WO2021088199A1 - 一种基于CRISPR-Cas12g的特异性核酸片段纳米荧光痕量快速检测方法 - Google Patents

一种基于CRISPR-Cas12g的特异性核酸片段纳米荧光痕量快速检测方法 Download PDF

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WO2021088199A1
WO2021088199A1 PCT/CN2019/124463 CN2019124463W WO2021088199A1 WO 2021088199 A1 WO2021088199 A1 WO 2021088199A1 CN 2019124463 W CN2019124463 W CN 2019124463W WO 2021088199 A1 WO2021088199 A1 WO 2021088199A1
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nucleic acid
cas12g
fluorescence
crispr
rapid detection
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陈全胜
刘蕊
吕鹏
李欢欢
黄栋
贺培欢
张运莲
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江苏大学
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  • the invention belongs to the technical field of nucleic acid detection, in particular to a CRISPR-Cas12g-based method for rapid detection of specific nucleic acid fragments with nano-fluorescence traces.
  • nucleic acid detection technology With the rapid development of nucleic acid detection technology, rapid detection methods for various biological samples have appeared one after another. For example, food-borne pathogens that cause food-borne diseases have become a hot issue of food safety in the world. In recent years, the threat of bioterrorism at home and abroad and food-borne disease incidents have caused people to pay great attention to food-borne pathogens. The rapid detection of specific nucleic acid fragments of food-borne pathogens in biological samples is an important means to prevent food-borne diseases.
  • nucleic acid detection technologies include PCR-based detection technologies (general PCR, multiplex PCR, real-time fluorescent quantitative PCR and real-time quantitative reverse transcription PCR, etc.) and non-PCR nucleic acid detection technologies (loop-mediated isothermal amplification, nucleic acid-dependent amplification Detection technology, gene chip and microfluidic chip, etc.).
  • PCR-based detection technologies general PCR, multiplex PCR, real-time fluorescent quantitative PCR and real-time quantitative reverse transcription PCR, etc.
  • non-PCR nucleic acid detection technologies loop-mediated isothermal amplification, nucleic acid-dependent amplification Detection technology, gene chip and microfluidic chip, etc.
  • the present invention proposes a CRISPR-Cas12g-based nano-fluorescence trace rapid detection method for specific nucleic acid fragments, which can be applied to the rapid, specific and sensitive detection of specific nucleic acid fragments in biological samples. method.
  • nucleic acid targets for specific nucleic acid fragments in biological samples as the research object, prepare nucleic acid targets, quenching fluorescent probes, Cas12g ternary complexes of biological samples; combine Cas12g ternary complexes, nucleic acid targets, quenching fluorescent probes, background RNA and The RNase inhibitor is mixed in the nuclease buffer and incubated.
  • the Cas12g ternary complex When the Cas12g ternary complex is matched with the nucleic acid target, it will not only cleave the nucleic acid target, but also attach the non-specific trans-cutting quenching fluorescent probe to obtain the Detected fluorescence; by collecting fluorescence spectrum data, constructing up-conversion nano-fluorescence intensity change value and quantitative detection model of nucleic acid targets (specific nucleic acid fragments of biological samples) with different concentrations to realize the detection of nucleic acid targets (specific nucleic acid fragments) in biological samples Fast detection of nano-fluorescence traces.
  • the preparation method of the nucleic acid target is: if the biological sample is DNA, the extraction method is: the target can be obtained through RPA amplification and in vitro transcription; if the biological sample is RNA, the extraction method is: through RT-RPA amplification and in vitro transcription. Transcription to get the target;
  • the fluorescent group of the quenching fluorescent probe adopts up-conversion nanoparticles (UCNP S ), and the quenching group uses a water-soluble non-fluorescent quencher
  • the quencher can absorb the light emitted by the fluorescent group within a certain distance, has a wide absorption spectrum range ( ⁇ 500nm to ⁇ 900nm), and has high quenching efficiency (>97%); the fluorescent group and quenching The groups are connected with single-stranded DNA or RNA, and finally a quenched fluorescent probe is obtained -RNA/DNA-UCNP S.
  • the quenching fluorescent probe has a signal reporting function.
  • the UCNP S in the quenching fluorescent probe emits detectable fluorescence.
  • the photochemical properties of the up-conversion nanoparticles (UCNP S ) are stable, basically not affected by the external environment, low detection background, simple device and low cost.
  • the up-conversion nanoparticles are synthesized by a high-temperature thermal decomposition method, and the process is as follows: using rare earth crystal hydrate chlorides as raw materials, oleic acid and 1-octadecene as solvents, to build a high-temperature heat doped based on rare earth elements.
  • the Cas12g ternary complex includes Cas12g, crRNA and tracrRNA, the crRNA and tracrRNA can be co-folded, the N region of crRNA is a variable spacer sequence region, and the variable spacer sequence region is complementary to the nucleic acid target sequence;
  • S1 construct a Cas12g protein expression plasmid.
  • To synthesize the Cas12g gene add BamH I and Xho I restriction sites at both ends of the Cas12g gene sequence; treat the pET28a plasmid with BamH I and Xho I double restriction enzymes; add the BamH I and Xho I restriction sites to Cas12g Connect to the digested pET28a plasmid to obtain the Cas12g protein expression plasmid, namely pET28a-Cas12g;
  • the novel ribonuclease Cas12g is small in size (720-830aa), and after identifying and matching the target RNA sequence, it can not only cut the target RNA, but also has the ability to cut single-stranded DNA or RNA non-specifically.
  • a CRISPR-Cas12g-based nano-fluorescence trace rapid detection method suitable for specific nucleic acid fragments in biological samples proposed by the present invention combines the CRISPR-Cas12g system, isothermal amplification technology, and nano-fluorescence particles with high-efficiency quenching
  • the new method of detection using up-conversion luminescence nanotechnology is used to realize the quantitative detection of specific nucleic acid fragments in biological samples. This method has the advantages of simple operation, low cost, fast detection speed, strong specificity and high sensitivity.
  • the present invention not only improves the sensitivity of detection of specific nucleic acid fragments in biological samples, but also extends the application range to the extent that both DNA and RNA can be detected, and it also has a fast detection speed. , Strong specificity, low temperature operation, loose sample volume, multiple, low cost, flexible reagent form and other advantages.
  • the novel quenching fluorescent probe related to the present invention uses up-conversion nanoparticles (UCNP S ) with stable photochemical properties, basically unaffected by the external environment, low detection background, simple device and low cost for the fluorescent group.
  • the fluorescent group is synthesized by high-temperature thermal decomposition method, and has the characteristics of small particle size, monodisperse, strong fluorescence, and good stability.
  • the quenching group uses a new water-soluble non-fluorescent quencher with a wide quenching range ( ⁇ 500nm to ⁇ 900nm) and a quenching efficiency of >97% Since the fluorescence spectrum of the fluorophore overlaps with the absorption spectrum of the quenching group, the quenching group can quench the fluorophore.
  • the fluorophore and the quenching group are connected by short strands of DNA or RNA.
  • the probe has the advantages of simple synthesis, short time and low cost.
  • crRNA and tracrRNA designed in the present invention are synthesized by chemical synthesis, and the preparation is simple.
  • the tracrRNA sequence is known and can be synthesized directly and quickly.
  • Figure 1 is a schematic diagram of the rapid detection of specific nucleic acid fragments based on CRISPR-Cas12g by nano-fluorescence trace;
  • Figure 3 is a schematic diagram of the co-folding of mature crRNA and tracrRNA (the N region of crRNA is a variable spacer sequence region, and the designed spacer sequence should be complementary to the target RNA sequence);
  • Figure 4 shows the fluorescence spectrum and transmission electron micrograph of 0.01 mg/mL up-conversion nanoparticles.
  • the present invention is suitable for the rapid detection of nano-fluorescence traces of specific nucleic acid fragments in biological samples.
  • MRSA methicillin-resistant Staphylococcus aureus
  • Cas12g1 protein expression plasmid In this example, Cas12g1 (767aa) in Cas12g (720-830aa) is selected. The pET28a plasmid was treated with two enzymes, BamH I and Xho I. Synthesize the Cas12g1 gene, add the BamH I and Xho I restriction sites at both ends of the Cas12g1 gene sequence, and connect the Cas12g1 gene sequence with the BamH I and Xho I restriction sites to the digested pET28a plasmid to obtain pET28a -Cas12g1 ( Figure 2A).
  • RNA Synthesis kit to incubate the dsDNA template with T7RNA polymerase at 37°C for 3h for in vitro transcription, DNase I to process the in vitro transcription product, and then use the column RNA rapid concentration purification kit to purify.
  • the prepared crRNA sequence is (The black bold sequence is complementary to the target RNA sequence), the tracrRNA sequence is 5'-GAUGCUUACUUAGUCAUCUGGUUGGCAAACCUCCGCGGACCUUCGGGACCAAUGGAGAGGAACCCAGCCGAGAAGCAUCGAGCCGGUAAAUGCCGGAAA-3'.
  • nucleic acid target use bacterial genomic DNA extraction kit to extract MRSA DNA.
  • RPA technology to amplify the extracted DNA.
  • the upstream primer of RPA used is mecA-F: 5'-TAATACGACTCACTATAGGGTGAAGATATACCAAGTGATT-3' (TAATACGACTCACTATAGG is the T7 promoter sequence), and the downstream primer is mecA-R: 5'-ATGCGCTATAGATTGAAAGGAT -3'.
  • the amplified product with T7 promoter sequence is transcribed in vitro under the action of T7 RNA polymerase to obtain the target RNA (sequence is The black bold sequence is the complementary sequence of the crRNA spacer sequence), the column-type RNA rapid concentration purification kit purifies the target RNA. Determine the target RNA concentration.
  • the fluorescent group is synthesized by high temperature thermal decomposition method. Weigh 0.8mM YCl 3 ⁇ 6H 2 O, 0.17mM YbCl 3 ⁇ 6H 2 O and 0.03mM ErCl 3 ⁇ 6H 2 O was dissolved in 5mL of methanol and added 3mL OA 7mL 1-ODE in a flask and heated to 160 °C Stir for 30 min and cool to room temperature. A 10 mL methanol solution containing 4 mM NH 4 F and 2.5 mM NaOH was added to the flask and stirred for 40 min, and methanol was volatilized at 70° C. for 30 min.
  • OA-UCNPs OA-UCNPs
  • surface of OA-UCNPs was amination modified to obtain water-soluble NH 2 -UCNP S.
  • quenching group Dark quencher, synthetic -RNA/DNA-SH and NH 2 -UCNP S are connected with Sulfo-SMCC cross-linking agent, and finally a quenched fluorescent probe is obtained -RNA/DNA-UCNP S (e.g.
  • the probe has a signal reporting function.
  • the RNA/DNA strand in the Cas12g1 non-specific cleavage probe is activated, it can release a fluorescent signal that can be detected.
  • Nano-fluorescence trace rapid detection of mecA gene in MRSA The quantitative analysis model of fluorescence intensity change value and different concentrations of target RNA is constructed as shown in Figure 4 to realize the rapid detection of nano-fluorescence trace of mecA gene in MRSA.

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Abstract

一种基于CRISPR-Cas12g的特异性核酸片段纳米荧光痕量快速检测方法：以生物样品中特异性核酸片段为研究对象，制备生物样品的核酸靶标、猝灭荧光探针、Cas12g三元复合体；将Cas12g三元复合体、核酸靶标、猝灭荧光探针、背景RNA和RNA酶抑制剂混合在核酸酶缓冲液中孵育，当Cas12g三元复合体与核酸靶标识别匹配后，不仅剪切核酸靶标，且附带非特异性反式剪切猝灭荧光探针，进而获取可被检测的荧光；通过采集荧光光谱数据，构建上转换纳米荧光强度变化值与不同浓度的核酸靶标的定量检测模型，实现生物样品中核酸靶标的纳米荧光痕量快速检测。能够适用于生物样品中特异性核酸片段快速、特异、灵敏的检测方法。

Description

一种基于CRISPR-Cas12g的特异性核酸片段纳米荧光痕量快速检测方法 技术领域
本发明属于核酸检测技术领域，尤其是一种基于CRISPR-Cas12g的特异性核酸片段纳米荧光痕量快速检测方法。
背景技术
伴随着核酸检测技术的快速发展，各种生物样品的快速检测方法相继出现。如致使食源性疾病的食源性致病菌，已成为世界食品安全的热点问题。近年来，国内外的生物恐怖主义威胁以及食源性疾病事件引发人们对食源性致病菌的高度关注。对生物样品中食源性致病菌特异性核酸片段的快速检测是预防食源性疾病的重要手段。
目前，核酸检测技术包括基于PCR的检测技术(普通PCR、多重PCR、实时荧光定量PCR和实时定量反转录PCR等)和非PCR核酸检测技术(环介导等温扩增、核酸依赖性扩增检测技术、基因芯片和微流体芯片等)。这些检测方法虽各有优势，但存在检测周期长或检测费用高或易出现假阳性和假阴性结果等缺陷。因此，迫切需要一种快速、特异、灵敏的适用于生物样品中特异性核酸片段的检测方法。国内外尚未有采用CRISPR-Cas12g系统实现生物样品中特异性核酸片段的纳米荧光定量检测方面的报道。
发明内容
为了解决现有技术中存在的问题，本发明提出了一种基于CRISPR-Cas12g的特异性核酸片段纳米荧光痕量快速检测方法，能够适用于生物样品中特异性核酸片段快速、特异、灵敏的检测方法。
本发明所采用的技术方案如下：
一种基于CRISPR-Cas12g的特异性核酸片段纳米荧光痕量快速检测方法：
以生物样品中特异性核酸片段为研究对象，制备生物样品的核酸靶标、猝灭荧光探针、Cas12g三元复合体；将Cas12g三元复合体、核酸靶标、猝灭荧光探针、背景RNA和RNA酶抑制剂混合在核酸酶缓冲液中孵育，当Cas12g三元复合体与核酸靶标识别匹配后，不仅剪切核酸靶标，且附带非特异性反式剪切猝灭荧光探针，进而获取可被检测的荧光；通过采集荧光光谱数据，构建上转换纳米荧光强度变化值与不同浓度的核酸靶标(生物样品特异性核酸片段)的定量检测模型，实现生物样品中核酸靶标(特异性核酸片段)的纳米荧光痕量快速检测。
进一步，所述核酸靶标的制备方法为：若生物样品为DNA则提取方法为：经过RPA扩增和体外转录可获得靶标；若生物样品为RNA则提取方法为：经过RT-RPA扩增和体外转录进而得到靶标；
进一步，所述猝灭荧光探针的荧光基团采用上转换纳米颗粒(UCNP S)，猝灭基团使用水溶性非荧光猝灭剂
Figure PCTCN2019124463-appb-000001
该淬灭剂能够将一定距离内荧光基团发出的光吸收，拥有较宽的吸收光谱范围(～500nm到～900nm),猝灭效率高(>97％)；所述荧光基团和猝灭基团之间用单链DNA或RNA连接，最终得到猝灭荧光探针
Figure PCTCN2019124463-appb-000002
-RNA/DNA-UCNP S。所述猝灭荧光探针拥有信号报告功能，当猝灭荧光探针中的单链RNA或单链DNA被激活的Cas12g蛋白附带切割时，其中的UCNP S发出可被检测的荧光。且上转换纳米颗粒(UCNP S)的光化学性质稳定、基本不受外界环境影响、检测背景低、装置简单以及成本低。
进一步，所述上转换纳米颗粒采用高温热分解法合成，过程为：以稀土结晶水合物氯化盐等为原料，油酸和1-十八烯为溶剂，搭建基于稀土元素掺杂的高温热分解法UCNPs合成平台，制备出粒径大小约为50nm的油相OA-UCNPs，在其表面修饰氨基转为水溶性的NH 2-UCNPs。
进一步，所述Cas12g三元复合体包括Cas12g、crRNA和tracrRNA，所述crRNA和tracrRNA可进行共折叠，crRNA的N区域为可变间隔序列区，且可变间隔序列区与核酸靶标序列互补；
进一步，所述Cas12g的制备方法：
S1，构建Cas12g蛋白表达质粒。合成Cas12g基因，在Cas12g基因序列两端分别加上BamH I和Xho I酶切位点；用BamH I和Xho I双酶切处理pET28a质粒；将加上BamH I和Xho I酶切位点的Cas12g连接到酶切后的pET28a质粒上，得到Cas12g蛋白表达质粒，即pET28a-Cas12g；
S2，将Cas12g蛋白表达质粒转化至感受态细胞，涂平板培养过夜，挑选单菌落扩大培养，待菌液OD600为1～1.5时，用0.2mM IPTG诱导蛋白表达，培养过夜后离心收集培养物，裂解缓冲液+蛋白酶抑制剂进行重悬；超声破碎细胞，4℃条件下28000xg离心20min，将上清液加到HisTrap FF柱上，通过FPLC经咪唑梯度(50mM～500mM)纯化；SDS-PAGE凝胶电泳后再浓缩，透析获得Cas12g蛋白。新型核糖核酸酶Cas12g尺寸小(720-830aa)，且与目标RNA序列识别匹配后不仅能剪切目标RNA，还附带非特异性反式剪切单链DNA或RNA的能力。
本发明的有益效果：
1、本发明所提出的一种基于CRISPR-Cas12g的适用于生物样品中特异性核酸片段的纳米荧光痕量快速检测方法，将CRISPR-Cas12g系统、等温扩增技术以及纳米荧光粒子和高效猝灭剂相结合，采用上转换发光纳米技术检测新思路，实现生物样品中特异性核酸片段的定量检测。该方法具有操作简单、成本低、检测速度快、特异性强、灵敏度高等优势。
2、本发明通过引入RPA/RT-RPA核酸扩增技术，不仅提高了生物样品中特异性核酸片段检测的灵敏度，而且将应用范围拓展到DNA和RNA均可检测的程度，还具备检测速度快，特异性强，可低温运行，宽松的样本容，多重，低成本，灵活的试剂形态等优势。
3、本发明涉及的新型猝灭荧光探针，其荧光基团使用光化学性质稳定、基本不受外界环境影响、检测背景低、装置简单以及成本低的上转换纳米粒子(UCNP S)。该荧光基团采用高温热分解法合成，并具备粒径小、单分散、荧光强、稳定性好等特点。猝灭基团使用拥有宽的猝灭范围(～500nm到～900nm),猝灭效率>97％的新型水溶性非荧光猝灭剂
Figure PCTCN2019124463-appb-000003
由于荧光基团的荧光光谱与淬灭基团的吸收光谱相重叠，故猝灭基团可将荧光基团淬灭。荧光基团和猝灭基团之间用DNA或RNA短链连接。该探针具有合成简单、用时短、成本低等优势。
4、本发明设计的crRNA和tracrRNA通过化学合成法合成，制备简单。crRNA：5’-UUUACCGGCUCUGACACC-间隔序列-3’,间隔序列依据目标RNA设计，其与目标RNA序列互补。tracrRNA序列已知，可直接快速合成。
附图说明
图1为基于CRISPR-Cas12g的特异性核酸片段纳米荧光痕量快速检测原理图；
图2中，2A为质粒pET28a-Cas12g1图谱；2B为纯化Cas12g1蛋白的SDS-PAGE图；
图3为成熟crRNA和tracrRNA共折叠示意图(crRNA的N区域为可变间隔序列区，设计的间隔序列应与目标RNA序列互补)；
图4为0.01mg/mL上转换纳米颗粒的荧光光谱图和透射电镜图。
具体实施方式
为了使本发明的目的、技术方案及优点更加清楚明白，以下结合附图及实施例，对本发明进行进一步详细说明。应当理解，此处所描述的具体实施例仅用于解释本发明，并不用于限定本发明。
本发明适用于生物样品中特异性核酸片段的纳米荧光痕量快速检测，本发明实例中仅以耐甲氧西林金黄色葡萄球菌(MRSA)的mecA基因检测为例，具体操作步骤如下：
(1)构建Cas12g1蛋白表达质粒：在本实施例中，选用Cas12g(720-830aa)中的Cas12g1 (767aa)。用BamH I和Xho I两个酶处理pET28a质粒。合成Cas12g1基因，在Cas12g1基因序列两端分别加上BamH I和Xho I酶切位点，将加上BamH I和Xho I酶切位点的Cas12g1基因序列与酶切后的pET28a质粒连接，得到pET28a-Cas12g1(如图2A)。
(2)Cas12g1蛋白的表达纯化：将Cas12g1蛋白表达质粒转化至感受态细胞，涂平板培养过夜，挑选单菌落扩大培养，待菌液OD600为1～1.5时，用0.2mM IPTG诱导蛋白表达，培养过夜后离心收集培养物，裂解缓冲液+蛋白酶抑制剂进行重悬。超声破碎细胞，4℃条件下28000xg离心20min，将上清液加到HisTrap FF柱上，通过FPLC经咪唑梯度(50mM～500mM)纯化。SDS-PAGE凝胶电泳后再浓缩，透析Cas12g1蛋白，测定Cas12g1浓度(如图2B)。
(3)如图3，crRNA和tracrRNA的制备：crRNA和tracrRNA的单链DNA寡核苷酸模板由生工生物工程(上海)股份有限公司合成。使用Next High-Fidelity 2X PCR Master Mix对pre-crRNA模板进行PCR扩增以产生双链体外转录模板DNA。T7引物与模板退火，DNA聚合酶I进行延伸得到成熟crRNA和tracrRNA的双链DNA模板。95℃退火5min，再以-5℃/min降温至4℃。使用HiScribe T7Quick High Yield RNA Synthesis试剂盒将dsDNA模板与T7RNA聚合酶在37℃下孵育3h进行体外转录，DNase I处理体外转录产物，再用柱式RNA快速浓缩纯化试剂盒纯化。测定制备的crRNA和tracrRNA浓度。制备的crRNA序列为
Figure PCTCN2019124463-appb-000004
(黑色粗体序列与目标RNA序列互补)，tracrRNA序列为5’-GAUGCUUACUUAGUCAUCUGGUUGGCAAACCUCCGCGGACCUUCGGGACCAAUGGAGAGGAACCCAGCCGAGAAGCAUCGAGCCGGUAAAUGCCGGAAA-3’。
(4)核酸靶标(目标RNA)的制备：使用细菌基因组DNA提取试剂盒提取MRSA的DNA。运用RPA技术对提取的DNA进行扩增反应，所使用的RPA上游引物为mecA-F:5'-TAATACGACTCACTATAGGGTGAAGATATACCAAGTGATT-3'(TAATACGACTCACTATAGG为T7启动子序列),下游引物为mecA-R:5'-ATGCGCTATAGATTGAAAGGAT-3'。接着带T7启动子序列的扩增产物在T7RNA聚合酶作用下进行体外转录获得目标RNA(序列为
Figure PCTCN2019124463-appb-000005
Figure PCTCN2019124463-appb-000006
黑色粗体序列为crRNA间隔序列的互补序列)，柱式RNA快速浓缩纯化试剂盒纯化目标RNA。测定目标RNA浓度。
(5)猝灭荧光探针的制备：荧光基团采用高温热分解法合成。称取0.8mM YCl 3·6H 2O,0.17mM YbCl 3·6H 2O和0.03mM ErCl 3·6H 2O溶于5mL甲醇中，加入3mL OA和7mL 1-ODE于烧瓶中，加热至160℃搅拌30min，冷却到室温。将溶有4mM NH 4F和2.5mM NaOH的10mL甲醇溶液加入烧瓶搅拌40min，70℃挥发甲醇30min。100℃通氩气排除空气10min，迅速加热到300℃维持1h，冷却至室温，乙醇与环己烷混合清洗多次，置于真空干燥箱60℃干燥得到OA-UCNPs。接着在OA-UCNPs表面进行氨基化修饰得到水溶性的NH 2-UCNP S。猝灭基团使用
Figure PCTCN2019124463-appb-000007
黑暗淬火剂，合成的
Figure PCTCN2019124463-appb-000008
-RNA/DNA-SH与NH 2-UCNP S用Sulfo-SMCC交联剂进行连接，最终得到猝灭荧光探针
Figure PCTCN2019124463-appb-000009
-RNA/DNA-UCNP S(如
Figure PCTCN2019124463-appb-000010
-rArCrGrUrUrUrGrGrUrG-UCNP S或
Figure PCTCN2019124463-appb-000011
-TAACACGCCAC-UCNP S)。该探针具有信号报告功能，当激活Cas12g1非特异性剪切探针中的RNA/DNA链时，能够释放可供检测的荧光信号。
(6)荧光光谱数据的采集分析(如图1)：将Cas12g1三元复合体、猝灭荧光探针、RNA酶抑制剂、背景RNA和不同浓度的目标RNA混合在核酸酶缓冲液中孵育；当Cas12g1三元复合体与核酸靶标识别匹配后，不仅剪切核酸靶标，且附带非特异性反式剪切猝灭荧光探针，进而获取可被检测的荧光；使用上转换荧光光谱仪记录不同浓度目标RNA对应的荧光强度。MRSA中mecA基因的纳米荧光痕量快速检测：构建荧光强度变化值与不同浓度目标RNA的定量分析模型如图4，实现MRSA中mecA基因的纳米荧光痕量快速检测。
以上实施例仅用于说明本发明的设计思想和特点，其目的在于使本领域内的技术人员能够了解本发明的内容并据以实施，本发明的保护范围不限于上述实施例。所以，凡依据本发明所揭示的原理、设计思路所作的等同变化或修饰，均在本发明的保护范围之内。

Claims (6)

  1. 一种基于CRISPR-Cas12g的特异性核酸片段纳米荧光痕量快速检测方法，其特征在于，以生物样品中特异性核酸片段为研究对象，制备生物样品的核酸靶标、猝灭荧光探针、Cas12g三元复合体；将Cas12g三元复合体、核酸靶标、猝灭荧光探针、背景RNA和RNA酶抑制剂混合在核酸酶缓冲液中孵育，当Cas12g三元复合体与核酸靶标识别匹配后，不仅剪切核酸靶标，且附带非特异性反式剪切猝灭荧光探针，进而获取可被检测的荧光；通过采集荧光光谱数据，构建上转换纳米荧光强度变化值与不同浓度的核酸靶标的定量检测模型，实现生物样品中核酸靶标的纳米荧光痕量快速检测。
  2. 根据权利要求1所述的一种基于CRISPR-Cas12g的特异性核酸片段纳米荧光痕量快速检测方法，其特征在于，所述核酸靶标的制备方法为：若生物样品为DNA则提取方法为：经过RPA扩增和体外转录可获得靶标；若生物样品为RNA则提取方法为：经过RT-RPA扩增和体外转录进而得到靶标。
  3. 根据权利要求1或2所述的一种基于CRISPR-Cas12g的特异性核酸片段纳米荧光痕量快速检测方法，其特征在于，所述猝灭荧光探针的荧光基团采用上转换纳米颗粒UCNP S，猝灭基团使用非荧光猝灭剂
    Figure PCTCN2019124463-appb-100001
    所述荧光基团和猝灭基团之间用单链DNA或RNA连接，最终得到猝灭荧光探针
    Figure PCTCN2019124463-appb-100002
  4. 根据权利要求3所述的一种基于CRISPR-Cas12g的特异性核酸片段纳米荧光痕量快速检测方法，其特征在于，所述上转换纳米颗粒采用高温热分解法合成，过程为：以稀土结晶水合物氯化盐等为原料，油酸和1-十八烯为溶剂，搭建基于稀土元素掺杂的高温热分解法UCNPs合成平台，制备出粒径大小约为50nm的油相OA-UCNPs，在其表面修饰氨基转为水溶性的NH 2-UCNPs。
  5. 根据权利要求4所述的一种基于CRISPR-Cas12g的特异性核酸片段纳米荧光痕量快速检测方法，其特征在于，所述Cas12g三元复合体包括Cas12g、crRNA和tracrRNA，所述crRNA和tracrRNA可进行共折叠，crRNA的N区域为可变间隔序列区，且可变间隔序列区与核酸靶标序列互补。
  6. 根据权利要求5所述的一种基于CRISPR-Cas12g的特异性核酸片段纳米荧光痕量快速检测方法，其特征在于，所述Cas12g的制备方法：
    S1，构建Cas12g蛋白表达质粒。合成Cas12g基因，在Cas12g基因序列两端分别加上BamH I和Xho I酶切位点；用BamH I和Xho I双酶切处理pET28a质粒；将加上BamH I和 Xho I酶切位点的Cas12g与酶切后的pET28a质粒连接，得到Cas12g蛋白表达质粒，即pET28a-Cas12g；
    S2，将Cas12g蛋白表达质粒转化至感受态细胞，涂平板培养过夜，挑选单菌落扩大培养，待菌液OD600为1～1.5时，用0.2mM IPTG诱导蛋白表达，培养过夜后离心收集培养物，裂解缓冲液+蛋白酶抑制剂进行重悬；超声破碎细胞，4℃条件下28000xg离心20min，将上清液加到HisTrap FF柱上，通过FPLC经50mM～500mM的咪唑梯度纯化；SDS-PAGE凝胶电泳后再浓缩，透析获得Cas12g蛋白。
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