阅读说明：本技术 一种快速检测血浆硫酸吲哚酚的电化学方法 (Electrochemical method for rapidly detecting indoxyl sulfate in blood plasma ) 是由 张晓清 朱阳 丁敏 蒋梦丹 李彦茹 于 2021-08-31 设计创作，主要内容包括：本发明公开了一种快速检测血浆硫酸吲哚酚的电化学方法。本发明采用免修饰丝网印刷碳电极,结合示差脉冲伏安法可有效降低背景电流的优点,采用示差脉冲伏安法进行电化学检测,根据电化学响应信号与待测物浓度间的线性关系,实现血浆中硫酸吲哚酚的快速定量检测。本发明所用仪器设备小型,丝网印刷碳电极具有设计简单、价格低廉、一次性使用、样品用量少、可微型化等优点,所述电化学检测方法简便快速,具有较好的重复性、稳定性和准确度,能实现血浆中硫酸吲哚酚的快速定量检测,有助于了解硫酸吲哚酚在妊娠期糖尿病中的代谢情况,为该疾病及其并发症的发生机制、诊断、治疗及预后提供实验室依据。(The invention discloses an electrochemical method for rapidly detecting indoxyl sulfate in blood plasma. According to the invention, a modification-free screen printing carbon electrode is adopted, the advantage of background current reduction can be effectively realized by combining with the differential pulse voltammetry, electrochemical detection is carried out by adopting the differential pulse voltammetry, and the rapid quantitative detection of indoxyl sulfate in plasma is realized according to the linear relation between an electrochemical response signal and the concentration of a substance to be detected. The instrument and equipment used by the invention are small, the silk-screen printing carbon electrode has the advantages of simple design, low price, one-time use, small sample dosage, miniaturization and the like, the electrochemical detection method is simple, convenient and quick, has better repeatability, stability and accuracy, can realize the quick quantitative detection of indoxyl sulfate in blood plasma, is beneficial to understanding the metabolic condition of indoxyl sulfate in gestational diabetes, and provides laboratory basis for the occurrence mechanism, diagnosis, treatment and prognosis of the disease and complications thereof.)

1. An electrochemical method for rapidly detecting indoxyl sulfate in plasma adopts a modification-free Screen Printing Carbon Electrode (SPCE) and combines the advantage that a Differential Pulse Voltammetry (DPV) technology can effectively reduce background current, so that rapid quantitative detection of indoxyl sulfate in plasma is realized.

2. The electrochemical detection method of claim 1, wherein the SPCE comprises a polyethylene terephthalate (PET) substrate with electrodes printed thereon, an external insulating layer printed on the PET substrate, and a wire interface at one end of the substrate, wherein the substrate further comprises three electrodes printed thereon, namely a carbon working electrode, an Ag/AgCl reference electrode, and a carbon counter electrode, the three electrodes forming a circular working area, each electrode being connected to the interface through a wire printed under the insulating film.

3. An electrochemical method for detecting indoxyl sulfate in plasma according to claim 2, comprising the following specific steps:

1) adding 300 μ L of plasma and 900 μ L of acetonitrile into 2ml lep tube, vortexing for 1min, standing for 10min, centrifuging at 4 deg.C at 13300g for 10min, and collecting supernatant;

2) placing the supernatant obtained in the step 1) at 45 ℃ for drying by nitrogen;

3) re-dissolving the sample obtained in the step 2) by using 300 mu L of 0.10mol/L PBS (phosphate buffer solution) with pH2.0, and vortexing for 90 seconds to obtain a reaction mixed solution;

4) dropwise adding the reaction mixture obtained in the step 3) onto the SPCE, connecting the SPCE with an electrochemical workstation, and performing electrochemical detection by adopting DPV.

4. The electrochemical detection method of claim 3, wherein the PBS solution is prepared from 0.10mol/L sodium dihydrogen phosphate and disodium hydrogen phosphate solution.

5. The electrochemical detection method of claim 3, wherein the volume of the reaction mixture dropped on the electrode working area is 50 μ L.

6. The electrochemical detection method according to claim 3, wherein the electrode is soaked in 1.0% BSA solution for 1h, rinsed with ultrapure water, and dried at room temperature for use.

7. The electrochemical detection method of claim 3, wherein the electrochemical workstation parameters are set to: 0.1V of low potential, 1.0V of high potential, 150mV of pulse amplitude, 0.05s of pulse width and 0.6s of pulse period.

Technical Field

The invention belongs to the field of electrochemical detection, and mainly relates to an electrochemical method for rapidly detecting indoxyl sulfate in blood plasma.

Background

Gestational Diabetes (GDM) is the most common complication of pregnancy, meaning diabetes or impaired glucose tolerance that is first discovered or developed during pregnancy, with GDM severely affecting maternal and fetal health. GDM women are prone to a variety of complications, including gestational hypertension, cardiovascular disease, and preeclampsia, etc., and their offspring have an increased risk of complications, including giant infants, premature birth, shoulder dystocia, neonatal hypoglycemia, and neonatal admission to hospital, etc. In addition, GDM recurrence rates are as high as 48%, with 20% to 50% of GDM women diagnosed with type 2 diabetes within 10 years. However, the pathogenesis of GDM is not clear, and GDM not only causes serious obstetric and perinatal complications, but also leaves a long-term health risk in the future, bringing a huge economic burden to the healthcare system.

The intestinal flora and metabolites thereof have important connection with metabolic diseases. It has been found that the intestinal flora may play an important role in the pathogenesis of GDM. Indoxyl sulfate is a metabolite of tryptophan. Under the action of intestinal flora, tryptophan is converted into indole by tryptophanase, the indole is metabolized into indoxyl sulfate in the liver, and finally is discharged out of the body through the kidney. Indoxyl sulfate has renal and cardiovascular toxicity, and has great influence on the physiological functions of organisms. Animal studies have shown that chronic kidney disease rats exposed to indoxyl sulfate for a long period of time have reduced GLUT1 expression in the aorta, impaired insulin receptor and PPAR α/γ function, increased insulin resistance, and significantly increased blood glucose levels.

At present, the commonly used indoxyl sulfate detection methods are high performance liquid chromatography-fluorescence detection method, high performance liquid chromatography-mass spectrometry and the like. Since these methods require large-scale equipment and require high demands on operators, POCT is difficult to realize. Therefore, a new method for rapidly and simply detecting indoxyl sulfate is needed.

The electrochemical analysis method is to realize qualitative and quantitative analysis of the object to be detected according to the electrochemical property of the object to be detected in the solution and through the relationship between the parameters of current, potential, resistance and the like and the concentration of the object to be detected. The modification-free Screen Printing Carbon Electrode (SPCE) has the characteristics of simple manufacture, batch production, easy realization of miniaturized detection and the like, and is widely applied to the electrochemical analysis technology. At present, although there are reports of electrochemical methods for detecting indoxyl sulfate in plasma at home and abroad, there is no research report on the electrochemical methods for quantitatively determining the indoxyl sulfate in plasma by using SPCE as an electrode material and using Differential Pulse Voltammetry (DPV) as a detection method.

Disclosure of Invention

The invention aims to provide an electrochemical method for rapidly detecting indoxyl sulfate in blood plasma. The electrochemical method of the invention adopts SPCE as an electrode material, and combines the advantage that the DPV technology can effectively reduce the background current, thereby realizing the rapid quantitative detection of indoxyl sulfate in blood plasma.

The electrochemical method has the detection principle that: under the acidic condition, indoxyl sulfate is hydrolyzed to generate indoxyl, the enol structure on the pyrrole ring of the indoxyl is changed into a ketone structure, and at a certain potential, indolone undergoes dimerization or coupling reaction and is oxidized into indigo and indirubin. And detecting an electrochemical response signal generated by the plasma indoxyl sulfate by using an electrochemical workstation, wherein the oxidation peak current and the concentration of the plasma indoxyl sulfate are in a linear relationship in a certain range, so that the quantitative analysis of the plasma indoxyl sulfate is realized.

The SPCE comprises a polyethylene terephthalate (PET) substrate with a printed electrode, an external insulating film on the PET substrate and a lead interface on the substrate. The device is characterized in that three electrodes, namely a carbon working electrode, an Ag/AgCl reference electrode and a carbon counter electrode, are printed on the substrate. The three electrodes form a circular working area, and each electrode is connected with the interface through a lead printed under the insulating film. And soaking the SPCE in 1.0% BSA solution for 1h, washing the SPCE with ultrapure water, and airing the SPCE at room temperature for later use.

1. The technical scheme of the invention comprises the following specific steps:

1) adding 300 μ L of plasma and 900 μ L of acetonitrile into 2ml lep tube, vortexing for 1min, standing for 10min, centrifuging at 13300g at 4 deg.C for 10min, and collecting supernatant;

2) placing the supernatant obtained in the step 1) at 45 ℃ for drying by nitrogen;

3) redissolving the sample obtained in the step 2) by 300 mu L of 0.10mol/LpH 2.0.0 PBS solution, and vortexing for 90s to ensure full dissolution to obtain reaction mixed liquid;

4) dropwise adding 50 mu L of the reaction mixed liquid obtained in the step 3) to an SPCE working area, wherein the SPCE is connected with an electrochemical workstation. Adopting DPV to carry out electrochemical detection, and setting the parameters as follows: 0.1V of low potential, 1.0V of high potential, 150mV of pulse amplitude, 0.05s of pulse width and 0.6s of pulse period.

Preferably, the PBS solution is prepared from 0.10mol/L sodium dihydrogen phosphate and disodium hydrogen phosphate solution.

2. The electrochemical method for rapidly detecting the indoxyl sulfate in the blood plasma has the following beneficial effects:

1) the electrochemical detection method disclosed by the invention is used for quantitatively determining the indoxyl sulfate in the blood plasma by connecting the modification-free SPCE with an electrochemical workstation, and is simple and quick to operate.

2) The screen printing electrode used in the electrochemical detection method has low manufacturing cost and simple and quick manufacturing process, and can realize batch production. The SPCE is a disposable electrode, so that the time and energy loss of the traditional column electrode in grinding and polishing can be avoided, and the problem of experimental cross contamination possibly caused in the repeated use process of the column electrode can be effectively avoided.

3) The electrochemical detection method provided by the invention adopts a DPV technology, so that the background current can be effectively reduced, the electrode does not need to be modified, the detection result has better repeatability and stability, and the fast and accurate quantification can be carried out on the indoxyl sulfate in the plasma.

4) The electrochemical detection method disclosed by the invention can realize the content determination of indoxyl sulfate in plasma, is beneficial to understanding the metabolic condition of indoxyl sulfate in GDM, and provides laboratory basis for the occurrence mechanism, diagnosis, treatment and prognosis of GDM and complications thereof.

Drawings

FIG. 1 is a schematic diagram of the detection principle of the method of the present invention.

FIG. 2 is a CV curve and a DPV curve for testing indoxyl sulfate according to the present invention.

In FIG. A, the solid line a and the dotted line b are CV curves of a PBS buffer solution and a PBS solution containing 40.0. mu. mol/L indoxyl sulfate, respectively; in FIG. B, the solid line a and the dotted line B are DPV curves of the PBS buffer solution and the PBS solution containing 40.0. mu. mol/L indoxyl sulfate, respectively.

FIG. 3 is a graph of oxidation peak current versus pH of PBS buffer solution in accordance with the present invention.

■ in the figure represents the oxidation peak current of indoxyl sulfate; in the figure, a dotted line a is a curve chart of the influence of the pH value of the PBS solution on the peak current of an indoxyl sulfate oxidation peak II; in the figure, the solid line b is a graph showing the effect of the pH value of the PBS solution on the peak current of the indoxyl sulfate oxidation peak I.

FIG. 4 is a graph of oxidation peak current versus PBS buffer concentration according to the present invention.

■ in the figure represents the oxidation peak current of indoxyl sulfate.

FIG. 5 is a graph of oxidation peak current versus precipitant species and precipitant ratio for the present invention.

■ in panel B represents the oxidation peak current of indoxyl sulfate.

FIG. 6 is a standard curve of the effective oxidation peak current versus plasma indoxyl sulfate concentration according to the present invention.

■ in the figure represents the effective oxidation peak current of indoxyl sulfate; c represents the plasma indoxyl sulfate concentration.

FIG. 7 is a histogram of plasma indoxyl sulfate concentration profiles of the control group and the GDM group measured by the method of the present invention.

FIG. 8 is a ROC curve for the diagnosis of GDM by the detection of plasma indoxyl sulfate according to the method of the present invention.

Detailed Description

The electrochemical workstation of the present invention is exemplified by CHI852C electrochemical workstation, which is available from Shanghai Chenghua instruments, Inc.

Example 1: preparation of the Silk-Screen printing carbon electrode

The screen printing carbon electrode is formed by printing carbon paste, Ag/AgCl paste and insulating paste on a PET substrate in sequence. The method specifically comprises the following steps:

1) cleaning a PET substrate, printing carbon slurry on the PET substrate after drying, manufacturing a carbon working electrode and a carbon paste auxiliary electrode, and drying at normal temperature;

2) printing silver paste containing silver chloride on the PET substrate to prepare an Ag/AgCl reference electrode, and drying at normal temperature;

3) printing insulating paste on the PET substrate to cover the wires while avoiding the round working area;

4) the working electrode, the auxiliary electrode and the reference electrode form a circular working area, and each electrode is connected with the interface through a lead under the insulating film, and then is dried at 30-40 ℃ and stored for later use.

5) Before use, the electrode needs to be soaked in 1.0% BSA solution for 1h, washed clean with ultrapure water and dried at room temperature for later use.

Example 2: the electrochemical method for rapidly detecting indoxyl sulfate in plasma specifically comprises the following steps:

1) adding 300 μ L of plasma and 900 μ L of acetonitrile into 2ml lep tube, vortexing for 1min, standing for 10min, centrifuging at 4 deg.C at 13300g for 10min, and collecting supernatant;

2) placing the supernatant obtained in the step 1) at 45 ℃ for drying by nitrogen;

3) re-dissolving the sample obtained in the step 2) by using 300 mu L0.10mol/LpH2.0 PBS solution, and vortexing for 90s to obtain a reaction mixed solution;

4) dropwise adding 50 mu L of the reaction mixed liquid obtained in the step 3) on the SPCE, connecting the SPCE with an electrochemical workstation, and performing electrochemical detection by adopting a DPV technology. The parameters are set as follows: 0.1V of low potential, 1.0V of high potential, 150mV of pulse amplitude, 0.05s of pulse width and 0.6s of pulse period.

Preferably, the PBS solution is prepared from 0.10mol/L sodium dihydrogen phosphate and disodium hydrogen phosphate solution.

Example 3:

this example is a study of the electrochemical behavior of indoxyl sulfate. The electrochemical behavior of indoxyl sulfate on SPCE was characterized by CV, which is a 0.10mol/LpH 2.0.0 PBS solution with a sweep rate of 50mV/s, and is shown in FIG. 2A. 40.0. mu. mol/L indoxyl sulfate showed two irreversible oxidation peaks I and II at 0.485V and 0.862V, respectively, with no reduction peak (dot-dash line b). The peak potential of the oxidation peak I is lower than that of the oxidation peak II, so that the low oxidation potential is beneficial to avoiding noise interference in the detection process, and the peak current of the oxidation peak I is higher than that of the oxidation peak II. Comprehensively, the quantitative analysis of indoxyl sulfate is carried out by adopting the peak current value of the oxidation peak I. The electrochemical behavior of indoxyl sulfate was further characterized by DPV, which was detected as a 0.10mol/LpH 2.0.0 PBS solution, and the results are shown in FIG. 2B. Electrochemical oxidation of 40.0. mu. mol/L indoxyl sulfate on SPCE resulted in two distinct oxidation peaks I and II (dotted line b), which was consistent with CV characterization, indicating that indoxyl sulfate was oxidized stepwise on SPCE. Because of the sensitivity advantage of DPV on indoxyl sulfate detection, the DPV method is adopted to carry out quantitative analysis on indoxyl sulfate.

Example 4:

in this example, the effect of the pH value of the test solution on the electrochemical behavior of indoxyl sulfate was examined, and the results are shown in FIG. 3. The detection solution with the pH value of 1.0 is prepared from 0.10mol/LHCl solution, and the PBS solution with the pH value of 2.0-7.0 is prepared from NaH with different proportions₂PO₄And Na₂HPO₄And (4) solution preparation. The results show that the indoxyl sulfate oxidation peak II (dotted line a) is greatly influenced by the pH value, and the peak currents of the oxidation peak I (solid line b) and the oxidation peak II are highest when the pH value is 2.0. Therefore, the pH of the PBS solution was chosen to be 2.0.

Example 5:

this example examines the effect of the concentration of the test buffer solution on the indoxyl sulfate peak current, and the results are shown in FIG. 4. When the concentration of the PBS solution is 0.05-0.10 mol/L, the peak current of the indoxyl sulfate gradually increases along with the increase of the concentration of the PBS, and when the concentration of the PBS is more than 0.10mol/L, the peak current gradually decreases. Therefore, the concentration of the detection buffer solution was selected to be 0.10 mol/L.

Example 6:

this example examines the effect of precipitant species on indoxyl sulfate peak current and results are shown in FIG. 5A. The present study used protein precipitation as a pretreatment method for plasma samples to reduce interference from matrix effects. Under the same condition, methanol, acetone and acetonitrile are selected as precipitating agents to carry out protein precipitation. When acetonitrile is usedThe peak current of indoxyl sulfate obtained when protein precipitation was performed on plasma samples was maximal. Therefore, acetonitrile was chosen as the optimal precipitant for plasma sample pretreatment. The effect of the volume ratio of plasma sample to precipitant on the peak current was further examined and the results are shown in fig. 5B. When V is_{Blood plasma}∶V_AcetonitrileAt a ratio of 1: 3, the peak current is maximized, and if the acetonitrile ratio is further increased, the peak current is decreased. In summary, acetonitrile was chosen as the precipitating agent and sample pretreatment was performed with a volume ratio of plasma to acetonitrile of 1: 3.

Example 7:

this example examines the correlation between the effective oxidation peak current (oxidation peak current is indicated at ■) and the plasma indoxyl sulfate concentration for the electrochemical method described and the results are shown in FIG. 6. 30 mul of indoxyl sulfate standard solution with the concentration of 10.0-1600.0 mul/L is added into 270 mul of plasma matrix to prepare working solution with serial concentrations. The spiked plasma samples were protein precipitated, nitrogen-dried, and redissolved in 300 μ L of 0.10mol/LpH 2.0.0 PBS for use in optimal experimental conditions. In the concentration range of 1.0-160.0 mu mol/L, the peak current of the indoxyl sulfate and the concentration thereof have a good linear relation, and the regression equation is as follows: y 0.0369x +0.3460, R²0.9942(x represents the concentration of plasma indoxyl sulfate, y represents the difference between the peak current of spiked and untagged plasma indoxyl sulfate, i.e. the effective peak current), and the LOD is 0.2. mu. mol/L (S/N-3).

Example 8:

this example is a study of the precision of the electrochemical method of the present invention for measuring indoxyl sulfate in plasma. The low, medium and high concentration indoxyl sulfate standard solutions are added into the plasma matrix to prepare working solutions with final concentrations of 5.0 mu mol/L, 20.0 mu mol/L and 120.0 mu mol/L respectively. After sample pretreatment, the concentration of indoxyl sulfate in plasma was determined under optimal conditions. The working solutions of the respective concentrations were repeatedly measured 5 times a day and continuously measured 5 days a day, and the intra-day and inter-day Relative Standard Deviations (RSD) of the respective concentrations were calculated to examine the intra-day and inter-day precision of the method, and the results are shown in table 1. The standard deviation in the day is lower than 5.1%, and the standard deviation in the day is lower than 6.9%, which shows that the electrochemical detection method has better repeatability.

TABLE 1 precision

Example 9:

in this example, the electrochemical method of the present invention is examined for determining the recovery rate of indoxyl sulfate in plasma, and indoxyl sulfate standard solution is added to a plasma matrix to prepare a working solution of indoxyl sulfate with a low concentration of 5.0 μmol/L, a medium concentration of 20.0 μmol/L, and a high concentration of 120.0 μmol/L, and each concentration is measured in parallel for 5 times to perform a recovery rate experiment. The relative recovery rate (indoxyl sulfate concentration in plasma measured after adding standard-indoxyl sulfate concentration in plasma measured before adding standard)/indoxyl sulfate standard concentration added x 100.0%, the results are shown in table 2. The average recovery rate of indoxyl sulfate in blood plasma is 96.1-106.9%, and the relative standard deviation is less than or equal to 7.1%, which shows that the electrochemical method has better accuracy.

TABLE 2 recovery

Example 10:

this example is a study of the anti-interference ability of the electrochemical method of the present invention for measuring indoxyl sulfate in plasma. The interference test, which determines the concentration of indoxyl sulfate (X) in a plasma matrix without added interfering substances, was carried out according to the guidelines established by the American society for Clinical and Laboratory Standards Institute (CLSI) (EP7-A2)_C) And indoxyl sulfate concentration after addition of interfering substances (X)_T). Interference value is (X)_T-X_C) Indicating that a plurality of interference values are lower than 1.96S (namely 95% credibility), and indicating that no significant interference exists, and indicating N; if the interference value exceeds 1.96S, the interference is marked and is represented by I.

Bilirubin and hemoglobin are common endogenous interferents in blood plasma. Furthermore, the structure of indolpropanoic acid is similar to indoxyl sulfate. Therefore, the study examined the interference of bilirubin, hemoglobin, and indolpropionic acid on the results of indoxyl sulfate detection. Different concentrations of the interferent were added to plasma samples containing 20.0. mu. mol/L indoxyl sulfate, and the indoxyl sulfate concentration in the plasma samples before and after the addition of the interferent was measured, and the results are shown in tables 3 and 4. The bilirubin concentration is lower than 30.79 mu mol/L, the hemoglobin concentration is lower than 2.06g/L or the indole propionic acid concentration is lower than 52.85 mu mol/L, so that the detection of the indoxyl sulfate in the blood plasma cannot be interfered. Under normal conditions, the bilirubin concentration in human blood is lower than 17.10 mu mol/L, and the interference concentration of bilirubin is obviously higher than a normal value, namely the bilirubin at a normal concentration in vivo does not cause interference to a detection result. Normal plasma only contains trace hemoglobin, the concentration of the hemoglobin is less than 10.0mg/L, and the interference concentration of the hemoglobin, namely 2.06g/L, is obviously greater than the normal value. However, when hemolysis occurs, red blood cells release hemoglobin into the plasma. Therefore, severe hemolysis should be avoided at the time of sample collection. The content of indolopropionic acid in human body is lower than 0.4 mu mol/L, and as can be seen from Table 4, the interference concentration is significantly higher than the actual concentration in plasma. Therefore, the electrochemical method has good anti-interference capability.

TABLE 3 interference of bilirubin and hemoglobin on plasma indoxyl sulfate detection

TABLE 4 interference of indolpropanoic acid on detection of indoxyl sulfate in plasma

Example 11:

this example is a study of the electrochemical method used to detect indoxyl sulfate in the plasma of pregnant women in the control and GDM groups. The concentration of indoxyl sulfate in the plasma of pregnant women in the GDM group and the control group was measured by an established electrochemical method, and the results are shown in Table 5. The average concentration of indoxyl sulfate in the plasma of pregnant women in the GDM group is 13.70 mu mol/L, which is obviously higher than that of indoxyl sulfate in the plasma of pregnant women in the control group, and the difference has statistical significance (p is less than 0.05). The distribution of the indoxyl sulfate concentration in the plasma of pregnant women in the control group and the GDM group is shown in figure 7, which indicates that the metabolic disorder of indoxyl sulfate exists in the GDM pregnant women. In conclusion, the electrochemical method can be used for detecting indoxyl sulfate in clinical plasma samples.

TABLE 5 plasma indoxyl sulfate concentrations in GDM and control groups

Example 12:

this example is a study of the diagnostic efficacy of plasma indoxyl sulfate on GDM. The ROC curve analysis is a comprehensive and accurate diagnostic test evaluation tool and can objectively reveal the diagnostic capability of the diagnostic method on diseases. The invention adopts ROC curve to analyze the diagnosis efficiency of indoxyl sulfate on GDM and searches the optimal diagnosis threshold value. The results show that AUC is 0.873, Cut-off value is 10.61 mu mol/L, sensitivity is 70.0%, specificity is 100.0%, and as shown in FIG. 8, indoxyl sulfate in the invention has better diagnostic efficacy on GDM.