERS-DISEASE - REPORT OF THE NINCDS-ADRDA WORK GROUP UNDER THE AUSPICES OF DEPARTMENT-OF-HEALTH-AND-HUMAN-SERVICES TASK-FORCE ON ALZHEIMERS-DISEASE 20596 605.76 61 THE ASSESSMENT AND ANALYSIS OF HANDEDNESS: THE EDINBURGH INVENTORY 20514 436.47 62 The rise of graphene 20505 1864.09 63 Distinctive image features from scale-invariant keypoints 20258 1447 64 A RATING SCALE FOR DEPRESSION 20238 348.93 65 AN INVENTORY FOR MEASURING DEPRESSION 20104 352.7 66 EQUATION OF STATE CALCULATIONS BY FAST COMPUTING MACHINES 19396 298.4 67 ESTIMATION OF CONCENTRATION OF LOW-DENSITY LIPOPROTEIN CHOLESTEROL IN PLASMA, WITHOUT USE OF PREPARATIVE ULTRACENTRIFUGE 19380 421.3 68 HIGH-RESOLUTION 2-DIMENSIONAL ELECTROPHORESIS OF PROTEINS 19179 446.02 69 COMPARISON OF SIMPLE POTENTIAL FUNCTIONS FOR SIMULATING LIQUID WATER 19023 543.51 70 THE MOS 36-ITEM SHORT-FORM HEALTH SURVEY (SF-36) .1. CONCEPTUAL-FRAMEWORK AND ITEM SELECTION 18987 730.27 71 MicroRNAs: Genomics, biogenesis, mechanism, and function 18845 1346.07 72 PHASE ANNEALING IN SHELX-90 - DIRECT METHODS FOR LARGER STRUCTURES 18787 670.96 73 A LOW-COST, HIGH-EFFICIENCY SOLAR-CELL BASED ON DYE-SENSITIZED COLLOIDAL TIO2 FILMS 18733 693.81 74 GAUSSIAN-BASIS SETS FOR USE IN CORRELATED MOLECULAR CALCULATIONS .1. THE ATOMS BORON THROUGH NEON AND HYDROGEN 18531 639 75 OPTIMIZATION BY SIMULATED ANNEALING 18374 524.97 76 A NEW METHOD OF CLASSIFYING PROGNOSTIC CO-MORBIDITY IN LONGITUDINAL-STUDIES - DEVELOPMENT AND VALIDATION 18044 582.06 77 MrBayes 3: Bayesian phylogenetic inference under mixed models 17994 1199.6 78 TISSUE SULFHYDRYL GROUPS 17989 304.9 79 VMD: Visual molecular dynamics 17956 816.18 80 METAANALYSIS IN CLINICAL-TRIALS 17945 560.78 81 IMPROVED PATCH-CLAMP TECHNIQUES FOR HIGH-RESOLUTION CURRENT RECORDING FROM CELLS AND CELL-FREE MEMBRANE PATCHES 17744 479.57 82 HOMEOSTASIS MODEL ASSESSMENT - INSULIN RESISTANCE AND BETA-CELL FUNCTION FROM FASTING PLASMA-GLUCOSE AND INSULIN CONCENTRATIONS IN MAN 17634 534.36 83 A SIMPLE METHOD FOR DISPLAYING THE HYDROPATHIC CHARACTER OF A PROTEIN 17621 489.47 84 Measuring inconsistency in meta-analyses 17584 1172.27 85 MEASUREMENT OF PROTEIN USING BICINCHONINIC ACID 17573 532.52 86 THE HOSPITAL ANXIETY AND DEPRESSION SCALE 17458 498.8 87 STUDY OF THE CONDITIONS AND MECHANISM OF THE DIPHENYLAMINE REACTION FOR THE COLORIMETRIC ESTIMATION OF DEOXYRIBONUCLEIC ACID 17232 277.94 88 The Protein Data Bank 17152 952.89 89 The NCEP/NCAR 40-year reanalysis project 17118 778.09 90 Collective dynamics of 'small-world' networks 17044 852.2 91 Hallmarks of Cancer: The Next Generation 16913 2416.14 92 ABINITIO MOLECULAR-DYNAMICS FOR LIQUID-METALS 16788 671.52 93 Bias in meta-analysis detected by a simple, graphical test 16785 799.29 94 DETERMINATION OF SERUM PROTEINS BY MEANS OF THE BIURET REACTION 16754 242.81 95 A MATHEMATICAL THEORY OF COMMUNICATION 16715 238.79 96 PROCHECK - A PROGRAM TO CHECK THE STEREOCHEMICAL QUALITY OF PROTEIN STRUCTURES 16710 668.4 97 MODELTEST: testing the model of DNA substitution 16619 830.95 98 MULTIPLE RANGE AND MULTIPLE F TESTS 16580 263.17 99 ESTIMATING DIMENSION OF A MODEL 16551 413.78 100 A SIMPLE METHOD FOR ESTIMATING EVOLUTIONARY RATES OF BASE SUBSTITUTIONS THROUGH COMPARATIVE STUDIES OF NUCLEOTIDE-SEQUENCES 16492 434 图.11 前100篇文章列表 注: 所有的数据来源为Web of science。 温馨提示 : iNature微信公众号是介绍一流的,最前沿的科研成果,提供专业的完整的同行解析;另外也会介绍全世界知名的实验室及业界大师;同时为公众提供一个了解生命科学及科研过程的平台。
第二代PCR引物质量评估软件:MFEprimer-2.0,可以针对全基因组数据库在1-3s内预测任意PCR引物对的特异扩增产物和非特异扩增产物: http://biocompute.bmi.ac.cn/CZlab/MFEprimer-2.0/ 该工作已发表在今年6月份的核酸研究(NAR)上,欢迎大家使用该工具,论文参考信息如下: Qu W, Zhou Y, Zhang Y, Lu Y, Wang X, Zhao D, Yang Y, Zhang C* . MFEprimer-2.0: a fast thermodynamics-based program for checking PCR primer specificity. Nucleic Acids Res . 2012 Jul;40(Web Server issue):W205-8. Epub 2012 Jun 11. QuWB 2012 MFEprimer-2.0 NAR.pdf 第一代MFEprimer于2009年发表在Bioinformatics上: Wubin Qu, Zhiyong Shen, Dongsheng Zhao, Yi Yang*, and Chenggang Zhang* . MFEprimer: multiple factor evaluation of the specificity of PCR primers, Bioinformatics , 2009, 25(2):276-278 QuWB 2009 MFEprimer Bioinformatics.pdf 这两篇论文都是由我们实验室 屈武斌 完成的,两篇论文PDF版本均见附件。
How to find the pcr product length, when the primer pairs are known by primer premier 1 F primer Ctrl V as is to get the seq NO 2 R primer Ctrl V reverse complement to get the seq NO and the length 3 the length of pcr product is seq NO(R primer)+ the length(R primer)-seq NO(F primer)
LEAF PCR PROTOCOL (Klimyuk et al., 1993, TPJ 3: 493-494) 1) Samples are harvested in 1.5 ml tubes and stored on ice. 2) 40ul of 0.25N NaOH was added and the samples boiled for 30 sec. 3) 40ul of 0.25N HCl then 20ul Tris mix was added and the samples boiled for another 2 min. -tissue samples can then be used immediatly or stored at 4 C for several weeks. -The amount of tissue used in each PCR reaction should not exceed 2mm2 or the reaction will not work. A small amount of treated material can be excised for use in a PCR reaction with a sterile Gilson tip. PCR reaction conditions are as follows: total volume= 50ul for 5.5 reactions 10X buffer 5ul 27.5uls 10mM dNTPs 1.25uls 6.875uls primer A 2.5uls 13.75uls primer B 2.5uls 13.75uls dH2O 38.75uls 213.1uls taq poly 1.0ul 5.5uls 95 C 10min 1X 95 C 30sec 55 C 30sec 72 C 45sec 30X 72 C 10min 1X run 15ul on a 2% agarose gel note: 2.5 times more primer is used and 2 times more taq polymerase in the leaf PCR protocol. If you could get by with less, Jonathan Jones would have done so! Stocks 0.25N HCl 0.25N NaOH Tris buffer: 0.5M Tris pH 8.0 0.25% Nonidet P-40 LEAF PCR ON ARABIDOPSIS TISSUE WITHOUT ALKALINE TREATMENT Preparation of Master mix: 1 x Taq-buffer 1.5 mM MgCl2 200 mM of each dNTP 1 mM each primer 0.5 ml 20 x Taq polymerase The mix is stored on ice until use. Preparation of leaf tissue: Put the leaf in a small Petri-dish. Make a hole in a leaf with the narrow end of the Pasteur pipette (a forceps might be helpful) and place the leaf in a PCR-tube, if necessary by blowing. On ice, add 50 ml the Master mix. Running the cycles: Transfer the tubes directly from ice to the prewarmed 94 C block on the Robocycler and run the following cycles: 94 C for 3 min 1 x 94 C for 30 s; Tann.* for 1 min; 72 C for 1 min-1 min 30 s 35 x 72 C for 10 min (optional) 1 x Appropriate controls: Positive Negative For screening transgenics: plasmid ColO ColO with endogenous primer-set g DNA gDNA with endogenous primer-set - DNA *The annealing temperature (Tann.) should be 2-3 C below the calculated Tann..
最近我们实验室在BMC Bioinformatics上发表了多重PCR引物设计程序MPprimer,对于提高PCR实验的效率具有一定帮助,有兴趣的朋友可以看看: http://www.biomedcentral.com/1471-2105/11/143/abstract Software MPprimer: a program for reliable multiplex PCR primer design Zhiyong Shen , Wubin Qu , Wen Wang , Yiming Lu , Yonghong Wu , Zhifeng Li , Xingyi Hang , Xiaolei Wang , Dongsheng Zhao and Chenggang Zhang BMC Bioinformatics 2010, 11 : 143 doi:10.1186/1471-2105-11-143 Published: 18March2010 Abstract (provisional) Background Multiplex PCR, defined as the simultaneous amplification of multiple regions of a DNA template or multiple DNA templates using more than one primer set (comprising a forward primer and a reverse primer) in one tube, has been widely used in diagnostic applications of clinical and environmental microbiology studies. However, primer design for multiplex PCR is still a challenging problem and several factors need to be considered. These problems include mis-priming due to nonspecific binding to non-target DNA templates, primer dimerization, and the inability to separate and purify DNA amplicons with similar electrophoretic mobility. Results A program named MPprimer was developed to help users for reliable multiplex PCR primer design. It employs the widely used primer design program Primer3 and the primer specificity evaluation program MFEprimer to design and evaluate the candidate primers based on genomic or transcript DNA database, followed by careful examination to avoid primer dimerization. The graph-expanding algorithm derived from the greedy algorithm was used to determine the optimal primer set combinations (PSCs) for multiplex PCR assay. In addition, MPprimer provides a virtual electrophotogram to help users choose the best PSC. The experimental validation from 2x to 5x plex PCR demonstrates the reliability of MPprimer. As another example, MPprimer is able to design the multiplex PCR primers for DMD (dystrophin gene which caused Duchenne Muscular Dystrophy), which has 79 exons, for 20x, 20x, 20x, 14x, and 5x plex PCR reactions in five tubes to detect underlying exon deletions. Conclusions MPprimer is a valuable tool for designing specific, non-dimerizing primer set combinations with constrained amplicons size for multiplex PCR assays.
(Text adoptedfrom www.protocol-online.org ) I often wondered, why some companies supply their PCR Ingredients with MgCl2 and some with MgSO4. Is there ANY difference between them ? -Fedex- Not much difference, won't affect normal PCR, where the key is the amount of available Mg2+. I think that SO42- might be useeful in methylation PCR, but I am not sure. -bob1- Recipes using Tris-HCl tend to use MgCl2, while recipes employing Tris-SO4/(NH4)2SO4 tend to use MgSO4. -tfitzwater-