Nanometer antibody capable of specifically recognizing staphylococcus aureus and application of nanometer antibody

Abstract

The invention discloses a nano antibody capable of specifically recognizing staphylococcus aureus as well as a preparation method and application of the nano antibody. A ribosome display technology is adopted, a nano antibody pair with a good pairing effect is screened out through construction of a nano antibody display library, three rounds of high-throughput screening and ELISA verification, and the nano antibody pair is used for in-vivo detection of actual pathogenic bacteria in combination with an immunochromatography technology. The nano antibody disclosed by the invention shows high affinity, high specificity and achievable detection limit when being combined with staphylococcus aureus, has the advantages of good stability, low cost and the like compared with a monoclonal antibody, can be produced on a large scale, and has a wide application prospect in the field of staphylococcus aureus detection and analysis.

Description

Technical Field

[0001] The present invention relates to a nanobody specifically recognizing Staphylococcus aureus and its application, belonging to the field of nanobodies. This invention is a divisional application of the invention titled "A nanobody specifically recognizing Staphylococcus aureus, its preparation method and application", with the application number: 2025102876827, and the application date: March 12, 2025. Background Art

[0002] Staphylococcus aureus belongs to the genus Staphylococcus and is a Gram-positive coccus. Its pathogenicity is related to a variety of virulence factors it secretes, including adhesins, invasins, and immune evasion proteins. For example, staphylococcal protein A (SpA) expressed on the surface of Staphylococcus aureus can bind to host IgG (immunoglobulin G), interfering with the host immune system, and coagulation factor A (ClfA) can bind to fibrinogen, promoting bacterial adhesion and immune escape. Currently, monoclonal antibodies against Staphylococcus aureus mainly target its surface proteins, such as SpA and ClfA, etc. However, due to the non-specific binding characteristics of staphylococcal protein A and the disadvantages of traditional antibodies, such as long preparation cycle, poor stability, and high cost, it limits their application in rapid detection.

[0003] Currently, the detection methods for Staphylococcus aureus mainly include bacterial culture, polymerase chain reaction (PCR), and immunoassay. Although bacterial culture is the gold standard method, it is time-consuming and requires professional laboratory equipment and personnel, which greatly limits the screening efficiency of Staphylococcus aureus. Although the PCR technique has high sensitivity, its operation is cumbersome and also requires professional equipment and personnel, making it unsuitable for rapid on-site detection. For example, the patent "Primer set for Staphylococcus aureus and kit for detecting or identifying Staphylococcus aureus" (Application No.: 202411109634.0) discloses a method for detecting Staphylococcus aureus by dual fluorescence quantitative PCR. Although this method attempts to improve the specificity and sensitivity of detection, problems such as the inherent operational complexity of the PCR technique itself and the long detection time still cannot be avoided, limiting its application in rapid on-site detection. Traditional immunoassays, such as ELISA, although having good specificity, have complex operation steps and long detection times. Traditional test strip detection methods, although simple and rapid, have limited sensitivity and high detection limits, making it difficult to meet the requirements of rapid on-site screening. Some emerging detection methods, such as the patent "SERS detection kit and detection method for Staphylococcus aureus" (Application No.: 202410970199.4) disclose a method for detecting Staphylococcus aureus based on surface-enhanced Raman spectroscopy (SERS). Although it can achieve extremely high detection sensitivity and accuracy, its high instrument and consumable costs limit its popularization in practical applications. Therefore, there is an urgent need for a more rapid, sensitive, and cost-controlled means for detecting Staphylococcus aureus. Summary of the Invention

[0004] Object of the Invention: The technical problem to be solved by the present invention is to provide a nanobody with high sensitivity and strong specificity that can specifically recognize Staphylococcus aureus and its application, which is applied to the rapid and in-situ detection of Staphylococcus aureus.

[0005] Technical Solution: To solve the above technical problem, the present invention provides a nanobody (VHH antibody), and the amino acid sequence of the nanobody is shown as any one of SEQ ID NO: 1-6.

[0006] Among them, in the amino acid sequences shown as SEQ ID NO: 1 (Nb26), SEQ ID NO: 2 (Nb33), SEQ ID NO: 3 (Nb42), SEQ ID NO: 4 (Nb57), SEQ ID NO: 5 (Nb63), SEQ ID NO: 6 (Nb84), through pairing experiments, it is found that Nb26 and Nb42 nanobodies have the best pairing effect and can form a paired antibody for use in a sandwich lateral flow chromatography test strip.

[0007] The present invention also provides a gene encoding the nanobody.

[0008] Among them, the nucleotide sequence of the gene is shown as any one of SEQ ID NO: 7-12.

[0009] Among them, the sequence shown as SEQ ID NO: 7 is the nucleotide sequence of the Nb26 nanobody, the sequence shown as SEQ ID NO: 8 is the nucleotide sequence of the Nb33 nanobody, the sequence shown as SEQ ID NO: 9 is the nucleotide sequence of the Nb42 nanobody, the sequence shown as SEQ ID NO: 10 is the nucleotide sequence of the Nb57 nanobody, the sequence shown as SEQ ID NO: 11 is the nucleotide sequence of the Nb63 nanobody, and the sequence shown as SEQ ID NO: 12 is the nucleotide sequence of the Nb84 nanobody.

[0010] The present invention also provides a method for preparing the nanobody, comprising the following steps: (1) Extract alpaca lymphocytes, splice and recombine specific gene fragments into phagemids and transfer them into Escherichia coli to construct a nanobody phage library; (2) Use heat-inactivated Staphylococcus aureus as the coating protein to screen for nanobodies against Staphylococcus aureus.

[0011] Among them, the method for constructing the nanobody phage display library comprises the following steps: (1) Amplify the fragment encoding the nanobody gene from alpaca lymphocytes and introduce Sfi I restriction enzyme sites at both ends of the nanobody; (2) Digest and recombine with the phagemid pComb3XSS, and ligate with T4 ligase to construct a phage display library.

[0012] Specifically, the present invention also provides a method for preparing the above-mentioned nanobody specifically recognizing Staphylococcus aureus, the method comprising the following steps: 1: In vitro transcription and translation: Clone the nanobody phage library into a ribosome display vector. Then, use an in vitro transcription and translation system to transcribe the ribosome display vector into mRNA and translate it into a nanobody-ribosome-mRNA complex to form a ribosome display library; 2: Affinity screening: Inactivate Staphylococcus aureus (ATCC 25923) and coat it on a solid-phase carrier (in this experiment, an ELISA plate was used). Then, add the ribosome display library obtained by in vitro transcription and translation into the system containing immobilized Staphylococcus aureus, and incubate at an appropriate temperature and time. During this period, the nanobodies displayed on the ribosomes will interact with Staphylococcus aureus. The nanobody-ribosome-mRNA complex that specifically binds to the target will be captured, while the unbound complex will remain in the solution. Remove the unbound nanobody-ribosome-mRNA complex to reduce background noise and improve the specificity of the screening. Finally, use a specific elution method to elute the nanobody-ribosome-mRNA complex bound to Staphylococcus aureus from the solid-phase carrier. (In this invention, acidic elution is used: elute with a buffer of low pH, 0.1 M glycine-HCl (pH 2.2). After elution, immediately neutralize with a neutral buffer to protect the integrity of mRNA).

[0013] 3: Recovery and amplification of VHH gene: Extract mRNA from the ribosome-mRNA complex bound to Staphylococcus aureus. Using the extracted mRNA as a template for reverse transcription PCR (RT-PCR), amplify the VHH gene fragment with primers matching the ribosome display vector. Finally, perform multiple rounds of screening to obtain specific nanobodies with high affinity. Extract mRNA from the eluate for subsequent RT-PCR amplification.

[0014] 4: Cloning, expression, and purification: Clone the amplified VHH gene fragment into a suitable expression vector, transform an expression system such as Escherichia coli for expression, and purify the soluble nanobody using affinity chromatography.

[0015] 5: Identification of binding activity and specificity: Use the ELISA method to identify the binding activity of the purified nanobody to Staphylococcus aureus. At the same time, perform cross-reaction experiments with other bacteria (Escherichia coli, Salmonella, Vibrio parahaemolyticus, etc.) to verify the specificity of the nanobody.

[0016] The present invention also provides the use of the nanobody or the gene in the preparation of a Staphylococcus aureus nanobody AIE fluorescence probe.

[0017] The present invention also provides a Staphylococcus aureus nanobody AIE fluorescence probe, comprising the nanobody or the gene.

[0018] The present invention also provides the use of the nanobody or the gene in the preparation of a detection reagent or kit for specifically recognizing Staphylococcus aureus.

[0019] The present invention also provides a detection reagent or test strip, comprising the nanobody or the gene.

[0020] The test strip proposed by the present invention can be applied to biological samples such as plasma and urine, food samples such as milk and meat products, and environmental samples such as wastewater and aerosol. When Staphylococcus aureus is present, the test line (T line) and the quality control line (C line) on the test strip show red fluorescence. When Staphylococcus aureus is absent, the quality control line shows red fluorescence while the test line does not develop color.

[0021] The present invention also provides the application of the nanobody or the gene in constructing an immunoassay platform for Staphylococcus aureus.

[0022] The present invention also provides a method for detecting Staphylococcus aureus in biological samples based on a POCT test strip, comprising the following steps: (1) Paste the NC membrane, absorbent pad, conjugate pad, and sample pad on the PVC bottom plate and assemble them according to the specifications of the test strip; draw the Super monoclonal antibody on the NC membrane as the quality control line (C line), and draw the anti-Staphylococcus aureus nanobody Nb26 on the NC membrane as the test line (T line), and dry for 1-2 h.

[0023] (2) Cut into test strips according to the specifications of the test strip with a test strip cutting machine, add AIE fluorescent microspheres labeled with anti-Staphylococcus aureus nanobody Nb42 to the conjugate pad, and dry at 37 °C for 1-2 h; use a pipette to add it dropwise to the sample pad of the prepared test strip, and after chromatography for 5-10 min, observe the luminescence of the T and C lines of the test strip under an ultraviolet lamp to evaluate the sensitivity of this method for detecting Staphylococcus aureus in biological samples.

[0024] Nanobody (VHH) is the variable region of a heavy chain antibody isolated from camelids, with a molecular weight of about 15 kDa, only 1 / 10 of that of traditional antibodies. Compared with traditional antibodies, nanobodies have many advantages: higher affinity and specificity, capable of recognizing hidden epitopes (such as region A of ClfA) that are difficult for traditional antibodies to recognize; excellent stability, still maintaining activity even under high temperature or extreme pH conditions; easy to be prepared and modified in large quantities by genetic engineering techniques; good tissue penetration, and lower production costs, etc. Combining nanobodies with lateral flow chromatography can develop rapid diagnostic test strips with higher sensitivity, stronger specificity, better stability, and lower cost, overcome the limitations of traditional methods, and achieve rapid, convenient, and in-situ detection of Staphylococcus aureus, having broad application prospects in the fields of food safety, clinical diagnosis, etc.

[0025] The present invention also provides an application of the above-mentioned nanobody pair specifically recognizing Staphylococcus aureus. The ribosome-displayed nanobody pair of the present invention can specifically bind to Staphylococcus aureus. Combining this pair of nanobodies with the lateral flow chromatography method can achieve in-situ and rapid detection of Staphylococcus aureus. The method includes the following steps: (1) Place the NC membrane in a vacuum drying oven and dry it for later use. Paste the NC membrane, absorbent pad, conjugate pad, and sample pad on the PVC bottom plate. The sample pad is on the conjugate pad, the conjugate pad is on the NC membrane, and the absorbent pad is about 2 - 4 mm on the NC membrane. Draw the SuperC monoclonal antibody on the NC membrane as the control line (C line), and draw the anti-Staphylococcus aureus nanobody Nb26 on the NC membrane as the test line (T line), and dry it in the vacuum drying oven for 1 - 2 h; (2) Cut it into test strips according to the specifications of the test strip. Drop the fluorescent microspheres labeled with the anti-Staphylococcus aureus nanobody Nb42 on the conjugate pad, dry it at 37 °C for 2 h. Add a certain volume of Tween-20 to the sample to be tested, and use a pipette to drop it on the sample pad of the prepared test strip. After chromatography for 10 min, observe the luminescence of the T and C lines of the test strip under ultraviolet light at 365 nm to evaluate the concentration of Staphylococcus aureus in the sample detected by this method.

[0026] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: 1. Compared with traditional monoclonal antibodies, the ribosome-displayed nanobodies of the present invention have the advantages of small size, high stability, simple preparation, low cost, and large-scale production; 2. The immunochromatography method provided by the present invention has a fast detection speed, strong specificity, and high sensitivity, and can achieve multi-scene, instant, and in-situ detection of Staphylococcus aureus; 3. Traditional monoclonal antibodies are affected by the binding of the Fc end to Staphylococcus aureus protein A (SPA), making it difficult to directly detect Staphylococcus aureus. They can only indirectly detect the toxic substances secreted by bacteria, and it is difficult to accurately evaluate the infection situation of patients and the pollution situation of water sources and foods. The present invention can achieve direct detection of Staphylococcus aureus; 4. The cell-free system of the nanobody library of the present invention can overcome the deficiencies such as biosafety and toxic proteins, and has advantages in expressing recombinant proteins or antibodies; therefore, developing a cell-free system-based nanobody library has important value for efficient screening of nanobodies; 5. A pair of Staphylococcus aureus nanobody pairs with particularly good pairing effects was screened out this time, effectively improving the detection effect. Description of the Drawings

[0027] Figure 1To verify the affinity results of 6 phage-displayed nanobodies by Phage-ELISA, the abscissa is the nanobody and the ordinate is the absorbance value at 450 nm; Figure 2 For the antigen specificity verification results of Listeria monocytogenes ATCC19115, the abscissa is the nanobody and the ordinate is the absorbance value at 450 nm; Figure 3 For the antigen specificity verification results of Vibrio parahaemolyticus ATCC17802, the abscissa is the nanobody and the ordinate is the absorbance value at 450 nm; Figure 4 For the antigen specificity verification results of Rotavirus, the abscissa is the nanobody and the ordinate is the absorbance value at 450 nm; Figure 5 For the antigen specificity verification results of Norovirus, the abscissa is the nanobody and the ordinate is the absorbance value at 450 nm; Figure 6 For the antigen specificity verification results of Escherichia coli (wild E. coli), the abscissa is the nanobody and the ordinate is the absorbance value at 450 nm; Figure 7 For the antigen verification specificity results of Salmonella ATCC13076, the abscissa is the nanobody and the ordinate is the absorbance value at 450 nm; Figure 8 For the detection of Staphylococcus aureus at different concentrations by the Staphylococcus aureus test strip; Figure 9 For the specific identification of the Staphylococcus aureus test strip; Figure 10 For the optimization of the fluorescence probe pH; Figure 11 To screen the pair of nanobodies with the best pairing effect by the checkerboard method. Detailed implementation manners

[0028] The technical solutions of the present invention will be further described below with reference to the accompanying drawings.

[0029] Main experimental materials: Standard strain of Staphylococcus aureus (ATCC 25923) Main reagents: Chicken ovalbumin and bovine ovalbumin were purchased from Sigma, USA. Horseradish peroxidase (HRP)-anti-M13 monoclonal antibody (product number: 11973-MMO5T) was purchased from Sino Biological Inc., Beijing. Skim milk powder, 3,3′,5,5′-tetramethylbenzidine (TMB) chromogenic solution, and isopropyl-β-D-thiogalactoside (IPTG) were purchased from Sangon Biotech Co., Ltd., Shanghai. LB broth and 2×YT medium were purchased from Qingdao Hope Bio-Technology Co., Ltd.

[0030] Main reagent formulations: 1. 2×YT liquid medium: Weigh 31 g of 2×YT powder, dissolve it in 1000 mL of ultrapure water, and autoclave at 121 °C for 15 min; 2. 2×YT solid medium: Weigh 31 g of 2×YT powder and 18 g of agar, dissolve them in 1000 mL of ultrapure water, and autoclave at 121 °C for 15 min; 3. LB liquid medium: Weigh 25 g of LB medium, dissolve it in 1000 mL of ultrapure water, and autoclave at 121 °C for 15 min; 4. 20% polyethylene glycol (PEG)-NaCl: 50 g of PEG-8000, 36 g of NaCl, dissolve by heating with ultrapure water, make up the volume to 250 mL, and autoclave for 15 min; 5. Elution buffer: 0.2 M glycine (Gly), adjust the pH to 2.2 with hydrochloric acid, and autoclave for 15 min; 6. Neutralization buffer: 1 M tris(hydroxymethyl)aminomethane (Tris), adjust the pH to 9.1 with hydrochloric acid, and autoclave for 15 min.

[0031] Example 1: Inactivation of Staphylococcus aureus (1) Streak the standard strain of Staphylococcus aureus on an LB plate and incubate at 37 °C for 12 - 14 h; (2) Pick a single colony on the plate and inoculate it into 5 ml of LB medium, incubate at 37 °C for 12 - 14 h; (3) Spread and count on an LB plate, incubate at 37 °C for 12 - 14 h; (4) Pipette 1 ml of the counted bacterial solution, centrifuge at 8000 rpm for 2 min, resuspend with PBS, and repeat 3 times; (5) Preheat the metal bath to 90 °C and heat at 90 °C for half an hour to obtain the inactivated strain.

[0032] Example 2: Amplification of VHH gene and construction of a nanobody ribosome display library (1) RNA extraction: Extract total RNA from B lymphocytes of immunized alpacas; (2)cDNA synthesis: Reverse transcribe RNA into cDNA using SuperScript IV reverse transcriptase (reaction system: 1 μg RNA, 1 μL reverse transcriptase, 4 μL 5X buffer, 2 μL 10 mM dNTPs, 1 μL RNase inhibitor, make up the volume to 20 μL with water; reaction conditions: 42°C for 60 minutes, 70°C for 15 minutes); (3)VHH gene amplification: Perform PCR amplification of the VHH gene from cDNA of multiple B lymphocytes using specific primers VHH-F and VHH-R with SfiI restriction enzyme sites (reaction system: 1 μL cDNA, 1 μL DNA polymerase, 5 μL 10X buffer, 1 μL 10 mM dNTPs, 1 μL primer VHH-F, 1 μL primer VHH-R, make up the volume to 50 μL with water; reaction conditions: 95°C for 3 minutes; 95°C for 30 seconds, 58°C for 30 seconds, 72°C for 1 minute, 35 cycles; 72°C for 7 minutes; primers are VHH-F (SEQ ID NO:13) and VHH-R (SEQ ID NO:14); (4)SfiI digestion: Digest the PCR product and the ribosome display vector pRibVec (purchased from Agilent) with SfiI restriction enzyme. Among them, the reaction system: 5 μL PCR product or vector, 1 μL SfiI, 2 μL 10X buffer, make up the volume to 20 μL with water; reaction conditions: 37°C for 2 hours; (5)Use T4 DNA ligase to ligate the digested VHH gene fragment and the vector pRibVec (reaction system: 1 μL vector, 3 μL PCR product, 1 μL T4 DNA ligase, 2 μL 10X buffer, make up the volume to 20 μL with water; reaction conditions: 16°C overnight); (6)In vitro transcription: Transcribe the ligation product into mRNA using the TNT T7 Quick Master Mix in vitro transcription kit to obtain a nanobody ribosome display library (operate according to the kit instructions, the kit is the TNT® T7 PCRDNA Quick System, purchased from Promega (Beijing) Biotechnology Co., Ltd.).

[0033] Example 3 Screening and Identification of Staphylococcus aureus Ribosome Display Nanobodies 1. Antigen coating: Coat the purified Staphylococcus aureus from Example 1 onto an ELISA plate, with a coating volume of 100 μL / well, and coat overnight at 4°C.

[0034] 2. Blocking: Block non-specific binding sites using 3% BSA. The blocking volume is 300 µL / well and incubate at 37°C for 2 hours.

[0035] 3. Binding: Add the mRNA-ribosome-nanobody complex in the nanolibrary constructed in Example 2 and incubate at 37°C for 60 minutes.

[0036] 4. Washing: Wash the unbound complex using PBST. The number of washing times is 5 times, and the washing solution concentration is 0.05%, which can be adjusted according to the screening rounds.

[0037] 5. Elution: Elute the bound mRNA using 200 µL of 0.1 M Gly-HCl (pH 2.2) for 15 minutes. Immediately add 20 µL of 1 M Tris-HCl (pH 9.1) to neutralize the eluate.

[0038] 6. Recover mRNA: Recover the mRNA in the eluate using a commercial kit.

[0039] 7. RT-PCR Amplification: Amplify the recovered VHH nanobody gene using reverse transcription PCR. Among them, the reaction system: 800 ng of cDNA + 1 µL of AlpVh-LD (10 uM) + 1 µL of CH2-R (10 uM) + 7 µL of 10× PCR Buffer + 0.1 µL of Hot STAR Taq DNA Polymerase + 0.4 µL of dNTP mix (10 uM), add ddH2O to 50 µL.

[0040] The reaction program is as follows: 1× 98°C 15 min 35× 96°C 1 min 35× 61.5 / 62.8 / 64.7 / 68°C 1 min 35× 70°C 1 min 1× 70°C 10 min 1× 4°C Store at 4°C Among them, the vector is pCMV-3Tag (purchased from Agilent); the primers were synthesized by Shanghai Sangon Biotech Co., Ltd. The specific primers are: CH2-R (as shown in SEQ ID NO: 15), AlpVh-LD (as shown in SEQ ID NO: 16), P4-S (as shown in SEQ ID NO: 17), P4-L (as shown in SEQ ID NO: 18), P5 (as shown in SEQ ID NO: 19), P6-new (as shown in SEQ ID NO: 20), AlpVh-FR1-Fnew (as shown in SEQ ID NO: 21).

[0041] Among them, the usage of the primers was carried out with reference to the instruction manual of TAKARA's RNAiso reagent: Using PrimeSTAR high-fidelity DNA polymerase, the variable region coding gene of the heavy chain antibody was obtained by nested PCR. In the first round of PCR, cDNA was amplified with the primers AlpVh-LD and CH2-R respectively. Then, the first-round amplification products were used as templates for the second-round amplification and amplified with the remaining primers respectively. After recovery and quantification with a recovery kit, they were stored at -20°C for later use.

[0042] 8. Multiple rounds of screening: Repeat steps 1-7 for 3 rounds of screening to gradually increase the screening stringency. Finally, the desired mRNA-ribosome-nanobody complex (amino acid sequence as shown in SEQ ID NO: 1-6) was obtained.

[0043] 9. A checkerboard method was used for the pairing experiment to screen out a pair of highly sensitive and strongly specific paired antibodies, which mainly included the following steps: (1) Coat the mRNA-ribosome-nanobody complex (amino acid sequence as shown in SEQ ID NO: 1-6) at 50 μg / ml and incubate overnight; (2) Wash the plate 3 times with 0.05% PBST, and incubate with 5% skim milk powder at 37°C for 2 h; (3) Wash the plate 3 times with 0.05% PBST, and add 10 8 cfu / ml of heat-inactivated Staphylococcus aureus obtained in Example 1 and incubate at 37°C for 1 h; (4) Wash the plate 3 times with 0.05% PBST, recover the bound mRNA, and incubate at 37°C for 45-60 min; (5) Wash the plate 6 times with 0.05% PBST, add 100 μL of horseradish peroxidase (HRP)-anti-M13 monoclonal antibody to each well, and incubate at 37°C for 45-60 min; (6) Wash the plate 7 times with 0.05% PBST, add 100 μL of TMB chromogenic solution, incubate at 37°C for 15 min and conduct identification; The results are as Figure 11As shown, the effects of Nb26 and Nb42 are the best.

[0044] Example 4: Synthesis of Staphylococcus aureus nanobody AIE fluorescence probe 1) Take 100 μL of AIE fluorescence microsphere solution (1 wt%), add 500 μL of MES PH6.0 buffer for washing once, and centrifuge at 12000 rpm for 15 min to remove the supernatant; 2) Add 500 μL of MES PH6.0 buffer to redissolve the microspheres, then add 30 μL of EDC and 90 μL of NHS (both with a concentration of 3 mg / mL, freshly prepared with MES PH6.0 buffer), rotate and shake in the dark for 30 min, and centrifuge at 12000 rpm for 15 min to remove the supernatant; 3) Add 500 μL of MES PH 6.5 buffer for washing once, add 500 μL of MES PH6.5 buffer to redissolve the microspheres, add 20 μg of labeled antibody Nb42 (the amount of antibody varies according to the concentration), rotate and shake in the dark for 2 h, and centrifuge at 12000 rpm for 15 min to remove the supernatant; 4) Add 500 μL of blocking solution (3% casein) to redissolve, rotate and shake in the dark for 1 h, and centrifuge at 12000 rpm for 15 min to remove the supernatant; 5) Add 500 μL of preservation solution (preservation solution: 0.02 m Tris + 0.1% Tween-20 + 0.5% BSA + 0.03% Proclin300) for washing once, and centrifuge to remove the supernatant; 6) Add 100 μL of preservation solution to redissolve, and store at 2 - 8 °C.

[0045] Furthermore, adjust the pH of the Staphylococcus aureus nanobody AIE fluorescence probe with potassium carbonate, and the addition amount is between 30 and 70 μL, so that the pH is 6 - 8. The results are as Figure 10 shown. When the pH is 8, the detection effect of the Staphylococcus aureus nanobody AIE fluorescence probe is the best. Among them, Figure 10 the pH values from left to right are 6, 7, and 8 respectively.

[0046] Example 5

[0047] (1) Coated antigen: Different target antigens (e.g., antigens / proteins of Staphylococcus aureus ATCC25923, Listeria monocytogenes ATCC19115, Vibrio parahaemolyticus ATCC17802, Rotavirus, Norovirus, Escherichia coli, Salmonella ATCC13076, and the specific concentration needs to be optimized according to the actual antigen characteristics) are respectively coated in different wells of a 96-well ELISA plate and incubated overnight at 4°C. After washing the plate, the unbound sites of the ELISA plate are blocked with 5% skim milk and incubated at 37°C for 2 hours.

[0048] (2) Adding ribosome display complex: The mRNA-ribosome-protein complex obtained by in vitro transcription and translation (where the mRNA encodes a nanobody library with different sequences) is added to each well of the ELISA plate coated with different antigens. Incubate at 37°C for 1 hour. Wash 3 times with 0.05% PBST to remove the unbound complex.

[0049] (3) Adding detection antibody: Add HRP-labeled anti-His tag antibody and incubate at 37°C for 45 - 60 minutes. Wash 6 times with 0.05% PBST to remove the unbound detection antibody.

[0050] (4) Adding chromogenic substrate and measurement: Add 100 μL of TMB chromogenic solution to each well, incubate at 37°C for 15 minutes, and measure the absorbance value (OD450nm) with an ELISA reader. The reaction results of each nanobody with different antigens are respectively plotted as a bar graph and compared with the blank control to obtain the results as Figures 1 - 7 shown.

[0051] Example 6: Rapid identification steps of test strip 1) Place the NC membrane in a vacuum drying oven and dry at 37°C for 60 - 100 min. According to the structure of the chromatographic test strip, paste the NC membrane on the PVC bottom plate. Press the sample pad on one side against the conjugate pad, the conjugate pad against the NC membrane, and press the absorbent pad on the other side against the NC membrane with a pressure of about 2 - 6 mm to assemble the test strip.

[0052] 2) Use a gold-spraying and membrane-stripping instrument to draw a detection line of Staphylococcus aureus-coated antibody Nb26 (pH 8) at 1 - 2 mg / mL and a quality control line of SuperC+ antibody at 2.5 mg / mL; the distance between the detection lines is 2 - 4 mm, and place it in a vacuum drying oven to dry for 4 - 6 h.

[0053] 3) Use a test strip cutter to cut the test strips into test strips of 2 - 8×60 - 100 mm, seal them in bags for later use.

[0054] 4) Sensitivity detection: Pipette 100 μL of amplification products with different initial concentrations (1×10 3 ~1×10 8 CFU / mL), add Tween - 20 with a final concentration of 0.05% to it, drip it onto the sample pad of the prepared test strip, and add the set blank control. Let it stand for 10 min, and observe the luminescence of the test line and the quality control line under the excitation of ultraviolet light at 365 nm. The results are as Figure 8 shown. The luminescence decreases from left to right in the order of 10 8 、10 7 、10 6 、10 5 、10 4 、10 3 CFU / mL, and the detection limit is 10 4 CFU / mL.

[0055] 5) Specificity detection: Pipette 100 μL of amplification products respectively, mix them with Staphylococcus aureus solution (ATCC 25923), Salmonella solution, Shigella solution (ATCC 25931), rotavirus, FOB (brand: Sigma - Aldrich, catalog number: H0267), and norovirus at the same concentration (10 6 CFU / mL), add Tween - 20 with a final concentration of 0.05% to it, drip it onto the sample pad of the prepared test strip, let it stand for 10 min, and observe the luminescence of the test line and the quality control line under the excitation of ultraviolet light at 365 nm. The results are as Figure 9 shown. The nanobody specifically recognizes Staphylococcus aureus antigen. Among them, from left to right are Staphylococcus aureus, Salmonella, Shigella, rotavirus, FOB, and norovirus.

Claims

1. A nanobody that specifically recognizes Staphylococcus aureus, characterized in that: The amino acid sequence of the nanobody is shown in SEQ ID NO:

6.

2. A gene encoding the Nanobody according to claim 1.

3. The gene according to claim 2, characterized in that The nucleotide sequence thereof is shown in SEQ ID NO:

12.

4. Use of the nanobody according to claim 1 in the preparation of a Staphylococcus aureus nanobody AIE fluorescent probe.

5. A Staphylococcus aureus nanobody AIE fluorescent probe, characterized in that: Comprising the Nanobody described in claim 1.

6. Use of the nanobody according to claim 1 in the preparation of a detection reagent or a kit for specifically recognizing Staphylococcus aureus.

7. A detection reagent or test strip, characterized in that: Comprising the Nanobody described in claim 1.

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