JP2007093378A - Endotoxin concentration measuring method and endotoxin concentration measuring kit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new endotoxin concentration measuring method and an endotoxin concentration measuring kit, capable of measuring the endotoxin concentration in a simple manner and at high sensitivity. <P>SOLUTION: This concentration measuring method of endotoxin included in a sample has characteristics, wherein a reversible oxidation-reduction material, having a reactive functional group forming a complex with endotoxin, is added to the sample, to thereby form the complex with endotoxin in the sample, and concentration change of the reversible oxidation-reduction material forming the complex non-forming is amplified selectively on a working electrode, and a current change at that time is measured electrochemically. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for measuring the concentration of endotoxin possessed by gram-negative bacteria and a kit for measuring the concentration of endotoxin.

  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).

  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. For example, a method of electrochemically measuring saccharides (polyols) is known (for example, Patent Document 2 and Non-Patent Document 1).

Such a measurement method is to convert and output the concentration component or concentration change as a current signal on the electrode for the target component in the solution or a specific component whose concentration changes in response to the concentration change of the target component. Since the target component which is the object of measurement can be measured easily and with high sensitivity, it can be considered that this electrochemical measurement method is applied to the measurement of endotoxin containing polysaccharides and lipids as main components.
Japanese Patent Laid-Open No. 06-324047 Japanese Unexamined Patent Publication No. 08-247998 J. CHEM. SOC. CHEM. COMM. (1995) 1771-1772

However, in the measurement methods such as Patent Document 2 and Non-Patent Document 1, the sugars being measured are monosaccharides and disaccharides, 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.

  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-mentioned problems, the present invention firstly relates to a method for measuring the concentration of endotoxin contained in a sample, comprising a reversible redox substance having a reactive functional group that forms a complex with endotoxin. Add to the sample, complex with the endotoxin in the sample, and selectively amplify the concentration change of the reversible redox substance that has not formed the complex on the working electrode, and measure the current change at this time electrochemically It is characterized by that.

  In the present invention, secondly, the working electrode is an enzyme electrode in which an oxidoreductase is immobilized on the electrode, and the reversible redox substance is oxidized or reduced by the oxidoreductase at the enzyme electrode. A reaction cycle consisting of a reaction and a reaction that reduces or oxidizes and regenerates the reversible redox substance by an electrode reaction, amplifies the change in the current signal accompanying the complex formation, and also forms a complex reversible redox It is characterized in that the permeation of the substance is suppressed by an enzyme film provided on the electrode, and the current change at this time is measured electrochemically.

  Furthermore, the present invention is characterized in that, thirdly, in the first or second invention, the reversible redox substance is a compound having a boronic acid group, and fourthly, a boronic acid group is added. The compound possessed is ferroceneboronic acid. Fifth, it is characterized by further adding a substrate for oxidoreductase, and sixth, oxidoreductase immobilized on the electrode is diaphorase, choline oxidase, lactate oxidase, glutamate oxidase and horseradish peroxidase. And seventh, the substrate is for at least one of diaphorase, choline oxidase, lactate oxidase, glutamate oxidase and horseradish peroxidase. Eighthly, the endotoxin to be measured is at least one of endotoxin, lipopolysaccharide, pyrogen, and pyrogen.

  Ninth, the present invention is a measurement kit for measuring the concentration of endotoxin in a sample, comprising an electrochemical cell having at least an oxidoreductase-immobilized electrode, and complexed with endotoxin. And a reversible redox substance having a reactive functional group, wherein tenth is further provided with a substrate for the redox enzyme, and eleventh, the redox enzyme is , Diaphorase, choline oxidase, lactate oxidase, glutamate oxidase and horseradish peroxidase, and twelfth, the substrate is diaphorase, choline oxidase, lactate oxidase, glutamate oxidase And at least one enzyme of horseradish peroxidase, That.

  According to the first to seventh inventions, electrochemical measurement can be used for measuring endotoxin, and as a result, the concentration of endotoxin can be measured easily and with high sensitivity.

  According to the eighth to twelfth inventions, 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 reversible redox substance having a reactive functional group that forms a complex with endotoxin is added to the sample, complexed with the endotoxin in the sample, and the complex is not formed on the working electrode. It is characterized by selectively amplifying a change in the concentration of and measuring the current change electrochemically.

  In order to apply electrochemical measurement to endotoxin concentration measurement, the inventor of the present invention first pays attention to the polysaccharide portion of endotoxin, and also recognizes saccharide-recognizing compounds such as boronic acid and its derivatives in an alkaline aqueous solution. As a result of intensive research based on the formation of a complex with a compound having a cis-diol structure such as a sugar (see, for example, J. ORG. CHEM. 24 (1959) 769), boronic acid and its derivatives By using a compound having both an interaction function with sugar and a reversible redox ability (that is, a reversible redox substance having a reactive functional group that forms a complex with endotoxin), It was found that the endotoxin concentration can be measured by the measurement method.

  More specifically, the inventor of the present invention uses a reversible redox substance or a derivative thereof capable of forming a complex with endotoxin and performs measurement with little influence from an oxidizing or reducing substance in a sample. We have earnestly researched the possible ways. As a result, attention was paid to the fact that the magnitude of the electrolysis current on the electrode changes before and after the reversible redox substance forms a complex with endotoxin. Further, when measuring the change in the electrolytic current, the above electrochemical activity change of the reversible redox substance is obtained by conjugating the electrolytic reduction or electrolytic oxidation of the reversible redox substance and the oxidation or reduction by the enzyme reaction. In addition, the enzyme membrane provided on the electrode for the enzyme reaction allows reversible complexed reversible redox substances and non-specific adsorption of endotoxin to the electrode surface. It was found that the decrease of the response current due to is significantly suppressed.

  That is, the present invention uses the above working electrode as an enzyme electrode formed by immobilizing an oxidoreductase on the electrode, and in this enzyme electrode, a reaction of oxidizing or reducing a reversible redox substance with an oxidoreductase, and an electrode reaction To form a reaction cycle consisting of a reaction that reduces or oxidizes the reversible redox material and regenerates it, amplifies the change in the current signal that accompanies complex formation, and transmits the complexed reversible redox material through the electrode. It is also characterized in that it is suppressed by the enzyme film provided above and the current change at this time is measured electrically. Although not shown in the figure, for example, when the oxidoreductase is not immobilized on the electrode (there is no enzyme membrane), endotoxin is adsorbed on the electrode surface, and the background current value itself decreases, that is, is insulated. It becomes the state. This occurs even when, for example, endotoxin is added to an electrolyte without an electrochemically active species such as ferroceneboronic acid, and is not due to the interaction between the electrochemically active species and endotoxin. Therefore, as described above, nonspecific adsorption of endotoxin on the electrode can be suppressed by immobilizing the oxidoreductase on the electrode and using the enzyme electrode.

  As a result, it has been found that the amount of endotoxin causing the change can be measured quantitatively, simply, with high sensitivity, and with high selectivity, and the present invention has been completed.

  Regarding the use of a reversible redox substance for the measurement of double-stranded DNA content, see, for example, BIOELECTROCHEM. 63 (2004) 257-259 and Japanese Patent Application Laid-Open No. 2004-257993. However, unlike the present invention, endotoxins (lipopolysaccharides) having different structures are not measured.

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.
When a solution containing a certain amount of reversible redox substance is added to a sample containing endotoxin, or when the sample is added to a solution containing a certain amount of reversible redox substance, depending on the amount of endotoxin in the sample, A reversible redox material causes complexation with the endotoxin. The reversible redox material that has formed a complex with the endotoxin and the reversible redox material that has not formed a complex have different electrochemical characteristics and can be distinguished. Therefore, by measuring the amount of the reversible redox material that has not been complexed, it becomes possible to know the amount of endotoxin in the sample corresponding to the amount of the reversible redox material that has been complexed.

  In order to measure the amount of this uncomplexed reversible redox substance with higher sensitivity, the present invention uses a reversible redox substance that forms a complex with endotoxin, and an electrode on which an oxidoreductase is immobilized as an electrode Is used. The reversible redox substance having the ability to form a complex with endotoxin is a reversible redox substance that can reversibly be in an oxidized or reduced state by transferring electrons. Specifically, the amount of endotoxin is determined by measuring the amount of reversible redox substances that have not formed complexes by measuring the current flowing through the electrodes that is generated by the exchange of electrons. It is characterized in that it can be measured with high sensitivity.

  That is, among the reversible redox substances added to the sample solution, the reversible redox substances that do not form a complex with endotoxin are oxidized or reduced on the electrode to which a constant potential is applied, and shift to the oxidized or reduced form. However, the current flowing through the electrode changes due to the exchange of electrons accompanying this electrode reaction. Furthermore, the reversible redox substance that has been transferred to the oxidized or reduced form by the electrode reaction is regenerated again to its original state (reduced or oxidized) by the oxidoreductase immobilized on the electrode. 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 when the amount of the reversible redox substance that has not been complexed is too high, the measurement current is amplified, which makes it possible to measure the amount of endotoxin with high sensitivity.

  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.

  As the reversible redox substance used in the present invention, a compound (ferrocene) having both a complex forming function (boronic acid group) with endotoxin and a reversible redox ability such as ferroceneboronic acid can be used. Not limited to substances such as polymyxin B and anti-LPS antibodies that specifically bind endotoxin, but substances that do not have reversible redox ability can be reversible such as ferrocene and quinone as the side chain of the molecule. It can be used by introducing a group having redox ability. Regarding the synthesis of ferroceneboronic acids, see, for example, J. Org. CHEM. SOC. CHEM. COMM. (1995) 1771-1772 and JP-A-08-245673.

  The oxidoreductase is not particularly limited as long as the reaction proceeds smoothly using the reversible redox substance or derivative thereof as an electron acceptor or donor, but is preferably stable and inexpensive. Specifically, when ferroceneboronic acid is used as a reversible redox substance, complex formation between boronic acid and cis-diol is likely to occur in a weakly alkaline aqueous solution, and high enzyme activity in a weakly alkaline aqueous solution. It is convenient to use a diaphorase exhibiting as an electron acceptor when NADH is used as a substrate. In addition, when using a reversible redox substance having a side chain of ferrocene or quinone that forms a complex with endotoxin in a neutral aqueous solution, an oxidase that uses this as an electron acceptor during substrate oxidation, For example, choline oxidase, lactate oxidase, glutamate oxidase, or the like, or a reductase used as an electron donor at the time of substrate reduction, such as peroxidase (particularly horseradish peroxidase (HRP)), can be appropriately used.

  The method for immobilizing the enzyme on the electrode is not particularly limited, but the enzyme can be kept highly active, the substrate and the reversible redox substance are sufficiently permeated, and complex with endotoxin. A carrier material and an immobilization method that suppress the permeation of the reversible redox substance are selected and used. For example, methods that are known to have good permeability, such as a method of binding an enzyme to a porous carrier formed on the electrode surface, a method of forming an enzyme-immobilized cross-linked membrane with albumin and glutaraldehyde on the electrode surface, etc. Can be adopted.

  Next, an embodiment of the present invention will be described with reference to an example. First, a predetermined pretreatment such as polishing is performed on an electrode serving as a substrate, and then an oxidoreductase immobilized film is provided on the electrode. The enzyme electrode thus prepared is used as a working electrode, and is inserted into an aqueous electrolyte solution containing a reversible redox substance in combination with an appropriate counter electrode and reference electrode. The concentration of the reversible redox substance is not particularly limited, but is preferably about 0.1 to 10 μmol / L at a low concentration and capable of giving a clear current response by amplification measurement using an enzyme electrode. The concentration and type of the electrolyte solution to be used are not particularly limited, but it is preferable to use a pH buffer solution that is likely to form a complex between endotoxin and a reversible redox substance and that can stably maintain enzyme activity. For example, when the ferroceneboronic acid is a reversible redox substance, a weakly alkaline phosphate buffer having a pH of around 8.5 and a concentration of around 1 to 100 mmol / L is conveniently used. In that case, diaphorase showing high enzyme activity on the weak alkali side is advantageously used. When a potential necessary for the oxidation or reduction of the reversible redox substance is applied to the enzyme electrode, a current accompanying the oxidation or reduction flows, but this current value is small because the reversible redox substance concentration is relatively low.

  In addition, when substrates such as diaphorase, choline oxidase, lactate oxidase, glutamate oxidase, and horseradish peroxidase are used in the solution, addition of a substrate for these enzymes can cause substrate oxidation or reduction by enzymatic reaction. As a result, a cyclic reaction of reversible redox substance as an electron acceptor or donor, re-oxidation or re-reduction on the electrode proceeds, and the electrolysis current becomes extremely large, and accurate measurement is possible. Reach an easy level. The substrate of the oxidoreductase in the present invention is, for example, generally that the substrate of diaphorase is “nicotinamide adenine dinucleotide (NADH)”, the substrate of choline oxidase is “choline acid”, and the substrate of lactate oxidase Is “lactic acid”, and the glutamate oxidase substrate is “glutamic acid”.

Specifically, for example, when ferroceneboronic acid is used as the reversible redox substance and diaphorase is used as the enzyme, when a potential of +0.30 V (to silver silver chloride electrode) is applied at pH 8.5, The following reaction occurs.
(A) Ferroceneboronic acid (reduced form) → Ferroceneboronic acid (oxidized form) + e
Moreover, when the enzyme substrate β-nicotinamide dinucleotide reduced form (NADH) is added, the following enzyme reaction occurs.
(B) Ferroceneboronic acid (oxidized) + NADH →
Ferroceneboronic acid (reduced form) + β-nicotinamide dinucleotide oxidized form (NAD ⁺ )
Therefore, ferroceneboronic acid (reduced form) is regenerated by this enzyme reaction, and the cycle of electrode reaction and enzyme reaction is repeated. Due to this cyclic reaction, an increase in current of about 10 to 1000 times is observed by addition compared to before NADH addition. In this reaction cycle, ferroceneboronic acid repeats an oxidized form and a reduced form, but the total amount of oxidized and reduced forms does not change, and ferroceneboronic acid also functions as a mediator. In addition, the amount of “e” in the above reaction formula, that is, the current at the electrode, depends on the amount of ferroceneboronic acid involved in this reaction if the amount of NADH added is excessive.

  On the other hand, a part of the reversible redox substance in the sample is complexed with a polysaccharide constituting site of endotoxin. Since this endotoxin and reversible redox substance formed into a rust form is bound to the macromolecular endotoxin, the diffusion rate in the solution is significantly reduced, that is, it is difficult to reach the vicinity of the electrode from the solution bulk. Even so, it is difficult to contact the electrode surface due to the enzyme membrane. Moreover, even if it reaches the electrode surface, it is blocked by endotoxin itself and the speed of electron transfer with the electrode is reduced. Thus, a reversible redox material complexed with endotoxin provides virtually no reduction or oxidation current.

  That is, only the reversible redox substance with no complex formed repeats the cycle of electrode reaction and enzyme reaction, and the current at this time is approximately proportional to the concentration of the reversible redox substance with no complex formed. Therefore, the current decreases as the endotoxin concentration in the sample increases, that is, as the complexed reversible redox material concentration increases and the uncomplexed concentration decreases. In other words, the amount (concentration) of added endotoxin can be determined from the degree of decrease in current.

  The endotoxin to be measured in the present invention is not particularly limited. For example, endotoxin (toxin that is a component of the cell wall and is not actively secreted), lipopolysaccharide, pyrogen, and pyrogen are included. If it is either, it can be measured more efficiently.

  The endotoxin concentration measurement kit of the present invention is a reversible electrochemical cell having at least an oxidoreductase-immobilized electrode (oxidoreductase-immobilized electrode) and a reactive functional group that forms a complex with endotoxin. It is characterized by having a redox substance. Furthermore, a substrate for the enzyme immobilized on the electrode, a pH adjusting agent, a current measuring device, or the like, or a member or reagent for constructing the measuring system of the present invention may be combined to form a measuring kit.

  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 electrochemical measurement are shown below using differential pulse amperometry, but other methods such as chronoamperometry, cyclic voltammetry, differential pulse voltammetry, and differential double pulse amperometry are used as appropriate. Is possible.

<Test Example 1> Endotoxin measurement with a diaphorase-immobilized enzyme electrode Diaphorase 4.0% (w / v) aqueous solution (adjusted to pH 8.5) 5 μL, Bovine serum albumin 4.0% (w / v) aqueous solution (adjusted to pH 7) 10 μL, Glutaraldehyde 1.0% (w / v) aqueous solution (pH 7 adjustment) 4.OμL is mixed well, 5μL of this mixture is dropped onto a 1.6mm diameter gold electrode, and left at room temperature for 2 hours or more to dry. A diaphorase-immobilized electrode was prepared.

  This enzyme electrode was inserted into a 0.1 mol / L phosphate buffer having a pH of 8.5, and connected to a potentiostat (manufactured by CHI Instruments, ALS1230) with a counter electrode. A diaphorase substrate NADH (2 mmol / L) and a ferrocene boronic acid (5 μmol / L) having both functions of reversible redox substance and sugar recognition are added, and the potential of the electrode is set to the first pulse potential +0.25 V, A second pulse potential +0.30 V (to silver-silver chloride electrode) and a pulse potential were applied for 50 milliseconds each.

  FIG. 2 shows the results when endotoxin derived from E. coli O111: B4 was added so that the concentration was 1 μg / mL. In FIG. 2, the horizontal axis represents time, and the vertical axis represents the difference value of the electrolytic current when the first pulse potential and the second pulse potential are applied. The solid line shows the measured value of the oxidation current, and the arrow shows the time when 1 μg / mL endotoxin was added.

As is clear from FIG. 2, an oxidation current of 6.4 μA / cm ² of ferroceneboronic acid was observed when E. coli O111-derived endotoxin was not added, and when 1 μg / mL O111 endotoxin was added thereto, A clear decrease in oxidation current was observed.

Incidentally, according to this result, current reduction upon addition of 1 [mu] g / mL of endotoxin is ^{100nA / cm 2, S / N} = 2 and the case, can be quantified for 500 ng / mL of endotoxin and also estimates It was.
<Test Example 2> Endotoxin measurement with horseradish peroxidase immobilized enzyme electrode Horseradish peroxidase (HRP) 4.0% (w / v) aqueous solution (adjusted to pH 7.0) 5 μL, bovine serum albumin 4.0% (w / v) 10 μL of aqueous solution (adjusted to pH 7.0) and 1.0 μl of glutaraldehyde 1.0% (w / v) aqueous solution (adjusted to pH 7.0) 4.0 μL were mixed well, and this mixture was 5 μL on a glassy carbon electrode with a diameter of 1.0 mm. The HRP-immobilized electrode was produced as an enzyme electrode by dropping and allowing to stand at room temperature for 2 hours or more and drying.

  This HRP-immobilized electrode was inserted into a 0.1 mol / L phosphate buffer solution having a pH of 7.0, and was connected to a potentiostat (manufactured by Bioanalytical systems, LC-4C) with a counter electrode. Hydrogen peroxide (2 mmol / L), which is an HRP substrate, and ferroceneboronic acid (5 μmol / L), which has both reversible redox substance and sugar recognition functions, were added to this, and +0.10 V (to silver silver chloride electrode) ) Was applied to the working electrode.

  Then, endotoxin derived from E. coli O55: B5 was added so that the concentration was 1 μg / mL, and the results are shown in FIG. In FIG. 3, the horizontal axis represents time, and the vertical axis represents the electrolytic current value when a constant potential is applied. The solid line indicates the measured value of the reduction current, and the arrow indicates the time when 1 μg / mL endotoxin is added.

As is clear from FIG. 3, when no endotoxin derived from Escherichia coli O55 was added, a reduction current of ferroceneboronic acid of 0.13 μA / cm ² was observed, but when 1 μg / mL of 055 endotoxin was added thereto, A clear reduction in reduction current was observed.

According to this result, the current decrease when 1 μg / mL endotoxin was added was 5 nA / cm ² , and when S / N = 2, 100 ng / mL endotoxin could be quantified. It was lost.
<Comparative example> Measurement of monosaccharides with a diaphorase-immobilized enzyme electrode In blood and culture solution containing monosaccharides in an actual measurement system, complex formation with ferroceneboronic acid easily occurs in these monosaccharides, It is expected to be an obstacle to endotoxin measurement.

  Thus, when the response to monosaccharides was examined under the same experimental conditions as in Test Example 1 above, D-glucose and D-galactose constituting the polysaccharide portion of endotoxin were added to 1 μg / mL, similar to endotoxin. In the case, no decrease in the electrolysis current value was observed.

  As shown in FIG. 4, the monosaccharide concentration corresponding to the response equivalent to that of Test Example 1 was about 90 mg / ml (500 μmol / L). Since monosaccharides have a small molecular weight, a large excess of monosaccharide concentration was required to obtain a current response equivalent to that of endotoxin. That is, it was found that the sensitivity of the measurement system to macromolecular endotoxin is high even when the measurement system may be contaminated with monosaccharides.

  As is clear from the above Test Examples 1 and 2 and Comparative Example, the present invention uses an enzyme-immobilized electrode and uses a reversible redox substance having a functional group capable of complexing with endotoxin. The amount (concentration) of endotoxin is measured, and a decrease in a reversible redox substance that has not formed a complex due to complexation with respect to endotoxin in a sample is measured as a decrease in current through an electrode. In particular, by using an enzyme-immobilized electrode, the concentration change of the reversible redox substance can be selectively amplified and captured. Furthermore, even when the same saccharide was used, the response due to the complex formation with the monosaccharide was much smaller than that of the endotoxin molecule. Therefore, the present invention is a method capable of measuring endotoxin with high sensitivity as a result.

  That is, the ferroceneboronic acid in the present invention is oxidized or reduced on the electrode, but is regenerated by an enzyme reaction, and the electrode reaction and the enzyme reaction are repeated. For this reason, one molecule of ferroceneboronic acid undergoes electron transfer many times and gives a large current signal. This gives an amplified signal as compared to the case of only an electrochemical reaction system that does not involve an enzyme reaction. Such signal amplification is possible only by providing an enzyme membrane on the electrode. Therefore, the measurement method of the present invention is simple and useful as a highly sensitive endotoxin concentration measurement method.

It is the schematic which illustrated the principle of the concentration measuring method of endotoxin in this invention. It is the figure which showed the graph which measured the electrolysis current at the time of adding an endotoxin at the time of using a diaphorase fixed electrode in presence of NADH and ferrocene boronic acid. The arrow indicates the time when endotoxin was added. It is the figure which showed the graph which measured the electrolysis current at the time of adding an endotoxin at the time of using an HRP fixed electrode in hydrogen peroxide and ferrocene boronic acid presence. The arrow indicates the time when endotoxin was added. It is the figure which showed the graph which measured the electrolysis current at the time of adding D-glucose and D-galactose which are monosaccharides in the case of using a diaphorase fixed electrode in presence of NADH and ferrocene boronic acid. Arrows indicate the time when each monosaccharide was added.

Claims (12)

  A method for measuring the concentration of endotoxin contained in a sample, wherein a reversible redox substance having a reactive functional group that forms a complex with endotoxin is added to the sample to form a complex with the endotoxin in the sample, and then on the working electrode. A method for measuring the concentration of endotoxin, comprising selectively amplifying a change in concentration of a reversible redox substance having no complex formed therein and electrochemically measuring a change in current at this time.   The working electrode is an enzyme electrode formed by immobilizing an oxidoreductase on the electrode. In this enzyme electrode, a reaction in which a reversible redox substance is oxidized or reduced by a redox enzyme, and a reversible redox substance by an electrode reaction. Enzyme membrane that forms a reaction cycle consisting of a reaction that reduces or oxidizes and regenerates to amplify the change in the current signal that accompanies the complex formation, and provides a permeation of the complexed reversible redox material on the electrode The method for measuring the concentration of endotoxin according to claim 1, wherein the current change at this time is measured electrochemically.   The method for measuring the concentration of endotoxin according to claim 1 or 2, wherein the reversible redox substance is a compound having a boronic acid group.   The method for measuring the concentration of endotoxin according to claim 3, wherein the compound having a boronic acid group is ferroceneboronic acid.   The measurement method according to claim 2, wherein a substrate for the oxidoreductase is further added.   The endotoxin concentration measurement method according to any one of claims 2 to 5, wherein the oxidoreductase immobilized on the electrode is at least one of diaphorase, choline oxidase, lactate oxidase, glutamate oxidase, and horseradish peroxidase.   The method for measuring the concentration of endotoxin according to claim 6, wherein the substrate is for at least one of diaphorase, choline oxidase, lactate oxidase, glutamate oxidase, and horseradish peroxidase.   The endotoxin concentration measuring method according to any one of claims 1 to 7, wherein the endotoxin to be measured is at least one of endotoxin, lipopolysaccharide, pyrogen and pyrogen.   A measurement kit for measuring the concentration of endotoxin in a sample, comprising an electrochemical cell equipped with at least an oxidoreductase-immobilized electrode, and a reversible oxidation having a reactive functional group that forms a complex with endotoxin An endotoxin concentration measurement kit comprising a reducing substance.   The endotoxin concentration measurement kit according to claim 9, further comprising a substrate for oxidoreductase.   The endotoxin concentration measurement kit according to claim 9 or 10, wherein the oxidoreductase is at least one of diaphorase, choline oxidase, lactate oxidase, glutamate oxidase, and horseradish peroxidase.   The endotoxin concentration measurement kit according to claim 11, wherein the substrate is for diaphorase, choline oxidase, lactate oxidase, glutamate oxidase and horseradish peroxidase.

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