CN114755277A - Biosensor and preparation method and application thereof - Google Patents

Biosensor and preparation method and application thereof Download PDF

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CN114755277A
CN114755277A CN202210212031.8A CN202210212031A CN114755277A CN 114755277 A CN114755277 A CN 114755277A CN 202210212031 A CN202210212031 A CN 202210212031A CN 114755277 A CN114755277 A CN 114755277A
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biosensor
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antibody
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孙文文
徐沁晨
孙继唯
林祥德
潘洪志
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Shanghai University of Medicine and Health Sciences
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Abstract

The invention belongs to the technical field of biosensors, and particularly relates to a biosensor and a preparation method and application thereof. The preparation method of the biosensor comprises the following steps: s1, preparing a carbon dot-multi-walled carbon nanotube composite material as an optical active material; s2, preparing silver-coated gold core-shell nano sol as an active substrate nano material; s3, connecting the aptamer and the active substrate nano material to form a bioconjugate as an amplifier; s4, assembling the antibody-aptamer-based cathode sandwich biosensor using the photoactive material and the amplifier. The invention increases the stability and optical adsorption performance of the photoactive material, and has excellent stability, higher conductivity and faster electron transfer capability. The stability of the active substrate nano material is increased, and the signal amplification capacity of the active substrate nano material is enhanced.

Description

Biosensor and preparation method and application thereof
Technical Field
The invention belongs to the technical field of biosensors, and particularly relates to a biosensor and a preparation method and application thereof.
Background
Progesterone (P4) is a small amount of C21 steroid hormone secreted by the corpus luteum, and has a diagnostic effect on amenorrhea or amenorrhea such as threatened abortion, habitual abortion, and the like. The traditional progesterone detection method comprises a liquid chromatography, a gas chromatography-mass spectrometry combined technology, an enzyme linked immunosorbent assay technology, a direct electrochemical method and the like. These detection methods either require precise instruments or the detection procedure is cumbersome.
The electrochemical aptamer biosensor becomes a hot point for researching the progesterone sensor due to the advantages of simple operation, high sensitivity, quick response and the like. An electrochemical aptamer biosensor is a bioanalytical detection device developed by using an aptamer (a specific DNA or RNA fragment) as a biological recognition element and utilizing the characteristic that the aptamer specifically binds to a target such as a protein or a small molecular substance, and the electrochemical aptamer biosensor detects a target substance by using changes in an electric signal before and after the specific recognition of the target at different concentrations.
The electrochemical aptamer biosensor is divided into a direct method, a competition method and a sandwich method, wherein the sandwich method is that a biological recognition element is immobilized on the surface of an electrode, and after a target object and the biological recognition element are subjected to biological recognition, the target object can be further connected with another recognition element to construct a sandwich model. The model is beneficial to introducing biological enzyme, electroactive substances, nano composite materials and the like to a sensing interface, and the sensitivity of the sensor is improved.
In the prior art, biosensing for sandwich methodsThe signal amplification strategy based on optically active nanomaterials established a visible light driven sandwich-type Photoelectrochemical (PEC) bioassay for the highly sensitive and selective detection of progesterone. Carbon dot-graphene oxide (CDs-GO) composite material is used as an optical active material, and aptamer-gold-copper oxide-cuprous oxide (aptamer-Au-CuO-Cu)2O) bioconjugates as PEC amplifiers, antibody-aptamer based cathode sandwich PEC biosensors for selective detection of P4. Referring to fig. 1, a material having photoactivity was first formed on a bare Glassy Carbon Electrode (GCE) using a carbon dot corresponding to a good cathode photocurrent in combination with a graphene oxide (CDs-GO) composite material, on which a progesterone antibody (Ab) was immobilized. At the same time, Au-CuO-Cu is prepared2O makes the crystal nano particles uniformly wrapped in CuO-Cu2O-surface, to which a high affinity truncated progesterone Aptamer (Aptamer-SH) is immobilized to form a bioconjugate. When progesterone is detected, progesterone molecules (P4) are connected with antibodies and aptamers and can interact with each other to amplify cathode photocurrent signals of CDs-GO modified electrodes, and finally the aptamers-Au-CuO-Cu are obtained2O/P4/Ab/CDs-GO structured biosensor.
However, the CDs-GO composite material adopted by the sandwich method biosensor is attached to the surface of an electrode, and has general signal amplification capability; CuO-Cu2O material is easily oxidized in humid air, Cu2O will oxidize to CuO, affecting the accuracy of the final sensor detection and the ability to amplify the signal.
In addition, in the prior art, an aptamer sensor based on SERS (surface enhanced Raman scattering) technology is adopted to detect estradiol and progesterone, and the characteristic that Au @ Ag NPs have strong SERS activity is utilized to realize the detection of trace samples. AuNPs have the advantages of simple and convenient preparation, stability, good dispersibility, good morphology controllability, good biocompatibility and the like, but have weaker Raman enhancement effect. The Raman enhancement effect of AgNPs is 103 times of that of AuNPs, but the chemical activity of Ag is stronger than that of Au, and the Ag is active and is difficult to control in the preparation process, so that the grain size of the obtained AgNPs is not uniform, and the stability is poor. Therefore, referring to fig. 2, in order to obtain an ideal SERS-active substrate, Au @ Ag NPs were synthesized combining the advantages of Au NPs and Ag NPs.
However, the reaction time is long in the manner of using Au @ Ag NPs as the enhanced substrate, and the reaction process of the progestogen and the aptamer can be completely carried out within 30 min.
Disclosure of Invention
The invention aims to solve the technical problems of poor detection stability or long reaction time of the existing electrochemical aptamer biosensor for progesterone detection, and aims to provide a biosensor and a preparation method and application thereof.
A biosensor comprises an electrode having an optically active material; an antibody immobilized on the photoactive material; a bioconjugate;
the photoactive material is a carbon dot-multiwalled carbon nanotube (CDs-NPCGO) composite material;
the bioconjugates include an aptamer and a silver-coated gold core-shell nanosol (Au @ AgNPs) linked to each other.
A method of making a biosensor, comprising:
s1, preparing a carbon dot-multi-walled carbon nanotube composite material as an optical active material;
s2, preparing silver-coated gold core-shell nano sol as an active substrate nano material;
s3, connecting an aptamer and the active substrate nano material to form a bioconjugate as an amplifier;
s4, assembling the antibody-aptamer-based cathode sandwich biosensor by using the photoactive material and the amplifier.
Preferably, in step S1, the carbon dot-multiwall carbon nanotube composite material is prepared as follows:
s101, obtaining a ZIF-8@ GO nano composite material, heating the ZIF-8@ GO nano composite material, and collecting black powder after pyrolysis;
s102, adding the black powder into a hydrochloric acid solution for reaction, then collecting a product through centrifugation, washing and drying overnight to obtain nanoporous carbon (NPCGO);
s103, dispersing the nano porous carbon in ultrapure water, ultrasonically stirring to obtain a nano porous carbon suspension, and directly injecting the nano porous carbon suspension into a carbon dot aqueous solution under ultrasonic stirring to prepare the carbon dot-multiwalled carbon nanotube composite material.
As a preferred scheme, in the step S101, a ZIF-8@ GO nano composite material is obtained, the ZIF-8@ GO nano composite material is heated to 750-850 ℃ at the speed of 5-20 ℃/min, and the temperature is measured in nitrogen (N)2) The black powder is pyrolyzed for 1.5 to 2.5 hours at the temperature of between 750 and 850 ℃ under the protection of the (A), and the black powder is collected after being cooled to the room temperature.
As a preferred scheme, in step S101, a ZIF-8@ GO nanocomposite is obtained, the ZIF-8@ GO nanocomposite is heated to 800 ℃ at a rate of 5 ℃/min, pyrolyzed at 800 ℃ for 2 hours under the protection of nitrogen gas, cooled to room temperature, and the obtained black powder is collected.
Preferably, in step S102, the black powder is added to a hydrochloric acid solution with a mass fraction of 3.5% to 10.5%, reacted for 20 hours to 30 hours with continuous stirring, and then the product is collected by centrifugation, washed with deionized water, and dried at 50 ℃ to 80 ℃ for 10 hours to 14 hours to obtain the nanoporous carbon.
Preferably, the black powder is added to a 10% hydrochloric acid solution by mass fraction, reacted for 24 hours with continuous stirring, and then the product is collected by centrifugation, washed with deionized water, and dried at 60 ℃ for 12 hours to obtain the nanoporous carbon in step S102.
Preferably, in step S103, 8mg to 12mg of the nanoporous carbon is dispersed in 4mL to 6mL of ultrapure water, and the resulting dispersion is ultrasonically stirred for 1.5 hours to 2.5 hours to obtain 1.4 mg/mL-1～3mg·mL-1The nano porous carbon suspension is directly injected into 1.4 mg/mL under ultrasonic stirring-1～3mg·mL-1And preparing the carbon dot-multi-walled carbon nanotube composite material in the carbon dot aqueous solution.
Preferably, in step S103, 10mg of the nanoporous carbon is dispersed in 5mL of ultrapure water, and the ultra-sonic agitation is performedStirring for 2 hours to obtain 2 mg/mL-1The nano porous carbon suspension is directly injected into 2 mg/mL under ultrasonic stirring-1The carbon dot-multi-walled carbon nanotube composite material is prepared in the carbon dot aqueous solution.
As a preferred scheme, in step S101, the ZIF-8@ GO nanocomposite is prepared in the following manner:
putting Graphene Oxide (GO) into 2-methylimidazole, adding zinc nitrate hexahydrate (Zn (NO) after ultrasonic stirring3)2·6H2O), centrifuging, washing and drying the generated mixture at room temperature, and collecting the product, namely the ZIF-8@ GO nano composite material.
Preferably, 1.5-2.5 mg of graphene oxide is put into 80-120 mL of 3-4 mol/L2-methylimidazole, ultrasonic stirring is carried out for 0.5-1.5 hours, then 7-9 mL of 3.5-4.5 mmol/L zinc nitrate hexahydrate is gradually dropped, the generated mixture is stirred for 0.5-1.5 hours at room temperature, then centrifugation is carried out, water washing is carried out for 2-4 times, drying is carried out for 10-14 hours at 50-70 ℃, and a product is collected, namely the ZIF-8@ GO nano composite material.
As a preferable scheme, 2mg of graphene oxide is put into 100mL of 3.5 mol/L2-methylimidazole, after the graphene oxide is ultrasonically stirred for 1 hour, 8mL of 4mmol/L zinc nitrate hexahydrate is gradually dropped, the generated mixture is stirred for 1 hour at room temperature, then the mixture is centrifuged, washed with water for 3 times, dried at 60 ℃ for 12 hours, and the product is collected, namely the ZIF-8@ GO nano composite material.
Preferably, in step S103, the carbon dot aqueous solution is prepared as follows:
dissolving citric acid in deionized water to obtain a citric acid aqueous solution, dropwise adding ethylenediamine under stirring to obtain a mixed solution, transferring the mixed solution into an autoclave, sealing the autoclave in a stainless steel tank, further heating the autoclave in an electric oven, naturally cooling a reactor to room temperature, collecting a reddish brown substance by a centrifugal machine, washing the reddish brown substance by absolute ethyl alcohol, drying the reddish brown substance in a drying oven to obtain carbon dots, and dissolving the carbon dots in water to obtain the carbon dot aqueous solution.
Preferably, 0.48 to 0.58g of citric acid is dissolved in 9 to 11mL of deionized water to obtain an aqueous citric acid solution, 150 to 185 μ L of ethylenediamine is gradually added dropwise under the stirring of a magnetic stirrer to obtain a mixed solution, the mixed solution is transferred to an autoclave with a polytetrafluoroethylene lining (teflon-lined), the autoclave is sealed in a stainless steel tank, the autoclave is further heated to 150 to 200 ℃ for 4.5 to 5.5 hours in an electric oven, after a reactor is naturally cooled to room temperature, a reddish brown substance is collected by a centrifuge, washed 2 to 4 times with absolute ethyl alcohol, and dried in a drying oven at 50 to 70 ℃ for 10 to 14 hours to obtain a carbon point.
As a preferable scheme, 0.53g of citric acid is dissolved in 10mL of deionized water to obtain an aqueous citric acid solution, 168 μ L of ethylenediamine is gradually added dropwise under the stirring of a magnetic stirrer to obtain a mixed solution, the mixed solution is transferred to a teflon-lined autoclave, sealed in a stainless steel can of the autoclave, further heated to 180 ℃ in an electric oven for 5 hours, after the reactor is naturally cooled to room temperature, a reddish brown substance is collected by a centrifuge, washed 3 times with absolute ethanol, and dried in a drying oven at 60 ℃ for 12 hours to obtain carbon dots.
Preferably, in step S2, the ag-coated au core-shell nano-sol is prepared as follows:
s201, adding tetrachloroauric acid (HAuCl)4) Boiling the solution, adding sodium citrate (stabilizer) into the vortex of the tetrachloroauric acid solution under stirring, changing the mixed solution from light yellow to purple, boiling and refluxing, stirring and cooling the purple solution of gold nanoparticles (Au NPs) to room temperature, and preparing the gold nanoparticles with preset concentration and gold core particle size;
s202, adding ultrapure water into a container, then adding the gold nanoparticles, and adding a stabilizer and a reducing agent to obtain a mixed solution;
s203, stirring the mixed solution at room temperature, transferring the mixed solution into a water bath for stirring, and then dropwise adding quantitative silver nitrate (AgNO)3) When the mixed liquid is used for the colorAnd continuously stirring after color stabilization, centrifuging the suspension, and washing with distilled water to obtain the silver-coated gold core-shell nano sol with the core-shell structure.
Preferably, the gold core particle size of the silver-coated gold core-shell nanosol is 21nm to 42nm, preferably 31nm, and the silver shell thickness is 5nm to 10nm, preferably 9 nm.
Preferably, in step S201, 19mL to 21mL of 0.9mmol/L to 1.1mmol/L tetrachloroauric acid solution is placed in a round bottom flask equipped with a condenser tube and boiled, 1.8mL to 2.2mL of 38.3mmol/L to 39.3mmol/L sodium citrate is added to the vortex of the tetrachloroauric acid solution with stirring for 6 to 10 times, the mixed solution turns from pale yellow to purple after 0.5 to 1 minute, and after boiling and refluxing for 15 to 30 minutes, the purple red solution of gold nanoparticles is stirred and cooled to room temperature.
Preferably, in step S201, 20mL of 1mmol/L tetrachloroauric acid solution is placed in a round-bottomed flask equipped with a condenser and boiled, 2mL of 38.8mmol/L sodium citrate is added to the vortex of the tetrachloroauric acid solution under 8 times of stirring at 2000rpm, the mixed solution changes from pale yellow to purple after 1 minute, and after boiling under reflux for 20 minutes, the purple red solution of gold nanoparticles is stirred and cooled to room temperature.
Preferably, in step S202, 13.3mL to 14.3mL of ultrapure water is added to the round-bottom flask, then 2.9mL to 3.1mL of the gold nanoparticles are added, 0.9mL to 1.1mL of a sodium citrate solution with a mass fraction of 0.95% to 1.05% and 0.9mL to 1.1mL of an ascorbic acid solution with a mass fraction of 9.5mmol/L to 10.5mmol/L are added, and a mixed solution is obtained.
Preferably, in step S202, 13.8mL of ultrapure water is added into a round-bottom flask, then 3mL of the gold nanoparticles are added, 1mL of a 1% sodium citrate solution by mass fraction and 1mL of a 10mmol/L ascorbic acid solution are added, and a mixed solution is obtained.
Preferably, in step S203, the mixed solution is stirred at room temperature for 4 to 6 minutes, then the mixed solution is transferred into a water bath at 35 to 45 ℃ and stirred for 10 to 20 minutes, then a certain amount of silver nitrate is dropwise added, the mixed solution is continuously stirred for 25 to 35 minutes after the color of the mixed solution is stable, and the suspension is centrifuged and washed with distilled water to obtain the silver-coated gold core-shell nano sol with a core-shell structure.
Preferably, in step S203, the mixed solution is stirred at room temperature for 5 minutes, then the mixed solution is transferred into a water bath at 40 ℃ and stirred for 15 minutes, then a certain amount of silver nitrate is dropwise added, the mixed solution is continuously stirred for 30 minutes after the color of the mixed solution is stable, and the suspension is centrifuged and washed with distilled water to obtain the silver-coated gold core-shell nano sol with a core-shell structure.
Preferably, the silver nitrate is added dropwise at 100. mu.L.
Preferably, in step S4, the assembly of the cathode sandwich biosensor comprises the following steps:
s401, attaching the carbon dot-multiwalled carbon nanotube composite material to a bare Glass Carbon Electrode (GCE) to form a photoactive material layer with photoactivity;
s402, fixing an antibody (Ab) on the photoactive material layer, and modifying the bare glass carbon electrode to obtain an antibody/carbon dot-multi-wall carbon nanotube (Ab/CDs-NPCGO) modified electrode;
s403, when a progesterone-containing sample needs to be detected, dropping the sample solution on the antibody/carbon dot-multi-walled carbon nanotube modified electrode, adding the bioconjugate for incubation, and obtaining an aptamer-silver-coated gold core-shell nanosol/progesterone/antibody/carbon dot-multi-walled carbon nanotube (aptamer-Au @ Ag NPs/P4/Ab/CDs-NPCGO) modified electrode as the biosensor.
Preferably, in step S401, 8 to 12 μ L of the carbon dot-multiwall carbon nanotube composite material suspension is coated on the surface of the bare glass carbon electrode and dried at 50 to 80 ℃ to form a uniform photoactive material layer.
Preferably, in step S401, 10 μ L of the carbon dot-multiwall carbon nanotube composite material suspension is coated on the surface of the bare glass carbon electrode, and dried at 60 ℃ to form a uniform photoactive material layer.
Preferably, before step S401, the method further includes:
and polishing the bare glassy carbon electrode on the surface of the chamois by using alumina slurry, sequentially carrying out ultrasonic cleaning by using ethanol and double distilled water, and drying by using nitrogen.
Preferably, after step S401, the method further includes:
the electrode surface was treated with EDC/NHS solution, carboxyl groups were activated, EDC solution and NHS were added to the electrode surface for incubation, and EDC/NHS was washed with PBS.
Preferably, the surface of the electrode is treated with EDC/NHS solution at 35-37 deg.C to activate carboxyl for 0.3-1 hr, and 95-105 μ L of 19 μ g/mL-1～21μg·mL-1And 95. mu.L to 105. mu.L of 9 mg. multidot.mL of the EDC solution of (1)-1～11mg·mL-1Adding the NHS to the surface of the electrode, then incubating for 1.5-2.5 hours at 3-5 ℃, and washing with PBS with the pH value of 7-7.6 to remove the redundant EDC/NHS.
Preferably, the surface of the electrode is treated with EDC/NHS solution at 37 ℃ to activate the carboxyl groups for 0.5 hour, and 100. mu.L of 20. mu.g.mL-1And 100. mu.L of 10 mg. multidot.mL of EDC solution (b)-1The NHS was added to the electrode surface followed by incubation at 4 ℃ for 2 hours and washing with PBS at pH 7.4 to remove excess EDC/NHS.
Preferably, in step S402, 4. mu.L to 6. mu.L of 6.5. mu.g/mL-1～9.5μg·mL-1The antibody is dripped on the surface of the photoactive material layer, and is incubated for 3 to 4 hours at the temperature of between 35 and 37 ℃ to wash off the loosely combined antibody;
and (3) treating the modified electrode with 3-5 mu L of 0.8-1.2 wt% BSA in 8-12 mmol/L PBS with the pH value of 7-7.6, treating at 35-37 ℃ for 1-2 hours to block non-specific binding sites, washing with the PBS, and drying under nitrogen to obtain the antibody/carbon dot-multi-walled carbon nanotube modified electrode.
Preferably, in step S402, 5. mu.L of 8. mu.g/mL is added-1The antibody is dripped on the surface of the photoactive material layer, and incubated for 4 hours at 37 ℃, and the loosely bound antibody is washed away;
the modified electrode was treated with 4 μ L of 1 wt% BSA in 10mmol/L PBS at pH 7.4, treated at 37 ℃ for 1 hour to block non-specific binding sites, washed with the PBS, and dried under nitrogen to obtain an antibody/carbon dot-multiwall carbon nanotube modified electrode.
Preferably, in step S403, when a sample containing progesterone needs to be detected, dropping the sample solution onto the antibody/carbon dot-multiwall carbon nanotube modified electrode, incubating at 35-37 ℃ for 0.5-1.5 hours, and washing off the physically adsorbed progesterone molecules;
adding the bioconjugate to incubate for 30-50 minutes at 35-37 ℃, washing with PBS (phosphate buffer solution) with the pH value of 7-7.6 of 8-12 mmol/L, and naturally drying to obtain the aptamer-silver coated gold core-shell nano sol/progesterone/antibody/carbon dot-multiwalled carbon nanotube modified electrode serving as the biosensor;
the biosensor is stored in a dry state at 0-5 ℃.
Preferably, in step S403, when a progesterone-containing sample needs to be detected, dropping the sample solution on the antibody/carbon dot-multiwall carbon nanotube modified electrode, incubating at 37 ℃ for 1 hour, and washing off the physically adsorbed progesterone molecules;
adding the bioconjugate to incubate for 40 minutes at 37 ℃, washing with 10mmol/L PBS with pH value of 7.4, and naturally drying to obtain the aptamer-silver-coated gold core-shell nanosol/progesterone/antibody/carbon dot-multi-walled carbon nanotube modified electrode as the biosensor;
the biosensor was stored in a dry state at 4 ℃.
Use of a biosensor for the detection of progesterone content.
The positive progress effects of the invention are as follows: the biosensor and the preparation method and the application thereof have the following advantages:
1. the stability and optical adsorption performance of the photoactive material are improved, and the photoactive material has excellent stability, higher conductivity and faster electron transfer capacity.
The absorption of the CDs-GO commonly adopted in the prior art can be enhanced in a visible light region, so that the optical active nano material has advantages in the aspect of constructing a photoelectrode. The multi-walled carbon nanotube is added on the basis of the material, the material has a similar conjugated structure with other carbon nanomaterials such as graphene quantum dots and the like, and can easily interact through p-p stacking, so that a three-dimensional network with excellent stability, higher conductivity and faster electron transfer kinetics is formed, and the optical adsorption performance and the material stability can be further improved.
2. The stability of the active substrate nano material is increased, and the signal amplification capacity of the active substrate nano material is enhanced.
AuNPs have the advantages of simple and convenient preparation, stability, good dispersibility, good morphology controllability, good biocompatibility and the like, while Ag NPs have optical enhancement effect superior to that of AuNPs, but Ag has stronger chemical activity than Au, and shows liveness and is difficult to control in the preparation process, so that the obtained Ag NPs have non-uniform particle size and poor stability. Therefore, in order to obtain an ideal active substrate, Au @ AgNPs are synthesized by combining the advantages of AuNPs and AgNPs, and the core-shell structure of the Au @ AgNPs has unique electronic and optical properties. Meanwhile, due to the stable characteristic of the noble metal, the noble metal is not easy to deteriorate after being exposed to air for a long time, and is easy to test.
Drawings
FIG. 1 is a schematic diagram showing a prior art process for preparing a biosensor;
FIG. 2 is a schematic diagram showing a simulation of a synthesis process of Au @ Ag NPs in the prior art;
FIG. 3 is a flow chart of a process of the present invention;
FIG. 4 is a schematic diagram of a simulation of a manufacturing process according to the present invention.
Detailed Description
In order to make the technical means, the creation characteristics, the achievement purposes and the effects of the invention easy to understand, the invention is further described with the specific drawings.
The invention provides a biosensor comprising an electrode, preferably a bare Glassy Carbon Electrode (GCE). The electrode has a photoactive material thereon. The photoactive material is a carbon dot-multiwalled carbon nanotube (CDs-NPCGO) composite material. An antibody (Ab) is immobilized on the photoactive material. Also included are bioconjugates comprising an aptamer and a silver-coated gold core-shell nanosol (Au @ AgNPs) interconnected.
In some embodiments, the aptamer is a nucleic acid aptamer of the prior art, and is an oligonucleotide sequence (DNA or RNA). For example, Aptamer-SH is used.
When performing reagent detection, a reagent such as progesterone sample is dropped onto the electrode, and a bioconjugate is added, and the reagent molecules are linked to the antibody and aptamer to form an antibody-aptamer based cathode sandwich biosensor.
The invention provides a preparation method of a biosensor, which comprises the following steps:
s1, preparing a carbon dot-multi-walled carbon nanotube (CDs-NPCGO) composite material as a photoactive material.
The multi-walled carbon Nanotube (NPCGO) has a unique geometric structure, good mechanical strength, excellent conductivity and strong catalytic performance. The unique network structure is beneficial to combination with the existing photoactive material (CDs-GO), so that the cathode photocurrent signal is obviously enhanced.
In some embodiments, the carbon dot-multiwall carbon nanotube composite is prepared as follows:
s101, obtaining a ZIF-8@ GO nano composite material, heating the ZIF-8@ GO nano composite material, and collecting black powder after pyrolysis.
S102, adding black powder into a hydrochloric acid solution for reaction, then collecting a product through centrifugation, washing and drying overnight to obtain nanoporous carbon (NPCGO);
s103, dispersing the nano porous carbon in ultrapure water, performing ultrasonic stirring to obtain a nano porous carbon suspension, and directly injecting the nano porous carbon suspension into a carbon dot aqueous solution under ultrasonic stirring to prepare the carbon dot-multiwall carbon nanotube composite material.
In some embodiments, in step S101, a ZIF-8@ GO nanocomposite is obtained, and the ZIF-8@ GO nanocomposite is heated to 750 ℃ to 850 ℃ at a rate of 5 ℃/min to 20 ℃/min, in nitrogen (N)2) At 750 ℃Pyrolyzing the mixture for 1.5 to 2.5 hours at 850 ℃, cooling the mixture to room temperature, and collecting the obtained black powder.
In some embodiments, in step S102, the black powder is added to a hydrochloric acid solution having a mass fraction of 3.5% to 10.5%, reacted for 20 hours to 30 hours with continuous stirring, and then the product is collected by centrifugation, washed with deionized water, and dried at 50 ℃ to 80 ℃ for 10 hours to 14 hours to obtain nanoporous carbon.
In some embodiments, in step S103, 8mg to 12mg of nanoporous carbon is dispersed in 4mL to 6mL of ultrapure water and ultrasonically stirred for 1.5 hours to 2.5 hours to obtain 1.4 mg-mL-1～3mg·mL-1The nano porous carbon suspension is directly injected into 1.4 mg/mL under ultrasonic stirring-1～3mg·mL-1And preparing the carbon dot-multi-walled carbon nanotube composite material in the carbon dot aqueous solution.
In some embodiments, in step S101, the ZIF-8@ GO nanocomposite is prepared as follows:
putting Graphene Oxide (GO) into 2-methylimidazole, adding zinc nitrate hexahydrate (Zn (NO) after ultrasonic stirring3)2·6H2O), centrifuging, washing and drying the generated mixture at room temperature, and collecting the product, namely the ZIF-8@ GO nano composite material.
In some embodiments, 1.5mg to 2.5mg of graphene oxide is put into 80mL to 120mL of 3mol/L to 4 mol/L2-methylimidazole, after ultrasonic stirring is carried out for 0.5 hour to 1.5 hours, 7mL to 9mL of 3.5mmol/L to 4.5mmol/L zinc nitrate hexahydrate is gradually dropped, the generated mixture is stirred for 0.5 hour to 1.5 hours at room temperature, then centrifugation is carried out, water washing is carried out for 2 times to 4 times, drying is carried out for 10 hours to 14 hours at 50 ℃ to 70 ℃, and the product is collected, namely the ZIF-8@ GO nano composite material.
In some embodiments, in step S103, the aqueous carbon dot solution is prepared as follows:
dissolving citric acid in deionized water to obtain a citric acid aqueous solution, dropwise adding ethylenediamine under stirring to obtain a mixed solution, transferring the mixed solution into an autoclave, sealing the autoclave in a stainless steel tank, further heating the autoclave in an electric oven, naturally cooling a reactor to room temperature, collecting a reddish brown substance by a centrifuge, washing the reddish brown substance with absolute ethyl alcohol, drying the substance in a drying oven to obtain carbon dots, and dissolving the carbon dots in water to obtain a carbon dot aqueous solution.
In some embodiments, 0.48g to 0.58g of citric acid is dissolved in 9mL to 11mL of deionized water to obtain an aqueous citric acid solution, 150 μ L to 185 μ L of ethylenediamine is gradually added dropwise under the stirring of a magnetic stirrer to obtain a mixed solution, the mixed solution is transferred to a polytetrafluoroethylene-lined autoclave, the autoclave is sealed in a stainless steel pot, the mixture is further heated to 150 ℃ to 200 ℃ in an electric oven for 4.5 hours to 5.5 hours, after the reactor is naturally cooled to room temperature, a reddish brown substance is collected by a centrifuge, washed 2 to 4 times with absolute ethanol, and dried in a drying oven for 10 hours to 14 hours at 50 ℃ to 70 ℃ to obtain carbon dots.
S2, preparing silver-coated gold core-shell nano sol (Au @ AgNPs) as an active substrate nano material.
In the step, a seed growth method can be utilized, Au NPs are used as seeds, a thin silver shell grows on the surface of the seeds, and Au @ Ag NPs with different shapes and sizes are obtained by regulating and controlling the grain size of a gold core and the thickness of the silver shell. Certain gold core particle size and silver shell thickness have different electrical signal amplification capabilities.
In some embodiments, the silver-coated gold core-shell nanosol has a gold core particle size of 21nm to 42nm and a silver shell thickness of 5nm to 10 nm.
In some embodiments, the signal amplification capability is strongest for the electrochemical aptamer biosensor of the present invention when the gold core particle size of the silver-coated gold core-shell nanosol is 31nm and the silver shell thickness is 9 nm.
In some embodiments, in step S2, the silver-coated gold core-shell nanosol is prepared as follows:
s201, adding tetrachloroauric acid (HAuCl)4) Boiling the solution, adding sodium citrate (stabilizer) into the vortex of tetrachloroauric acid solution under stirring, changing the mixed solution from pale yellow to purple, boiling and refluxing, and stirring the purple solution of gold nanoparticles (Au NPs)Stirring and cooling to room temperature, and preparing gold nanoparticles with preset concentration and gold core particle size;
s202, adding ultrapure water into a container, then adding gold nanoparticles, and adding a stabilizer and a reducing agent to obtain a mixed solution;
s203, stirring the mixed solution at room temperature, transferring the mixed solution into a water bath for stirring, and then dropwise adding quantitative silver nitrate (AgNO)3) And continuing stirring after the color of the mixed solution is stable, centrifuging the suspension, and washing with distilled water to obtain the silver-coated gold core-shell nano sol with the core-shell structure.
In some examples, in step S201, 19mL to 21mL of 0.9mmol/L to 1.1mmol/L tetrachloroauric acid solution is placed in a round bottom flask equipped with a condenser tube and boiled, 1.8mL to 2.2mL of 38.3mmol/L to 39.3mmol/L sodium citrate is added to vortex of the tetrachloroauric acid solution under strong stirring for 6 to 10 times, the mixed solution turns to mauve from pale yellow after 0.5 to 1 minute, and after boiling and refluxing for 15 to 30 minutes, the mauve solution of gold nanoparticles is stirred and cooled to room temperature.
In some embodiments, in step S202, 13.3mL to 14.3mL of ultrapure water is added into the round-bottom flask, then 2.9mL to 3.1mL of gold nanoparticles are added, 0.9mL to 1.1mL of a sodium citrate solution with a mass fraction of 0.95% to 1.05% and 0.9mL to 1.1mL of an ascorbic acid solution with a mass fraction of 9.5mmol/L to 10.5mmol/L are added, and a mixed solution is obtained.
In some embodiments, in step S203, the mixed solution is stirred at room temperature for 4 to 6 minutes, then the mixed solution is transferred into a water bath at 35 to 45 ℃ and stirred for 10 to 20 minutes, then a certain amount of silver nitrate is added dropwise, stirring is continued for 25 to 35 minutes after the color of the mixed solution is stable, and the suspension is centrifuged and washed with distilled water to obtain the silver-coated gold core-shell nano sol with the core-shell structure. The formation sign of the core-shell structure of the silver-coated gold core-shell nano sol is that two SPR absorption peaks appear at the same time.
In some embodiments, the dropwise addition of silver nitrate is 100 μ L.
And S3, connecting the aptamer and the active substrate nano material to form a bioconjugate as an amplifier.
The aptamer in this step is a nucleic acid aptamer, which is an oligonucleotide sequence (DNA or RNA). Usually oligonucleotide fragments are obtained from libraries of nucleic acid molecules using in vitro screening techniques, i.e.exponential enrichment of ligand phylogenetic techniques.
The traditional antigen-antibody reaction has better sensitivity and specificity, enzyme-linked immune reaction plays a significant role in the detection of various biomolecules, and a plurality of kits on the market are developed based on the principle. However, proteins as probe molecules are easily denatured by environmental factors such as pH and temperature, and are expensive to synthesize. The aptamer is composed of DNA or RNA (mainly DNA), has smaller volume than protein, can have sensitivity comparable to antigen-antibody reaction after SELEX screening and enrichment, and is easier to synthesize and better in stability.
S4, assembling the antibody-aptamer-based cathode sandwich biosensor using the photoactive material and the amplifier.
The step is to assemble the progesterone selective detection biosensor based on the antibody-aptamer by taking a carbon dot-multi-walled carbon nanotube composite material as an optically active material and taking the aptamer-Au @ AgNPs bioconjugate as a PEC (cathode photoelectrochemistry biosensor) amplifier.
In some embodiments, assembling the biosensor employs the following process:
s401, attaching a carbon dot-multiwalled carbon nanotube composite material to a bare Glass Carbon Electrode (GCE) to form a photoactive material layer with photoactivity;
s402, fixing an antibody (Ab) on the photoactive material layer, and modifying a bare glassy carbon electrode to obtain an antibody/carbon dot-multi-walled carbon nanotube (Ab/CDs-NPCGO) modified electrode;
s403, when a progesterone-containing sample needs to be detected, dropping a sample solution on the antibody/carbon dot-multi-walled carbon nanotube modified electrode, adding a bioconjugate, and incubating to obtain an aptamer-silver-coated gold core-shell nanosol/progesterone/antibody/carbon dot-multi-walled carbon nanotube (aptamer-Au @ Ag NPs/P4/Ab/CDs-NPCGO) modified electrode serving as a biosensor.
In some embodiments, before step S401, comprising:
polishing the bare glassy carbon electrode on the surface of chamois leather by using alumina slurry, sequentially carrying out ultrasonic cleaning by using ethanol and double distilled water, and drying by using nitrogen.
In some embodiments, in step S401, 8 to 12 μ L of the carbon dot-multiwalled carbon nanotube composite material suspension is coated on the surface of the bare glassy carbon electrode and dried at 50 to 80 ℃ to form a uniform photoactive material layer.
In some embodiments, after step S401, comprising:
the electrode surface was treated with EDC/NHS solution to activate carboxyl groups, EDC solution and NHS were added to the electrode surface for incubation, and excess EDC/NHS was removed by washing with PBS.
In some embodiments, 95-105 μ L of 19 μ g/mL is treated with EDC/NHS solution at 35-37 deg.C to activate carboxyl groups for 0.3-1 hour-1～21μg·mL-1And 95. mu.L to 105. mu.L of 9 mg. multidot.mL of the EDC solution of (1)-1～11mg·mL-1Adding the NHS to the surface of the electrode, then incubating for 1.5-2.5 hours at 3-5 ℃, and washing with PBS with the pH value of 7-7.6 to remove the redundant EDC/NHS.
In some embodiments, in step S402, 4 μ L to 6 μ L of 6.5 μ g/mL-1～9.5μg·mL-1The antibody is dripped on the surface of the optically active material layer, and is incubated for 3 to 4 hours at the temperature of between 35 and 37 ℃, and the loosely combined antibody is washed away; and (3) treating the modified electrode by 3-5 mu L of 0.8-1.2 wt% BSA in 8-12 mmol/L PBS with the pH value of 7-7.6, treating for 1-2 hours at 35-37 ℃ to block non-specific binding sites, washing with PBS, and drying under nitrogen to obtain the antibody/carbon dot-multi-walled carbon nanotube modified electrode.
In some embodiments, in step S403, when the progesterone-containing sample needs to be detected, dropping the sample solution on the antibody/carbon dot-multiwall carbon nanotube modified electrode, incubating at 35-37 ℃ for 0.5-1.5 hours, and washing off the physically adsorbed progesterone molecules; adding the bioconjugate to incubate for 30-50 minutes at 35-37 ℃, washing with PBS (phosphate buffer solution) with the concentration of 8-12 mmol/L and the pH value of 7-7.6, naturally drying to obtain the aptamer-silver-coated gold core-shell nano sol/progesterone/antibody/carbon dot-multi-walled carbon nanotube modified electrode which is used as a biosensor, and storing the biosensor in a dry state at 0-5 ℃.
The invention also provides an application of the biosensor, and the biosensor is applied to the detection of progesterone content.
Referring to fig. 3, in one embodiment of the present invention, the biosensor is prepared as follows:
1) preparing a CDs-NPCGO composite material as a photoactive material;
2) preparing Au @ AgNPs as an active substrate nano material;
3) connecting the aptamer and Au @ AgNPs to form a bioconjugate;
4) coating CDs-NPCGO suspension on a bare glassy carbon electrode;
5) treating the surface of the bare glassy carbon electrode with EDC/NHS solution at 37 ℃;
6) adding an antibody;
7) treating and modifying a bare glass carbon electrode by BSA and PBS;
8) adding a progesterone sample;
9) the aptamer-Au @ AgNPs bioconjugate was added for incubation.
In a first embodiment, the preparation of the CDs-NPCGO composite material comprises the following steps:
dissolving 0.53g of citric acid in 10mL of deionized water to obtain 0.276mol/L of an aqueous citric acid solution, gradually adding 168. mu.L of ethylenediamine dropwise under stirring by a magnetic stirrer to obtain a mixed solution, transferring the mixed solution into a 20mL polytetrafluoroethylene-lined autoclave, sealing the autoclave in a stainless steel can, further heating the autoclave to 180 ℃ for 5 hours in an electric oven, naturally cooling the reactor to room temperature, collecting the reddish brown material by a centrifuge, washing the reddish brown material with absolute ethanol for 3 times, and drying the reddish brown material in a drying oven at 60 ℃ for 12 hours to obtain carbon dots. The obtained carbon dots were prepared to 2 mg. multidot.mL-1The aqueous solution of carbon dots of (a) is ready for use.
2mg of graphene oxide is put into 100mL of 3.5 mol/L2-methylimidazole, after the graphene oxide is ultrasonically stirred for 1 hour, 8mL of 4mmol/L zinc nitrate hexahydrate is gradually dropped, the generated mixture is stirred for 1 hour at room temperature, then the centrifugation is carried out, the water is used for washing for 3 times, the drying is carried out for 12 hours at the temperature of 60 ℃, and the product is collected, namely the ZIF-8@ GO nano composite material.
The preparation method comprises the steps of obtaining a ZIF-8@ GO nano composite material, heating the ZIF-8@ GO nano composite material to 800 ℃ at the speed of 5 ℃/min, pyrolyzing the material for 2 hours at 800 ℃ under the protection of nitrogen, cooling the material to room temperature, and collecting obtained black powder. The black powder was added to a 10% hydrochloric acid solution by mass fraction, reacted for 24 hours with continuous stirring, and then the product was collected by centrifugation, washed with deionized water, and dried at 60 ℃ for 12 hours to obtain nanoporous carbon.
Dispersing 10mg of nanoporous carbon in 5mL of ultrapure water, and ultrasonically stirring for 2 hours to obtain 2 mg/mL-1The nano porous carbon suspension is directly injected into 2 mg/mL under ultrasonic stirring-1And preparing the CDs-NPCGO composite material in the carbon dot aqueous solution.
Example two, Au @ AgNPs was prepared using the following procedure:
20mL of 1mmol/L tetrachloroauric acid solution was placed in a 50mL round-bottom flask equipped with a condenser tube and boiled, 2mL of 38.8mmol/L sodium citrate was added to the vortex of tetrachloroauric acid solution under vigorous stirring for 8 times, after 1 minute the mixed solution changed from pale yellow to purple, and after boiling under reflux for 20 minutes, the purple red solution of gold nanoparticles was cooled to room temperature under stirring. The concentration of the magenta solution for preparing gold nanoparticles was 3.27nmol/L (gold core particle diameter of 21nm), 1.50nmol/L (gold core particle diameter of 31nm), and 0.82nmol/L (gold core particle diameter of 42nm), respectively.
Adding 13.8mL of ultrapure water into a 100mL round-bottom flask, then adding 3mL of a mauve solution of gold nanoparticles (the mauve solutions of the gold nanoparticles with three concentrations are respectively tested in parallel), adding 1mL of a sodium citrate solution with the mass fraction of 1% and 1mL of an ascorbic acid solution with the mass fraction of 10mmol/L to obtain a mixed solution.
Stirring the mixed solution for 5 minutes at room temperature, then transferring the mixed solution into a water bath at 40 ℃ and stirring for 15 minutes, then dropwise adding 100 mu L of silver nitrate, continuing stirring for 30 minutes after the color of the mixed solution is stable, centrifuging the suspension, and washing with distilled water to obtain three Au @ AgNPs with core-shell structures.
Referring to fig. 4, example three, biosensor preparation:
four bare Glassy Carbon Electrodes (GCE) were prepared, three of which were added with reactants for parallel control experiments, one being blank control.
Polishing the bare glassy carbon electrode on the surface of chamois leather by using 0.05-micron alumina slurry, carrying out ultrasonic cleaning by using ethanol and double-distilled water in sequence, and drying by using nitrogen.
At a geometric surface area of 0.096cm2The surface of the bare glassy carbon electrode was coated with 10 μ L of the CDs-NPCGO composite prepared in example one and dried at 60 ℃ to form a uniform layer of photoactive material.
The surface of the electrode was treated with EDC/NHS solution at 37 ℃ to activate carboxyl groups for 0.5 hour, and 100. mu.L of 20. mu.g.mL-1And 100. mu.L of 10 mg. multidot.mL of EDC solution (b)-1The NHS was added to the electrode surface followed by incubation at 4 ℃ for 2 hours and washing with PBS at pH 7.4 to remove excess EDC/NHS.
5. mu.L of 8. mu.g/mL-1Dropping the antibody (Ab) on the surface of the photoactive material layer, incubating for 4 hours at 37 ℃, and washing off the loosely bound antibody; and (3) treating the modified electrode with 4 mu L of 1 wt% BSA (bovine serum albumin) in 10mmol/L PBS (phosphate buffer solution) with the pH value of 7.4, treating at 37 ℃ for 1 hour to block non-specific binding sites, washing with PBS, and drying under nitrogen to obtain the antibody/carbon dot-multi-walled carbon nanotube modified electrode.
When a sample containing progesterone (P4) needs to be detected, dripping a sample solution on an antibody/carbon dot-multi-wall carbon nanotube modified electrode, incubating at 37 ℃ for 1 hour, and washing off physically adsorbed progesterone molecules; the aptamer-Au @ Ag NPs, which are the Au @ AgNPs having a core-shell structure prepared in example two, were added and incubated for 40 minutes at 37 ℃. Washing with PBS (phosphate buffer solution) with the concentration of 10mmol/L and the pH value of 7.4, and naturally drying to obtain an aptamer-Au @ Ag NPs/P4/Ab/CDs-NPCGO modified electrode serving as a biosensor; the biosensor was stored in a dried state at 4 ℃.
Example four, method for quantitative determination of progesterone content in biological fluids:
and respectively connecting and fixing the working electrode, the reference electrode and the inert electrode with the three-color electrode clamps, and soaking the heads of the three electrodes in a PBS (phosphate buffer solution) solution to ensure that the working electrode is not contacted with the wall of the container. And then, opening an electrochemical analysis instrument, firstly carrying out software test, then selecting a constant potential electrolytic current-time curve method (I-T) and a bias potential 0v, carrying out detection, wherein the progesterone concentration is in negative correlation with a current value, and substituting the current value of the measured progesterone sample into a curve equation to obtain the progesterone content.
The foregoing shows and describes the general principles, essential features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims (10)

1. A biosensor comprises an electrode having an optically active material; an antibody attached to a reactant immobilized on the photoactive material; a bioconjugate; it is characterized in that the preparation method is characterized in that,
the photoactive material is a carbon dot-multiwalled carbon nanotube composite material;
the bioconjugate comprises a silver-coated gold core-shell nanosol interconnected and an aptamer linked to the reactant.
2. A method for preparing the biosensor according to claim 1, comprising:
s1, preparing a carbon dot-multi-wall carbon nanotube composite material as a photoactive material;
s2, preparing silver-coated gold core-shell nano sol as an active substrate nano material;
s3, connecting an aptamer and the active substrate nano material to form a bioconjugate as an amplifier;
s4, assembling the cathode interlayer biosensor based on the antibody-aptamer by using the photoactive material and the amplifier.
3. The method of claim 2, wherein in step S1, the carbon dot-multiwall carbon nanotube composite is prepared by:
s101, obtaining a ZIF-8@ GO nano composite material, heating the ZIF-8@ GO nano composite material, and collecting black powder obtained after pyrolysis;
s102, adding the black powder into a hydrochloric acid solution for reaction, then collecting a product through centrifugation, washing and drying to obtain the nanoporous carbon;
s103, dispersing the nano porous carbon in ultrapure water, performing ultrasonic stirring to obtain a nano porous carbon suspension, and directly injecting the nano porous carbon suspension into a carbon dot aqueous solution under ultrasonic stirring to prepare the carbon dot-multiwall carbon nanotube composite material.
4. The method of manufacturing a biosensor according to claim 3, wherein in step S101, ZIF-8@ GO nanocomposite is obtained, the ZIF-8@ GO nanocomposite is heated to 750 ℃ to 850 ℃, preferably to 800 ℃, at a rate of 5 ℃/min to 20 ℃/min, preferably at a rate of 5 ℃/min, pyrolyzed under nitrogen for 1.5 hours to 2.5 hours, preferably for 2 hours, and after cooling to room temperature, the resulting black powder is collected;
in step S102, the black powder is added to a hydrochloric acid solution with a mass fraction of 3.5% to 10.5%, preferably 10%, and reacted for 20 to 30 hours, preferably 24 hours, under continuous stirring, and then the product is collected by centrifugation, washed with deionized water, and dried at 50 to 80 ℃, preferably 60 ℃, for 10 to 14 hours, preferably 12 hours, to obtain the nanoporous carbon;
in step S103, 8mg to 12mg, preferably 10mg of the nanoporous carbon is dispersedUltrasonic stirring in 4-6 mL, preferably 5mL of ultrapure water for 1.5-2.5 hours, preferably 2 hours, to give 1.4 mg/mL-1～3mg·mL-1Preferably 2 mg/mL-1The nano porous carbon suspension is directly injected into 1.4 mg/mL under ultrasonic stirring-1～3mg·mL-1Preferably 2 mg/mL-1And preparing the carbon dot-multi-walled carbon nanotube composite material in the carbon dot aqueous solution.
5. The method of claim 3, wherein in step S101, the ZIF-8@ GO nanocomposite is prepared by:
putting graphene oxide into 2-methylimidazole, adding zinc nitrate hexahydrate after ultrasonic stirring, centrifuging, washing and drying the generated mixture at room temperature, and collecting the product, namely the ZIF-8@ GO nanocomposite;
in step S103, the carbon dot aqueous solution is prepared as follows:
dissolving citric acid in deionized water to obtain a citric acid aqueous solution, dropwise adding ethylenediamine under stirring to obtain a mixed solution, transferring the mixed solution into an autoclave, sealing the autoclave in a stainless steel tank, further heating the autoclave in an electric oven, naturally cooling a reactor to room temperature, collecting a reddish brown substance by a centrifuge, washing the reddish brown substance with absolute ethyl alcohol, drying the substance in a drying oven to obtain carbon dots, and dissolving the carbon dots in water to obtain the carbon dot aqueous solution.
6. The method for preparing the biosensor according to claim 2, wherein in step S2, the silver-coated gold core-shell nanosol is prepared as follows:
s201, boiling a tetrachloroauric acid solution, adding sodium citrate into a vortex of the tetrachloroauric acid solution while stirring, changing the mixed solution from light yellow to purple, boiling and refluxing, stirring and cooling the purple red solution of gold nanoparticles to room temperature, and preparing the gold nanoparticles with preset concentration and gold core particle size;
s202, adding ultrapure water into a container, then adding the gold nanoparticles, and adding a stabilizer and a reducing agent to obtain a mixed solution;
s203, stirring the mixed solution at room temperature, transferring the mixed solution into a water bath for stirring, then dropwise adding quantitative silver nitrate, continuing stirring after the color of the mixed solution is stable, centrifuging the suspension, and washing with distilled water to obtain the silver-coated gold core-shell nano sol with the core-shell structure.
7. The method for preparing the biosensor according to claim 2, wherein the silver-coated gold core-shell nanosol has a gold core particle size of 21nm to 42nm, preferably 31nm, and a silver shell thickness of 5nm to 10nm, preferably 9 nm.
8. The method for manufacturing a biosensor in accordance with any one of claims 2 to 7, wherein in step S4, the following procedure is used for assembling the biosensor:
s401, attaching the carbon dot-multiwalled carbon nanotube composite material to a bare glass carbon electrode to form an optically active material layer with optical activity;
s402, fixing an antibody on the photoactive material layer, and modifying the bare glassy carbon electrode to obtain an antibody/carbon dot-multi-walled carbon nanotube modified electrode;
and S403, when a progesterone-containing sample needs to be detected, dripping the sample solution on the antibody/carbon dot-multi-walled carbon nanotube modified electrode, adding the bioconjugate for incubation to obtain an aptamer-silver-coated gold core-shell nanosol/progesterone/antibody/carbon dot-multi-walled carbon nanotube modified electrode, and drying to obtain the biosensor.
9. The method for preparing the biosensor as claimed in claim 8, wherein in step S401, 8 μ L to 12 μ L, preferably 10 μ L, of the carbon dot-multiwall carbon nanotube composite material suspension is coated on the surface of the bare glass carbon electrode, and dried at 50 ℃ to 80 ℃, preferably 60 ℃, to form a uniform photoactive material layer;
before step S401, the method further includes:
polishing the bare glassy carbon electrode on the surface of chamois by using alumina slurry, sequentially performing ultrasonic cleaning by using ethanol and double distilled water, and drying by using nitrogen;
after step S401, the method further includes:
treating the surface of the electrode with an EDC/NHS solution, activating carboxyl, adding the EDC solution and NHS to the surface of the electrode for incubation, and washing the EDC/NHS with PBS;
in step S402, 4. mu.L to 6. mu.L of 6.5. mu.g/mL-1～9.5μg·mL-1Preferably 5. mu.L of 8. mu.g/mL-1The antibody is dripped on the surface of the optically active material layer, incubated for 3 to 4 hours, preferably 4 hours at the temperature of between 35 and 37 ℃, preferably at the temperature of 37 ℃, and the loosely bound antibody is washed off; treating the modified electrode with 3-5 mu L of 0.8-1.2 wt%, preferably 4 mu L of 1 wt% BSA in PBS (phosphate buffer solution) with 8-12 mmol/L, preferably 10mmol/L, and pH value of 7-7.6, preferably 7.4, treating at 35-37 ℃, preferably 37 ℃ for 1-2 hours, preferably 1 hour, so as to block non-specific binding sites, washing with the PBS, and drying under nitrogen to obtain the antibody/carbon dot-multiwalled carbon nanotube modified electrode;
in step S403, when a sample containing progesterone needs to be detected, dropping the sample solution onto the antibody/carbon dot-multiwalled carbon nanotube modified electrode, incubating at 35-37 ℃, preferably 37 ℃, for 0.5-1.5 hours, preferably 1 hour, and washing off the physically adsorbed progesterone molecules; adding the bioconjugate to incubate for 30-50 minutes, preferably 40 minutes at 35-37 ℃, preferably 37 ℃, washing with PBS (phosphate buffer solution) with the pH value of 7-7.6, preferably 7.4 and 8-12 mmol/L, preferably 10mmol/L, and naturally drying to obtain the aptamer-silver coated gold core-shell nanosol/progesterone/antibody/carbon dot-multiwalled carbon nanotube modified electrode serving as the biosensor; the biosensor is stored in a dried state at 0 ℃ to 5 ℃, preferably at 4 ℃.
10. Use of a biosensor according to claim 1 for the detection of progesterone content.
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