1. A preparation method of a carbon-based electrochemical sensor for detecting heavy metal lead ions is characterized by comprising the following steps:

1) pretreating hydrophobic carbon paper, and then carrying out electrodeposition reduction on graphene oxide by using a cyclic voltammetry method to obtain a CP/rGO electrode;

2) and (3) dripping dsDNA solution on the surface of the CP/rGO electrode, and drying to obtain the CP/rGO/DNA carbon-based electrochemical sensor.

2. The method for preparing a carbon-based electrochemical sensor for detecting heavy metal lead ions according to claim 1, wherein in the step 1), the pretreatment process of the hydrophobic carbon paper comprises the following steps: and (3) ultrasonically cleaning the hydrophobic carbon paper by using ethanol and water in sequence, and sealing a non-deposition area of the hydrophobic carbon paper by using insulating glue after drying.

3. The method for preparing the carbon-based electrochemical sensor for detecting the heavy metal lead ions according to claim 1, wherein in the step 1), the process of electrodepositing and reducing the graphene oxide by using cyclic voltammetry comprises the following steps: and immersing the pretreated hydrophobic carbon paper into the graphene oxide suspension, carrying out electrodeposition reduction on the graphene oxide by using cyclic voltammetry, washing out unstable graphene oxide adhered to the surface of the hydrophobic carbon paper, and drying.

4. The preparation method of the carbon-based electrochemical sensor for detecting the heavy metal lead ions as claimed in claim 3, wherein during the electrodeposition process, the scanning range is-0.96V to 0.78V, the scanning speed is 0.05V/s to 0.15V/s, and the scanning is carried out for 4-6 circles.

5. The method for preparing the carbon-based electrochemical sensor for detecting the lead ions in the heavy metal according to claim 3, wherein the graphene oxide suspension is prepared by the following steps: adding graphene oxide into a phosphate buffer solution, and then carrying out ultrasonic dispersion for 1-2h to obtain a uniform suspension of 0.4-0.6mg/mL, namely the graphene oxide suspension.

6. The method as claimed in claim 1, wherein in step 2), the concentration of the dsDNA solution is 80-100 μ g/mL, and the drying is infrared drying.

7. A carbon-based electrochemical sensor for detecting heavy metal lead ions, which is prepared by the method of any one of claims 1 to 6.

8. Use of a carbon-based electrochemical sensor according to claim 7 for detecting the concentration of heavy metal lead ions in an aqueous environment.

9. A method for detecting the concentration of heavy metal lead ions in an aqueous environment, which is based on the carbon-based electrochemical sensor according to claim 7, and is characterized in that the method comprises the following steps: a three-electrode system is used, a carbon-based electrochemical sensor is used as a working electrode, a saturated calomel electrode is used as a reference electrode, a platinum sheet is used as a counter electrode, and lead ions in a water environment are detected by adopting a differential pulse anodic stripping voltammetry.

10. The method for detecting the concentration of the heavy metal lead ions in the water environment according to claim 9, wherein a series of lead ion standard buffers with different concentrations are deposited at a constant potential under a stirring condition, and then are dissolved in a blank buffer solution without the lead ions to obtain an anode dissolution peak current, a working curve is drawn according to the size of the anode dissolution peak current and the lead ion concentration in the lead ion standard buffer solution, and the lead ions in the water environment are detected by using the drawn working curve.

Background

Heavy metal ion pollution has attracted wide attention in the world nowadays, and particularly, lead ions and lead-containing materials are widely applied to the manufacture of various daily life and industrial production articles, such as pigments, lead storage batteries, coal combustion and the like. The lead content in drinking water is not more than 0.01mg/L according to the provisions of sanitary Standard for Drinking Water in China, which is consistent with the provisions of the world health organization. Lead not only causes serious pollution to the environment, but also damages human health, especially children. The united nations foundation of children, in combination with Pure Earth organization, has noted in the report issued at 7 months 2020 that about one third of children (up to eight billion worldwide) have blood lead levels up to or exceeding 5 μ g/dL, which can lead to mental retardation, behavioral, learning disabilities, and irreversible damage to the brain and nervous system. Therefore, the research on the detection and control of the lead ions with high sensitivity and high selectivity has important research significance and application value.

At present, lead ion analysis and detection methods mainly comprise a spectrometry method, a colorimetry method, a mass spectrometry method and the like, but all of the methods have certain defects, such as the need of professional instruments, a complex sample pretreatment process, a long analysis period and the like. The electrochemical method has the advantages of lower cost, good portability, good stability, short response time and the like, and is suitable for real-time detection. Meanwhile, biomolecules based on DNA and DNAzyme are suitable for detection of heavy metal ions because they have good biodegradability and high selectivity for heavy metal ions. However, how to increase the detection signal and sensitivity becomes a bottleneck in the electrochemical method for detecting lead ions.

Disclosure of Invention

The invention aims to provide a carbon-based electrochemical sensor for detecting heavy metal lead ions and application thereof. The method has high sensitivity and high selectivity to lead ions, and is simple to operate.

The purpose of the invention can be realized by the following technical scheme:

a preparation method of a carbon-based electrochemical sensor for detecting heavy metal lead ions comprises the following steps:

1) pretreating hydrophobic carbon paper, and then carrying out electrodeposition reduction on graphene oxide by using a cyclic voltammetry method to obtain a CP/rGO electrode;

2) and (3) dripping dsDNA solution on the surface of the CP/rGO electrode, and drying to obtain the CP/rGO/DNA carbon-based electrochemical sensor.

Wherein, CP is hydrophobic carbon paper, rGO is reduced graphene oxide.

Further, in step 1), the pretreatment process of the hydrophobic carbon paper comprises: and (3) ultrasonically cleaning the hydrophobic carbon paper by using ethanol and water in sequence (respectively cleaning for 5min), and sealing a non-deposition area of the hydrophobic carbon paper by using insulating glue after drying.

Further, in the step 1), the process of electrodepositing and reducing the graphene oxide by using cyclic voltammetry comprises the following steps: and immersing the pretreated hydrophobic carbon paper into the graphene oxide suspension, carrying out electrodeposition reduction on the graphene oxide by using cyclic voltammetry, washing out unstable graphene oxide adhered to the surface of the hydrophobic carbon paper, and drying.

Furthermore, in the electrodeposition process, the scanning range is-0.96V to 0.78V, the scanning speed is 0.05V/s to 0.15V/s, and the scanning is carried out for 4 to 6 circles.

Further, the preparation process of the graphene oxide suspension comprises the following steps: adding graphene oxide into Phosphate Buffer Solution (PBS), and then carrying out ultrasonic dispersion for 1-2h to obtain a uniform suspension of 0.4-0.6mg/mL, namely the graphene oxide suspension.

Further, in the step 2), the concentration of the dsDNA solution is 80-100 mug/mL, and the drying is infrared drying. The dsDNA solution is preferably an aqueous solution of dsDNA.

A carbon-based electrochemical sensor for detecting heavy metal lead ions is prepared by the method.

The application of the carbon-based electrochemical sensor is used for detecting the concentration of heavy metal lead ions in a water environment.

A method for detecting the concentration of heavy metal lead ions in a water environment is based on the carbon-based electrochemical sensor, and the method comprises the following steps: a three-electrode system is used, a carbon-based electrochemical sensor is used as a working electrode, a saturated calomel electrode is used as a reference electrode, a platinum sheet is used as a counter electrode, and lead ions in a water environment are detected by adopting a Differential Pulse Anodic Stripping Voltammetry (DPASV).

Further, a series of lead ion standard buffers with different concentrations are deposited at a constant potential under the stirring condition (the deposition potential is-0.1V, the deposition time is 360s), then the lead ions are dissolved out in a blank buffer solution without containing the lead ions (the scanning range of the dissolution potential is-0.8V to 0V), the anode dissolution peak current is obtained, a working curve is drawn according to the size of the anode dissolution peak current and the lead ion concentration in the lead ion standard buffer solution, and the lead ions in the water environment are detected by using the drawn working curve.

The method for selectively measuring the carbon-based electrochemical sensor comprises the following steps: adding other solutions containing interfering ions into a PBS buffer solution containing lead ions, carrying out DPASV measurement by adopting the same method and under the same condition, researching the change of the peak potential and the peak current of the anode dissolution characteristic of the lead ions, and investigating the selection performance of the simple carbon-based electrochemical sensor. Wherein the interference ions are nickel ions, cobalt ions, zinc ions, copper ions, cadmium ions, magnesium ions, calcium ions, iron ions or chromium ions.

The differential pulse anodic stripping voltammetry reduces background current and improves sensitivity by adding short pulses into step wave reference potential and taking the current difference before and after the pulses as signals. The stripping peak potentials of metal ions in the anodic stripping voltammetry are different, and the stripping peak current is in direct proportion to the ion concentration, so that an effective and rapid platform is provided for real-time detection of a target object.

It was found that the use of ordinary dsDNA specifically adsorbs lead ions to enhance signal without the need to use special DNA sequences, thus reducing modification steps and cost. Therefore, a key factor for increasing the detection signal and sensitivity is how to achieve high-flux, high-stability loading of the DNA molecules on the electrode substrate. According to the invention, the graphene oxide (rGO) is electrodeposited and reduced on the surface of hydrophobic carbon paper by adopting a cyclic voltammetry method so as to improve the conductivity of the carbon paper and promote the subsequent DNA loading, and then the DNA is stably assembled on a CP/rGO electrode through pi-pi accumulation and hydrophobic action between the DNA and the rGO, so that the CP/rGO/DNA carbon-based electrochemical sensor is prepared. The invention not only utilizes the characteristic of specific combination between DNA and lead ions, improves the sensitivity and selectivity of the sensor, but also utilizes pi-pi accumulation and hydrophobic effect between rGO and DNA to effectively increase the loading capacity of the DNA. During detection, the anode stripping peak current of a Differential Pulse Anode Stripping Voltammetry (DPASV) is used as a quantitative detection basis, the detection sensitivity can be effectively enhanced, the detection limit is as low as 1pM, the detection method is rapid, simple and convenient, and the method can be used for detection and analysis of trace heavy metal lead ions. Therefore, the invention combines the differential pulse anodic stripping voltammetry, rGO and dsDNA to construct the carbon-based electrochemical sensor for detecting lead ions, thereby obtaining good detection sensitivity and selectivity.

Compared with the prior art, the invention has the following characteristics:

1) the dsDNA is used as an identification element, the loading capacity of the DNA is increased by utilizing pi-pi accumulation and hydrophobic effect between rGO and the DNA, the DNA is directly modified by a dripping method, the operation process is simple, additional treatment on electrodes is not needed, specific combination on target lead ions can be realized in the detection process, the selectivity and the sensitivity of the sensor are effectively improved, the detection limit is as low as 1pM, and the dsDNA can be used for real-time analysis and qualitative and quantitative detection of water samples in the environment.

2) The carbon paper is used as a substrate material, is a three-dimensional net material formed by staggered arrangement of carbon fibers, can provide stable load performance, and can be used for preparing disposable electrodes with low cost and simple construction.

3) A differential pulse anodic stripping voltammetry is introduced, a short pulse is added into a step wave reference potential, and a current difference value before and after the pulse is used as a signal, so that background current is reduced, and the sensitivity is improved compared with the traditional anodic stripping voltammetry.

Detailed Description

The present invention will be described in detail with reference to specific examples. The present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the scope of the present invention is not limited to the following embodiments.

The invention provides a preparation method of a carbon-based electrochemical sensor for detecting heavy metal lead ions, which comprises the following steps:

1) pretreating hydrophobic carbon paper, and then carrying out electrodeposition reduction on graphene oxide by using a cyclic voltammetry method to obtain a CP/rGO electrode;

2) and (3) dripping dsDNA solution on the surface of the CP/rGO electrode, and drying to obtain the CP/rGO/DNA carbon-based electrochemical sensor.

In the step 1), the pretreatment process of the hydrophobic carbon paper comprises the following steps: and (3) ultrasonically cleaning the hydrophobic carbon paper by using ethanol and water in sequence, and sealing a non-deposition area of the hydrophobic carbon paper by using insulating glue after drying. The process of utilizing cyclic voltammetry to electrodeposit and reduce the graphene oxide comprises the following steps: and immersing the pretreated hydrophobic carbon paper into the graphene oxide suspension, carrying out electrodeposition reduction on the graphene oxide by using cyclic voltammetry, washing out unstable graphene oxide adhered to the surface of the hydrophobic carbon paper, and drying. In the electrodeposition process, the scanning range is-0.96V to 0.78V, the scanning speed is 0.05V/s to 0.15V/s, and the scanning is carried out for 4-6 circles. The preparation process of the graphene oxide suspension liquid comprises the following steps: adding graphene oxide into a phosphate buffer solution, and then carrying out ultrasonic dispersion for 1-2h to obtain a uniform suspension of 0.4-0.6 mg/mL.

In the step 2), the concentration of the dsDNA solution is 80-100 mug/mL, and the drying is infrared drying.

The invention also provides a carbon-based electrochemical sensor for detecting the heavy metal lead ions, which is prepared by adopting the method. The carbon-based electrochemical sensor is used for detecting the concentration of heavy metal lead ions in a water environment.

The invention also provides a method for detecting the concentration of heavy metal lead ions in the water environment, which is based on the carbon-based electrochemical sensor and comprises the following steps: a three-electrode system is used, a carbon-based electrochemical sensor is used as a working electrode, a saturated calomel electrode is used as a reference electrode, a platinum sheet is used as a counter electrode, and lead ions in a water environment are detected by adopting a differential pulse anodic stripping voltammetry. Depositing a series of lead ion standard buffer solutions with different concentrations at a constant potential under the stirring condition, dissolving in a lead ion-free blank buffer solution to obtain an anode dissolution peak current, drawing a working curve according to the magnitude of the anode dissolution peak current and the lead ion concentration in the lead ion standard buffer solution, and detecting the lead ions in the water environment by using the drawn working curve.

Example 1:

the preparation method of the carbon-based electrochemical sensor for detecting the heavy metal lead ions comprises the following steps:

(1) and (4) pretreating the carbon paper. And (3) ultrasonically cleaning hydrophobic carbon paper of 0.9cm multiplied by 1.7cm in absolute ethyl alcohol and deionized water for 5min in sequence, and drying to obtain a clean carbon paper surface. The other part of the carbon paper was sealed with an insulating paste, leaving a conductive area of 2mm × 2mm, to obtain a CP electrode.

(2) Preparation of CP/rGO electrodes. Graphene Oxide (GO) was ultrasonically dispersed in 0.1mol/L PBS buffer solution at pH 9.18 for 1.5h to form a homogeneous suspension at a concentration of 0.5 mg/mL. And immersing the obtained CP electrode into the GO suspension, and electrodepositing rGO by using Cyclic Voltammetry (CV), wherein the scanning range is-0.96-0.78V, the scanning speed is 0.1V/s, and the scanning is carried out for 5 circles. And after scanning is finished, immersing the electrode into deionized water to wash off unstable GO adhered to the surface, and then placing the electrode in air for drying to obtain the CP/rGO electrode.

(3) Preparation of CP/rGO/DNA electrodes. And dripping 2.5 mu L of calf thymus dsDNA solution which is prepared by deionized water and is 90 mu g/mL for three times on the surface of the electrode, wherein the total amount is 7.5 mu L, and drying to obtain the CP/rGO/DNA carbon-based electrochemical sensor.

The electrochemical properties of the CP/rGO/DNA electrochemical sensor were characterized using the CHI6043E workstation. The prepared CP/rGO/DNA electrochemical sensor is taken as a working electrode, a saturated calomel electrode is taken as a reference electrode, a platinum wire electrode is taken as a counter electrode, and the concentration of the metal ions in the electrochemical sensor is 5mmol/L[Fe(CN)₆]^4-/[Fe(CN)₆]^3-The AC impedance (EIS) measurement was carried out in a mixed solution (containing 0.1mol/L KCl). The results show that the electrode resistance values decreased significantly after rGO deposition, indicating that the electrochemical performance of the electrode was significantly improved because rGO has good charge transfer capability. After DNA continues to be loaded, the resistance of the CP/rGO/DNA electrode is improved because the double-helix structure of the DNA has larger resistance, which is not beneficial to charge transfer, and meanwhile, the DNA has partial negative electricity and can react with [ Fe (CN) ]₆]^4-/[Fe(CN)₆]^3-The redox couple produces repulsion. The results of EIS indicate that both rGO and DNA were successfully loaded.

Example 2:

electrochemical detection of lead ions was performed using the CP/rGO/DNA electrochemical sensor prepared in example 1.

The lead ions are detected by adopting a Differential Pulse Anodic Stripping Voltammetry (DPASV), a three-electrode system is used, a CP/rGO/DNA electrochemical sensor is used as a working electrode, a saturated calomel electrode is used as a reference electrode, and a platinum sheet is used as a counter electrode. Firstly, depositing a series of lead ion standard buffer solutions with different concentrations at constant potential under the stirring condition, wherein the deposition potential is-0.1V, and the deposition time is 360 s. Then dissolving in a blank buffer solution without lead ions, wherein the scanning range of dissolving potential is-0.8-0V, and obtaining the anode dissolving peak current. When the lead ion concentration increases, the peak current value also increases accordingly, because the amount of lead ions deposited to the electrode surface increases. Drawing a working curve according to the size of the anode dissolution peak current and the lead ion concentration in the lead ion standard buffer solution, namely performing quantitative detection on the lead ions, wherein the detection limit is as low as 1pM, and the linear ranges are 1pM-0.05nM and 0.05nM-0.1nM respectively.

Example 3:

the CP/rGO/DNA electrochemical sensor prepared in example 1 was used for selective and reproducible detection.

The lead ions are detected by adopting a Differential Pulse Anodic Stripping Voltammetry (DPASV), a three-electrode system is used, a CP/rGO/DNA electrochemical sensor is used as a working electrode, a saturated calomel electrode is used as a reference electrode, and a platinum sheet is used as a counter electrode. Firstly, under the stirring condition, constant potential deposition is carried out on 10nmol/L lead ion standard buffer solution, the deposition potential is-0.1V, and the deposition time is 360 s. Then dissolving in a blank buffer solution without lead ions, wherein the scanning range of dissolving potential is-0.8-0V, and obtaining the anode dissolving peak current. The same method is adopted in the lead ion solution, the test is repeated for 10 times under the same condition, and the RSD of the peak current is 6.2 percent, which shows that the electrochemical sensor can still keep better repeatability under the condition of multiple measurements. Adding other solutions containing interfering ions into the lead ion solution, performing DPASV measurement by the same method under the same conditions, and studying changes of characteristic peak potential and peak current of lead ion anode dissolution. The interference ions are nickel ions, cobalt ions, zinc ions, copper ions, cadmium ions, magnesium ions, calcium ions, iron ions and chromium ions. When the concentration of the interference ions is 1 time and 10 times of that of the lead ions, the deviation of the peak current is 7.7 percent and 3.6 percent respectively, the position of the peak is not obviously changed, and other dissolution peaks do not appear, so that the electrochemical sensor has good anti-interference capability and selectivity.

The embodiments described above are described to facilitate an understanding and use of the invention by those skilled in the art. It will be readily apparent to those skilled in the art that various modifications to these embodiments may be made, and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above embodiments, and those skilled in the art should make improvements and modifications within the scope of the present invention based on the disclosure of the present invention.