JP2013055921A - Nucleic acid amplification method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for amplifying a nucleic acid in a channel at ultrahigh speed.SOLUTION: This method for amplifying a nucleic acid carries out a PCR reaction by feeding a PCR sample solution to a nucleic acid amplification device equipped with a meandering channel with which at least one PCR cycle can be performed. The nucleic acid amplification device has one temperature zone for DNA modification corresponding to one side loop section, a temperature zone for annealing corresponding to opposite side loop section and a temperature zone for extension between the temperature zone for annealing and a temperature zone for DNA modification. The PCR sample solution is sent to the meandering channel by a pump in a form of sample plug sandwiched between gases, and supplied into the meandering channel in a state separated by one cycle portion or more by the gas.

Description

  The present invention relates to a method for amplifying nucleic acid in a meandering flow path at an ultra-high speed. More specifically, the present invention uses a continuous-flow microfluidic system to provide fluid delivery conditions and flow path design for precise temperature control and to perform ultrafast polymerase chain reaction (PCR). Regarding the method.

  Genetic testing is at the heart of various fields such as drug development, forensic medicine, clinical testing, identification of crops and pathogenic microorganisms, disease and risk diagnosis, search for markers, food and environmental safety assessment, crime It has become a universal technology for verification. It is a well-known fact that it is also used for definitive tests for infectious diseases such as foot-and-mouth disease and new influenza that became a problem last year. In 2007, the Ministry of Health, Labor and Welfare Insurance approved the inclusion of health insurance for cancer genetic testing, and clinical testing companies announced the commercialization of genetic testing equipment and kits. It is starting to turn.

  One of the most powerful basic techniques for detecting a small amount of nucleic acid as a gene with high sensitivity is a technique for analyzing a product obtained by exponentially replicating and amplifying part or all of a nucleic acid sequence.

PCR is a powerful technique for selectively amplifying a specific region of DNA. Using PCR, millions of copies of DNA fragments can be generated from a single template DNA for a target DNA sequence in the template DNA. PCR repeats a three-phase temperature condition called a thermal cycle to denature DNA into single strands, anneal denatured DNA single strands and primers, and extend primers with a thermostable DNA polymerase enzyme. Individual reactions are repeated sequentially. This cycle is repeated until a sufficient copy number is obtained for analysis. In principle, it is possible to double the number of copies in one cycle of PCR. In fact, as the thermal cycle continues, the concentration of the amplified DNA product eventually stops as the concentration of the required reaction reagent decreases. For general details of PCR, see "Clinical Applications of PCR", Dennis Lo (edited), Humana Press (Totowa, NJ) (1998), and "PCR Protocols A Guide."
to Methods and Applications ", M. et al. A. Innis et al. (Edit), Academic Press Inc. (San Diego, Calif.) (1990).

The PCR method is a powerful technique for exponentially amplifying genes by thermal cycling, but the general-purpose thermal cycler used for PCR has a slow temperature control due to the huge heat capacity of the aluminum block that is the heater. The conventional PCR operation of 30 to 40 cycles takes 1-2 hours. Therefore, even if the latest genetic testing equipment is used, it takes a total of several hours for the analysis, and speeding up the PCR operation has been a major issue since the technology appeared.

  In order to solve such problems, microfluidic devices relating to DNA amplification by PCR have also been developed. Sample thermal cycling is typically done in one of three ways.

The first method is a method in which a sample solution is introduced into a device, and temperature cycling is performed over time while the solution is held in the same part. This is very similar to a conventional PCR instrument (Non-patent Documents 1 and 2 and Patent Document 1). However, although this method aims to reduce the heat capacity by reducing the sample amount and speed up the thermal cycle, there is a limit to reducing the heat capacity of the chamber and the heater itself, so in order to perform a sufficient amplification reaction, At least about 30 seconds per cycle is required, and even the earliest equipment to complete the PCR reaction must spend 15 minutes or more.

In the second method, a plurality of spatially separated temperature zones are connected by a micro flow channel, and the sample solution is repeatedly repeated on the same flow channel so that the sample solution stops in these temperature zones for a predetermined time. It is a method of moving alternately and heating. Although this method is excellent in that each temperature time can be freely set and thermal cycling is possible, a large number of integrated units are used to introduce samples and feed them to those temperature zones by rotating them using a pump. Therefore, it is difficult to reduce the size of the apparatus (Patent Document 3).
Similarly to the second method, the third method is a continuous flow PCR in which a sample solution moves through a plurality of temperature zones spatially separated through a microchannel, and the sample solution is continuously fed without stopping. Among these continuous-flow PCR methods, a method of controlling the sample temperature at a high speed by flowing it through three meandering channels on three heaters controlled at a constant temperature has attracted attention (non-patented). Reference 3). Since this method does not require temperature changes in external devices such as containers and heaters, the theoretically the fastest temperature control can be expected, and development was carried out with the aim of commercialization, but bubbles were accidentally generated in the heating area. However, due to problems such as frequent stopping of the flow, it has not yet been put into practical use. Specifically, in the continuous flow PCR, the PCR sample is continuously fed so as to fill the entire microchannel through two or three separate temperature regions. However, such continuous flow requires a large amount of PCR sample and requires complex control. Further, bubbles are likely to be generated in the denaturation temperature region of 95 ° C., and the flow is frequently disturbed or stopped. In addition, since it passes through several micro-tubes and micro-channels so that it can repeatedly pass through each temperature zone about 30 to 40 times, it is efficient and fast because the fluid resistance is large and the liquid feeding speed is slow. As a result, it took about 1 hour until the end of continuous flow PCR, even 15 minutes or more even for a high-speed system.

The market for genetic testing using PCR / real-time PCR equipment is growing steadily. In particular, genetic testing for infectious diseases such as viral hepatitis, sexually transmitted diseases and influenza has begun to spread rapidly in Japan. In addition, genetic testing in cancer treatment has been clarified for its usefulness, such as EGFR gene mutation as an indication of application of anticancer drug Iressa, so EGFR gene, K-ras gene, etc. in lung cancer and pancreatic cancer, Genetic testing for EWS-Flil, TLS-CHOP, SVT-SSX, and c-kit genes has recently become a health application.

  At present, genetic testing is carried back to laboratories and analysis centers. However, if there is a high-speed genetic testing system that can be implemented quickly on site, treatment and countermeasure policies can be decided on the spot, so current genetic testing It will be a revolutionary technology that will replace equipment. In particular, pandemic borderline measures such as foot-and-mouth disease and highly pathogenic influenza are important for quick and accurate on-site judgment and prevention of secondary infection associated with movement. In particular, in order to realize a service that can perform genetic testing immediately in the clinical or infectious disease field, a genetic testing method that can be implemented at a low cost and that is fast and simple is necessary.

However, with the conventional technology, it is impossible to perform rapid and simple PCR that can be processed in the field, and a method capable of performing amplification at an extremely high speed has been desired.

Patent No. 3041423 US Pat. No. 6,960,437 WO2006 / 124458

Lagally et al. (Anal Chem 73: 565-570 (2001)). Nagai et al. Anal Chem 73: 1015-1019 (2001)) Kopp et al. (Science 280: 1046-1048 (1998)).

  An object of this invention is to provide the method for amplifying the nucleic acid in a flow path at ultra high speed.

Therefore, in order to solve the above-mentioned problems, the present inventor does not continue to flow the sample solution as in the continuous flow PCR that fills the whole of the conventional microtubule and the microchannel, but sends the solution in the size of several microliters with air. By making the segment flow to continue to push, the influence of bubble generation was eliminated, and further, high-speed annealing due to high-speed convection inside the sample liquid and high-speed liquid feeding due to low pressure loss were achieved.

  In the present invention, the sample solution moves slowly in the temperature rising direction and moves fast in the temperature decreasing direction due to a change in vapor pressure during sequential heating in the middle of liquid feeding, while ensuring a long extension reaction time, and a transition temperature. It is a high-speed and highly efficient PCR technique that can suppress the extension of by-products in

In particular, in a thermal cycle using such a flow path, control for accurately changing the temperature of the sample solution in a short time is indispensable. Therefore, the present invention appropriately sets the flow channel design and liquid feeding conditions for accurately controlling the temperature of the PCR sample flowing in the segment flow using the micro flow channel, and the nucleic acid in the flow channel is determined. An object is to provide a method for amplifying at ultra-high speed.

The present invention provides the following nucleic acid amplification method.
Item 1. In a nucleic acid amplification method for performing a PCR reaction by supplying a PCR sample solution to a nucleic acid amplification device having a meandering flow path capable of performing at least one PCR cycle, the nucleic acid amplification device corresponds to a loop portion on one side. There is an annealing temperature zone corresponding to the loop portion opposite to one DNA denaturing temperature zone, an extension temperature zone between the annealing temperature zone and the DNA denaturing temperature zone, and the PCR sample solution is a gas In the shape of a sample plug sandwiched between the two, the liquid is fed into the meandering channel by a pump, and is supplied into the meandering channel in a state separated by one cycle of PCR or more by gas. Nucleic acid amplification method.
Item 2. By utilizing the difference in vapor pressure generated at the interface with the gas before and after the sample plug, the liquid feeding speed in the heating process from the annealing temperature zone to the DNA denaturation temperature zone is delayed, and the enzymatic temperature in the elongation temperature zone is reduced. A temperature control method is used that ensures an extension reaction time and conversely accelerates the liquid feeding speed in the cooling process from the DNA denaturing temperature zone to the annealing temperature zone and allows it to pass faster than the heating process. Item 2. The nucleic acid amplification method according to Item 1.
Item 3. Item 3. The nucleic acid amplification method according to Item 1 or 2, wherein a thin film for observing the temperature of the solution in the chip channel is used.
Item 4. The temperature control method for the sample plug is as follows: (i) cooling the annealing heater temperature for lowering the temperature to 40 ° C. or less; (ii) maintaining the heat capacity at 200 μm or more between the parallel flow paths of the meandering flow path (Iii) including at least one temperature control method of setting the aspect ratio of the cross section of the flow path to be larger than 1/8 and smaller than 1 for the generation of bubbles and stable liquid feeding 4. The nucleic acid amplification method according to any one of 3.

Realization of a system capable of testing the presence or absence of a gene with high sensitivity from a biological sample collected in a small amount at a medical site, such as genetic testing, is required. Therefore, it is necessary to establish a gene amplification technique that is as small and as fast as possible by taking advantage of the characteristics of minimizing the analysis capacity of the microfluidic device and maximizing the heat transfer efficiency associated with the increase in the surface area relative to the volume. In the present invention, a form (shape) of a sample plug sandwiched in air, which was not an existing method of PCR, which is a gene amplification technique, is utilized, and has been a problem in conventional continuous flow PCR using a flat plate type microfluidic device. Both high speed and high efficiency can be realized by utilizing the vapor pressure of the sample liquid itself generated at the interface with the air before and after the sample plug. As a result, there is a feature that contributes to miniaturization and high speed of the continuous flow PCR system that makes the best use of the advantages of the microfluidic device without requiring a special external device.

It is a figure which shows the microfluidic device 4 for continuous flow PCR. In the continuous flow PCR microfluidic device shown in FIG. 1, it is a figure which shows the method of controlling temperature for every area | region of a meandering flow path for a thermal cycle. In FIG. 2, temperature control 1 (about 95 ° C.) is a DNA denaturation heater block 7, temperature control 2 (about 72 ° C.) is an extension reaction heater block 6, and temperature control 3 (about 55 ° C.) is annealing. The heater block 5 and the sample solutions 1 to 3 are sample plugs 8. It is a graph which shows the fluctuation | variation of the passage time and speed of the sample plug which passes on each heater block of the microfluidic device for continuous flow PCR by the influence of the vapor pressure difference before and behind a sample plug. FIG. 3 is a schematic diagram showing measurement points on a meandering channel for measuring the temperature of a sample plug passing through a microfluidic device for continuous flow PCR. It is a figure which shows the measurement result of the temperature in each point of FIG. It is a figure which shows the measurement result in each point of FIG. 4 when the time per cycle on the microfluidic device for continuous flow PCR is 1 to 10 seconds. Using a continuous flow PCR microfluidic device, the reagent plug volume and flow rate were changed, and the result of continuous flow PCR in the form of a sample plug was obtained as a result of amplification of the DNA fragment of the real-time PCR kit. It is a figure which shows the fluorescence intensity. Using a continuous flow PCR microfluidic device, the depth of the meandering flow path and the interval between the parallel straight flow paths were changed, and as a result of performing continuous flow PCR in the form of a sample plug, the DNA of the real-time PCR kit It is a figure which shows the fluorescence intensity obtained with amplification of a fragment | piece. The figure shows the fluorescence intensity detected at the meandering channel outlet of the microfluidic device for continuous-flow PCR as a result of continuous-flow PCR for Bacillus subtilis genes with varying amounts of Bacillus subtilis mixed in the sample plug. is there. It is a figure which shows the relationship between the measured fluorescence amount of FIG. 9, and the quantity of Bacillus subtilis previously mixed with the sample plug.

The present invention relates to a method for amplifying a nucleic acid by polymerase chain reaction (PCR) at a very high speed in a microchannel that repeatedly passes through a plurality of temperature zones while meandering. More specifically, the present invention accurately controls the temperature of a PCR sample flowing as a sample plug sandwiched between gases using a microchannel in a flat plate microfluidic system for continuous flow PCR. It is an object of the present invention to provide a method for amplifying nucleic acid in a flow path at an ultra-high speed by appropriately setting a flow path design and liquid feeding conditions.

In the present specification, examples of the plurality of temperature zones include a temperature zone for DNA denaturation, a temperature zone for annealing, and a temperature zone for extension. These three temperature zones may be clearly distinguished by a heating device (heater) or cooling device, etc., and adjacent temperature zones (DNA denaturation temperature zone and extension temperature zone, or extension temperature zone and annealing). The boundary of the temperature zone is not necessarily clear. In particular, the temperature zone for extension and the temperature zone for annealing may appear to be one temperature zone that appears to be integrated, but in this specification, even in such a case, the higher temperature part is stretched. The temperature range is expressed as a temperature range, and the lower temperature portion is expressed as an annealing temperature range.

  Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention is related. Next, the present invention will be specifically described with reference to embodiments, but the present invention is not limited to these embodiments, and is similar or equivalent to that described in this specification. Any of a number of methods and materials can be used in practicing the present invention. Preferred materials and methods are described below.

  A schematic diagram of a microfluidic device 4 for continuous flow PCR for carrying out the present invention is shown in FIG. This device includes a PCR reagent inlet 1, a meandering channel 2, and a reservoir 3 for storing a solution after the PCR reaction. One cycle of PCR is a unit consisting of a pair of loops on both sides (corresponding to a high temperature denaturation region (corresponding to the temperature region for DNA denaturation) and a low temperature annealing region), and two linear parts connecting the loops. Can be performed. The high temperature denaturation region corresponds to the “DNA denaturation temperature region”, the low temperature annealing region corresponds to the “annealing temperature region”, and the two straight portions connecting the loop portions correspond to the “annealing temperature region”. To do. In the microfluidic device used in the present invention, this unit may be formed by one meandering channel 3 or may be formed by a meandering channel 3 in which a large number of the units are connected. When one PCR sample solution advances in the meandering channel, one cycle of PCR reaction or multiple cycles of PCR reaction is performed according to the number of units in the meandering channel, and the necessary number of PCR products are formed. Released into the reservoir.

  The microfluidic device 4 for continuous flow PCR shown in FIG. 1 uses, for example, an NC processing machine and a flow path shape designed on CAD on a cycloolefin resin (COP) flat plate having a length of 76 mm, a width of 52 mm, and a thickness of 2 mm. It was made by cutting. The material of the microfluidic device may be acrylic resin, polycarbonate resin, polystyrene resin, fluorine resin, or the like other than polyolefin resin such as COP. In addition to the machining process such as an NC processing machine, the flow path shape may be formed by a method that can be used for resin microfabrication such as injection molding, nanoimprinting, or soft lithography. In the case of cutting, a micro flow path is cut using a resin end mill having a diameter of 200 μm, and the cross section of the flow path has a width of 10 to 1000 μm and a depth of 10 to 1000 μm, preferably a width of 400 μm and a depth of 500 μm. A semicircular shape or a rectangular shape. In the practice of the present invention, a straight groove having a width and depth of 0.65 mm is cut from the injection side end of the microchannel to the end of the COP plate, and the exit end has a diameter of 2 mm. A cylindrical reservoir was connected. Insert a metal tube with an outer diameter of 0.65 mm or more into the groove on the injection side for a length that does not come off naturally, and apply an adhesive only to the outer periphery of the metal tube to prevent leakage, and then coat with a pressure sensitive adhesive. The microplate seal (97M manufactured by 3M) was joined to the entire surface of the meandering flow path including the metal tube portion to produce a microfluidic device for continuous flow PCR incorporating a PCR sample injection tube. The PCR sample injection tube may not be made of metal but may be made of resin such as a silicon tube, or may be a tube using a rubber material or a glass material. About the cover of this meandering flow path part, the heat sealing | fusion by a different sealing agent, a tape agent, or a resin material may be sufficient. The seal at the portion covering the reservoir on the microchannel outlet side was cut.

As shown in Fig. 2, three heater blocks 5, 6, and 7 (temperature control 3, 2, and 1 respectively) with a length of 150mm, a width of 15mm, and a height of 10mm with built-in heaters are approximately 0.5mm to 1mm in parallel. 2 were arranged at intervals of and were brought into contact with the microfluidic device for continuous flow PCR produced thereon, whereby the temperature was controlled individually and locally in the three contact areas. Each heater block has the ability to uniformly heat the heater block surface to 120 ° C or higher, and has a function of cooling to 5 ° C or lower by bonding a Peltier element to the bottom side. . The temperature of each aluminum block 5, 6 and 7 is kept uniform and constant by a heater or Peltier element by PID control based on a temperature sensor provided inside. The set temperatures of the individual aluminum blocks 5, 6, and 7 shown in FIG. 2 were set so that the temperature of the sample solution was 95 ° C., 72 ° C., and 55 ° C. necessary for PCR denaturation, extension, and annealing. It is not necessary to change the temperature of the aluminum block once set as long as continuous flow PCR is performed under the same conditions.

  Regarding the design of the meandering channel of the microfluidic device for continuous flow PCR, the serpentine channel that folds continuously with an interval of 10 to 1000 μm, preferably 400 μm every 30 mm length, and three heater blocks and the meandering flow The design was such that the paths were orthogonal and the looped portion of the meandering flow path was in contact with the heater blocks at both ends by 7 mm. In addition, the position of the meandering flow path in contact with the heater blocks at both ends can be appropriately changed according to the target temperature and control time. In the practice of the present invention, the heater block for continuous flow PCR uses a stainless steel structure with a length of 150 mm, a width of 15 mm, and a thickness of 10 mm with a built-in temperature sensor. The one on the end side was brought into contact with a Peltier to control the temperature to below room temperature. Moreover, it was set as the design which can perform the thermal cycle required for PCR 40 times by making it the design which folds back 40 times each on the heater block of both ends among three heater blocks. 1 and 2 show an example using a meandering flow path capable of executing 40 thermal cycles and three temperature zones, but the meandering flow path may be designed so that a thermal cycle can be executed once. You may design so that there may be two temperature zones.

  The recommended ratios of preferred temperatures and times for annealing, elongation and denaturation are shown in Table 1 below.

  Continuous flow PCR microfluidic device for extension reaction corresponding to one DNA denaturation heater block corresponding to one loop part, annealing heater block corresponding to the other loop part, and straight part connecting both loop parts If the heater block has three temperature zones, it should be set to the recommended ratio shown in Table 1 above. One heater block for DNA denaturation corresponding to the loop part on one side and the other loop part / straight line When PCR is performed with two temperature settings of the heater block (extension process is performed at a temperature midway from the annealing temperature to the denaturation temperature) that can perform the extension process corresponding to the part, the recommended ratio in Table 1 is used. What is necessary is just to carry out so that it may correspond.

The temperature of each heater block was controlled to a desired temperature by PID control. The surface temperature of the heater block surface or the microfluidic device for continuous flow PCR is checked with a contact or non-contact temperature sensor as necessary, and the temperature required for each PCR reaction as shown in Table 1 Thus, the temperature of the heater block can be adjusted. In the practice of the present invention, the temperature of the surface of the continuous-flow PCR microfluidic device or the flowing fluid, or the surface of the peripheral portion of the microfluidic device for continuous-flow PCR is measured with an infrared camera,
Adjustments were made to achieve the desired temperature.

As a sample solution for PCR, a standard kit for real-time PCR (Cyclave PCR Core Kit manufactured by Takara) was used. A 134 bp DNA sample (Positive Control) attached to the kit was used as an amplification target in PCR, and PCR reagents were prepared according to the kit. The composition and concentration of reagents such as PCR primers and probes can be changed according to the type of gene to be detected.

The PCR sample was fed using a syringe pump that had been filled with a gas in excess of the volume of the microfluidic device for continuous flow PCR and the sample injection tube connected in the middle. By aspirating 0.1 to 10 μL, preferably 1 to 5 μL of a PCR sample through a silicone tube using a 1 mL syringe pump filled with air, and then connecting it to the PCR sample injection tube of the chip. The PCR sample was fed. Alternatively, after aspirating a certain amount of PCR sample with Pipetteman, remove the PCR sample while keeping it inside the pipetteman replacement tip, insert the tip into the PCR sample injection tube, and connect the other end to a syringe pump. The PCR sample could be injected. In the practice of the present invention, a PCR sample injection tube of a microfluidic device for continuous-flow PCR is passed through a silicon tube with an inner diameter of 0.5 mm connected to a syringe pump (Model 11 manufactured by Harvard) from 1 μL to 30 μL of a PCR reagent of 300 μL or more. Injected from. At that time, the syringe pump is prefilled with 300 μL of air so that the sample solution can flow from the PCR sample injection tube of the continuous flow PCR microfluidic device to the reservoir at the outlet of the microchannel. The flow rate of the syringe pump was set to 65 to 225 μl / min, and the solution was continuously fed until the syringe pump was discharged to the reservoir at the outlet end of the microchannel. This corresponds to 1 sec / cycle to 10 sec / cycle as the time required to flow through the flow path length for one cycle in continuous flow PCR. In addition to the syringe pump, the pump for feeding the PCR sample may be any pump as long as a trace amount of solution can be fed. Thereby, as shown in FIG. 2, the method of performing continuous flow PCR which sends a very small amount of PCR sample in the shape of a sample plug was established. In the present invention, a high-speed convection and a diffusion-controlled annealing reaction can be achieved in the sample liquid by supplying a segment flow of several microliters and continuing to push with air. One feature of the present invention is that the PCR solution can quickly pass through the high temperature region before the flow becomes unstable due to the generation of bubbles.

In the real-time PCR such as the above-mentioned Takara Cycle PCR Core Kit, when the target DNA sequence is amplified, it is a technique for confirming and detecting the amplification of the target DNA by simultaneously increasing the fluorescence. . Therefore, in the practice of the present invention, in order to confirm the amplification of the target DNA, whether the fluorescence intensity of the PCR sample after PCR is directly measured by a SELFOC fluorescent fiber detector installed on a meandering channel or in a reservoir position. Alternatively, the PCR sample was transferred to a microplate and then measured using a fluorescent microreader.

The use of a microfluidic device for continuous-flow PCR with a sample plug is thought to enable rapid flow and simple PCR control, but excessively rapid fluid delivery is the temperature required for PCR above each temperature zone. There is a possibility of passing before reaching. Therefore, in the present invention, the vapor pressure generated at the interface with the gas before and after the sample plug in the microchannel is effective for the purpose of ensuring a sufficient reaction time for each of the DNA denaturation, annealing, and elongation reactions. One of the features is that the feeding speed is varied so that the sample plug passes through each heater block over a period of time necessary for each PCR reaction.

The results of measuring the time and speed at which the sample plug passes over the heater block for each reaction using a video camera are shown in FIG. As is clear from the graph of FIG. 3, the passage time became longer in the heating process related to the extension reaction in the parallel linear flow path portions on the meandering flow path. this is,
This is because the high vapor pressure generated in the DNA denaturation reaction heater block is decelerated because it works in the direction opposite to the progress of the sample plug. On the other hand, in the cooling process from DNA denaturation to annealing, the sample plug was accelerated by the influence of the same vapor pressure difference, so the transit time was the shortest. Since denaturation and annealing of PCR proceed extremely rapidly, the ratio of each reaction time is equivalent to that in Table 1, so it is optimal for PCR, and the time for enzymatic extension reaction that proceeds relatively slowly is significant. Suitable for securing.

In contrast, in the conventional continuous-flow PCR, which is not a sample plug shape, but is fed so that the entire meandering flow path is filled with the PCR sample, the solution feeding speed is constant, and the DNA denaturation temperature range is changed to the annealing temperature range. Also in the cooling process toward the bottom, it moves at a low speed as in other temperature zones. During the annealing process, at a transient temperature where the primer cools down to the transition temperature at which it binds to the target DNA sequence, the primer may bind to sites other than the target sequence, which generates by-products other than the target gene sequence. Cause. Therefore, the high-speed cooling realized by the present invention is advantageous in that it suppresses the generation of by-products and is advantageous for accurate DNA amplification.

Due to the difference in vapor pressure before and after the sample plug, the passage speed of each heater block varies as shown in FIG. 3. Therefore, it is necessary to optimize the flow path design and set temperature to reach the set reaction time and temperature. Become. Only when these conditions are satisfied, accurate DNA amplification can be realized. For this purpose, it is necessary to accurately measure the temperature in each temperature region including the temperature gradient between the heaters on the chip. Therefore, in the implementation of the present invention, the measurement of the temperature of the PCR sample flowing inside the microchannel with an infrared camera through a polyolefin thin film as a sealing material was examined. The film thickness of the polyolefin sealing material used in the practice of the present invention is 50 μm, and the temperature of the sample plug can be measured via the sealing material. However,
The film thickness of the sealing material is preferably 0.5 mm or less, or preferably 50 μm or less.
The material of the thin film used as the sealing material may be an acrylic resin, a polycarbonate resin, a polystyrene resin, or a fluorine resin in addition to the polyolefin resin such as COP. One feature of the present invention is that it has a method of accurately measuring the temperature of the sample plug inside the meandering flow path by using a thin film sealing material, cover material or film material.

In the practice of the present invention, in order to measure the temperature of the sample plug that actually passes through the microfluidic device for continuous flow PCR, the measurement points on the meandering channel are shown in FIG. Moreover, the measurement result of the temperature in each point of FIG. 4 is shown in FIG. The important point in rapid temperature control by liquid transfer using the sample plug is that the cooling process time for annealing is quite short, so the temperature of the annealing heater block is set to 55 to 65 ° C, which is the normal annealing temperature Even in this case, as shown in FIG. 5, it was not cooled to the set temperature, and the cooling effect was insufficient. This is because the thermal conductivity of COP, which is a component of microfluidic devices for continuous-flow PCR, is several times lower than the thermal conductivity of water, which is the main component of the sample plug, and higher temperature for rapid heat conduction. This is because a difference is necessary. Therefore, when the temperature of the annealing heater block was lowered and observed, the temperature of the sample plug decreased depending on the temperature of the annealing heater block as shown in FIG. Furthermore, when the fluorescence intensity after PCR was compared, as shown in Table 2, it was confirmed that when the temperature of the annealing heater block was 40 ° C. or less, the fluorescence intensity increased and DNA was amplified. In particular, in the practice of the present invention, when the temperature of the annealing heater block is 20 ° C., the fluorescence intensity is most amplified, and as is clear from FIG. 5, the sample plug is sufficiently cooled to the temperature required for the annealing reaction. It is thought that it was made. In the present invention, one of the features is that each heater temperature is heated or cooled more than the normal annealing temperature for high-speed temperature control on the sample plug.

As described above, the temperature reached by the sample plug in each temperature region is affected by the flow rate. Therefore, the flow rate of the syringe pump is changed and measured at each point in FIG. 4, and the time per cycle is 1 to 10 s. FIG. 6 shows the measurement result of the temperature in the case of the above. 1-2 per cycle
In the case of an extremely fast solution such as s, the temperature required for PCR was not reached in all temperature ranges.
On the other hand, if the temperature of the annealing heater block is 20 ° C, the time per cycle is 7
It has been found that when the temperature exceeds s, it is excessively cooled and reaches 40 ° C. or less, which is likely to cause misannealing.

From the above, optimization of the set temperature and flow rate of each heat block is important for temperature control of continuous flow PCR using a sample plug. In the practice of the present invention, when the temperature of the annealing heater block is 20 ° C. The optimal flow rate was 5-6 s per cycle.

  Amplification of DNA by PCR is confirmed by collecting the sample solution that has reached the reservoir and determining the amount of change in fluorescence intensity before and after continuous flow PCR with a fluorescence plate reader (Thermochemical Fluorscan Ascent) set for FAM dye. did. As a result of continuous flow PCR, the increase in fluorescence intensity indicating amplification of the target DNA fragment was dependent on the time required for each cycle, as shown in FIG. This is because the heat conduction and reaction time necessary for each reaction of denaturation, annealing, and extension of PCR are sufficiently secured when the flow rate is decreased and the required time for each cycle is lengthened.

  As is clear from FIG. 7, when the continuous flow PCR was sent as a sample plug that is one of the features of the present invention, it became clear that the smaller the volume of the sample solution, the better the PCR efficiency. . In the embodiment of the present invention, when the amount of the reagent solution is 10 μl or more, the size of the sample plug exceeds the length of one cycle, so the influence of the vapor pressure difference before and after the sample plug is eliminated and the sample solution flows at a constant speed. The 72 ° C. region between 55 ° C. and 95 ° C., which contributes to the elongation reaction, and the 72 ° C. region moved between the 95 ° C. and 55 ° C. cooling times were equal. However, since the flow path length of the straight part of the meandering flow path used is 30 mm and the volume corresponds to about 5.5 μl, when the volume of the sample solution is smaller than 5.5 μl, the sample plug is placed in the straight line part. The size will fit. Therefore, in the heating or cooling for the thermal cycle, the vapor pressure changes individually at the gas-liquid interface upstream and downstream of the sample plug and changes every moment depending on the position of the meandering channel. Thereby, in the process of the extension reaction from 55 ° C. to 95 ° C., the vapor pressure at the upstream gas-liquid interface increases from the downstream side, so that a force against the flow direction is generated, as shown in FIG. The sample plug moved at a low speed. On the other hand, in the micro flow path from 95 ° C. to 55 ° C., the vapor pressure on the gas-liquid interface side on the downstream side increases and the flow is accelerated so that the sample plug moves at a speed of 2 to 3 times. .

  As is clear from FIG. 7, comparing the amount of fluorescence amplification by PCR when the volume of the sample solution is 5 μl or less and the case of 10 μl or more, the efficiency is about 2 to 6 times higher even at the same average flow rate. Met. Thus, by using the difference in vapor pressure at both ends of the sample plug, the extension reaction time of 72 ° C. following 55 ° C. is long, which is advantageous for PCR reaction. By passing through the extension region (72 ° C) unnecessary for PCR while returning from the (95 ° C) to the annealing region (55 ° C), an ideal thermal cycle without any by-products can be realized, and continuous flow PCR For the first time, both high speed and high efficiency were realized.

On the other hand, the shape of the meandering channel of the microfluidic device for continuous flow PCR also affects the temperature control of the sample plug. Therefore, in the implementation of the present invention, the distance between the parallel straight flow paths is changed when the aspect ratio of the cross section (the ratio of the flow path depth to the flow path width) is changed by changing the depth of the micro flow path. The effect on the amplification of the target DNA was evaluated.

  The flow width was fixed at 800μm, and the change in the amount of fluorescence due to the difference in flow path depth was examined. As shown in Fig. 8, the aspect ratio should be set to a value greater than 1/8 and less than 1. Is desirable. When the channel depth corresponding to 1/8 was 100 μm, the increase in the amount of fluorescence by real-time PCR was reduced, but this was because the channel became too shallow, so the heater block for DNA denaturation reaction This is because the heat is excessively propagated at the position, and the sample plug evaporates. On the other hand, when the channel depth corresponding to an aspect ratio of 1 was 800 μm, the amount of increase in fluorescence due to real-time PCR was reduced. This is because, when heating or cooling from the bottom surface of the micro flow channel device for continuous flow PCR, temperature unevenness occurred in the cross-sectional direction of the meandering flow channel, and the temperature could not be uniformly controlled to an accurate temperature.

  In addition, when the interval between the straight flow paths parallel to the meandering flow path is narrowed, the ratio of the flow area per unit area increases, so the proportion of air increases, and the temperature is sufficiently transmitted from the heat block to the chip surface. Not confirmed. When the distance between the straight flow paths is short, the heat capacity around the flow path is small, so that it is not heated sufficiently. Similarly, in the case of cooling, the temperature changes more efficiently as the distance between the flow paths is wider.

As shown in FIG. 8, it is desirable that the interval between the parallel linear channels of the meandering channel for maintaining a sufficient heat capacity is 200 μm or more, preferably 400 μm or more, and most preferably 600 μm or more. From the above, when using COP-made micro-channels, it is considered effective for accurate temperature control to secure the distance between the channels at the same interval as the channel width. In order to maintain a sufficient heat capacity, the space between the parallel flow paths of the meandering flow path should be secured, and the aspect ratio of the cross section of the flow path should be set to be larger than 1/8 and less than 1 for the generation of bubbles and stable liquid feeding. It is clear that this is necessary for more efficient DNA amplification, and a technique for accurate and high-speed temperature control to these sample plugs is one of the features of the present invention.

As another example of gene detection, amplification of DNA fragments by continuous flow PCR was examined for Bacillus subtilis genes. PCR reagents were prepared using Takara's Cycleleave PCR Bacteria Screening Kit as per the kit. Each PCR reagent was individually subjected to continuous flow PCR. The prepared PCR reagent is used as a 3 μL sample plug.
At the same time, it was injected into a microfluidic device for continuous flow PCR, and was fed at a flow rate of 100 to 680 μl / min by a syringe pump (Model 11 manufactured by Harvard).

  When continuous flow PCR is performed with multiple sample plugs introduced at the same time, if two or more sample plugs enter the length of one cycle on the microchannel, the vapor pressure required for an ideal thermal cycle can be obtained. The rhythm of the used liquid delivery is disturbed. Therefore, each sample plug was injected with a sufficient interval of one cycle or more. Thereby, in each sample plug, the extension process is decelerated, and the rhythm of the liquid feeding that the cooling process is accelerated is confirmed. In one continuous flow PCR, the number of sample plugs is not limited to one, It can handle a large amount of sample liquid.

A SELFOC fiber fluorescence detector was installed at the position of the meandering channel near the outlet of the microfluidic device for continuous flow PCR, and the fluorescence intensity increased by continuous flow PCR was measured in real time. The fluorescence intensity obtained was changed in proportion to the amount of Bacillus subtilis mixed with. FIG. 10 shows the change in fluorescence intensity as a numerical value and graphed as a calibration curve. As a result, the obtained fluorescence intensity was confirmed to have an excellent correlation with the amount of Bacillus subtilis contained in the reagent plug originally prepared as a PCR sample, and it was confirmed that the target gene could be detected. In addition, as shown in FIG. 9, it was confirmed that by using a microfluidic device for continuous flow PCR, the time from gene amplification to detection can be realized very rapidly, about 6 minutes.

In these studies, a real-time PCR method for confirming amplification of DNA fragments by fluorescence change is used. However, the technique used in this specification is not limited to real-time PCR, and RT-PCR. From the above results, it was revealed that the present invention can perform a PCR reaction at a very high speed.

DESCRIPTION OF SYMBOLS 1 PCR sample injection tube 2 Serpentine flow path 3 Reservoir 4 Continuous flow PCR microfluidic device 5 Annealing heater block 6 Extension reaction heater block 7 DNA denaturation heater block 8 Sample plug

Claims (4)

In a nucleic acid amplification method for performing a PCR reaction by supplying a PCR sample solution to a nucleic acid amplification device having a meandering flow path capable of performing at least one PCR cycle, the nucleic acid amplification device corresponds to a loop portion on one side. There is an annealing temperature zone corresponding to the loop portion opposite to one DNA denaturing temperature zone, an extension temperature zone between the annealing temperature zone and the DNA denaturing temperature zone, and the PCR sample solution is a gas In the shape of a sample plug sandwiched between the two, the liquid is fed into the meandering channel by a pump, and is supplied into the meandering channel in a state separated by one cycle of PCR or more by gas. Nucleic acid amplification method. By utilizing the difference in vapor pressure generated at the interface with the gas before and after the sample plug, the liquid feeding speed in the heating process from the annealing temperature zone to the DNA denaturation temperature zone is delayed, and the enzymatic temperature in the elongation temperature zone is reduced. A temperature control method is used that ensures an extension reaction time and conversely accelerates the liquid feeding speed in the cooling process from the DNA denaturing temperature zone to the annealing temperature zone and allows it to pass faster than the heating process. The nucleic acid amplification method according to claim 1.   The nucleic acid amplification method according to claim 1 or 2, wherein a thin film for observing the temperature of the solution in the chip channel is used. The temperature control method for the sample plug includes (i) cooling the annealing heater temperature for lowering the temperature to 40 ° C. or less, (ii) ensuring that the interval between the parallel meandering channels is 200 μm or more, (iii 4) The method includes at least one temperature control method in which the aspect ratio of the channel cross section is set to be larger than 1/8 and smaller than 1 for the generation of bubbles and stable liquid feeding. The nucleic acid amplification method according to 1.