JP2014052224A - Method for measuring concentration of endotoxin and device for measuring concentration of endotoxin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel method for measuring the concentration of endotoxin and a kit for measuring the concentration of endotoxin that can easily measure the concentration of endotoxin with high sensitivity.SOLUTION: There is provided a method for measuring the concentration of endotoxin included in a sample, the method including the steps of: (1) adding a sample including endotoxin onto an electrode where a first endotoxin recognition molecule is immobilized and capturing the endotoxin on the electrode; (2) adding a second endotoxin recognition molecule modified with a reversible oxidation-reduction material or an enzyme capable of producing the reversible oxidation-reduction material onto the electrode where the endotoxin is captured and capturing the second endotoxin recognition molecule; and (3) measuring current change when a voltage is applied to the electrode, and measuring the concentration of the endotoxin included in the sample from a measured value.

Description

  The present invention relates to an endotoxin concentration measurement method and an endotoxin concentration measurement apparatus possessed by gram-negative bacteria.

  Endotoxin is a general term for toxic substances that constitute the outer membrane of Gram-negative bacteria such as Escherichia coli and Salmonella, and its main body is Lipopolysaccharide (LPS).

  When endotoxin is mixed in blood even in a very small amount (for example, on the order of ng / mL), it causes fever, shock death, intravascular blood pseudo-solidification, or sepsis. Therefore, the endotoxin content in these preparations is legally regulated.

  Endotoxins can be released by the destruction (killing or lysis) of bacteria that inhabit the production process of pharmaceuticals, and can be mixed into pharmaceuticals. For example, parenteral pharmaceuticals such as infusion solutions and injectable preparations are mainly produced by fermentation technology or genetic recombination technology, and there is concern about contamination from host cell wall components in the production process. Therefore, in order to ensure the safety of these pharmaceuticals, it is essential to measure the endotoxin content simply and with high sensitivity.

  As a method for measuring and quantifying endotoxin concentration, the Limulus test has become the mainstream. This Limulus test utilizes the phenomenon that the blood cell extract of horseshoe crab coagulates with endotoxin. The clotting reaction of Limulus reagent occurs in a cascade reaction similar to that of mammalian blood pseudosolid systems. Therefore, it is a highly sensitive measurement system that amplifies a small amount of endotoxin signal to cause pseudo-solidification.

In detail, first, endotoxin activates factor C to form factor Ca, which activates factor B to produce factor Ba. This Ba factor activates the precoagulant enzyme into a coagulase, which hydrolyzes the coagulation protein (coagulogen). The degradation product of the coagulated protein forms a disulfide bond to become coagulin, which further collects and gels.
Furthermore, a highly sensitive measurement method for endotoxin using this phenomenon is also known, and there are a turbidimetric method and a colorimetric method.

  The turbidimetric method has a measurement principle that the gelation time of the Limulus reagent is proportional to the endotoxin concentration. In the measurement method by the turbidimetric method, the measurement of gelation time is captured as a change in transmitted light, and the amount of endotoxin is quantified using the reaction time from the start of reaction of the sample until reaching a certain turbidity as the gelation time. Both logarithmic plots of gelation time and endotoxin concentration show a nearly linear correlation (turbidimetric time method).

On the other hand, the colorimetric method (chromogenic substrate method) uses a chromogenic synthetic peptide instead of coagulin, and determines the endotoxin concentration from its hydrolysis rate. The chromogenic substrate used here is a peptide in which p-nitroaniline (pNA) is peptide-bonded to the carboxyl group of Arg of Leu-Gly-Arg, which is a part of the amino acid sequence of coagulin. The clotting enzyme (clotting enzyme) hydrolyzes this chromogenic substrate and releases pNA. The measuring method includes an endpoint method using the absorbance after a certain time and a kinetic method using the initial rate of the hydrolysis reaction. The initial rate of reaction is obtained as the slope of the tangent at the rising portion of the reaction curve, and is expressed as the change in absorbance per unit time (Abs./min). The plot of the initial velocity measured with each concentration of endotoxin and the endotoxin concentration shows a correlation (see, for example, Patent Document 1).
Recently, a method for measuring the endotoxin concentration in a sample from the amount of luminescence using a highly sensitive luciferase having a luminescence intensity of 10 times or more and a luminescent synthetic substrate by genetic modification has been developed. The luminescent synthetic substrate used here is Benzoyl-Leu-Arg-Arg-aminoluciferin. The clotting enzyme (clotting enzyme) hydrolyzes this luminescent synthetic substrate to release aminoluciferin. Since the released aminoluciferin emits light by ATP and high-sensitivity luciferase, endpoint measurement can be performed with a luminometer (for example, see Patent Document 2).
However, the conventional limulus test and the measurement method based on the limulus test as described above are expensive for both the measuring apparatus and the reagent, and it is difficult to perform on-site measurement.

In addition, as is clear from the fact that the measurement principle is the change over time in the coagulation process that undergoes multiple stages of reaction, the endotoxin concentration, especially at lower concentrations, requires more coagulation time (measurement time), and moreover it is measured by the measurer. There were problems such as variations in values.
By the way, in a method for quantifying a target component in a sample, there is an electrochemical measurement method as a simple and highly sensitive measurement method. This method is characterized in that a target component in a solution or a specific component whose concentration changes in response to a change in the concentration of the target component is converted and output as a current signal on the electrode.

  From the background as described above, the present invention provides a simple and highly sensitive method for measuring endotoxin by an electrochemical method, which is the most suitable method for the goal of high sensitivity, as a novel method for measuring endotoxin that replaces the Limulus test. It is to provide. However, since the main components constituting the endotoxin to be measured are polysaccharides and lipids, and they themselves do not show any electrochemical activity, the present inventors recognize the polysaccharide portion of endotoxin, By using a boronic acid to be formed and its derivative and a compound having a reversible redox ability, the endotoxin was successfully measured by the electrochemical method described above (Patent Document 3, Non-Patent Document 1).

  Specifically, focusing on the fact that the magnitude of the electrolytic current on the electrode changes before and after the reversible redox substance is complexed with endotoxin, It has been found that it is possible to amplify and measure the change in the electrochemical activity of the reversible redox substance by coupling electrolytic oxidation with oxidation or reduction by enzymatic reaction.

As a result, it was found that the amount of endotoxin causing the change can be measured quantitatively, simply, with high sensitivity and with high selectivity. In addition, a mediator in which polymyxin with high endotoxin recognizing ability was introduced instead of boronic acid was developed, and the selectivity for endotoxin was further improved over boronic acid (Non-patent Document 2).
Japanese Patent Laid-Open No. 06-324047 WO2009 / 063840 JP 2007-093378 A J. CHEM. SOC. CHEM. COMM. (1995) 1771-1772 Biosensors and Bioelectronics 22 (2007) 1527-1531 Biosensors and Bioelectronics 26 (2011) 2080-2084

However, in the measurement method as described in Non-Patent Document 1, the sugar being measured is a monosaccharide and a disaccharide, and the quantitative range is 10 ^{−5 to 1} M, which is a relatively high concentration range. That is, there is a problem that it cannot be applied to the measurement of endotoxin containing a polysaccharide as a main component. In addition, as described above, the main components constituting endotoxin are polysaccharides and lipids, but they themselves do not exhibit any electrochemical activity. A typical measurement method could not be used.

  In addition, the measurement methods described in Patent Document 3 and Non-Patent Documents 2 and 3 enable electrochemical measurement of endotoxin. When boronic acid and its derivatives are used, the detection limit concentration is 100 to 500 ng / mL. Yes, it was an excellent measurement method with a detection limit concentration of 50 ng / mL when polymyxin was used. However, as a method for measuring endotoxin that causes sepsis and the like on the order of ng / mL, further improvement in detection sensitivity has been desired.

  Therefore, based on the background as described above, in order to solve the conventional problems, it is based on the results of earnest research of the inventor, and by using electrochemical measurement, endotoxin can be easily and highly sensitively. It is an object of the present invention to provide a new endotoxin concentration measurement method and an endotoxin concentration measurement kit capable of adjusting the concentration.

In order to solve the above problems, the present invention first includes the following steps,
(1) A step of adding a sample containing endotoxin on the electrode on which the first endotoxin recognition molecule is immobilized and capturing the endotoxin on the electrode (2) reversible redox substance or reversible on the electrode capturing the endotoxin Adding a second endotoxin recognition molecule modified with one of the enzymes capable of generating a selective redox substance and capturing the second endotoxin recognition molecule (3) Current change when voltage is applied to the electrode Measuring the concentration of endotoxin contained in the sample from the measured value,
It is characterized by including.

  In the present invention, secondly, the first endotoxin recognition molecule immobilized on the electrode and the second endotoxin recognition molecule are protein, polypeptide, polyamino acid, nucleic acid, polyethyleneimine, polyallylamine, N, N -Diethylaminoethanol (DEAE) polysaccharide is at least one kind. The third feature is that a chemical crosslink is formed with a functional group present on the electrode surface by any one of an amino group, a carboxyl group and a disulfide group contained in the molecule of the first endotoxin recognition molecule. Fourth, the reversible redox substance that modifies the second endotoxin recognition molecule is one of ferrocene, ruthenium complex, and quinone, and fifth, the second endotoxin recognition molecule is modified. The enzyme capable of generating a reversible redox substance is at least one of alkaline phosphatase, horseradish peroxidase, diaphorase, glucose oxidase, lactate oxidase, and glutamate oxidase.

  Further, sixthly, in the endotoxin concentration measurement method described in any one of the first to fifth inventions, reversible oxidation by a redox species added to a sample or an oxidoreductase separately immobilized on an electrode. A reaction cycle consisting of a reaction that oxidizes or reduces the reducing substance and a reaction that reduces or oxidizes and regenerates the reversible redox substance by electrode reaction is formed, and an electrochemical signal is amplified depending on the presence of endotoxin. Measure the current change when. Seventh, reversible redox substances that modify the second endotoxin-recognizing molecule are ferrocene, ruthenium complex, quinone and the like, and further, iron (II) ion, cerium (III) ion, ferricene are contained in the sample. By mixing at least one redox species such as potassium cyanide, ruthenium complex, iridium complex, and ferrocene derivative, the response current value of the reversible redox substance can be amplified. Eighth, the enzyme that modifies the second endotoxin recognition molecule is at least one of alkaline phosphatase, horseradish peroxidase, diaphorase, glucose oxidase, lactate oxidase, and glutamate oxidase, and a substrate for each enzyme Is characterized by being able to amplify the response current value of the reversible redox substance by mixing in the sample. Ninth, the endotoxin to be measured is at least one of endotoxin, lipopolysaccharide, pyrogen, and pyrogen.

  A tenth aspect is an endotoxin concentration measurement kit, characterized in that the endotoxin concentration measurement method according to any one of the first to ninth inventions can be implemented.

  According to the method for measuring the concentration of endotoxin of the present invention, the sensitivity in electrochemical measurement of endotoxin can be improved, and as a result, the concentration of endotoxin can be measured easily and with high sensitivity.

  Furthermore, according to the endotoxin concentration measurement kit of the present invention, the endotoxin concentration can be measured easily and with high sensitivity regardless of the skill level of the user by utilizing electrochemical measurement.

  The present invention has the features as described above, and the embodiment thereof will be described in detail below.

  The present invention is a method for measuring the concentration of endotoxin contained in a sample by an electrochemical measurement method. Specifically, a sample is added to the electrode on which the first endotoxin recognition molecule that recognizes endotoxin is immobilized, the endotoxin in the sample is adsorbed, and a second endotoxin recognition molecule having reversible redox ability is added. Then, the concentration change of the reversible redox substance is amplified on the electrode, and the current change at this time is measured electrochemically.

  The inventor of the present invention has conducted extensive research based on the development of the electrochemical endotoxin measurement method described above (JP 2007-093378). As a result, the first endotoxin that recognizes endotoxin with high selectivity. We focused on providing the recognition molecule on the electrode and concentrating the endotoxin in the sample onto the electrode. In addition, a second endotoxin recognition molecule modified with a reversible redox substance capable of obtaining an electrochemical signal or an enzyme capable of generating a reversible redox substance is allowed to act on the electrochemical signal. I found out that Furthermore, the redox species capable of regenerating this reversible redox substance, and the combination of the enzyme and its substrate make it possible to further amplify and measure the resulting electrochemical response.

Next, the principle of endotoxin concentration measurement of the present invention will be described below. FIG. 1 illustrates the principle of the endotoxin concentration measurement method according to the present invention as a schematic diagram.
In the present invention, an electrode obtained by chemically crosslinking and fixing an endotoxin recognition molecule (first endotoxin recognition molecule) on an electrode is used as a working electrode. Add and capture endotoxin sample on working electrode. Next, a substance (second endotoxin recognition molecule) having both an endotoxin recognition site and a reversible redox substance or an enzyme capable of generating a reversible redox substance is allowed to act on the endotoxin. At this time, a second endotoxin recognition molecule having reversible redox properties is captured according to the amount of endotoxin.

  Therefore, a calibration curve is created between the known endotoxin amount and the amount of the reversible redox substance modified by the second endotoxin captured accordingly or the reversible redox substance produced by the enzyme, and the reversible The amount of endotoxin in the sample can be known by measuring the active redox substance.

  This reversible oxidation-reduction substance is a substance that can reversibly take the oxidized and reduced states by the exchange of electrons. The present invention is basically applied to the electrode that is produced by the exchange of electrons. The amount of reversible redox substance is measured by measuring the flowing current to grasp the amount of endotoxin. This measurement current is amplified and can be measured with high sensitivity.

Furthermore, the reversible redox substance that has been transferred to the oxidized or reduced form by the electrode reaction is restored to its original state (reduced or oxidized) by the redox molecule mixed in the solution or the redox enzyme immobilized on the electrode. Type). Oxidation, reduction, and regeneration reaction through the reversible redox substance form a reaction cycle, and the current flowing through the electrode is amplified by repeating this reaction cycle. Therefore, even if the amount of reversible redox substance captured on the electrode via the second endotoxin recognition molecule captured on endotoxin and the reversible redox substance generated by the enzyme is small, the measured current is amplified. This makes it possible to measure the amount of endotoxin with high sensitivity.
These series of reactions were made possible by immobilizing endotoxin-recognizing molecules on the electrode and concentrating endotoxin in the solid phase. Sensitivity that could not be realized with conventional methods for measuring endotoxin concentration in the liquid phase It brings about improvement.

  The material of the electrode used in the present invention is not particularly limited, but a noble metal such as platinum or gold or a carbon-based material is advantageously used from the viewpoint of corrosion resistance.

  The recognition molecules immobilized on the electrodes are mainly biomolecules and polycation synthesis molecules composed of proteins, polypeptides, polyamino acids, and nucleic acids. Specifically, poly α lysine, poly ε lysine, etc. Specific binding to endotoxin, such as polyamino acid, polymyxin B, LPS binding protein, endotoxin neutralizing protein, anti-LPS antibody, polypeptide, oligopeptide, oligonucleotide, polyethyleneimine, polyallylamine, DEAE polysaccharide A recognition molecule with the ability can be used. The specific adsorptivity of polyε-lysine to LPS is described in, for example, JP-A-2002-263486 and Analytical Biochemistry 385 (2009) 368-370.

  Further, the recognition molecule can be stably immobilized by chemically crosslinking with a functional group present on the electrode surface by an amino group, a carboxyl group, a disulfide group, or the like contained in these molecules. For example, when a carbon electrode is selected as an electrode, a compound having a triethoxysilyl group that specifically reacts with a hydroxyl group on the carbon surface and an N-hydroxysuccinimide group that reacts with an amino group of a biomolecule at the opposite end. Can be used. As an example, the structural formula of N-hydroxysuccinimide ester-triethoxysilane is shown.

  As the second recognition molecule used in the present invention, a compound (ferrocene) having both a complex formation function with endotoxin (polymyxin B) and a reversible redox ability such as polymyxin B-ferrocene complex is used. However, the recognition molecules are not limited to these, poly-amino acid such as poly-α-lysine and poly-ε-lysine, polymyxin B, LPS binding protein, endotoxin neutralizing protein, anti-LPS antibody, polypeptide, oligopeptide, oligonucleotide Even if it is a biomolecule composed of at least one kind, or a substance that has the ability to specifically bind to endotoxin, such as polyethyleneimine, polyallylamine, and DEAE polysaccharide, but does not have reversible redox properties, Has reversible redox ability of ferrocene, ruthenium complex, quinone, etc. as side chain of molecule By introducing the functional molecular group, it can be used.

  In addition, an enzyme that can generate a reversible redox substance, not just the reversible redox substance itself, specifically alkaline phosphatase, horseradish peroxidase, diaphorase, glucose oxidase, lactate oxidase, and glutamate oxidase, etc. Can be used.

  Furthermore, as a substance for regenerating the electrode reaction product, a reversible redox substance modified by the second endotoxin recognition molecule or a reversible redox substance produced by a modifying enzyme is used as an electron acceptor or a donor. As long as the reaction proceeds smoothly, there is no particular limitation, but a stable and inexpensive one is advantageously used.

  Specifically, when a polymyxin B-ferrocene complex is used as a reversible redox substance as a second endotoxin recognition molecule, a redox species in which polymyxin is easily dissolved in a weakly acidic aqueous solution and is not easily oxidized. Specifically, it can be used to amplify the current value by mixing iron (II) ions, cerium (III) ions, ferricyanide, ruthenium complexes, iridium complexes, ferrocene derivatives, etc. in the sample solution.

  In addition, when polymyxin B modified with alkaline phosphatase as the second recognition molecule is used as a reversible redox substance, electron acceptance during the oxidation of p-aminophenol with glucose oxidase as a substrate in an aqueous solution near neutrality Can be used as a body. When amplification is performed with other enzymes, oxidase, such as choline oxidase, lactate oxidase, glutamate oxidase, or a reductase used as an electron donor during substrate reduction, such as peroxidase, is appropriately used. .

  The method for immobilizing the enzyme on the electrode is not particularly limited, but a carrier material that can hold the enzyme highly active and has sufficient permeation of the substrate and the reversible redox substance, and immobilization. Method is selected and used. For example, a method that is known to have good permeability, such as a method of binding an enzyme to a porous carrier formed on the electrode surface or a method of forming an enzyme-immobilized cross-linked membrane with albumin and glutaraldehyde on the electrode surface, is adopted. it can.

  Next, an embodiment of the present invention will be described in detail with an example. Here, a carbon thin film will be described as an example. First, a cross-linking agent (linker) is reacted with the carbon thin film electrode serving as the substrate. Specifically, the hydroxyl group on the carbon surface and the triethoxysilyl group of the crosslinking agent are subjected to a coupling reaction. Thereafter, an N-hydroxysuccinimide (NHS) group which is one end of the crosslinking agent is introduced onto the electrode. When the polymyxin B solution is added here, the amino group of polymyxin B and the NHS of the cross-linking agent cause a coupling reaction, so that chemically cross-linked polymyxin B is introduced and modified on the electrode. The endotoxin recognition molecule-immobilized electrode thus prepared is used as a working electrode.

  Endotoxin is dropped onto the working electrode, and the endotoxin is captured on the electrode. Next, a second endotoxin recognition molecule having both an endotoxin recognition site and a reversible redox substance or an enzyme capable of generating a reversible redox substance is allowed to act and further captured on the endotoxin. At this time, the second endotoxin recognition molecule is captured according to the amount of endotoxin.

  By performing electrochemical measurements in combination with a working electrode that has been treated in this way, an appropriate counter electrode, and a reference electrode, reversible redox substances captured according to the amount of endotoxin are oxidized and reduced on the electrode. Is done.

  In addition, a redox species capable of regenerating and responsive amplification of this reversible redox substance is added to the aqueous electrolyte solution, or a separately prepared reversible redox substance capable of regenerating and responsive amplification and its substrate By inserting it into a buffer solution containing, the responsiveness of the reversible redox substance is amplified.

The concentration of the substance having the reversible redox ability in the second endotoxin recognition molecule captured on the electrode surface is not particularly limited, but a concentration capable of giving a clear current response by amplification measurement is 0.1-10 μmol / L. The degree is convenient. The type of electrolyte solution to be used must be avoided in the production of a reversible redox substance by alkaline phosphatase because the phosphate buffer inhibits the enzyme activity, but otherwise there is no particular limitation.
In addition, it is preferable to use a buffer solution having a pH capable of stably holding both the enzyme for obtaining the modified enzyme activity and the amplification effect and the enzyme, for example, when the alkaline phosphatase and glucose oxidase are shared. A neutral Tris buffer solution having a neutral pH of about 7.0 to 8.0 and a concentration of 1 to 100 mmol / L is conveniently used.

Specifically, when ferrocene-PMB and iron (II) ions are used as reversible redox substances, cyclic voltammograms measured at pH 5.0 show that near + 0.55-0.60 V (to silver-silver chloride electrode) The following reactions occur on the electrodes.
(A) Ferrocene-PMB (reduced) → Ferrocene-PMB (oxidized) + e
In addition, when iron (II) ions, which are redox species, are added as a reducing agent, the following reduction reaction occurs in ferrocene-PMB (reversible oxidation-reduction substance regeneration reaction).
(B) Ferrocene-PMB (oxidized form) + Fe ²⁺ → Ferrocene-PMB (reduced form) + Fe ³⁺
In addition, for example, when alkaline phosphatase (ALP) -PMB capable of generating a reversible redox substance is used, addition of p-aminophenol phosphate (PAPP), which is an enzyme substrate, results in an enzyme reaction product. p-aminophenol (PAP) is produced. When cyclic voltammogram is measured with 50 mM Tris-HCl buffer (pH 7.4) after PAP generation, the following reaction occurs on the electrode near +0.45 V (vs. silver-silver chloride electrode).
(A) PAP → p-iminoquinone (PIQ) + e
Further, for example, when an enzyme membrane separately provided on the electrode, for example, glucose oxidase is used as an enzyme, the following enzyme reaction occurs when glucose which is a substrate of glucose oxidase is added thereto.
(B) PIQ + glucose → PAP + gluconolactone Therefore, PAP is regenerated by the reduction reaction of ferrocene-PMB (reduced form) by iron (II) ions and the enzymatic reaction by glucose oxidase, and further at the electrode. The oxidation reaction of ferrocene-PMB and PAP and the cycle of these regeneration reactions are repeated. Due to this cyclic reaction, an increase in current of about 3-1000 times is observed with addition of iron (II) ions and glucose before addition. In this reaction cycle, ferrocene-PMB repeats an oxidized form and a reduced form. PAP repeats PAP and PIQ. The total amount of these two substances does not change, and ferrocene-PMB and PAP also function as mediators. In addition, the amount of e in the above reaction formula, that is, the current at the electrode, can be increased by adding iron (II) ions and glucose in excess, respectively, ferrocene-PMB, which is a reversible redox substance involved in this reaction, Depends on the amount of PAP.

  That is, only the reversible redox substance concentrated and generated on the electrode surface repeats the cycle of electrode reaction and regeneration reaction with a reducing agent or enzyme, and the current at this time is the reversible redox substance concentrated and generated on the electrode surface. Is almost proportional to the concentration of. Therefore, the current increases as the endotoxin concentration in the sample increases, that is, as the concentration of the reversible redox material that is concentrated and produced on the electrode surface increases. In other words, the amount (concentration) of endotoxin present can be determined from the degree of increase in current.

In the above embodiment, an example of a combination of ferrocene-PMB and iron (II) ions and a combination of ALP-PMB and glucose oxidase / glucose has been described. Of course, ferrocene-PMB and glucose oxidase / glucose, ALP- A combination of PMB and iron (II) ions may be used.
The endotoxin to be measured in the present invention is not particularly limited. For example, endotoxin (a toxin that is a component of the cell wall and is not secreted actively), lipopolysaccharide, pyrogen, and pyrogen are included. If it is, it can measure more efficiently.
Since it has the above configuration, the present invention can improve the sensitivity by about 1.25 to 300 times as compared with the conventional electrochemical measurement method of endotoxin.

  The endotoxin measurement kit of the present invention is characterized by comprising an electrochemical cell having at least an electrode on which an endotoxin recognition molecule is immobilized, and a substance having both endotoxin recognition ability and reversible oxidation-reduction ability. . In addition, an amplification reagent for amplifying the response current, an amplification enzyme, a substrate for the enzyme, a pH adjuster, a current measurement device, etc., or a member or reagent for constructing the measurement system of the present invention is combined to form a measurement kit. Also good.

Here, as the oxidoreductase, electrode, substrate and the like, the same endotoxin concentration measuring method of the present invention as described above can be used.
The measurement method and measurement kit of the present invention as described above are related to the manufacture, storage, analysis, utilization, etc. of pharmaceuticals such as culture fluids, biological samples, injection solutions, infusion solutions, dialysate, and purified water that is a raw material thereof. Used in For example, parenteral drugs such as injectable preparations are mainly produced by fermentation technology or genetic recombination technology, and there is concern about contamination from host cell wall components. It is necessary to remove the endotoxin that causes it. In the treatment of septic patients, blood endotoxin is removed by artificial dialysis by extracorporeal circulation. In order to determine whether or not these endotoxins have been removed as intended, a method for simply measuring a minute amount of endotoxins is required. Furthermore, endotoxin confirmation tests are indispensable also in the manufacture of medical devices such as syringes and dialysis membranes. Under such circumstances, the measurement method and measurement kit of the present invention are extremely effective in measuring these endotoxins, and in the measurement kit of the present invention, regardless of the skill level of the user, Endotoxin concentration can be measured.

  The specific form in that case is not specifically limited to the said measurement kit, For example, you may use as a detector for flow injection analysis. In this case, it is more preferable to use a form incorporated in the final step after treatment such as purification of production and artificial dialysis.

  Hereinafter, although this invention is demonstrated in detail using an Example and a comparative example, this invention is not limited to these Examples. Examples of cyclic voltammetry are shown below as electrochemical measurement methods, but other methods such as rectangular wave voltammetry, differential pulse voltammetry, normal pulse voltammetry, and alternating current voltammetry can be used as appropriate.

<Endotoxin concentration measurement using polymyxin B immobilized electrode and ferrocene-modified polymyxin B>
Example 1 A 1 mM toluene solution of a bifunctional crosslinking agent N-hydroxysuccinimide ester-triethoxysilane was subjected to a coupling reaction at 30 ° C. for 15 hours on the surface of a carbon thin film electrode formed on a silicon wafer. N-hydroxysuccinimide (NHS) groups were introduced on the electrode surface. This was immersed in 1 mM polymyxin B aqueous solution (adjusted to pH 5.0 with 50 mM acetate buffer) and allowed to stand at 30 ° C. for 1 hour, and then the electrode surface was washed with PBS to prepare a polymyxin B-immobilized electrode.

  Add 10 μL of Japanese Pharmacopoeia endotoxin standard so that the concentration is 200 ng / mL on a polymyxin B-immobilized electrode, and allow it to stand at room temperature for 30 minutes to adsorb endotoxin. Washed with saline (PBS). Subsequently, 10 μL of 200 μg / mL ferrocene-modified polymyxin B (Fc-PMB) (adjusted to pH 5.0 with 50 mM acetate buffer) was added dropwise, and allowed to stand at room temperature for 30 minutes. Adsorbed and the electrode was washed with PBS. By this operation, a ferrocene group that is a functional group having reversible redox ability can be introduced into the electrode.

This electrode was inserted into a 50 mmol / L acetic acid buffer solution at pH 5.0, a potentiostat (CHI Instruments, ALS760B), a reference electrode (silver-silver chloride: Ag / AgCl), a counter electrode (platinum: Pt) Connected with. FIG. 2 shows the results when cyclic voltammetry measurement was performed at a constant running speed of 100 mV / sec. In FIG. 2, the horizontal axis represents the applied voltage, and the vertical axis represents the response current.
(Example 2)
FIG. 2 shows the result of cyclic voltammetry measurement performed in the same manner as in Example 1 except that 1 mmol / L iron (II) chloride aqueous solution was added to the sample before measurement. .
(Comparative Example 1)
Except that the endotoxin standard was not added to the polymyxin B-immobilized electrode, the same operation as in Example 1 was performed, and the results of cyclic voltammetry measurement are shown in FIG.
(Comparative Example 2)
Except that no endotoxin standard was added to the polymyxin B-immobilized electrode, the same operation as in Example 2 was performed, and the results of cyclic voltammetry measurement are shown in FIG.
As apparent from FIG. 2, in Example 1 in which the endotoxin standard product was adsorbed on the electrode surface, a response of about 53 nA was observed around 0.59V. This response is considered to be an oxidation reaction in which Fc-PMB (red) adsorbed on the surface is oxidized to Fc-PMB (ox). On the other hand, in Comparative Example 1 in which endotoxin was not adsorbed, the current response was about 30 nA, so this current response difference (23 nA) was presumed to be caused by endotoxin adsorbed on the electrode surface.
According to this result, the increase in current due to the endotoxin adsorption described above depends on its concentration. In this method, when S / N = 2 (noise width 1 nA), endotoxin of approximately 20 ng / mL can be quantified. It was estimated.

  Furthermore, in Example 2 in which iron (II) ions as a reducing agent were added here, the oxidation current value increased greatly. This is because Fc-PMB (ox) generated by oxidation near the surface is reduced and returned to Fc-PMB (red). By passing through the cycle of regeneration by this oxidation / reduction reaction of Fc-PMB, the current response of Fc-PMB (red) was amplified about 3 times compared to Example 1 and Comparative Example 1 in which regeneration reaction was not performed. .

When 2 ng / mL endotoxin was actually added, the amplification current value was 11 nA. At this time, since the noise width was 4 nA, when S / N = 2, it was considered that the actually measured 2 ng / mL was close to the detection limit value, and the detection limit value was improved by amplification.
<Measurement of endotoxin with poly-ε-lysine immobilized electrode and alkaline phosphatase-modified polymyxin B>
(Example 3)
The same crosslinking agent as in Example 1 was subjected to a coupling reaction at 30 ° C. for 15 hours on the surface of the carbon thin film electrode formed on the silicon wafer in the same manner as in Example 1 to introduce NHS groups on the electrode surface. This electrode was immersed in a 0.25% polyε-lysine aqueous solution (diluted with PBS) and allowed to stand at 30 ° C. for 1 hour, and then the electrode surface was washed with PBS to prepare a polyε-lysine-immobilized electrode.

  A standard endotoxin sample is dropped onto a poly-ε-lysine-immobilized electrode so that the concentration is 2000 ng / mL, and left at room temperature for 20 minutes to adsorb endotoxin. Washed with Tris buffer. Subsequently, approximately 6 μg / mL alkaline phosphatase-modified polymyxin B aqueous solution (diluted with PBS) was added dropwise and allowed to stand at room temperature for 20 minutes to supplement the electrode surface with alkaline phosphatase-modified polymyxin B (ALP-PMB). Was washed with 50 mmol / L Tris buffer at pH 7.4. By this operation, the enzyme ALP capable of generating a reversible redox substance can be introduced into the electrode.

This electrode was inserted into a 50 mmol / L Tris-HCl buffer solution at pH 7.4, and connected to a potentiostat with a reference electrode (Ag / AgCl) and a counter electrode (Pt). In addition, 100 μmol / L p-aminophenol phosphate (PAPP) solution (50 mmol / L Tris-HCl buffer (pH 7.4)), which is a substrate for ALP, was added, and ALP captured on the electrode and substrate PAPP. The enzyme reaction was performed for 3 minutes. Thereafter, the results of cyclic voltammetry measurement with this electrode set at a constant running speed of 100 mV / sec are shown in FIG. 3 (solid line).
(Comparative Example 3)
Except that no endotoxin standard was added to the poly-ε-lysine immobilized electrode, the same operation as in Example 3 was performed, and the result of cyclic voltammetry measurement is shown in FIG. 3 (dotted line).

  From Fig. 3, the peak of the substrate p-aminophenol phosphate (PAPP) was confirmed around 0.55V, and the peak of the enzyme product p-aminophenol (PAP) was confirmed around 0.4V. It was done. These two peaks indicate that ALP-PMB is present on the electrode surface and the enzymatic reaction proceeds.

In addition, since there was a marked difference in the current value of the produced PAP depending on the presence or absence of endotoxin captured on the surface, it is clear that the amount of ALP-PMB adsorbed depends on the amount of endotoxin captured. That is, since there is a correlation between the amount of PAP produced and the captured endotoxin, this system suggests that endotoxin can be quantified by measuring PAP.
According to this result, the increase in current due to the endotoxin described above depends on its concentration.In this method, when 0.2 μg / mL endotoxin is added, the oxidation current value of the produced PAP is 92 nA, and S When / N = 2 (noise width 0.8 nA), it was estimated that about 40 ng / mL of endotoxin could be quantified.
Example 4
Except that glucose oxidase (GOD) was separately immobilized on a poly-ε-lysine immobilized electrode and glucose as its substrate was added, the same operation as in Example 3 was performed, and the results of cyclic voltammetry measurement are shown in FIG. Indicated.
(Comparative Example 4)
A cyclic voltammetry measurement result is shown in FIG. 4 except that GOD was separately immobilized on the poly-ε-lysine immobilized electrode and glucose as a substrate was not added.

As shown in FIG. 4 (solid line), the generated PAP causes GOD to be separately immobilized on the electrode, and glucose, which is the substrate, is added to cause a regeneration / reoxidation cycle by the enzyme. The current value of PAP is amplified compared to the case where 4 (dotted line) enzyme regeneration / reoxidation cycle is not provided. Thereby, the further highly sensitive measurement of endotoxin is attained.
According to this result, the current amplification by endotoxin described above depends on its concentration. In this method, when 0.2 μg / mL endotoxin is added, the amplification current value is 480 nA, and S / N = 2 (noise width 0.65 nA), it was estimated that endotoxin of approximately 1.67 ng / mL could be quantified.

It is the conceptual diagram which showed the principle of the density | concentration measuring method of endotoxin in this invention. It is the graph which showed the result of the cyclic voltammetry measured by capturing ferrocene-polymyxin B after capturing endotoxin on the carbon electrode modified with endotoxin recognition molecule. It is the graph which showed the result of the cyclic voltammetry of PAP produced | generated by the enzymatic reaction of ALP after ATP-polymyxin B was captured after endotoxin was captured on the endotoxin recognition molecule fixed carbon electrode. This graph shows the results of cyclic voltammetry by the regeneration reaction of the PAP molecule that occurs when glucose oxidase is immobilized on the carbon electrode with the endotoxin-recognizing molecule immobilized and the substrate glucose is added after capturing the endotoxin. is there.

DESCRIPTION OF SYMBOLS 1 Measurement system in which reversible redox substance is modified to endotoxin recognition molecule 2 Electrode 3 Linker 4 First endotoxin recognition molecule 5 Endotoxin 6 Second endotoxin recognition molecule 7 Enzyme capable of generating reversible redox substance in endotoxin recognition molecule Modified measurement system

Claims (10)

The following steps,
(1) A step of adding a sample containing endotoxin on the electrode on which the first endotoxin recognition molecule is immobilized and capturing the endotoxin on the electrode (2) reversible redox substance or reversible on the electrode capturing the endotoxin Adding a second endotoxin recognition molecule modified with one of the enzymes capable of generating a selective redox substance and capturing the second endotoxin recognition molecule (3) Current change when voltage is applied to the electrode Measuring the concentration of endotoxin contained in the sample from the measured value,
Endotoxin concentration measurement method characterized by the above.   The first endotoxin recognition molecule and the second endotoxin recognition molecule immobilized on the electrode are at least one of protein, polypeptide, polyamino acid, nucleic acid, polyethyleneimine, polyallylamine, and N, N-diethylaminoethanol (DEAE) polysaccharide. The method for measuring the concentration of endotoxin according to claim 1, wherein The first endotoxin recognition molecule immobilized on the electrode is characterized by forming a chemical crosslink with a functional group present on the electrode surface by any of an amino group, a carboxyl group, or a disulfide group contained in the molecule. The endotoxin concentration measuring method according to claim 1 or 2.   The method for measuring the concentration of endotoxin according to claim 1 or 2, wherein the reversible redox substance that modifies the second endotoxin recognition molecule is ferrocene, a ruthenium complex, or a quinone.   The enzyme capable of generating a reversible redox substance that modifies the second endotoxin recognition molecule is at least one of alkaline phosphatase, horseradish peroxidase, diaphorase, glucose oxidase, lactate oxidase, and glutamate oxidase The endotoxin concentration measuring method according to claim 1 or 2.   The endotoxin concentration measurement method according to any one of claims 1 to 5, wherein a reversible redox substance is oxidized or reduced by a redox species added to a sample or an oxidoreductase separately immobilized on an electrode. A reaction cycle consisting of a reaction and a reaction that reduces or oxidizes and regenerates the reversible redox substance by electrode reaction is formed, an electrochemical signal is amplified according to the presence of endotoxin, and the current change at this time is measured A method for measuring the concentration of endotoxin.   Reversible redox substances that modify the second endotoxin recognition molecule include ferrocene, ruthenium complex, and quinone. Furthermore, in the sample, iron (II) ion, cerium (III) ion, potassium ferricyanide, ruthenium complex, The method for measuring the concentration of endotoxin according to claim 6, wherein the response current value of the reversible redox substance can be amplified by mixing at least one redox species such as an iridium complex and a ferrocene derivative.   The enzyme that modifies the second endotoxin recognition molecule is at least one of alkaline phosphatase, horseradish peroxidase, diaphorase, glucose oxidase, lactate oxidase, and glutamate oxidase, and a substrate for each enzyme is mixed in the sample. The endotoxin concentration measuring method according to claim 6, wherein the response current value of the reversible redox substance can be amplified. The method for measuring endotoxin according to any one of claims 1 to 8, wherein the endotoxin to be measured is at least one of endotoxin, lipopolysaccharide, pyrogen, and pyrogen.   An endotoxin concentration measurement kit capable of performing the endotoxin concentration measurement method according to any one of claims 1 to 9.

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