JP2009092647A - Device and element for measuring anion concentration - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simplify a structure and a fabrication method of an ion selective electrode in an ion concentration measuring device for measuring an anion, particularly a chloride ion, in a biological component. <P>SOLUTION: A quaternary ammonium salt derivative 1109 serving as a ligand for an anion is immobilized to the surface of a gold electrode 1110 by using as a linker an insulative molecule forming a self-assembled monolayer, and a potential difference measuring device 1104 measures an electromotive force generated with anion binding, as an interface potential change on the surface of the gold electrode. In order to reduce the effect of adsorption of impurities on the electrode surface, a high-molecular weight polymer is physically adsorbed on the gold electrode and used when a biological component is measured. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an ion concentration measuring apparatus that measures anions, particularly chlorine ions, in biological components.

  As a method for analyzing the concentration of biological components in the medical field, particularly electrolytes (sodium ions, potassium ions, chloride ions, etc.) in serum and plasma, the ion selective electrode method is widely used. The ion-selective electrode method can be used to determine the concentration of ions in a sample by simply immersing the ion-selective electrode in a sample solution together with a reference electrode. Has been.

  Among the ion selective electrodes, the chlorine ion selective electrodes include a solid electrode using a hardly soluble chloride and a liquid membrane electrode added with an ion exchange type ligand. A conventional liquid membrane type chloride ion selective electrode comprises a quaternary ammonium salt as a ligand, for example, trioctylmethylammonium chloride, tridecylmethylammonium chloride, tetraoctylammonium chloride, and an epoxy resin and vinyl chloride. A quaternary ammonium salt as a ligand and a plasticizer (for example, dialkyl adipate or dialkyl phthalate) have been added to the plastic film. In addition, in order to improve physical strength and increase selectivity to chloride ions, it comprises a copolymer of a styrene trimer having a tri-long-chain alkylammonium group as a ligand in the side chain and a polymer having a hydrophilic group in the side chain. A chloride ion selective electrode has been developed (Japanese Patent Laid-Open No. 2004-184365). On the other hand, in order to improve physical strength and prevent degradation due to elution of the ligand, a chemically modified glass membrane ion-selective electrode using porous glass immobilized with a quaternary ammonium salt as a ligand was also developed. (Japanese Patent Laid-Open No. 61-170645).

  In order to simplify the structure and manufacturing method of the ion selective electrode described above and cope with future miniaturization of an analyzer, an ion selective electrode in which a ligand is immobilized on the gold electrode surface has been proposed. However, in any case, potential measurement was not possible, and a desired ion concentration was obtained by impedance measurement. As an example of a sodium ion selective electrode, there is a report that a mercapto crown ether compound is immobilized on a gold electrode as a neutral carrier type ligand (J. Am. Chem. Soc., 120 (1998) 4652-4657). In addition, as an example of a lithium ion selective electrode, a neutral carrier type ligand is similarly immobilized on the gold electrode surface using a bond between thiol and gold (Anal. Chem., 78 (2006) 7132- 7137, and WO2006 / 113440). On the other hand, anion-selective electrodes include a fluorine ion ligand (Tetra-amide Calix [6] arene derivative) immobilized on the gold electrode surface using a bond between thiol and gold (Langmuir, 2006, 22, 10732-10738).

JP-A-61-170645 JP 2004-184365 A WO2006 / 113440 J. Am. Chem. Soc., 120 (1998) 4652-4657 Anal. Chem., 78 (2006) 7132-7137 Langmuir 22 (2006) 10732-10738

  In the ion-selective electrode in which the above-mentioned ligand is immobilized on the gold electrode surface, consideration has not been given to the insulation property of the gold electrode surface and the environment surrounding the ligand, and potential measurement has not been possible. Therefore, a desired ion concentration has been obtained using impedance measurement. In conventional ligand-immobilized ion-selective electrodes, no consideration is given to the insulation between the gold electrode surface on which the ligand is immobilized and the measurement solution. In actual measurement, leakage current from the gap between the immobilized ligands This is because the interface potential could not be stably measured under the influence of the above. In the impedance measurement method, a working electrode made of gold or platinum, a counter electrode, and a reference electrode for keeping the potential of the working electrode constant are placed in a solution, and a potentiostat that is a current measuring device is used. The frequency responsiveness to the voltage applied between the counter electrodes is measured by the current value. At that time, it is necessary to put an oxidation-reduction substance which is an electrochemically active substance into the measurement solution. Therefore, the advantage of the conventional ion-selective electrode method in which the ion concentration in the sample can be determined simply by immersing it in the sample solution together with the reference electrode cannot be utilized. Further, since the impedance measurement method is a current measurement method, there is a problem that the measurement concentration range is narrow in principle.

  The purpose of the present invention is to maintain the basic performance of the conventional liquid membrane ion-selective electrode method, which can quantitate the ion concentration in the sample by simply immersing it in the sample solution together with the reference electrode, and to select the ions. It is an object of the present invention to provide an ion concentration measuring device that simplifies the structure and manufacturing method of the conductive electrode.

  In order to achieve the above object, in the present invention, a quaternary ammonium salt derivative, which is a ligand for anions, is immobilized using an insulating molecule (for example, alkanethiol) that forms a self-assembled film on the gold electrode surface as a linker. The electromotive force generated with the coordination of the anion is measured as a change in the interfacial potential on the gold electrode surface. At that time, when the side chain alkyl group of the quaternary ammonium salt derivative is larger than the interval of the self-assembled membrane and there is a gap between the immobilized ligand molecules, it has a carbon chain shorter than the linker, An alkanethiol having a hydrophilic end, such as an alkanethiol having a terminal hydrophilic group being an amino group or a hydroxyl group, is immobilized in the presence of a quaternary ammonium salt derivative. The number of carbon atoms in the linker is preferably 6 or more and 20 or less in order to efficiently form a self-assembled film. Also, the carbon number of the other three side chain alkyl chains of the quaternary ammonium salt is preferably less than the carbon number of the linker so as not to prevent the formation of a self-assembled film. Further, an insulated gate field effect transistor formed on the same substrate as the gold electrode is used as a potential difference measuring device. At that time, measurement is performed by superimposing an AC voltage of 1 KHz or more on the reference electrode. Further, in order to reduce the influence due to adsorption of impurities on the electrode surface when measuring biological components, the polymer is physically adsorbed on the gold electrode.

  According to the present invention, the insulation between the gold electrode and the solution can be improved by immobilizing the quaternary ammonium salt derivative, which is a ligand for anions, on the surface of the gold electrode via an insulating molecule. By improving the insulating property, the leakage current in the gap between the ligands can be suppressed, and the electromotive force generated by the coordination of the anion can be stably measured as the change in the interface potential on the gold electrode surface. When the side chain alkyl group of the quaternary ammonium salt derivative is larger than the interval of the self-assembled film, an alkanethiol having a carbon chain shorter than the linker and hydrophilic at one end is converted to a quaternary ammonium salt. By immobilizing the coexisting derivative, the gap between the immobilized ligand molecules can be eliminated, and the insulation between the gold electrode and the solution can be maintained. In that case, there is an effect of increasing the response speed by using an alkanethiol having an amino group at the end as an alkanethiol having a hydrophilic end at one end. Furthermore, by using an insulated gate field effect transistor formed on the same substrate as the gold electrode as the potential difference measuring device, leakage current can be reduced and the interface potential on the gold electrode surface can be stably measured. . At that time, by superimposing an AC voltage of 1 KHz or more on the reference electrode, the interface potential on the gold electrode surface can be stabilized, and the measurement accuracy is improved. In addition, noise and drift due to adsorption of contaminants on the electrode surface during measurement of biological components can be reduced by physically adsorbing the polymer on the gold electrode.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing an example of an ion concentration measuring apparatus according to the present invention. The measurement apparatus of this embodiment includes a measurement unit 101, a signal processing circuit 102, and a data processing apparatus 103. The measurement unit 101 includes a potential difference measuring device 104, a reference electrode 105, a sample solution injector 106 for supplying a sample solution having a measurement substance, and a measurement cell 107. In the measurement solution 108 in the measurement cell 107, there are disposed a gold electrode 111 and a reference electrode 105, in which a quaternary ammonium salt derivative 109, which is an anion ligand, and an alkanethiol 110 having an amino group at the terminal are immobilized. ing. An example of a method for immobilizing a ligand on a gold electrode is shown in FIG. FIG. 2 (a) shows an example in which only a ligand is immobilized, and FIG. 2 (b) shows an example of solidification by coexisting a ligand and an alkanethiol having an amino group at the terminal. The ligand for chloride ion is N, N, N-trimethyl (10-mercaptodecyl) ammonium chloride, and the terminal alkanethiol is 8-amino-1 -Octanethiol. In addition, the carbon chain of the alkyl group in the side chain of the quaternary ammonium salt derivative that is a ligand for chloride ions can be changed according to the measurement conditions. At that time, the carbon number of the alkyl group in the side chain of the quaternary ammonium salt derivative is preferably smaller than the carbon number of the linker so as not to prevent the self-assembly during the immobilization of the ligand to the gold electrode. In addition, there is no problem as long as the length of the carbon chain of the alkanethiol coexisting is not more than the length of the carbon chain of the linker of the quaternary ammonium salt derivative. For example, when the carbon chain length of the quaternary ammonium salt derivative linker is 10, 6-amino-1-hexanethiol, 8-amino-1-octanethiol, 11- Amino-1-undecanethiol, 6-hydroxy-1-hexanethiol, 8-hydroxy-1-octanethiol, and 11-hydroxy-1-undecanethiol having a terminal hydroxyl group can also be used.

  The measurement procedure is as follows. First, a sample solution is injected into the measurement solution 108 in the measurement cell 107 using the sample solution injector 106. Chlorine ions to be measured in the sample solution are bonded to the quaternary ammonium derivative 109, which is a ligand for anions, by an ion exchange action, and the interface potential on the gold electrode 111 changes. The potential measurement is performed by measuring the interface potential of the gold electrode 111 changing before and after the sample solution injection by the sample solution injector 106 in real time by the potential difference measuring device 104 and recording it by the signal processing circuit 102 and the data processing device 103. The change in the interfacial potential on the gold electrode 111 depends on the concentration of the chlorine ion to be measured. Therefore, based on a calibration curve prepared by measuring a standard solution in advance, the chloride ion concentration of a sample having an unknown concentration can be obtained from the measured potential change value.

  As the sample solution injector 106, a syringe pump or a pressurized liquid feeding device can be used. Further, instead of the gold electrode 111, an electrode made of other noble metal such as silver or carbon may be used. Moreover, in order to reduce the influence by the adsorption | suction to the electrode surface of the contaminant at the time of a biological component measurement, you may use a high molecular polymer by physically adsorbing on a gold electrode. As the polymer, methyl cellulose, acrylamide, dextran, polyethylene glycol, or the like may be used.

  The reference electrode 105 gives a reference potential in order to stably measure a potential change based on an equilibrium reaction or a chemical reaction occurring on the surface of the gold electrode 111 in the measurement solution 108. Usually, the reference electrode is a silver / silver chloride electrode or calomel electrode using saturated potassium chloride as the internal solution. However, if the composition of the sample solution to be measured is constant, There is no problem even if only a silver / silver chloride electrode is used as an electrode.

  FIG. 3 is a block diagram showing an example of an ion concentration measuring apparatus according to the present invention using a field effect transistor (FET) sensor. The measurement apparatus of this embodiment includes a measurement unit 301, a signal processing circuit 302, and a data processing apparatus 303. The measurement unit 301 includes an insulated gate field effect transistor 304, a reference electrode 305, a power source 306 that applies a voltage to the reference electrode 305, a sample solution injector 307 that supplies a sample solution having a measurement substance, and a measurement cell 308. The insulated gate field effect transistor 304 includes a source 309, a drain 310, and a gold electrode 311 electrically connected to the gate. On the gold electrode 311, a quaternary ammonium salt derivative 312 as an anion ligand and an alkanethiol 313 having an amino group at the terminal are immobilized. In the measurement solution 314 in the measurement cell 308, a gold electrode 311 and a reference electrode 305 to which a quaternary ammonium derivative 312 and an alkanethiol 313 as an anion ligand are immobilized are arranged.

  The measurement procedure is as follows. First, the sample solution is injected into the measurement solution 314 in the measurement cell 308 using the sample solution injector 307. Chlorine ions to be measured in the sample solution are bonded to the quaternary ammonium derivative 312 that is a ligand for anions by an ion exchange action, and the interface potential on the gold electrode 311 changes. In the potential measurement, the current between the source 309 and the drain 310 in the insulated gate field effect transistor 304 that changes before and after the sample solution injection by the sample solution injector 307 is monitored in real time, and the signal processing circuit 302 and the data processing device 303 are used. This is done by recording. The change in the interfacial potential on the gold electrode 311 depends on the concentration of the chlorine ion to be measured. Therefore, based on a calibration curve prepared by measuring a standard solution in advance, the chloride ion concentration of a sample having an unknown concentration can be obtained from the measured potential change value. In order to reduce the influence due to external measurement fluctuations, the power source 306 is preferably a power source including an AC component. In that case, the surface potential of the gold electrode 311 can be stabilized by superimposing an AC voltage of 1 KHz or more on the DC component.

  The sample solution injector 307 can use a syringe pump or a pressurized liquid delivery device. The gold electrode 311 may be an electrode made of other noble metal such as silver or carbon. Moreover, in order to reduce the influence by the adsorption | suction to the electrode surface of the contaminant at the time of a biological component measurement, you may use a high molecular polymer by physically adsorb | sucking on a gold electrode. There is no problem if methylcellulose, acrylamide, dextran, polyethylene glycol or the like is used as the polymer.

  The reference electrode 305 gives a reference potential in order to stably measure a potential change based on an equilibrium reaction or a chemical reaction occurring on the surface of the gold electrode 311 in the measurement solution 314. Usually, the reference electrode is a silver / silver chloride electrode or calomel electrode using saturated potassium chloride as the internal solution. However, if the composition of the sample solution to be measured is constant, There is no problem even if only a silver / silver chloride electrode is used as an electrode.

  FIG. 4 is a diagram showing an example of the structure of an analysis element that uses an FET sensor and is used in the ion concentration measurement apparatus of the present invention. 4 (a) and 4 (b) show a cross-sectional structure and a planar structure, respectively. In the insulated gate field effect transistor 401, a source 402, a drain 403, and a gate insulator 404 are formed on a surface of a silicon substrate, and a gold electrode 405 is provided. The gold electrode 405 and the gate 406 of the insulated gate field effect transistor are connected by a conductive wiring 407. Preferably, the insulated gate field effect transistor is a metal-oxide semiconductor field effect transistor (FET) using silicon oxide as an insulating film, but there is no problem even if a thin film transistor (TFT) is used. By adopting this structure, the gold electrode 405 can be formed at any location and in any size, and the volume of the measurement cell can be changed according to the amount of the sample solution to be measured.

The insulated gate field effect transistor used in the present invention is a depletion type FET having an insulating layer using SiO ₂ (thickness: 17.5 nm), and a gold electrode is fabricated in a size of 400 μm × 400 μm. . Since normal measurement uses an aqueous solution, the device must operate in solution. When measuring in a solution, it is necessary to operate in an electrode potential range of −0.5 to 0.5 V that hardly causes an electrochemical reaction. Therefore, in this embodiment, the fabrication condition of the depletion type n-channel FET, that is, the ion implantation condition for adjusting the threshold voltage (Vt) is adjusted, and the threshold voltage of the FET is set to around −0.5V. Instead of the gold electrode, an electrode made of other noble metal such as silver may be used. An element having two or more FET sensors on the same substrate is manufactured by forming a plurality of the FET sensors of FIG. 4 on the same substrate. Crosstalk between the FET sensors, which is a problem at that time, can be reduced by adopting an SOI (Silicon on Insulator) structure.

  Next, when the quaternary ammonium derivative, which is a ligand for anions, is immobilized on the gold electrode surface via a linker, which is an insulating molecule, an alkanethiol having a hydrophilic property, particularly an amino group, is added to the quaternary ammonium. The effect of immobilizing the coexisting derivative will be described.

  The ligand was immobilized on the gold electrode surface by the following procedure. First, the gold electrode used for immobilization was washed with 1N nitric acid, pure water, and ethanol in this order, and the gold electrode surface was purged with nitrogen. Next, it was immersed in a mixed solution of ligand and alkanethiol (each concentration: 0.5 mM, solvent: ethanol) for 1 hour. After completion of immobilization, heat treatment was performed at 95 ° C. for 10 minutes in a 300 mM sodium chloride solution. Thereafter, it was washed with ethanol and pure water and stored in a 300 mM sodium chloride aqueous solution until use.

  The influence of the terminal residue of alkanethiol and the length of the carbon chain on the chloride ion coexisting with the quaternary ammonium salt derivative, which is a ligand for anions, on the response rate to chloride ions will be described below.

  In this example, N, N, N-trimethyl (10-mercaptodecyl) ammonium chloride (N, N, N), which is an example of a quaternary ammonium salt derivative having 1-decanethiol as a linker as a ligand for chloride ion, is used. 1-octanethiol (1-OT), 1-undecanethiol (1-UDT), 1-octanethiol (1-UDT), 1-octanethiol (1-UDT), which is a hydrophobic alkanethiol. Tetradecanethiol (1-TDT), 1-octadecanethiol (1-ODT) is used as an alkanethiol whose terminal is a hydroxyl group, 6-hydroxy-1-hexanethiol (6-HHT), 8-hydroxy-1-octanethiol (8-HOT), 11-hydroxy-1-undecanethiol (11-UUT), triethylene glycol mono-11- having hydrophilic ethylene glycol and corresponding to 18 carbon chains Mercaptodecyl ether (Triethyleneglycol-mono-11-mercaptodecylether; TGM) is used as an alkanethiol having an amino group at its end as 6-amino-1-hexanethiol (6-AHT), 8-amino-1-octanethiol (8- AOT), 11-amino-1-undecanethiol (11-AUT) was used. The response speed to chloride ions was measured as the time until the potential response to the ion concentration changed by 90%.

  FIG. 5 (a) shows the effect of the length of the carbon chain on the response rate to chloride ions when an alkanethiol having a methyl group at the terminal coexists with the ligand in a ratio of 1: 1. In FIG. 5A, the horizontal axis represents A: a gold electrode in which only the ligand is immobilized, B: a gold electrode in which the ligand and 1-OT are immobilized, C: a gold electrode in which the ligand and 1-UDT are immobilized, and D: E represents a gold electrode on which a ligand and 1-TDT are immobilized, and E: a gold electrode on which a ligand and 1-ODT are immobilized. As shown in FIG. 5 (a), the response speed of the chloride ion electrode immobilized by coexisting alkanethiols with various carbon chain lengths became slower as the carbon chain length of the coexisting alkanethiols became longer. . This is because the alkanethiol simply fills the gaps between the ligands and prevents ions from entering the gaps between the ligands, resulting in a slower response due to increased hydrophobicity around the ligands. It shows that the negative effect is greater. That is, it is shown that chloride ions are difficult to approach the ligand due to the increase in hydrophobicity around the ligand.

  FIG. 5 (b) shows the influence of the length of the carbon chain on the response rate to chloride ions when an alkanethiol having a hydroxyl group at the terminal and the ligand coexists in a ratio of 1: 1. The horizontal axis of FIG. 5 (b) is A: a gold electrode in which only the ligand is immobilized, B: a gold electrode in which the ligand and 6-HHT are immobilized, C: a gold electrode in which the ligand and 8-HOT are immobilized, D: A gold electrode on which a ligand and 11-HUT are immobilized, and E: a gold electrode on which a ligand and TGM are immobilized. As shown in FIG. 5 (b), the response speed of the chloride ion electrode immobilized by coexisting an alkanethiol having a hydroxyl group at the terminal with different carbon chain lengths was similar to that when only the ligand was immobilized. It was. In addition, when TGM having hydrophilic ethylene glycol and 18 carbon chains is present, the same response as 1-ODT, which is a hydrophobic alkanethiol having the same carbon chain length. The speed was slow. This indicates that the steric hindrance effect is greater than the hydrophilic effect. Thus, if the length of the carbon chain of the alkanethiol is too long, it is considered that chloride ions are difficult to approach due to steric hindrance around the ligand, and the response speed is slow.

  FIG. 5 (c) shows the influence of the length of the carbon chain on the response rate to chloride ions when an alkanethiol having an amino group at the terminal is coexisted with the ligand in a ratio of 1: 1. The horizontal axis of FIG. 5 (c) is A: a gold electrode in which only the ligand is immobilized, B: a gold electrode in which the ligand and 6-AHT are immobilized, C: a gold electrode in which the ligand and 8-AOT are immobilized, D: This represents a gold electrode on which a ligand and 11-AUT are immobilized. As shown in FIG. 5 (c), the response sensitivity of the chloride ion electrode immobilized by coexisting alkanethiols with different carbon chain lengths is higher than that of the gold electrode immobilized with only the ligand. As the carbon chain length increased, it became faster. This is presumably because the alkanethiol fills the gaps between the ligands and prevents ions from entering.

  As shown in FIGS. 5A to 5C, by introducing a hydrophilic group, particularly an amino group, into the alkanethiol coexisting with the ligand, the response speed to chloride ions is improved. That is, it is preferable that the alkanethiol coexisting with the ligand for chloride ions is hydrophilic and the carbon chain length is shorter than the ligand. In particular, an alkanethiol having an amino group which is shorter than the length of the coexisting ligand is desirable.

  Using an ion electrode according to the present invention in which a quaternary ammonium derivative as an anion ligand and an alkanethiol having an amino group at the end coexist through a linker as an insulating molecule and immobilized on the gold electrode surface, chloride ion is used. The measurement result of the potential response to is described below.

  In this example, N, N, N-trimethyl (10-mercaptodecyl) ammonium chloride (N, N, N), which is an example of a quaternary ammonium salt derivative having 1-decanethiol as a linker as a ligand for chloride ion, is used. 11-Amino-1-undecanethiol (11-AUT) was used as an alkanethiol having an amino group at the end as -trimethyl (10-mercaptodecyl) ammonium chloride). The potential response to chloride ions was measured using a sodium chloride aqueous solution, and the slope sensitivity in a concentration range of 4.5 mM to 300 mM was compared (FIG. 6). The measured potential value is the value after 5 minutes after immersion. The horizontal axis in FIG. 6 represents the chlorine ion concentration in terms of activity. The vertical axis represents the electromotive force generated according to chlorine ions. As a result, the potential response to chlorine ions was approximately 60 mV according to the Nernst equation.

  FIG. 7 is a block diagram showing an example of an ion concentration measuring apparatus according to the present invention in which an FET sensor and a reference electrode are formed on the same plane. The measurement apparatus of this embodiment includes a measurement unit 701, a signal processing circuit 702, and a data processing apparatus 703. The measurement unit 701 includes an insulated gate field effect transistor 704, a pseudo reference electrode 705, a sample solution injector 706 for supplying a sample solution having a measurement substance, and a measurement cell 707. The insulated gate field effect transistor 704 includes a source 708, a drain 709, and a gold electrode 710 electrically connected to the gate. A pseudo reference electrode 705 is provided on the same plane as the gold electrode 710. The pseudo reference electrode 705 is connected to the outside through a conductive wiring. As the pseudo reference electrode, silver / silver chloride, gold, platinum or the like can be used. In this embodiment, a quaternary ammonium salt derivative 711 that is a ligand for chlorine ions and an alkanethiol 712 having an amino group at the terminal are immobilized on the gold electrode 710. In the measurement solution 713 in the measurement cell 707, a gold electrode 710 in which a quaternary ammonium salt derivative 711 that is a ligand for chloride ions and an alkanethiol 712 having an amino group at the terminal are immobilized, and a pseudo reference electrode 705 are disposed. Has been. The pseudo reference electrode 705 is applied with an AC voltage of 1 kHz or more superimposed on a DC component.

  FIG. 8 shows the effect of the side chain length of the quaternary ammonium salt used as a ligand of a chloride ion selective electrode on the response time with respect to the chloride ion concentration. In this example, as an example of a quaternary ammonium salt, N, N, N-trimethyl (10-mercaptodecyl) whose side chain is a methyl group, as shown in FIGS. 9 (a), (b) and (c), is used. Ammonium chloride (N, N, N-Trimethyl (10-mercaptodecyl) ammonium chloride), N, N, N-triethyl (10-mercaptodecyl) ammonium chloride (N, N, N-Triethyl () 10-mercaptodecyl) ammonium chloride) and N, N, N-tripropyl (10-mercaptodecyl) ammonium chloride (N, N, N-Tripropyl (10-mercaptodecyl) ammonium chloride) whose side chain is a propyl group . In this example, the influence of the side chain of the quaternary ammonium salt, which is a ligand, is shown and compared in the case where the ligand and the hydrophilic alkanethiol coexist in addition to the case where only the ligand is immobilized. It is. TMA, TEA, TPA, 11-HUT, and 11-AUT in the figure are N, N, N-trimethyl (10-mercaptodecyl) ammonium chloride and N, N, N-triethyl (10-mercaptodecyl) ammonium, respectively. It represents N, N, N-tripropyl (10-mercaptodecyl) ammonium chloride, 11-hydroxy-1-undecanethiol, 11-amino-1-undecanethiol which is chloride and propyl group.

  As a result, in both the case where only the ligand was immobilized and the case where the ligand and hydrophilic alkanethiol were allowed to coexist, when the carbon chain in the side chain of the quaternary ammonium salt was increased, the response time was extremely shortened. In this example, when only the ligand was immobilized, it was 88 seconds when the side chain was a methyl group, 14 seconds when the side chain was ethyl group, and 6 seconds when the side chain was propyl group. Further, when the side chain is a methyl group, as shown in FIG. 8 (c), the response time is faster when the ligand and the alkanethiol having an amino group coexist than when only the ligand is used. However, the effect became smaller as the side chain of the quaternary ammonium salt became longer. When the side chain was a propyl group, the response time was the shortest when only the ligand was immobilized.

  Thus, by lengthening the side chain of the quaternary ammonium salt, other hydrophilic alkanethiol is not required and can be immobilized on the gold electrode with a simple composition. At that time, the carbon number of the alkyl group in the side chain of the quaternary ammonium salt derivative is less than the carbon number of the linker so as not to prevent self-assembly during the fixation of the quaternary ammonium salt to the gold electrode. Is preferable. For example, in the case of the present embodiment, the length of the carbon chain of the linker is 10 carbons, so the number of carbons in the side chain is preferably 10 or less. The carbon chain of the quaternary ammonium salt derivative linker, which is a ligand for chloride ions, can be changed according to the measurement conditions, but the chemical synthesis method, the purification method after synthesis, and the immobilization method on the gold electrode In consideration of the above, the carbon number is preferably 20 or less.

  FIG. 10 shows the relationship between the side chain length of the quaternary ammonium salt derivative that is a ligand and the potential response to the chloride ion concentration. In this example, examples shown in FIGS. 9A, 9B, and 9C were used as examples of quaternary ammonium salts. FIG. 10 (a) shows a case where N, N, N-trimethyl (10-mercaptodecyl) ammonium chloride (N, N, N-Trimethyl (10-mercaptodecyl) ammonium chloride) whose side chain is a methyl group is used. When 10 (b) uses (N, N, N-Triethyl (10-mercaptodecyl) ammonium chloride) whose side chain is an ethyl group, FIG. 10 (c) shows that the side chain is a propyl group (N, N , N-Tripropyl (10-mercaptodecyl) ammonium chloride) is shown. The potential response to the sodium ion ion concentration was measured using a sodium chloride aqueous solution, and the electromotive force of the ligand-immobilized electrode surface in the concentration range of 0.001 mM to 1000 mM was compared.

  The horizontal axis of FIG. 10 represents the chlorine ion concentration as an activity. The vertical axis represents the electromotive force generated according to chlorine ions. When the side chain length of the quaternary ammonium salt was increased, the potential response to the chlorine ion concentration was shown up to a low concentration. In this example, linearity can be maintained in a concentration range of 10 to 1000 mM when the side chain is a methyl group, 1 to 1000 mM when the side chain is an ethyl group, and 0.1 to 1000 mM when the side chain is a propyl group. That is, as the side chain of the quaternary ammonium salt is longer, not only the response time is shortened but also the range (measurement range) showing a linear response is widened.

  FIG. 11 is a block diagram showing an example of an ion concentration measuring apparatus according to the present invention. The measurement apparatus according to the present exemplary embodiment includes a measurement unit 1101, a signal processing circuit 1102, and a data processing apparatus 1103. The measurement unit 1101 includes a potential difference measurement device 1104, a reference electrode 1105, a sample solution injector 1106 for supplying a sample solution having a measurement substance, and a measurement cell 1107. In the measurement solution 1108 in the measurement cell 1107, a gold electrode 1110 and a reference electrode 1105 to which a quaternary ammonium salt derivative 1109 that is a ligand for anion is immobilized are arranged. In this example, since N, N, N-tripropyl (10-mercaptodecyl) ammonium chloride is used as a ligand for chloride ions, it is not necessary to coexist and fix a hydrophilic alkanethiool. A fast response speed can be obtained. In addition, the carbon chain of the alkyl group in the side chain of the quaternary ammonium salt derivative that is a ligand for chloride ions can be changed according to the measurement conditions. At that time, the carbon number of the alkyl group in the side chain of the quaternary ammonium salt derivative is preferably smaller than the carbon number of the linker so as not to prevent the self-assembly during the immobilization of the ligand to the gold electrode. For example, in the case of this example, the length of the carbon chain of the linker is 10 carbons, so the number of carbons in the side chain is preferably 10 or less.

The block diagram which shows an example of the ion concentration measuring apparatus by this invention. It is a figure which shows the example which fix | immobilized the ligand for chlorine ions to the gold electrode, (a) is a figure which shows the example which fix | immobilized only the quaternary ammonium salt derivative which is a ligand for chlorine ions, (b) is a chloride ion Of an example in which a quaternary ammonium salt derivative that is a ligand for use and an alkanethiol having an amino group at the end coexist and immobilized. The block diagram which shows an example of the ion concentration measuring apparatus by this invention using a FET sensor. It is a figure which shows the structural example of the analysis element using the FET sensor used for the ion concentration measuring apparatus of this invention, (a) is sectional drawing, (b) is a top view. It is a figure showing the influence of the terminal residue of the alkanethiol coexisting with the ligand and the response speed to the chloride ion concentration, and (a) coexists the hydrophobic alkanethiol having a methyl group at the terminal. (B) is a diagram in the case where a hydrophilic alkanethiol having a hydroxyl group at the end coexists, (c) is a diagram in the case of coexisting a hydrophilic alkanethiol having an amino group at the end. The figure which shows the result of having measured the chlorine ion density | concentration using the quaternary ammonium salt derivative and the ion electrode which coexisted the alkanethiol which has an amino group at the terminal as a ligand. The block diagram which shows an example of the ion concentration measuring apparatus by this invention which formed the FET sensor and the reference electrode on the same plane. The figure which shows the influence which the length of the side chain of the quaternary ammonium salt used as a ligand of a chloride ion selective electrode has on the response time with respect to a chloride ion concentration. The figure which shows an example of the quaternary ammonium salt which is a ligand for chloride ions. The figure which shows the electric potential response with respect to the length of the side chain of a quaternary ammonium salt derivative which is a ligand of a chloride ion selective electrode, and a chloride ion concentration. The block diagram which shows an example of the ion concentration measuring apparatus by this invention.

Explanation of symbols

  101, 301, 701, 1101 ... measurement unit, 102, 302, 702, 1102 ... signal processing circuit, 103, 303, 703, 1103 ... data processing device, 104, 1104 ... potential difference measuring device, 105, 305, 1105 ... see Electrodes 106, 307, 706, 1106... Sample solution injector for supplying a sample solution having a measurement substance, 107, 308, 707, 1107... Measurement cell, 108, 314, 713, 1108. 711, 1109 ... quaternary ammonium salt derivatives as anion ligands, 110, 313, 712 ... alkanethiols having amino groups at the ends, 111, 311, 405, 710, 1110 ... gold electrodes, 304, 401, 704 ... Insulated gate field effect transistor, 306 ... Power supply, 309, 402 708 ... Source, 310,403,709 ... drain, 404 ... Gate insulator 406 ... insulated gate field effect transistor gates, 407 ... conductive wire, 705 ... pseudo reference electrode.

Claims (20)

A container into which a measurement solution containing a substance to be measured is introduced;
An ion selective electrode in contact with the measurement solution in the vessel;
A reference electrode in contact with the measurement solution in the container;
In an anion concentration measuring apparatus comprising a means for measuring an interface potential of the ion selective electrode,
A quaternary ammonium salt is immobilized on the ion selective electrode, one side chain of the quaternary ammonium salt is an alkanethiol group immobilized on the ion selective electrode, and the other three side chains. Is an alkyl chain, an anion concentration measuring device.   2. The anion concentration measuring apparatus according to claim 1, wherein the number of carbon atoms in the other three side chain alkyl chains of the quaternary ammonium salt is 1 or more and 20 or less.   2. The anion concentration measuring apparatus according to claim 1, wherein an alkanethiol having one end hydrophilic in addition to the quaternary ammonium salt is coexistingly immobilized on the ion selective electrode. Characteristic anion concentration measuring device.   4. The anion concentration measuring apparatus according to claim 3, wherein a hydrophilic group at the terminal of the alkanethiol coexisting with the quaternary ammonium salt is an amino group or a hydroxyl group.   4. The anion concentration measuring apparatus according to claim 3, wherein the alkanethiol carbon chain coexisting with the quaternary ammonium salt is longer than the alkanethiol carbon chain which is one side chain of the quaternary ammonium salt. Anion concentration measuring device characterized by being short. A container into which a measurement solution containing a substance to be measured is introduced;
A field effect transistor;
An ion-selective electrode that is connected to the gate of the field-effect transistor by a wiring and is in contact with the measurement solution in the container;
A reference electrode in contact with the measurement solution in the container;
A power supply for applying a voltage between the electrode and the reference electrode;
A detector for detecting the output of the field effect transistor;
A quaternary ammonium salt is immobilized on the ion selective electrode, one side chain of the quaternary ammonium salt is an alkanethiol group immobilized on the ion selective electrode, and the other three side chains. Is an alkyl chain, an anion concentration measuring device.   The anion concentration measuring apparatus according to claim 6, wherein the number of carbon atoms in the other three side chain alkyl chains of the quaternary ammonium salt is 1 or more and 20 or less.   8. The anion concentration measuring apparatus according to claim 7, wherein an alkanethiol having one hydrophilic end in addition to the quaternary ammonium salt coexists on the ion selective electrode. Characteristic anion concentration measuring device.   7. The anion concentration measuring apparatus according to claim 6, wherein the hydrophilic group at the terminal of the alkanethiol coexisting with the quaternary ammonium salt is an amino group or a hydroxyl group.   7. The anion concentration measuring apparatus according to claim 6, wherein the alkanethiol carbon chain coexisting with the quaternary ammonium salt is longer than the alkanethiol carbon chain which is one side chain of the quaternary ammonium salt. Anion concentration measuring device characterized by being short.   The anion concentration measuring apparatus according to claim 6, wherein the power source applies an AC voltage.   7. The anion concentration measuring apparatus according to claim 6, wherein an AC voltage having a frequency of 1 kHz or more is applied by the power source.   7. The anion concentration measuring apparatus according to claim 6, wherein the reference electrode is formed on the same substrate as the field effect transistor. Electrodes,
A quaternary ammonium salt immobilized on the electrode surface;
One side chain of the quaternary ammonium salt is an alkanethiol group, and the other three side chains are alkyl chains.   15. The anion analysis element according to claim 14, wherein the other three side chain alkyl chains of the quaternary ammonium salt have 1 to 20 carbon atoms.   15. The molecular element according to claim 14, wherein an alkanethiol having one end hydrophilic in addition to the quaternary ammonium salt is immobilized on the electrode together with the quaternary ammonium salt.   The analytical element according to claim 14, wherein the hydrophilic group at the terminal of the alkanethiol coexisting with the quaternary ammonium salt is an amino group or a hydroxyl group.   15. The analytical element according to claim 14, wherein the length of carbon chain of the alkanethiol coexisting with the quaternary ammonium salt is shorter than the carbon chain of alkanethiol which is one side chain of the quaternary ammonium salt. A characteristic analytical element.   15. The analytical element according to claim 14, wherein the electrode is formed on the same substrate as the reference electrode.   15. The analytical element according to claim 14, further comprising a field effect transistor, wherein the gate of the field effect transistor and the electrode are connected by a conductive wiring.

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