A filter membrane and method for extracting DNA from evidence specimens

Abstract

The present invention discloses a filter membrane and a method for extracting DNA from physical evidence samples, comprising the following steps: S1: soaking the filter membrane with a first magnetic bead suspension, filtering the first magnetic bead suspension soaked with the filter membrane until the liquid on the filter membrane is drained, thereby obtaining a filter membrane adsorbed with magnetic beads; S2: flushing the surface of the physical evidence sample with a mixture of a buffer solution and a second magnetic bead suspension to obtain an enriched liquid, filtering the enriched liquid with the filter membrane adsorbed with magnetic beads until the enriched liquid on the filter membrane is drained, thereby obtaining a filter membrane enriched with DNA and / or body cells; S3: extracting DNA from the filter membrane enriched with DNA and / or body cells. The present invention solves the problem that existing extraction methods cannot accurately extract DNA from physical evidence samples that are large in size, have good water resistance, are irregular in shape, have few detached cells, and are scattered, thereby achieving the purpose of accurately extracting trace DNA from multi-type, multi-morphological, and irregular physical evidence samples.

Description

Technical Field

[0001] The present invention relates to the technical field of DNA collection and detection, and in particular to a filter membrane and a method for extracting DNA from a physical evidence sample. Background Art

[0002] With the rapid development of DNA testing technology, it is playing an increasingly important role in combating theft crimes, which are large-scale, widespread, frequent, and prone to occur, becoming a new growth point for solving cases. In many district and county-level public security organs, the number of suspects identified through DNA has surpassed that through fingerprint identification. The number of biological samples extracted from theft cases far exceeds the total number of biological samples collected from homicide, assault, rape, and other personal injury cases. Because biological samples extracted from theft cases are mostly contact-derived exfoliated cells, the DNA detection rate is low and contamination is prone to occur. Therefore, the ability of investigators to extract high-quality DNA from physical evidence samples at the scene is fundamental to the ability to detect and identify DNA. The type of physical evidence, the location of extraction, and the extraction and transfer method are all important factors that influence DNA testing results.

[0003] Currently, in the field of DNA collection and testing, the main methods for extracting trace DNA from various physical evidence samples include wiping, sticking, shearing, scraping, negative pressure adsorption, and oscillating washing. However, in actual DNA extraction, for some physical evidence that is large, water-resistant, or has an unusual shape, it is difficult to obtain accurate DNA test results using only conventional, mobile extraction methods such as wiping, sticking, or scraping.

[0004] In addition, hats, masks, clothing, gloves, sneakers, and socks left at crime scenes by suspects are becoming increasingly common physical evidence because they contain shed cells and cell-free DNA. However, these shed cells and cell-free DNA are rare and dispersed, making DNA extraction difficult. Summary of the Invention

[0005] In order to overcome the shortcomings of the existing technology, the present invention provides a filter membrane and a method for extracting DNA from physical evidence samples, which solves the problem that the existing DNA extraction methods cannot accurately extract DNA from physical evidence samples that are large in size, have good water resistance, are irregular in shape, have few detached cells and free DNA, and are scattered, thereby achieving the purpose of accurately extracting trace DNA from multi-type, multi-morphological, and irregular physical evidence samples.

[0006] In order to solve the above problems, the technical solutions adopted by the present invention are as follows:

[0007] A filter membrane for extracting DNA from a physical evidence specimen has a pore size of 0.45-1.5 μm and magnetic beads with a particle size of 1-3 μm are attached to the surface.

[0008] A method for extracting DNA from a physical evidence specimen comprises the following steps:

[0009] Step S1: soaking the filter membrane with the first magnetic bead suspension, and filtering the first magnetic bead suspension soaked with the filter membrane until the liquid on the filter membrane is drained, thereby obtaining a filter membrane adsorbed with magnetic beads;

[0010] Step S2: After washing away DNA and / or somatic cells on the surface of the physical evidence sample using a mixture of a buffer solution and a second magnetic bead suspension, an enriched solution is obtained, and the enriched solution is filtered through a filter membrane adsorbed with magnetic beads until the enriched solution on the filter membrane is drained, thereby obtaining a filter membrane enriched with DNA and / or somatic cells;

[0011] Step S3: extracting DNA from the filter membrane enriched with DNA and / or body cells.

[0012] As a preferred embodiment of the present invention, the first magnetic bead suspension is a mixture of silicon micropowder, sodium polyacrylate and pure water; the second magnetic bead suspension is a mixture of mixed powder solution, silicon micropowder and pure water;

[0013] The mixed powder solution is prepared by adding ethylenediaminetetraacetic acid, sodium chloride, guanidine salt and sodium acetate into isopropyl alcohol solution and mixing them evenly.

[0014] As a preferred embodiment of the present invention, the soaking in step S1 specifically comprises: soaking the filter membrane in the first magnetic bead suspension for 1-10 minutes.

[0015] As a preferred embodiment of the present invention, the ratio of the buffer solution to the second magnetic bead suspension in the mixed solution is 10-20:1 by mass.

[0016] As a preferred embodiment of the present invention, the pore size of the filter membrane is 0.45-1.5 μm.

[0017] As a preferred embodiment of the present invention, the filtration in step S1 and step S2 is specifically: vacuum negative pressure filtration, and the vacuum negative pressure value is -60Kpa to -95Kpa.

[0018] As a preferred embodiment of the present invention, the flushing treatment specifically includes: flushing the surface of the physical evidence material and / or positioning and immersing part or all of the surface of the physical evidence material.

[0019] As a preferred embodiment of the present invention, the buffer solution is prepared by adding ethylenediaminetetraacetic acid, sodium chloride, perchlorate and sodium acetate to an isopropanol solution, mixing them evenly, and then adjusting the pH value to 6-7 using acetic acid;

[0020] Wherein, the concentration of the isopropyl alcohol solution is 10%-30% by mass percentage, the content of the ethylenediaminetetraacetic acid is 1-100 by millimole per liter, the content of the sodium chloride is 0.5-1, the content of the perchlorate is 0.5-2, and the content of the sodium acetate is 100-200.

[0021] As a preferred embodiment of the present invention, the buffer solution is prepared by adding ethylenediaminetetraacetic acid, sodium chloride, guanidine salt and sodium acetate to an isopropanol solution, mixing them evenly, and then adjusting the pH value to 6-7 with acetic acid;

[0022] Wherein, the concentration of the isopropanol solution is 10%-30% by mass percentage, the content of the ethylenediaminetetraacetic acid is 1-100 by millimole per liter, the content of the sodium chloride is 0.5-1, the content of the guanidine salt is 0.5-2L, and the content of the sodium acetate is 100-200.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) For physical evidence samples with special shapes, it is difficult to extract them using conventional adsorption, adhesion, and wiping methods. The extraction method of the present invention can more easily enrich the body's exfoliated cells and free DNA, thereby improving the accuracy of DNA detection;

[0025] (2) Physical evidence samples with special shapes are inevitably prone to slipping or rolling during wiping or sticking operations, which can cause contamination of the physical evidence samples. The extraction method of the present invention can avoid contamination of the physical evidence samples during the experimental operation, thereby improving the purity of the extracted DNA and further improving the accuracy of DNA detection;

[0026] (3) The present invention makes up for the shortcomings of traditional DNA transfer and extraction methods such as wiping, sticking, shearing, scraping, negative pressure adsorption and shaking washing, such as high DNA loss and missed extraction.

[0027] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 - is a schematic diagram of a process for extracting DNA from a data line according to Example 1 of the present invention;

[0029] Figure 2- is a diagram showing the typing results of DNA extracted online from the data in Example 1 of the present invention;

[0030] Figure 3 - is a diagram showing the typing results of DNA extracted online from the data in Example 2 of the present invention;

[0031] Figure 4 - is a diagram showing the typing results of DNA extracted online from the data in Example 3 of the present invention;

[0032] Figure 5 - is a diagram showing the typing results of DNA extracted online from the data in Example 4 of the present invention;

[0033] Figure 6 - is a diagram showing the typing results of DNA extracted online from the data of Example 5 of the present invention;

[0034] Figure 7 - is a diagram showing the typing results of DNA extracted online from the data of Example 6 of the present invention;

[0035] Figure 8 - is a diagram showing the typing results of DNA extracted from a key in Example 7 of the present invention;

[0036] Figure 9 - is a diagram showing the typing results of DNA extracted from the data line of Comparative Example 1 of the present invention;

[0037] Figure 10 - is a diagram of the typing results of DNA extracted from the key of Comparative Example 2 of the present invention;

[0038] Figure 11 - is a schematic diagram of the process for extracting DNA from a key according to Example 7 of the present invention. DETAILED DESCRIPTION

[0039] The filter membrane provided by the present invention is used for extracting DNA from evidence test materials. The pore size of the filter membrane is 0.45-1.5um, and magnetic beads with a particle size of 1-3um are attached to the surface.

[0040] The method for extracting DNA from a physical evidence sample provided by the present invention comprises the following steps:

[0041] Step S1: soaking the filter membrane with the first magnetic bead suspension, and filtering the first magnetic bead suspension soaked with the filter membrane until the liquid on the filter membrane is drained, thereby obtaining a filter membrane adsorbed with magnetic beads;

[0042] Furthermore, the pore size of the filter membrane is 0.45-1.5 μm. Acid- and alkali-resistant materials, such as nylon, can be used to impart a certain degree of acid and alkali resistance to the filter membrane, thereby preventing damage during the filtration process. The pore size of the filter membrane is 0.45-1.5 μm, ensuring that valid cells with a conventional diameter of 3-50 μm are retained on the filter membrane, while the liquid after rinsing or soaking can be discharged through the filter membrane into a collection bottle for later use.

[0043] Furthermore, the soaking in step S1 is specifically as follows: soaking the filter membrane in the first magnetic bead suspension for 1-10 minutes.

[0044] Furthermore, the first magnetic bead suspension in step S1 is a mixture of silicon micropowder, sodium polyacrylate and pure water.

[0045] Furthermore, the filtration in step S1 is specifically: vacuum negative pressure filtration, and the vacuum negative pressure value is -60Kpa to -95Kpa.

[0046] Step S2: After washing away the DNA and / or somatic cells on the surface of the physical evidence sample with a mixture of a buffer solution and a second magnetic bead suspension, an enriched solution is obtained, and the enriched solution is filtered through a filter membrane adsorbed with magnetic beads until the enriched solution on the filter membrane is drained, thereby obtaining a filter membrane enriched with DNA and / or somatic cells;

[0047] Furthermore, the ratio of the buffer solution to the second magnetic bead suspension in the mixed solution is 10 to 20:1 by mass.

[0048] Furthermore, the second magnetic bead suspension in step S2 is a mixture of a mixed powder solution, silicon powder and pure water; wherein the mixed powder solution is prepared by adding ethylenediaminetetraacetic acid, sodium chloride, guanidine salt and sodium acetate into an isopropanol solution and mixing them evenly.

[0049] The buffer solution of the present invention can avoid damaging detached cells when washing articles; and can quickly adsorb free DNA by combining with a magnetic bead suspension, thereby avoiding the loss of free DNA.

[0050] Furthermore, the preparation of the buffer solution is specifically as follows: ethylenediaminetetraacetic acid, sodium chloride, perchlorate and sodium acetate are added to an isopropanol solution, mixed evenly, and then the pH value is adjusted to 6-7 using acetic acid.

[0051] The isopropyl alcohol solution has a concentration of 10%-30% by mass, and has a content of 1-100 ethylenediaminetetraacetic acid, 0.5-1 sodium chloride, 0.5-2 perchlorate, and 100-200 sodium acetate by millimole per liter.

[0052] Furthermore, the preparation of the buffer solution is specifically as follows: ethylenediaminetetraacetic acid, sodium chloride, guanidine salt and sodium acetate are added to an isopropanol solution, mixed evenly, and then the pH value is adjusted to 6-7 using acetic acid.

[0053] The concentration of the isopropanol solution is 10%-30% by mass percentage, the content of ethylenediaminetetraacetic acid is 1-100 by millimole per liter, the content of sodium chloride is 0.5-1, the content of guanidine salt is 0.5-2L, and the content of sodium acetate is 100-200.

[0054] Furthermore, the flushing treatment specifically includes: flushing the surface of the physical evidence material and / or positioning and immersing part or all of the surface of the physical evidence material.

[0055] Furthermore, the filtration in step S2 is specifically: vacuum negative pressure filtration is adopted, and the vacuum negative pressure value is -60Kpa to -95Kpa.

[0056] Step S3: extracting DNA from the filter membrane enriched with DNA and / or body cells.

[0057] Furthermore, DNA is extracted using a magnetic bead method or a silica gel membrane method DNA extraction kit.

[0058] In actual use, the filter membrane and method for extracting DNA from physical evidence specimens provided by the present invention can be combined with the patent submitted by the applicant (patent name: A cell enrichment device and its filtration device, application number: 202221330572.2). The above-mentioned filtration device adopts a double-layer filtration mode, with the upper layer being a filter membrane with a pore size of 150-300μm. The lower layer is a filter membrane with a pore size of 0.45-1.5μm. Combined with a negative pressure filtration device, the buffer solution is filtered into a collection bottle of an enrichment cup for retention. The detached body cells and magnetic beads adsorbed with free DNA are enriched in the second layer of the filter membrane in the enrichment cup for sample testing.

[0059] Furthermore, it is also possible to combine fully automatic integrated equipment for efficiently enriching ultra-trace DNA on different carriers, use a robotic arm to automatically grab physical evidence samples, position them through an automatic positioning device, spray the physical evidence samples with buffer solution, and use the robotic arm to regularly oscillate in the buffer solution to effectively dissolve the body cells and free DNA in the buffer solution. Use negative pressure to filter the buffer solution through two layers of filter membranes. The first layer of filter membrane filters impurities, and the second layer of filter membrane efficiently enriches the body cells and free DNA for the next step of testing. The entire equipment also has a disinfection function.

[0060] The following examples are provided to further illustrate the present invention, but the scope of the present invention is not limited thereto.

[0061] Example 1

[0062] Physical evidence: Data lines with attached organic cells and / or free DNA (e.g. Figure 1 shown)

[0063] Step 1) Immerse a filter membrane with a pore size of 0.45 μm in 1 ml of a first magnetic bead suspension and allow it to stand for 1 minute to allow the first magnetic bead suspension to fully immerse the filter membrane. Then, vacuum negative pressure filtration is performed using a negative pressure filtration device with a vacuum negative pressure value of -60 kPa. Filtration is performed for 1 hour until the first magnetic bead suspension is drained, thereby obtaining a filter membrane adsorbed with magnetic beads, the surface of which is attached with magnetic bead particles having a particle size of 1-3 μm. Wherein, the first magnetic bead suspension is a mixture of silicon micropowder, sodium polyacrylate, and pure water.

[0064] Step 2) Based on the surface area of ​​the physical evidence sample, select an enrichment cup of appropriate capacity (1-1000 ml), and use a mixture of a buffer solution and a second magnetic bead suspension to flush the physical evidence sample. 1 nmol / L ethylenediaminetetraacetic acid, 0.5 nmol / L sodium chloride, 0.5 nmol / L perchlorate, and 100 nmol / L sodium acetate are added to 10% (by mass percentage) isopropanol, mixed evenly, and then the pH is adjusted to 6 with acetic acid to prepare a buffer solution. The buffer solution and the second magnetic bead suspension are mixed at a mass ratio of 10:1 (by mass percentage) to prepare a mixed solution. A spray nozzle is aimed at the physical evidence sample, and the physical evidence sample is sprayed with the mixed solution. If necessary, part or all of the physical evidence sample can be immersed in a fixed position to ensure that free DNA and / or body cells on the physical evidence sample are evenly flushed. The second magnetic bead suspension is a mixture of a mixed powder solution, silicon powder and pure water; the mixed powder solution is prepared by adding ethylenediaminetetraacetic acid, sodium chloride, guanidine salt and sodium acetate into an isopropyl alcohol solution and mixing them evenly.

[0065] Step 3) The physical evidence sample is vacuum filtered at -60 kPa until all the mixed solution after the flushing treatment enters the enrichment cup, thereby enriching the free DNA and / or somatic cells on the filter membrane adsorbed with magnetic beads, obtaining a filter membrane enriched with DNA and / or somatic cells. 1 / 4 of the filter membrane enriched with DNA and / or somatic cells is cut using sterilized scissors and tweezers and placed in a 1.5 ml centrifuge tube;

[0066] Step 4) DNA extraction was performed using a magnetic bead DNA extraction kit;

[0067] Step 5) The extracted DNA was subjected to Nanodrop quantitative detection;

[0068] Step 6) The extracted DNA is subjected to multi-color fluorescent labeling and PCR multiplex amplification using an AGCU EX25 fluorescence detection kit to obtain amplified products, and the polymorphism of the STR loci in the human genomic DNA in the amplified products is detected and individual identification is performed;

[0069] Step 7) performing electrophoresis detection using an ABI genetic analyzer, comprising the following steps: centrifuging the amplified product at 2000-5000 rpm for 1-10 minutes, mixing 1-10 μL of the centrifuged product or EX25 Allelic Ladd er with 0.5-3 μL AGCU Marker SIZ-500 and 1-12 μL deionized formamide, denaturing at 50° C.-120° C. for 1-10 minutes, and performing electrophoresis detection in an ice bath;

[0070] Step 8) Finally, the DNA typing result diagram required by the police is obtained, such as Figure 2 shown.

[0071] Depend on Figure 2 It can be seen that by detecting and analyzing the data lines of attached organic cells and / or free DNA using the filter membrane and extraction method of the present invention, complete DNA typing results can be obtained.

[0072] Example 2

[0073] Physical evidence: Data cables with attached organism cells and / or free DNA

[0074] Other experimental conditions were consistent with those in Example 1. A filter membrane with a pore size of 1 μm was used to perform vacuum negative pressure filtration on the physical evidence sample at a vacuum negative pressure of -80 KPa. 50 nmol / L ethylenediaminetetraacetic acid, 0.7 nmol / L sodium chloride, 1 nmol / L perchlorate, and 150 nmol / L sodium acetate were added to 20% (by mass) isopropanol, mixed well, and then the pH was adjusted to 6.5 with acetic acid to prepare a buffer solution. The DNA typing results required by the public security were obtained, as shown in the figure. Figure 3 shown.

[0075] Depend on Figure 3 It can be seen that by detecting and analyzing the data lines of attached organic cells and / or free DNA using the filter membrane and extraction method of the present invention, complete DNA typing results can be obtained, and the peak heights of the spectrum are balanced, and the detection efficiency and specificity are good.

[0076] Example 3

[0077] Physical evidence: Data cables with attached organism cells and / or free DNA

[0078] Other experimental conditions were consistent with those in Example 1. A filter membrane with a pore size of 1.5 μm was used to perform vacuum negative pressure filtration on the physical evidence sample at a vacuum negative pressure of -95 KPa. 100 nmol / L ethylenediaminetetraacetic acid, 1 nmol / L sodium chloride, 2 nmol / L perchlorate, and 200 nmol / L sodium acetate were added to 30% (by mass) isopropanol, mixed well, and then the pH was adjusted to 7 with acetic acid to prepare a buffer solution. The DNA typing results required by the public security were obtained, as shown in the figure. Figure 4 shown.

[0079] Depend on Figure 4 It can be seen that by detecting and analyzing the data lines of attached organic cells and / or free DNA using the filter membrane and extraction method of the present invention, complete DNA typing results can be obtained, and the peak heights of the spectrum are balanced, and the detection efficiency and specificity are good.

[0080] Example 4

[0081] Physical evidence: Data cables with attached organism cells and / or free DNA

[0082] Other experimental conditions were consistent with those in Example 1, wherein the buffer solution and the second magnetic bead suspension were mixed at a ratio of 15:1 by mass to prepare a mixed solution, and the DNA typing result diagram required by the public security was obtained, as shown in FIG. Figure 5 shown.

[0083] Depend on Figure 5 It can be seen that by detecting and analyzing the data lines of attached organic cells and / or free DNA using the filter membrane and extraction method of the present invention, complete DNA typing results can be obtained.

[0084] Example 5

[0085] Physical evidence: Data cables with attached organism cells and / or free DNA

[0086] Other experimental conditions were consistent with those in Example 1, wherein the buffer solution and the second magnetic bead suspension were mixed at a ratio of 20:1 by mass to prepare a mixed solution, and the DNA typing result diagram required by the public security was obtained, as shown in FIG. Figure 6 shown.

[0087] Depend on Figure 6 It can be seen that by detecting and analyzing the data lines of attached organic cells and / or free DNA using the filter membrane and extraction method of the present invention, complete DNA typing results can be obtained.

[0088] Example 6

[0089] Physical evidence: Data cables with attached organism cells and / or free DNA

[0090] Other experimental conditions were consistent with those in Example 1. 1 nmol / L ethylenediaminetetraacetic acid, 0.5 nmol / L sodium chloride, 0.5 nmol / L guanidine salt, and 100 nmol / L sodium acetate were added to 10% (by mass) isopropanol, mixed evenly, and then the pH was adjusted to 6 with acetic acid to prepare a buffer solution. The DNA typing results required by the police were obtained, as shown in the figure. Figure 7 shown.

[0091] Depend on Figure 7 It can be seen that by detecting and analyzing the data lines of attached organic cells and / or free DNA using the filter membrane and extraction method of the present invention, complete DNA typing results can be obtained.

[0092] Example 7

[0093] Physical evidence: Keys attached to organism cells and / or free DNA (e.g. Figure 11 shown)

[0094] The experimental conditions were consistent with those in Example 1, and the DNA typing results required by the public security were obtained, as shown in FIG. Figure 8 shown.

[0095] Depend on Figure 8 It can be seen that by detecting and analyzing keys attached to organism cells and / or free DNA using the filter membrane and extraction method of the present invention, complete DNA typing results can be obtained.

[0096] Comparative Example 1

[0097] Physical evidence: Data cables with attached organism cells and / or free DNA

[0098] Use a cotton swab to repeatedly wipe the data line with attached organism cells and / or free DNA, and try to completely remove the organism cells and / or free DNA. Use sterilized scissors and tweezers to cut the cotton swab tip and place it in a 1.5ml centrifuge tube.

[0099] Step 4) DNA extraction was performed using a magnetic bead DNA extraction kit;

[0100] Step 5) The extracted DNA was subjected to Nanodrop quantitative detection;

[0101] Step 6) The extracted DNA is subjected to multi-color fluorescent labeling and PCR multiplex amplification using an AGCU EX25 fluorescence detection kit to obtain amplified products, and the polymorphism of the STR loci in the human genomic DNA in the amplified products is detected and individual identification is performed;

[0102] Step 7) performing electrophoresis detection using an ABI genetic analyzer, comprising the following steps: centrifuging the amplified product at 2000-5000 rpm for 1-10 minutes, mixing 1-10 μL of the centrifuged product or EX25 Allelic Ladd er with 0.5-3 μL AGCU Marker SIZ-500 and 1-12 μL deionized formamide, denaturing at 50° C.-120° C. for 1-10 minutes, and performing electrophoresis detection in an ice bath;

[0103] Step 8) Finally, the DNA typing result diagram required by the police is obtained, such as Figure 9 shown.

[0104] Depend on Figure 9 It can be seen that when the cotton swab method is used to detect the data lines of attached organic cells and / or free DNA, the overall peak height of the spectrum obtained is relatively low, and peaks are lost at some loci, indicating that the extraction efficiency of the existing cotton swab method cannot meet practical applications, and a more efficient extraction method needs to be found as a supplement.

[0105] Comparative Example 2

[0106] Physical evidence: Keys attached to organism cells and / or free DNA

[0107] Use a cotton swab to repeatedly wipe the key attached to the organism cells and / or free DNA, and try to completely remove the organism cells and / or free DNA. Use sterilized scissors and tweezers to cut the cotton swab tip and place it in a 1.5ml centrifuge tube;

[0108] Step 4) DNA extraction was performed using a magnetic bead DNA extraction kit;

[0109] Step 5) The extracted DNA was subjected to Nanodrop quantitative detection;

[0110] Step 6) The extracted DNA is subjected to multi-color fluorescent labeling and PCR multiplex amplification using an AGCU EX25 fluorescence detection kit to obtain amplified products, and the polymorphism of the STR loci in the human genomic DNA in the amplified products is detected and individual identification is performed;

[0111] Step 7) performing electrophoresis detection using an ABI genetic analyzer, comprising the following steps: centrifuging the amplified product at 2000-5000 rpm for 1-10 minutes, mixing 1-10 μL of the centrifuged product or EX25 Allelic Ladd er with 0.5-3 μL AGCU Marker SIZ-500 and 1-12 μL deionized formamide, denaturing at 50° C.-120° C. for 1-10 minutes, and performing electrophoresis detection in an ice bath;

[0112] Step 8) Finally, the DNA typing result diagram required by the police is obtained, such as Figure 10 shown.

[0113] Depend on Figure 10 It can be seen that when the cotton swab method is used to detect keys attached to organic cells and / or free DNA, the overall peak height of the obtained spectrum is relatively low, and peaks are lost in some loci, which once again confirms that the extraction efficiency of the existing cotton swab method cannot meet practical applications.

[0114] The above embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and replacements made by technicians in this field on the basis of the present invention fall within the scope of protection required by the present invention.

Claims

1. A method for extracting DNA from a physical evidence specimen, characterized in that: The following steps are involved: Step S1: soaking the filter membrane with the first magnetic bead suspension, and filtering the first magnetic bead suspension soaked with the filter membrane until the liquid on the filter membrane is drained, thereby obtaining a filter membrane adsorbed with magnetic beads; Step S2: After washing away DNA and / or somatic cells on the surface of the physical evidence sample using a mixture of a buffer solution and a second magnetic bead suspension, an enriched solution is obtained, and the enriched solution is filtered through a filter membrane adsorbed with magnetic beads until the enriched solution on the filter membrane is drained, thereby obtaining a filter membrane enriched with DNA and / or somatic cells; Step S3: extracting DNA from the filter membrane enriched with DNA and / or body cells; The first magnetic bead suspension is a mixture of silicon micropowder, sodium polyacrylate and pure water; the second magnetic bead suspension is a mixture of a mixed powder solution, silicon micropowder and pure water; wherein the mixed powder solution is prepared by adding ethylenediaminetetraacetic acid, sodium chloride, guanidine salt and sodium acetate to an isopropyl alcohol solution and mixing them uniformly; The buffer solution is prepared specifically by adding ethylenediaminetetraacetic acid, sodium chloride, perchlorate and sodium acetate to an isopropanol solution, mixing them evenly, and then adjusting the pH value to 6-7 using acetic acid; wherein, the concentration of the isopropanol solution is 10%-30% by mass, the content of the ethylenediaminetetraacetic acid is 1-100, the content of the sodium chloride is 0.5-1, the content of the perchlorate is 0.5-2, and the content of the sodium acetate is 100-200 in millimoles per liter; or, The preparation of the buffer solution is specifically as follows: ethylenediaminetetraacetic acid, sodium chloride, guanidine salt and sodium acetate are added to an isopropanol solution, mixed evenly, and then the pH value is adjusted to 6-7 using acetic acid; wherein, the concentration of the isopropanol solution is 10%-30% by mass, the content of the ethylenediaminetetraacetic acid is 1-100, the content of the sodium chloride is 0.5-1, the content of the guanidine salt is 0.5-2L, and the content of the sodium acetate is 100-200 in millimoles per liter.

2. The method for extracting DNA from a physical evidence sample according to claim 1, wherein: The soaking in step S1 specifically includes soaking the filter membrane in the first magnetic bead suspension for 1-10 minutes.

3. The method for extracting DNA from a physical evidence sample according to claim 1, wherein: The ratio of the buffer solution to the second magnetic bead suspension in the mixed solution is 10-20:1 by mass.

4. The method for extracting DNA from a physical evidence sample according to claim 1, wherein: The pore size of the filter membrane is 0.45-1.5 μm.

5. The method for extracting DNA from a physical evidence sample according to claim 1, wherein: After the operation of step S1 is completed, a filter membrane adsorbed with magnetic beads is obtained, and magnetic beads with a particle size of 1-3 μm are attached to the surface of the filter membrane.

6. The method for extracting DNA from a physical evidence sample according to claim 1, wherein: The filtration in step S1 and step S2 is specifically: vacuum negative pressure filtration, and the vacuum negative pressure value is -60KPa to -95KPa.

7. The method for extracting DNA from a physical evidence sample according to claim 1, wherein: The flushing treatment specifically includes: flushing the surface of the physical evidence material and / or positioning and immersing part or all of the surface of the physical evidence material.

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