CN111269320B

CN111269320B - Nano antibody NT8 for specifically recognizing 19-nortestosterone and application thereof

Info

Publication number: CN111269320B
Application number: CN202010108416.0A
Authority: CN
Inventors: 沈玉栋; 王弘; 杨媛媛; 张咏仪; 陈浩宇; 徐振林; 肖治理; 孙远明
Original assignee: South China Agricultural University
Current assignee: South China Agricultural University
Priority date: 2020-02-21
Filing date: 2020-02-21
Publication date: 2021-09-14
Anticipated expiration: 2040-02-21
Also published as: CN111269320A

Abstract

The invention discloses a nano antibody NT8 for specifically recognizing 19-nortestosterone and application thereof. The invention obtains a nano antibody NT8 capable of being specifically combined with 19-NT by screening, wherein the amino acid sequence of the VHH of the nano antibody NT8 is shown as SEQ ID NO. 1. The nano antibody NT8 has high thermal stability and organic tolerance, the range of 19-NT detection is 0.48 ng/mL-4.93 ng/mL, IC50 is 1.53ng/mL, the lowest limit of detection (LOD) is 0.13ng/mL, and the detection sensitivity is strong; based on the nano antibody NT8, the invention also provides a 19-nortestosterone immunological detection method, and the method is simple to operate, short in consumed time, strong in sensitivity and high in accuracy when applied to detection of actual samples of 19-NT residues; therefore, the nano antibody NT8 has wide application prospect in detecting 19-nortestosterone or preparing 19-nortestosterone detection reagent/kit.

Description

Nano antibody NT8 for specifically recognizing 19-nortestosterone and application thereof

Technical Field

The invention belongs to the field of biotechnology. More particularly, relates to a nano antibody NT8 specifically recognizing 19-nortestosterone and application thereof.

Background

19-nortestosterone (19-nortestosterone, 19-NT) is called nandrolone for short, and is an endogenous and exogenous protein assimilation hormone formed by removing the 19 th carbon atom from a testosterone steroid ring structure. Birch first synthesized exogenous 19-NT in 1950, and subsequently Wilds and Nelson succeeded in 1953, and was widely used for hematological diseases, cachexia and progesterone replacement therapy, and protein-deficient diseases in humans and animals, osteoporosis, burn treatment, and the like. The research also finds that the 19-NT has strong capacity of promoting protein synthesis, can participate in the physiological regulation of growth and development, promotes the growth of bones and muscles and reduces fat storage. Therefore, 19-NT is used as a growth promoter for livestock and poultry in many countries and regions to improve productivity and increase feed return. After the athletes take the 19-NT, the muscle strength can be enhanced, and the competition performance can be improved by combining proper exercise and diet.

However, by the end of the 70's 20 th century, a series of accidents led people to recognize the harmfulness of hormone residues. Research shows that 19-NT and metabolite residues thereof can affect liver functions of human, damage cardiovascular systems, and also cause toxic and side effects such as reproductive organ damage, adrenal atrophy, emotional runaway, endocrine dyscrasia and the like. This requires strict monitoring of hormone abuse in food-derived animal production to protect the physical and mental health of the consumer. Therefore, a rapid, sensitive and efficient detection method is urgently needed to realize the rapid detection of 19-NT.

Common methods for detecting 19-NT include gas chromatography-mass spectrometry, liquid chromatography-mass spectrometry, and other quantitative detection methods, but these methods require specialized technicians, cumbersome sample pretreatment processes, and expensive instrumentation, and are not suitable for mass-market detection and field monitoring. The immunological detection technology has the advantages of strong sensitivity, strong specificity, simple operation and low price, can realize the detection of small volume and large flux of biological liquid, and gradually becomes an alternative method for detecting toxic and harmful residues. At present, the immunology detection mainly takes a monoclonal antibody and a polyclonal antibody, but the antibody stability is poor under extreme conditions, so that the accuracy of an immunoassay method established based on the antibody is poor, and therefore, the method for quickly detecting 19-NT with good stability and high detection result accuracy is provided, and has important significance for residue detection and monitoring of 19-NT.

Disclosure of Invention

The invention aims to solve the technical problem of overcoming the defects and shortcomings of the existing 19-NT detection method and provides a nano antibody NT8 for specifically recognizing 19-nortestosterone and application thereof.

The first purpose of the invention is to provide a nanobody NT8 specifically recognizing 19-nortestosterone.

The second purpose of the invention is to provide a gene for coding the nano antibody NT 8.

The third object of the present invention is to provide a recombinant vector.

It is a fourth object of the present invention to provide a recombinant cell.

The fifth purpose of the invention is to provide the application of the nano antibody NT8, the gene, the recombinant vector or the recombinant cell in detecting 19-nortestosterone.

The sixth purpose of the invention is to provide the application of the nano antibody NT8, the gene, the recombinant vector or the recombinant cell in the preparation of a 19-nortestosterone detection reagent/kit.

The seventh purpose of the invention is to provide an immunological detection method of 19-nortestosterone.

The eighth purpose of the invention is to provide a 19-nortestosterone detection kit.

The above purpose of the invention is realized by the following technical scheme:

the invention provides a nano antibody NT8 for specifically recognizing 19-nortestosterone, wherein the amino acid sequence of VHH of the nano antibody NT8 is shown as SEQ ID NO. 1.

According to the invention, a nano antibody NT8 capable of being specifically combined with 19-NT is obtained by screening from a camel immune antibody library by using a phage display technology, and the nano antibody NT8 can specifically recognize 19-NT.

The nanobody NT8 comprises 4 framework regions FR1, FR2, FR3, FR4 and 3 complementarity determining regions CDR1, CDR2, CDR3, the 4 framework regions and 3 complementarity determining regions being arranged in the order FR1, CDR1, FR2, CDR2, FR3, CDR3, FR 4; the amino acid sequence of FR1 is shown as SEQ ID NO.2, the amino acid sequence of CDR1 is shown as SEQ ID NO.3, the amino acid sequence of FR2 is shown as SEQ ID NO.4, the amino acid sequence of CDR2 is shown as SEQ ID NO.5, the amino acid sequence of FR3 is shown as SEQ ID NO.6, the amino acid sequence of CDR3 is shown as SEQ ID NO.7, and the amino acid sequence of FR4 is shown as SEQ ID NO. 8.

The invention also provides a gene for coding the nano antibody NT8, which is characterized in that the nucleotide sequence of the gene is shown in SEQ ID NO. 9.

The invention also provides a recombinant vector which is connected with the gene.

The invention also provides a recombinant cell, which is a cell carrying the recombinant vector or capable of expressing the nano antibody NT 8.

The application of the nano antibody NT8, the gene, the recombinant vector or the recombinant cell in detecting 19-nortestosterone and the application in preparing a 19-nortestosterone detection reagent/kit are all within the protection scope of the invention.

In addition, the invention also provides a 19-nortestosterone immunological detection method, which uses a 19-nortestosterone complete antigen obtained by coupling the 19-nortestosterone hapten and carrier protein in the formula (I) as a coating antigen and uses the nano antibody NT8 as a detection antibody for detection.

Preferably, the structural formula of the 19-nortestosterone hapten is shown as formula (I):

the invention also provides a 19-nortestosterone detection kit, which comprises the nano antibody NT 8.

The invention has the following beneficial effects:

the nano antibody NT8 capable of being specifically combined with 19-NT is obtained by screening, the nano antibody NT8 can specifically identify 19-NT, has higher thermal stability and organic tolerance, can improve the sensitivity of immunodetection of 19-NT, and has the advantages of detection range of 0.48 ng/mL-4.93 ng/mL of 19-NT, IC50 of 1.53ng/mL, lowest detection Limit (LOD) of 0.13ng/mL, and strong detection sensitivity;

the invention also provides a 19-nortestosterone immunological detection method, which has the advantages of simple operation, short time consumption, strong sensitivity of detection results and high accuracy, and the preparation method of the nano antibody NT8 has universal applicability; therefore, the nano antibody NT8 can be well applied to the detection of 19-NT residual actual samples, and has extremely high application value in the detection of 19-nortestosterone or the preparation of 19-nortestosterone detection reagents/kits.

Drawings

Fig. 1 is a schematic diagram of the amino acid sequence and domain division of specific nanobody NT 8.

Fig. 2 is a standard graph of indirect competition ELISA established based on specific nanobody NT 8.

Detailed Description

The invention is further described with reference to the drawings and the following detailed description, which are not intended to limit the invention in any way. Reagents, methods and apparatus used in the present invention are conventional in the art unless otherwise indicated.

Unless otherwise indicated, reagents and materials used in the following examples are commercially available.

Example 1 construction of camelid immune antibody library

(1) Preparation of complete antigens 19-NT-KLH and 19-NT-OVA

The complete antigens 19-NT-KLH and 19-NT-OVA are prepared by coupling the 19-nortestosterone hapten with Ovalbumin (OVA) and Keyhole Limpet Hemocyanin (KLH) which have the structural formula shown in the formula (I) through an active ester method.

The structural formula of the 19-nortestosterone hapten is shown as the formula (I):

(2) camel immunization

Healthy camels were used as experimental animals and 19-NT-KLH as immunogen and injected subcutaneously in the back and neck of camels at a dose of 0.5mL (containing 0.5mg of immunogen) per dose. The first immunization is carried out after emulsifying 0.5mL of complete Freund's adjuvant and immunogen, the subsequent boosting immunization is carried out after emulsifying 0.5mL of incomplete Freund's adjuvant and immunogen, and the interval of each immunization is 1-2 weeks.

Serum was isolated in 10mL of blood before immunization as a negative control. From the second immunization, 10mL of blood after one week of each immunization was taken for serum titer and competition reaction detection. When a better immune response effect appears, 100mL of peripheral blood is taken for separating lymphocytes and is used for constructing a nano antibody library.

(3) Isolation of camel lymphocytes

Mixing camel whole blood with physiological saline with the same volume to obtain 1:1 diluted blood, and standing at normal temperature. 20mL of lymph isolate was added to a sterile 50mL centrifuge tube and 20mL of diluted blood was added slowly along the tube wall using a sterile pasteur dropper. 500g, centrifuge for 30 min. The lymphocyte layer was taken out to a new 50mL centrifuge tube, diluted 2-fold with physiological saline, centrifuged at 2000g at 4 ℃ for 10min, and the supernatant was discarded. The lymphocytes were blown off with 5mL of physiological saline, centrifuged again at 2000g for 10min, and the supernatant was discarded to sufficiently wash the lymphocytes. Lysis solution (TRNsol) was added to each lymphocyte, and 1mL aliquots were dispensed into 2mL centrifuge tubes and stored at-80 ℃ until use.

(4) Extraction of Total RNA

The total RNA extraction was performed according to the Trizol reagent method of Invitrogen corporation. The specific method comprises the following steps:

0.2mL of chloroform was added to 1mL of the above lysate. The centrifuge tube lid was closed, shaken vigorously for 15 seconds, and incubated on ice for 5 min. Centrifuge at 12000rpm for 10min at room temperature. Transferring not more than 80% of the upper aqueous phase to a new centrifuge tube, slowly adding 0.7 volume times of anhydrous ethanol, and mixing; transferring the obtained solution and the precipitate into a GBC adsorption column, centrifuging at 12000rpm for 30s, and discarding the waste liquid; adding 500 mu L of Wash Buffer I into the GBC adsorption column, centrifuging for 1min, and discarding the waste liquid; add 600. mu.L of Wash Buffer II to GBC adsorption column at 12000rpm, centrifuge for 30 seconds, and discard waste. Centrifuging at 12000rpm for 1min, discarding waste liquid, and opening the cover at room temperature to air-dry the residual rinsing liquid in the adsorption column. Transferring the GBC adsorption column into a new centrifuge tube, and adding 30-100 mu L ddH₂O, room temperatureThe mixture was left to stand at 12000rpm for 1min at 4 ℃ for 2 min. The liquid in the tube was collected and stored at-80 ℃.

(5) Synthesis of cDNA

First strand cDNA synthesis was performed using RNA as a template, according to the Takara first Strand reverse transcription kit instructions. The specific method comprises the following steps:

A. according to the first reaction system of cDNA synthesis shown in Table 1, the reagents were mixed in a nuclease-free centrifuge tube and operated in an ice bath;

TABLE 1 first step reaction System for cDNA Synthesis

Total RNA	3μg
		Oligo(dT)₁₈primer	1μL
RNase free ddH₂O	Up to12μL
		Total	12μL

B. Incubating the reaction system at 65 ℃ for 5min, and cooling for 2min in an ice bath;

C. according to the second reaction system of cDNA synthesis shown in Table 2, adding reagent into the system after the reaction of step A;

TABLE 2 second step reaction System for cDNA Synthesis

System after step A reaction	12μL
		5×Reaction Buffer	4μL
RiboLock RNase Inhibitor(20U/μL)	1μL
		10mM dNTP Mix	2μL
RevertAid M-MiLVRT(200U/μL)	1μL
		Total	20μL

D.42 ℃ for 60min and 70 ℃ for 5 min. The reverse transcription product cDNA was stored at-80 ℃.

(6) Amplification of Nano antibody VHH target Gene

First round PCR: the reverse transcription product cDNA obtained in the step (5) is used as a template, a first round PCR reaction is carried out by using a primer Q1/Q2, the nucleotide sequence of the primer Q1/Q2 is shown in Table 5, and the reaction system of the first round PCR is shown in Table 3.

TABLE 3 reaction System for the first round PCR

The reaction conditions for the first round of PCR were: 5min at 94 ℃; 30s at 94 ℃; 30s at 55 ℃; 1min30 cycles at 72 ℃; 10min at 72 ℃.

Second round PCR: the first round PCR reaction product is recovered by using the kit, and is used as a template for the second round PCR after being properly diluted, the second round PCR reaction is carried out by using a primer Q3/Q4, the nucleotide sequence of the primer Q3/Q4 is shown in Table 5, and the reaction system of the second round PCR is shown in Table 4.

TABLE 4 reaction System for the second round of PCR

The reaction conditions for the second round of PCR were: 5min at 94 ℃; 30s at 94 ℃; 30s at 55 ℃; 1min30 cycles at 72 ℃; 10min at 72 ℃.

TABLE 5 primers and nucleotide sequences thereof for amplification of VHH target genes of Nanobodies

(7) Library construction

Digestion of VHH target Gene and vector

Carrying out enzyme digestion on the VHH target gene and the pComb3xss vector by adopting Sfi I enzyme. Enzyme cutting conditions are as follows: reacting for 16 hours in a water bath kettle at 50 ℃.

B. Ligation of the cleavage products

The vector pComb3xss and VHH fragments were mixed well (molar ratio 1: 3), ligated at 16 ℃ for 16h, and then recovered by clean kit.

C. Electric conversion

Adding 5 mu L of the ligation product into 50 mu L of electrotransformation competent E.coil TG1, gently mixing uniformly, transferring into a 0.1cm electrotransfer cup for electric shock transformation (voltage is 1.8kv), immediately adding 950 mu L of SOC culture medium into the electrotransfer cup, culturing at 37 ℃ and 250rpm for 1h, coating the bacterial liquid on an LB-Amp plate, and performing inversion culture at 37 ℃ overnight.

(8) Rescue of library

Inoculating cells with more than 10 times of library volume into 200mL LB (Amp) at 37 ℃, culturing at 250rpm until the OD600 is about 0.4-0.6; the helper phage M13K07(20:1 multiplicity of infection) was added, left to stand at 37 ℃ for 30min, and then cultured at 250rpm for 1h, and kanamycin antibiotic (1: 1000) was added and cultured at 37 ℃ and 250rpm overnight. Centrifuging at 12000rpm and 4 ℃ for 15min, taking supernatant, adding 1/5 volume of PEG/NaCl, and carrying out ice bath for 2-3 h. Centrifuging at 12000rpm for 15min at 4 deg.C, discarding supernatant, resuspending the precipitate with 1mL TBS, transferring to 2mL centrifuge tube, centrifuging at 12000rpm for 5min at 4 deg.C, filtering with 0.22 μm polyethersulfone filter membrane, collecting 10 μ L of assay reservoir, adding glycerol with final concentration of 50%, and preserving at-80 deg.C.

Example 2 affinity panning and identification of Nanobodies

(1) Affinity panning of Nanobodies

First, 19-NT-OVA was used as a coating source, and the 19-NT-OVA coating source was diluted with a coating solution to a final concentration of 12. mu.g/mL and coated overnight at 37 ℃. The following day, after washing twice with PBST (0.01M PBS, 0.05% Tween-20(v/v)), 1% fish glue protein was added and blocked for 2h at 37 ℃. Spin-dry the liquid in the wells and dry them, add 100. mu.L phage pool per well (titer about 10)¹²cfu/mL), incubated at 37 ℃ for 1 h. Unbound phage were discarded, washed 5 times with PBST (0.01M PBS, 0.05% Tween-20(v/v)), 15 times with PBS (pH 7.0), eluted with Gly-HCl (0.2M, pH 2.2) for 10min at 37 ℃ and immediately neutralized with 10. mu.L Tris-HCl (1M, pH 9.0). mu.L of eluted phage was titered and the remainder was used to infect 4mL of E.coil TG1 strain grown to log phase for amplification. On the third day, amplified phages were precipitated with PEG/NaCl and the titer of the phages was determined.

In the second, third and fourth panning processes, 19-NT-OVA coating is diluted by coating liquid until the final concentration is 3 mug/mL, 0.75 mug/mL and 0.1875 mug/mL respectively, phage is added for incubation for 1h, PBST (0.01M PBS, 0.05% Tween-20(v/v)) and PBS are used for washing, a drug competition elution mode is adopted, namely drugs with certain concentration are added, incubation is carried out for 1h at 37 ℃, and liquid in holes is sucked out, namely eluted phage are obtained. The rest steps are the same as above. The elution concentrations of the drugs were 1200ng/mL, 300ng/mL and 150ng/mL, respectively.

(2) Identification of Positive phage clones

The method adopts an indirect enzyme-linked immunosorbent assay to identify the positive phage clone, and comprises the following specific steps:

A. wrapping a plate: the 19-NT-OVA coating stock was diluted to 1. mu.g/mL with the coating solution and coated overnight at 37 ℃. The following day, the cells were washed twice with PBST (0.01M PBS, 0.05% Tween-20(v/v)), then 2% skim milk powder was added, 150. mu.L per well, blocked at 37 ℃ for 2h, the blocking solution was discarded, and the cells were washed twice with PBST (0.01M PBS, 0.05% Tween-20 (v/v)). Oven drying at 37 deg.C for 30min, and packaging in a sealed bag at 4 deg.C.

B. From the plates for which the titer was determined after the third and fourth rounds of panning, 30 clones were randomly selected in 96-well deep-well plates supplemented with Amp-resistant LB medium, and simultaneously inoculated with a single TG1 clone as a negative control, and cultured overnight at 37 ℃. The next day, 10. mu.L of the bacterial suspension was taken out from the 96-well deep-well plate, added to another 96-well deep-well plate, cultured at 37 ℃ and 180rpm for 2 hours, and IPTG (1:1000 ratio, v/v) was added to each well, cultured at 37 ℃ and 180rpm overnight. Centrifuging at 4000rpm on the third day, taking 100 mu L of supernatant, adding the supernatant into a coated enzyme label plate, incubating for 40min at 37 ℃, washing for five times by using PBST (0.01M PBS, 0.05% Tween-20(v/v)), patting the liquid in the hole, adding 100 mu L of HRP-labeled anti-HA secondary antibody diluted by 1:5000, incubating for 40min at 37 ℃, washing for five times by using PBST (0.01M PBS, 0.05% Tween-20(v/v)), patting the liquid in the hole, adding 100 mu L of LTMB substrate solution, and developing for 10min at 37 ℃ in a dark place; add 50. mu.L of stop solution (2M H)₂SO₄) Terminating the reaction; the absorbance at 450nm was measured with a microplate reader. Selection of OD₄₅₀Phage clones that were more than 3 times negative were positive phage clones.

(3) Identification of specific Nanobodies

The method for identifying the positive nano antibody by adopting an indirect competitive ELISA method comprises the following steps:

the 19-NT-OVA coating stock was diluted to 1. mu.g/mL with the coating solution and coated overnight at 37 ℃. The following day, the cells were washed twice with PBST (0.01M PBS, 0.05% Tween-20(v/v)), then 2% skim milk powder was added, 150. mu.L per well, blocked at 37 ℃ for 2h, the blocking solution was discarded, and the cells were washed twice with PBST (0.01M PBS, 0.05% Tween-20 (v/v)). Adding a titer group: 50 μ L of supernatant identified as positive clones by indirect ELISA and 50 μ L of PBS; inhibition group: 50 μ L of supernatant identified as positive clones by indirect ELISA and 50 μ L of 19-NT standard (concentration)1 μ g/mL), incubation at 37 ℃ for 40min, washing with PBST (0.01M PBS, 0.05% Tween-20(v/v)) five times, patting off the liquid in the wells, adding 100 μ L of HRP-labeled anti-HA secondary antibody diluted 1:5000, incubation at 37 ℃ for 40min, washing with PBST (0.01M PBS, 0.05% Tween-20(v/v)) five times, patting off the liquid in the wells, adding 100 μ LTMB substrate solution, and developing at 37 ℃ for 10min in the absence of light; add 50. mu.L of stop solution (2M H)₂SO₄) Terminating the reaction; the absorbance at 450nm was measured with a microplate reader.

The results show that: a nanobody capable of specifically recognizing 19-NT is obtained and named as specific nanobody NT 8.

Example 3 sequencing of Gene encoding specific Nanobody NT8 and determination of amino acid sequence thereof

1. Experimental methods

Sending the bacterial strain of the specific nano antibody NT8 obtained by indirect competitive ELISA identification to a sequencing company for sequencing to obtain a nucleotide sequence of the specific nano antibody NT 8; and obtaining the amino acid sequence of the specific nano antibody NT8 according to the DNA sequencing result and the codon table.

2. Results of the experiment

The amino acid sequence of VHH of specific nanobody NT8 is shown in SEQ ID No.1, and the amino acid sequence and domain division scheme of specific nanobody NT8 is shown in fig. 1, and it can be seen that the specific nanobody NT8 includes 4 Framework Regions (FRs) and 3 complementary-determining regions (CDRs); the framework regions (FR1-FR4) are respectively selected from SEQ ID NO.2, SEQ ID NO.4, SEQ ID NO.6 and SEQ ID NO. 8; the complementarity determining regions (CDR1-CDR3) are respectively selected from SEQ ID NO.3, SEQ ID NO.5, SEQ ID NO. 7; the structure of the framework region is relatively conserved, and the framework region mainly plays a role in maintaining the structure of the protein; the CDR structure is relatively diverse and is primarily responsible for antibody recognition.

Wherein the 1-26 amino acid sequence is FR1, and the amino acid is shown as SEQ ID NO. 2; the amino acid sequence from position 27 to position 38 is CDR1, and the amino acid sequence is shown in SEQ ID NO. 3; the amino acid sequence at the 39 th position to the 55 th position is FR2, and the amino acid is shown as SEQ ID NO. 4; the 56 th-65 th amino acid sequence is CDR2, and the amino acid is shown in SEQ ID NO. 5; the amino acid sequence at the positions 66-104 is FR3, and the amino acid sequence is shown as SEQ ID NO. 6; the 105-120 amino acid sequence is CDR3, the amino acid thereof is shown as SEQ ID NO. 7; the amino acid sequence at position 121-130 is FR4, and the amino acid sequence is shown as SEQ ID NO. 8.

The nucleotide sequence of the specific nano antibody NT8 is shown in SEQ ID NO. 9.

EXAMPLE 5 Mass production of specific Nanobody NT8

The specific nano antibody NT8 is prepared in a protein expression mode, and the specific method comprises the following steps:

the obtained specific nano antibody NT8 strain is extracted with a kit, and the plasmid is transferred into E.coil BL21(DE3) by a chemical transformation method. A single colony from the transformation plate was inoculated in 10mL of LB (Amp) medium and cultured at 37 ℃ and 250rpm overnight. The overnight cultures were incubated at 1:100 was inoculated into 100mL of LB (Amp) medium and cultured at 37 ℃ and 250rpm until the OD600 became about 0.4 to 0.6, and IPTG (1:1000 ratio, v/v) was added and cultured overnight at 37 ℃ and 250 rpm. Centrifuging at 12000rpm for 5min at 4 deg.C in the next day, collecting thallus precipitate, centrifuging at 12000rpm for 10min by sucrose osmotic freeze thawing method, collecting supernatant, and subjecting the supernatant to affinity chromatography purification to obtain expressed specific nanometer antibody NT 8.

Example 5 application of specific Nanobody NT8

1. Coating and sealing

The 19-NT-OVA coating stock was diluted to 1. mu.g/mL with the coating solution and coated overnight at 37 ℃. The following day, the cells were washed twice with PBST (0.01M PBS, 0.05% Tween-20(v/v)), then 2% skim milk powder was added, 150. mu.L per well, blocked at 37 ℃ for 2h, the blocking solution was discarded, and the cells were washed twice with PBST (0.01M PBS, 0.05% Tween-20 (v/v)). Oven drying at 37 deg.C for 30min, and packaging in a sealed bag at 4 deg.C.

2. Establishment of a Standard Curve

(1) Experimental methods

The 19-NT-OVA coating stock was diluted to 1. mu.g/mL with the coating solution and coated overnight at 37 ℃. The following day, the cells were washed twice with PBST (0.01M PBS, 0.05% Tween-20(v/v)), then 2% skim milk powder was added, 150. mu.L per well, blocked at 37 ℃ for 2h, the blocking solution was discarded, and the cells were washed twice with PBST (0.01M PBS, 0.05% Tween-20 (v/v)). Adding 50 mu L of nano antibody and a series of 50 mu L of 19-NT standard substances with different concentrations into each well, incubating for 40min at 37 ℃, washing for five times by PBST, patting off liquid in the wells, adding 100 mu L of HRP-labeled anti-HA secondary antibody diluted by 1:5000, incubating for 40min at 37 ℃, washing for five times by PBST, patting off liquid in the wells, adding 100 mu L of LTMB substrate solution, and developing for 10min at 37 ℃ in a dark place; adding 50 μ L stop solution (2M H2SO4) to stop the reaction; the absorbance at 450nm was read with a microplate reader. An indirect competition standard curve was established with the 19-NT standard concentration versus the abscissa, B/B0 (OD 450 of 19-NT added wells/OD 450 of 19-NT not added wells) as the ordinate.

(2) Results of the experiment

An indirect competition ELISA standard curve graph established based on the specific nano antibody NT8 is shown in FIG. 2, and it can be seen that the standard curve is S-shaped, the linear correlation is good, the detection range is 0.48 ng/mL-4.93 ng/mL, the IC50 is 1.53ng/mL, the lowest limit of detection (LOD) is 0.13ng/mL, and the detection sensitivity is strong.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

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gccgactccg tgaagggccg attcaccatc tcccgaaaca acgccaaaga cacgctctat 240

ctgcagatgg acagcctgaa acctgaggac actgccatgt actactgtac ggcagacatt 300

cgtactagcg tctgccgctc acttagagcc gatcaatttt atttgtgggg ccaggggacc 360

caggtcaccg tctcctca 378

Claims

1. The nano antibody NT8 specifically recognizing 19-nortestosterone is characterized in that the amino acid sequence of VHH of the nano antibody NT8 is shown as SEQ ID No. 1.

2. A gene encoding the nanobody NT8 of claim 1, wherein the nucleotide sequence of the gene is shown in SEQ ID No. 9.

3. A recombinant vector having the gene of claim 2 linked thereto.

4. A recombinant cell, wherein the recombinant cell is a cell carrying the recombinant vector of claim 3 or capable of expressing the nanobody NT8 of claim 1.

5. Use of the nanobody NT8 of claim 1, the gene of claim 2, the recombinant vector of claim 3 or the recombinant cell of claim 4 for detecting 19-nortestosterone.

6. Use of the nanobody NT8 of claim 1, the gene of claim 2, the recombinant vector of claim 3 or the recombinant cell of claim 4 for the preparation of a 19-nortestosterone detection reagent/kit.

7. An immunological detection method of 19-nortestosterone, which is characterized in that a complete antigen of 19-nortestosterone, which is obtained by coupling a hapten of 19-nortestosterone with a carrier protein, is used as a coating antigen, and the nano antibody NT8 of claim 1 is used as a detection antibody for detection; the structural formula of the 19-nortestosterone hapten is shown as the formula (I):

8. a 19-nortestosterone detection kit, characterized in that said kit comprises the nanobody NT8 of claim 1.