1. A detection method of a tumor cell marker miRNA-21 is characterized by comprising the following steps:

(1) preparing an AuNPs probe and a GNS probe;

(2) carrying out double-signal detection on miRNA-2 in the buffer solution by the AuNPs probe and the GNS probe prepared in the step (1);

(3) preparation of functionalized MnO₂Nanosheets;

(4) and (3) carrying out fluorescence imaging and Raman quantitative detection on the miRNA-21 in the cells.

2. The method for detecting the tumor cell marker miRNA-21 of claim 1, wherein the AuNPs probe is prepared in the step (1) by the following steps:

HAuCl with the mass fraction of 0.01 percent is added under stirring₄Heating the solution to boiling, and quickly adding 1% by weight of trisodium citrate solution, HAuCl₄The volume ratio of the solution to the sodium citrate solution is 100: 3.5, when the color of the solution changes from light yellow to colorless and then changes from colorless to wine red, after boiling for 10min, stirring and cooling to room temperature, filtering the solution by using a 0.45 mu m Millipore membrane filter to obtain an AuNPs solution and storing the AuNPs solution at 4 ℃;

preparation of hybrid chain C1: adding 100nM 1.5. mu.L of TCEP to 10. mu.M 100. mu.L of S1 DNA, activating at room temperature for 1h, mixing the activated S1 DNA with 50. mu.M 30. mu.L of F1 DNA and 50. mu.M 30. mu.L of Walker DNA, heating to 75 ℃ and incubating for 10min, cooling to room temperature and hybridizing under dark conditions for at least 12 h; preparation of hybrid chain C2: adding 100nM 1.5. mu.L of TCEP to 10. mu.M 100. mu.L of S2 DNA, activating at room temperature for 1h, mixing the activated S2 DNA with 50. mu.M 30. mu.L of F2 DNA and 50. mu.M 30. mu.L of Walker DNA, heating to 75 ℃ and incubating for 10min, cooling to room temperature and hybridizing under dark conditions for at least 12 h; mixing 100 μ L of the mixture at a volume ratio of 6: adding a C1/C2 mixed system of 1 into 2mL of AuNPs solution, stirring for 24h at 25 ℃, continuously adding 10 mu L of Tween20 solution with the mass fraction of 10%, finally adding 100 mu L of PBS solution containing 2M NaCl, continuously passivating for 3 times, and continuously culturing for 20h to obtain a mixed solution;

after centrifuging the mixed solution, the gold nanoparticles were washed with 10mmol/LTris HCl buffer solution, and the gold nanoparticles were dispersed in 10mmol/LTris HCl buffer solution with a volume fraction of 0.02% Tween-20, the pH of the buffer solution being 8.0.

3. The method for detecting the tumor cell marker miRNA-21 of claim 1 or 2, wherein the step (1) of preparing the GNS probe comprises the following steps:

dissolving 0.1g of PVP in 25mL of DEG, heating until reflux, injecting 2mL of DEG solution containing 20mg of HAuCl 4.3H 2O after 5min, stopping reaction after 10min, cooling to room temperature, centrifuging to obtain icosahedron gold seeds, washing the icosahedron gold seeds twice by DMF, and dispersing in 27mL of DMF;

dissolving 1.2g PVP in 15mL DMF, adding 50 μ L DMA solution with mass fraction of 40% and 80 μ L2.5M HCl solution, sequentially adding 1mL DMF solution containing icosahedron gold seed and 20 μ L0.5M HAuCl₄Obtaining a reaction solution from the solution; stirring the reaction solution at 80 ℃ for 4h, centrifuging to obtain highly symmetric gold nano-star GNS, washing the highly symmetric gold nano-star GNS twice with ethanol, and dispersing in 2mL of water to obtain GNS mixed solution;

heating 100 μ L of 10 μ M hairpin H1 DNA strand in water bath at 95 deg.C for 5min, then cooling to room temperature in ice bath, adding 1.5 μ L of 100nM TCEP to hairpin H1 DNA strand, and activating hairpin H1 DNA strand for 1H; 1mL of the GNS mixed solution and 100. mu.L of 10. mu.M of the activated hairpin H1 DNA strand were mixed and placed in a beaker, shaken in a shaker at 37 ℃ for 24 hours, centrifuged and washed in sequence, and then dispersed in 10mmol/L Tris HCl buffer solution with volume fraction of 0.02% Tween-20, wherein the pH of the buffer solution was 8.0.

4. The method for detecting the tumor cell marker miRNA-21 of claim 1 or 2, wherein in the step (2), the miRNA-21 in the buffer is subjected to dual-signal detection: mixing 200 mu g/ml of 1ml of dispersed AuNP probe, 60 mu g/ml of 1ml of dispersed GNS probe and 20 mu M of 100 mu L of fuel DNA, adding the mixture into miRNA-21 to prepare miRNA-21 solutions with different concentrations, incubating the miRNA-21 solutions at 37 ℃ for 3 hours respectively, centrifuging the solutions, using the supernatant for fluorescence spectrum detection, and collecting 500-600 nm FAM fluorescence under the maximum excitation wavelength of 492 nm; resuspend the pellet in PBS, then drop the solution onto the surface of a slide, and examine the raman spectrum and intensity of the sample with a confocal raman spectrometer under the following conditions: the laser excitation wavelength is 633nm, the accumulation time is 10s, the scanning time is 10s, the laser power is 30mW, and the range is 400-1700 cm < -1 >; repeating the experiment for three times to obtain a fluorescence spectrum and a Raman spectrum; fuel DNA was measured from 1: 1 Fuel 1DNA and Fuel H DNA were mixed and prepared.

5. The method for detecting miRNA-21 as a tumor cell marker according to claim 1 or 2, wherein the functionalized MnO is prepared in step (3)₂The process of the nanosheet is as follows: 20mL of 0.6M tetramethylammonium hydroxide and 3 wt% H were added over 15s₂O₂The mixed aqueous solution of (2) was added to 10mL of 0.3M MnCl₂Stirring the dark brown suspension at room temperature overnight, centrifuging, washing the obtained precipitate with distilled water and methanol in sequence, and drying at 60 deg.C to obtain manganese dioxide block; dispersing 10mg of blocky manganese dioxide in 20mL of water, performing ultrasonic treatment, and centrifuging to obtain MnO₂Nanosheets; MnO at room temperature₂Mixing the nanosheet with 20 mu M100 mu L fuel DNA for 20min, wherein the fuel DNA is 1: 1 Fuel 1DNA and Fuel H DNA were mixed and incubated at room temperature for 20min with HEPES buffer.

6. The method for detecting miRNA-21, a tumor cell marker, according to claim 5, wherein the HEPES buffer solution in step (3) has a concentration of 20mM and a pH of 7.2, and comprises 150mM NaCl and 2mM MgCl₂。

7. The method for detecting the tumor cell marker miRNA-21 according to claim 1 or 2, wherein the specific process of the step (4) is as follows: when the cells are in the logarithmic growth phase, 1mL of cell suspension with the cell concentration of 2X 104/mL is inoculated in a laser confocal culture dish, and after the cells are attached to the wall, the CO with the volume fraction of 5 percent at 37 ℃ is added₂Under the condition, the cells are respectively cultured for 1h, 2h, 3h, 4h and 6h in a fresh culture medium containing 2mL of mixed probes, and the preparation process of the mixed probes comprises the following steps: respectively centrifuging an AuNP probe with the concentration of 60 mu g/mL and a GNS probe with the concentration of 200 mu g/mL, and then suspending in 2mL of a functionalized MnO2 nanosheet solution with the concentration of 50 mu g/mL; removing the mixed solution, washing the cells with PBS for three times, fixing the cells with 4% paraformaldehyde, dyeing the cells with DAPI, washing the cells with PBS for two times, and performing fluorescence imaging; the raman spectrum and intensity of the cells were measured with a confocal raman spectrometer under the following conditions: the laser excitation wavelength is 633nm, the accumulation time is 10s, the scanning time is 10s, the laser power is 30mW, and the range is 400-1700 cm < -1 >; 20 cells were selected for SERS detection and the average was calculated.

8. The method for detecting the tumor cell marker miRNA-21 of claim 7, wherein a regression equation is determined by taking a standard curve of lg value of the concentration of the miRNA-21 standard substance and the detected Raman and fluorescence signal intensity, and the applicability of the regression equation in the cell is verified by simulating the intracellular environment; and calculating the content of the miRNA-21 in the living cells according to the detected Raman signal intensity or fluorescence signal intensity of the miRNA-21 in each cell.

Background

Detection of the dynamic changes in tumor-associated nucleic acid markers in tumor progression is critical to accurately direct therapy and understand the mechanisms of tumorigenesis. Research on the tumor-associated marker miRNA shows that the dynamic change of the expression level of the miRNA is closely related to tumor progression and prognosis. However, the miRNA has small volume and low expression level, and sequences of similar homologous families are easy to degrade, so that the change of the level of the miRNA in the cell is difficult to dynamically monitor.

The traditional methods for detecting miRNA mainly comprise RNA blotting technology, quantitative instant polymerase chain reaction, microarray analysis, surface plasma resonance, electrochemical technology and the like. Although these methods have high sensitivity and selectivity, their use is limited by complex sample handling, expensive reagents and lengthy experimental time. A number of fluorescence imaging techniques have been reported for the in situ detection of mirnas in cells. These fluorescence techniques have the advantages of high resolution, high selectivity and no trauma, however, most of these methods are used for qualitative imaging of miRNA in living cells, and few fluorescence methods are used for quantitative studies of intracellular miRNA. Although in situ quantification methods using multifunctional gold nanoprobes with fluorescein isothiocyanate fluorescence as the detection signal have been reported, photobleaching, optical instability of fluorescent dyes, and background autofluorescence still severely limit intracellular quantification of mirnas.

Surface Enhanced Raman Scattering (SERS) is a phenomenon in which the raman scattering signal of an adsorbed molecule is significantly enhanced compared to the Normal Raman Scattering (NRS) signal due to the enhancement of an electromagnetic field on the surface or near the surface of a sample in a specially prepared metal conductor surface or sol. In recent years, Surface Enhanced Raman Scattering (SERS) has attracted much attention from the scientific community because of its excellent sensitivity, inherent chemical fingerprint information, and the like. The nanoscale regions of the enhanced electromagnetic field are randomly distributed on the SERS substrate and are very rare (< 0.1% of the total number of SERS-active sites) and the analyte is not necessarily located at a hot spot, so the reproducibility of the SERS signal is generally poor. In recent years, self-assembly structures using DNA double strands as linkers and gold nanoparticles as assemblies have attracted much attention due to their uniqueness in controllable parameters, DNA programmability, and specific detection of biological targets. Compared to dimers, nuclear satellite structures (CS structures) often form a regular array of enhanced electric fields (hot spots), which are mainly formed by the coupling of Localized Surface Plasmon Resonance (LSPR) in CS structures, which can greatly enhance the sensitivity of SERS signals.

Although raman imaging is a promising biological imaging technique, SERS requires a long spectral acquisition time and thus causes non-specific accumulation, resulting in unclear edges of the imaged image and ineffective guidance of multi-effect therapy. In clinical diagnosis, the combined application of different optical techniques can utilize complementary advantages to collect multi-scale data for accurate medical diagnosis. The difference in the mechanisms of the different diagnostic modes greatly limits the construction of the dual-mode strategy, and therefore establishing an effective dual-mode diagnostic strategy is a formidable challenge.

The key factors determining the SERS effect are the number of sites (active hot spots) that can excite the local plasma elements and the distribution density. In the prior art, gold nanospheres (AuNPs) with few active hot spots are selected as a surface enhanced Raman scattering substrate, which greatly influences the improvement of SERS sensitivity; in addition, in the prior art, additional adsorption of Raman reporter molecules is selected, so that the method has complicated steps and the operation process is difficult to control.

Disclosure of Invention

The invention aims to provide a detection method of a tumor cell marker miRNA-21, which has the advantages of conveniently controlling the operation process, simply, accurately and efficiently carrying out in-situ imaging and quantitative detection on the miRNA-21, improving the sensitivity of SERS and meeting the requirements on the aspects of sensitivity, specificity and the like in the verification process of the method.

In order to achieve the aim, the invention provides a detection method of a tumor cell marker miRNA-21, which comprises the following steps:

(1) preparing an AuNPs probe and a GNS probe;

(2) carrying out double-signal detection on miRNA-2 in the buffer solution by the AuNPs probe and the GNS probe prepared in the step (1);

(3) preparation of functionalized MnO₂Nanosheets;

(4) and (3) carrying out fluorescence imaging and Raman quantitative detection on the miRNA-21 in the cells.

Further, in the step (1), the process for preparing the AuNPs probe comprises the following steps:

stirring the mixture0.01% by weight of HAuCl₄Heating the solution to boiling, and quickly adding 1% by weight of trisodium citrate solution, HAuCl₄The volume ratio of the solution to the sodium citrate solution is 100: 3.5, when the color of the solution changes from light yellow to colorless and then changes from colorless to wine red, after boiling for 10min, stirring and cooling to room temperature, filtering the solution by using a 0.45 mu m Millipore membrane filter to obtain an AuNPs solution and storing the AuNPs solution at 4 ℃;

preparation of hybrid chain C1: adding 100nM 1.5. mu.L of TCEP to 10. mu.M 100. mu.L of S1 DNA, activating at room temperature for 1h, mixing the activated S1 DNA with 50. mu.M 30. mu.L of F1 DNA and 50. mu.M 30. mu.L of Walker DNA, heating to 75 ℃ and incubating for 10min, cooling to room temperature and hybridizing under dark conditions for at least 12 h; preparation of hybrid chain C2: adding 100nM 1.5. mu.L of TCEP to 10. mu.M 100. mu.L of S2 DNA, activating at room temperature for 1h, mixing the activated S2 DNA with 50. mu.M 30. mu.L of F2 DNA and 50. mu.M 30. mu.L of Walker DNA, heating to 75 ℃ and incubating for 10min, cooling to room temperature and hybridizing under dark conditions for at least 12 h; mixing 100 μ L of the mixture at a volume ratio of 6: adding a C1/C2 mixed system of 1 into 2mL of AuNPs solution, stirring for 24h at 25 ℃, continuously adding 10 mu L of Tween20 solution with the mass fraction of 10%, finally adding 100 mu L of PBS solution containing 2M NaCl, continuously passivating for 3 times, and continuously culturing for 20h to obtain a mixed solution;

and (3) centrifuging the mixed solution, washing the gold nanoparticles by using 10mmol/L Tris HCl buffer solution, and dispersing the gold nanoparticles in 10mmol/L Tris HCl buffer solution with the volume fraction of 0.02 percent Tween-20, wherein the pH value of the buffer solution is 8.0.

Further, in the step (1), the process for preparing the GNS probe is as follows: 0.1g PVP was dissolved in 25mL DEG, heated to reflux, and after 5min, 2mL HAuCl 20mg was injected₄·3H₂Stopping reaction after 10min in DEG solution of O, cooling to room temperature, centrifuging to obtain icosahedron gold seeds, washing the icosahedron gold seeds twice with DMF, and dispersing in 27mL of DMF;

dissolving 1.2g PVP in 15mL DMF, adding 50 μ L DMA solution with mass fraction of 40% and 80 μ L HCl solution of 2.5M, and sequentially adding 1mL DMF solution containing icosahedron gold seed and 20 μ L HCl solution0.5M HAuCl of L₄Obtaining a reaction solution from the solution; stirring the reaction solution at 80 ℃ for 4h, centrifuging to obtain highly symmetric gold nano-star GNS, washing the highly symmetric gold nano-star GNS twice with ethanol, and dispersing in 2mL of water to obtain GNS mixed solution;

heating 100 μ L of 10 μ M hairpin H1 DNA strand in water bath at 95 deg.C for 5min, then cooling to room temperature in ice bath, adding 1.5 μ L of 100nM TCEP to hairpin H1 DNA strand, and activating hairpin H1 DNA strand for 1H; 1mL of the GNS mixed solution and 100. mu.L of 10. mu.M of the activated hairpin H1 DNA strand were mixed and placed in a beaker, shaken in a shaker at 37 ℃ for 24 hours, centrifuged and washed in sequence, and then dispersed in 10mmol/L Tris HCl buffer solution with volume fraction of 0.02% Tween-20, wherein the pH of the buffer solution was 8.0.

Further, in the step (2), double-signal detection is carried out on miRNA-21 in the buffer: mixing 200 mu g/ml of 1ml of dispersed AuNP probe, 60 mu g/ml of 1ml of dispersed GNS probe and 20 mu M of 100 mu L of fuel DNA, adding the mixture into miRNA-21 to prepare miRNA-21 solutions with different concentrations, incubating the miRNA-21 solutions at 37 ℃ for 3 hours respectively, centrifuging the solutions, using the supernatant for fluorescence spectrum detection, and collecting 500-600 nm FAM fluorescence under the maximum excitation wavelength of 492 nm; resuspend the pellet in PBS, then drop the solution onto the surface of a slide, and examine the raman spectrum and intensity of the sample with a confocal raman spectrometer under the following conditions: laser excitation wavelength of 633nm, accumulation time of 10s, scanning time of 10s, laser power of 30mW, and laser power range of 400-1700 cm^-1(ii) a Repeating the experiment for three times to obtain a fluorescence spectrum and a Raman spectrum; fuel DNA was measured from 1: 1 Fuel 1DNA and Fuel H DNA were mixed and prepared.

Further, in the step (3), functionalized MnO is prepared₂The process of the nanosheet is as follows: 20mL of 0.6M tetramethylammonium hydroxide and 3 wt% H were added over 15s₂O₂The mixed aqueous solution of (2) was added to 10mL of 0.3M MnCl₂Stirring the dark brown suspension at room temperature overnight, centrifuging, washing the obtained precipitate with distilled water and methanol in sequence, and drying at 60 deg.C to obtain manganese dioxide block; 10mg of manganese dioxide cake was dispersed in 20mL of water and sonicatedThen centrifugating to obtain MnO₂Nanosheets; MnO at room temperature₂The nanosheets and 20 mu M100 mu L of fuel DNA are mixed and stirred for 20min, and the fuel DNA is prepared from the following components in percentage by weight of 1: 1 Fuel 1DNA and Fuel H DNA were mixed and incubated at room temperature for 20min with HEPES buffer.

Preferably, in step (3), the HEPES buffer solution has a concentration of 20mM and a pH of 7.2, and contains 150mM NaCl and 2mM MgCl₂。

Further, the specific process of the step (4) is as follows: when the cells were in the logarithmic growth phase, 1mL of cells were seeded in a confocal laser culture dish at a concentration of 2X 10⁴A cell suspension of 5% volume fraction CO at 37 ℃ after cell attachment₂Under the condition, the cells are respectively cultured for 1h, 2h, 3h, 4h and 6h in a fresh culture medium containing 2mL of mixed probes, and the preparation process of the mixed probes comprises the following steps: after the AuNP probe with the concentration of 60. mu.g/mL and the GNS probe with the concentration of 200. mu.g/mL were centrifuged respectively, the mixture was resuspended in 2mL of functionalized MnO with the concentration of 50. mu.g/mL₂Nano-sheet solution; removing the mixed solution, washing the cells with PBS for three times, fixing the cells with 4% paraformaldehyde, dyeing the cells with DAPI, washing the cells with PBS for two times, and performing fluorescence imaging; the raman spectrum and intensity of the cells were measured with a confocal raman spectrometer under the following conditions: laser excitation wavelength of 633nm, accumulation time of 10s, scanning time of 10s, laser power of 30mW, and laser power range of 400-1700 cm^-1(ii) a 20 cells were selected for SERS detection and the average was calculated.

Furthermore, a regression equation is determined by taking the lg value of the concentration of the miRNA-21 standard substance and the detected Raman and fluorescence signal intensity as a standard curve, and the applicability of the regression equation in cells is verified by simulating the environment in the cells; and calculating the content of the miRNA-21 in the living cells according to the detected Raman signal intensity or fluorescence signal intensity of the miRNA-21 in each cell.

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

(1) the invention combines the fluorescence analysis technology with the Raman analysis technology by using the DNA cascade amplification technology, and collects multi-scale data by using the complementary advantages of the two technologies so as to carry out accurate medical diagnosis;

(2) the target-triggered nuclear satellite structure self-assembles to generate a large number of electromagnetic hot spots, and compared with DNA-mediated oligomers (dimers or trimers), the nuclear satellite structure can form a regular enhanced electric field (hot spot) array, so that the sensitivity of Raman detection is greatly enhanced;

(3) the invention selectively converts the target into a large amount of adenine residing in the electromagnetic hot spot through a DNA cascade amplification technology, which ensures that the analyte is positioned in the hot spot region, thereby improving the stability of Raman detection.

The detection method provided by the invention is convenient to control the operation process, can simply, accurately and efficiently carry out in-situ imaging and quantitative detection on miRNA-21, improves the sensitivity of SERS, and meets the requirements on sensitivity, specificity and the like in the verification process of the method.

Drawings

FIG. 1 is a representation of the composite probe prepared in the example: (A) transmission electron images (TEMs) of highly symmetric gold nanostars GNS; (B) high-magnification Scanning Electron Micrographs (SEM) of highly symmetric gold nanostars GNS; (C) a low-magnification Scanning Electron Map (SEM) of highly symmetric gold nanostars GNS; (D) transmission Electron Micrographs (TEM) of gold nanoparticles AuNP; (E) functional MnO₂Transmission electron images (TEMs) of the nanoplates; (F) functional MnO₂X-ray photoelectron spectroscopy (XPS) spectra of nanoplates, AuNP, and GNS; (G) the particle size distribution diagram of the gold nanoparticles AuNP; (H) the grain size distribution diagram of the high-symmetry gold nano star GNS; (I) high-symmetry gold nano star GNS, gold nano particle AuNP and functionalized MnO₂Zeta potential statistical chart of the nano sheet; (J) ultraviolet absorption spectrograms of the gold nano star GNS and the gold nano particle AuNP with high symmetry;

fig. 2 is a target-responsive assembled nuclear satellite structure: (A) when no target is present; (B) a nuclear satellite structure assembled in the presence of a target.

FIG. 3 is a fluorescence-Raman correlation spectrogram of the composite probe responding to miRNA-21 with different concentrations when performing double-signal detection on miRNA-21 in a buffer: (A) a fluorescence spectrum; (B) a scatter plot of fluorescence intensity; (C) a Raman spectrum; (D) raman intensity and lgC_(miRNA-21)The calibration curve of (1);

fig. 4 is a fluorescence-raman correlation spectrogram of the response of the composite probe when DTN detects dual signals of endogenous miRNA-21 of different cells: (A) confocal fluorescence microscopy of different cells after DTN treatment; (B) fluorescence flow of different cells after DTN treatment; (C) fluorescence shift of different cells after DTN treatment; (D) raman signal spectra of different cells after DTN treatment; (E) statistical analysis of raman signal intensity of different cells after DTN treatment.

Detailed Description

The invention is described in further detail below with reference to the figures and specific examples.

The reagents, methods and apparatus employed in the present invention are conventional in the art, unless otherwise indicated.

The MCF-7 cells, tumor cells (hepG2, Hela) and normal cells (L929, LO2) used in this example were purchased from Shanghai cell Bank, Chinese academy of sciences.

The detection method of the tumor cell marker miRNA-21 provided by the embodiment of the invention comprises the following steps:

(1) preparing an AuNPs probe and a GNS probe;

(2) carrying out double-signal detection on miRNA-2 in the buffer solution by the AuNPs probe and the GNS probe prepared in the step (1);

(3) preparation of functionalized MnO₂Nanosheets;

(4) and (3) carrying out fluorescence imaging and Raman quantitative detection on the miRNA-21 in the cells.

The DNA sequence used in the detection method of the tumor cell marker miRNA-21 provided by the embodiment of the invention is shown in the following table 1.

TABLE 1 preparation of composite probes and nucleotide sequences required for experiments

The above sequences were purchased from Shanghai bioengineering, Inc.

The detection method of the tumor cell marker miRNA-21 provided by the embodiment of the invention comprises the following specific steps:

1. preparation of AuNPs probes:

under the condition of vigorous stirring, 100mL of HAuCl with the mass fraction of 0.01 percent₄Heating the solution to boiling, quickly adding a trisodium citrate solution with the mass fraction of 1% into 3.5mL of the solution, changing the color of the solution from light yellow to colorless, changing the color from colorless to wine red, continuing boiling for 10min, stirring and cooling to room temperature, filtering the solution by using a Millipore membrane filter with the diameter of 0.45 mu m to obtain an AuNPs solution, and storing the AuNPs solution at the temperature of 4 ℃;

preparing a hybrid chain C1: adding 100nM 1.5. mu.L of TCEP to 10. mu.M 100. mu.L of S1 DNA, activating at room temperature for 1h, mixing the activated S1 DNA with 50. mu.M 30. mu.L of F1 DNA and 50. mu.M 30. mu.L of Walker DNA, heating to 75 ℃ and incubating for 10min, slowly cooling to room temperature and hybridizing under dark conditions for at least 12 h; preparation of hybrid chain C2: adding 100nM 1.5. mu.L of TCEP to 10. mu.M 100. mu.L of S2 DNA, activating at room temperature for 1h, mixing the activated S2 DNA with 50. mu.M 30. mu.L of F2 DNA and 50. mu.M 30. mu.L of Walker DNA, heating to 75 ℃ and incubating for 10min, slowly cooling to room temperature and hybridizing under dark conditions for at least 12 h; mixing 100 μ L of the mixture at a volume ratio of 6: adding a C1/C2 mixed system of 1 into 2mL of AuNPs solution, stirring for 24h at 25 ℃, continuously adding 10 muL of Tween20 solution with the mass fraction of 10%, finally adding 100 muL of PBS solution containing 2M NaCl, continuously passivating for 3 times, and continuously and stably culturing for 20h to obtain a mixed solution;

③ to transfer excess DNA, after the mixed solution was centrifuged at 13500rpm for 30min, the gold nanoparticles were washed with 2mL of 10mmol/L Tris HCl buffer solution and dispersed in 1mL of 10mmol/L Tris HCl buffer solution with a volume fraction of 0.02% Tween-20 (pH 8.0).

2. Preparation of GNS probe:

first 0.1g PVP was dissolved in 25mL DEG, heated to reflux, and after 5min 2mL of HAuCl containing 20mg were rapidly injected₄·3H₂Of OStopping reaction after 10min of DEG solution, cooling to room temperature, centrifuging to obtain icosahedron gold seeds, washing the icosahedron gold seeds twice with DMF, and dispersing in 27mL of DMF;

② dissolving 1.2g PVP in 15mL DMF, adding 50 μ L DMA solution with mass fraction of 40% and 80 μ L2.5M HCl solution, then adding 1mL DMF solution containing icosahedron gold seed and 20 μ L0.5M HAuCl₄Obtaining a reaction solution from the solution; slightly stirring the reaction solution in an oil bath at 80 ℃ for 4 hours, centrifuging to obtain a highly symmetric gold nano-star GNS, washing the highly symmetric gold nano-star GNS twice with ethanol, and dispersing in 2mL of water to obtain a GNS mixed solution;

③ when preparing GNS probe, in order to prevent the base mismatch of hairpin, 100 uL 10 uM hairpin H1 DNA chain is heated in 95 ℃ water bath for 5min, then cooled to room temperature in ice bath, 1.5 uL 100nM TCEP is added into hairpin H1 DNA chain, and the hairpin H1 DNA chain is activated for 1H; 1mL of the GNS mixture and 100. mu.L of 10. mu.M activated hairpin H1 DNA strand were mixed in a clean 10mL beaker and shaken in a shaker at 37 ℃ for 24H, and centrifuged (6000rpm, 20min) and washed twice in order to remove excess DNA, and then dispersed in a buffer solution of 10mmol/LTris HCl (pH 8.0) with a volume fraction of 0.02% Tween-20.

3. Preparation of functionalized MnO₂Nanosheet:

20mL of 0.6M tetramethylammonium hydroxide and 3 wt% H in 15s₂O₂The mixed aqueous solution of (2) was added to 10mL of 0.3M MnCl₂In solution, the solution turned dark brown immediately after mixing, indicating Mn²⁺Is oxidized to Mn⁴⁺(ii) a Stirring the obtained dark brown suspension at room temperature overnight, centrifuging (2000rpm, 10min), washing the obtained precipitate with distilled water and methanol in sequence, and drying at 60 deg.C to obtain manganese dioxide block;

② to prepare MnO₂Nanosheet, 10mg of blocky manganese dioxide is dispersed in 20mL of water, subjected to ultrasonic treatment for 10h and then centrifuged (2000rpm) to obtain MnO₂Nanoplatelets, the supernatant is retained for further use; MnO at room temperature₂Mixing and stirring nanosheet and 20 mu M100 mu L fuel DNAFor 20min, so that MnO₂The nanosheets physically adsorb fuel DNA, and the fuel DNA is prepared from the following components in percentage by weight of 1: 1 and Fuel H DNA, and HEPES buffer (20mM, pH 7.2) containing 150mM NaCl and 2mM MgCl₂) Incubate at room temperature for 20 min.

4. Carrying out double-signal detection on miRNA-21 in the buffer solution:

mixing 200 mu g/ml of 1ml of dispersed AuNP probe, 60 mu g/ml of 1ml of dispersed GNS probe and 20 mu M of 100 mu L of fuel DNA, adding the mixture into miRNA-21 to prepare miRNA-21 solutions with different concentrations (0nM, 0.2nM, 0.5nM, 0.8nM, 1nM, 2nM, 10nM, 20nM, 50nM, 100nM, 150nM and 200nM), respectively incubating for 3h at 37 ℃, centrifuging, using the supernatant for fluorescence spectrum detection, and collecting 500-600 nM FAM fluorescence under the maximum excitation wavelength of 492 nM;

resuspending the pellet in PBS using a pipettor, dropping the solution onto the surface of a slide, and measuring the raman spectrum and intensity of the sample using a confocal raman spectrometer under the following conditions: laser excitation wavelength of 633nm, accumulation time of 10s, scanning time of 10s, laser power of 30mW, and laser power range of 400-1700 cm^-1(ii) a Repeating the experiment for three times to obtain a fluorescence spectrum and a Raman spectrum; fuel DNA was measured from 1: 1 Fuel 1DNA and Fuel H DNA were mixed and prepared.

5. Fluorescence imaging and Raman quantitative detection of intracellular miRNA-21:

when the cells are in the logarithmic growth phase, 1mL of cells with the concentration of 2X 10 are inoculated in a laser confocal culture dish⁴A cell suspension of 5% volume fraction CO at 37 ℃ after cell attachment₂Under the condition, the cells are respectively cultured for 1h, 2h, 3h, 4h and 6h in a fresh culture medium containing 2mL of mixed probes, and the preparation process of the mixed probes comprises the following steps: after the AuNP probe with the concentration of 60. mu.g/mL and the GNS probe with the concentration of 200. mu.g/mL were centrifuged respectively, the mixture was resuspended in 2mL of functionalized MnO with the concentration of 50. mu.g/mL₂Nano-sheet solution; removing the mixed solution, washing the cells with PBS for three times, fixing the cells with 4% paraformaldehyde for 10min, dyeing the cells with DAPI for 10min, washing the cells with PBS for two times, and performing fluorescence imaging;

detecting the Raman spectrum and the intensity of the cell by using a confocal Raman spectrometer under the following conditions: laser excitation wavelength of 633nm, accumulation time of 10s, scanning time of 10s, laser power of 30mW, and laser power range of 400-1700 cm^-1(ii) a Selecting 20 cells for SERS detection, and calculating an average value;

thirdly, taking the lg value of the concentration of the miRNA-21 standard substance and the detected Raman and fluorescence signal intensity as a standard curve, determining a regression equation, and simulating an intracellular environment to verify the applicability of the regression equation in the cell; and calculating the content of the miRNA-21 in the living cells according to the detected Raman signal intensity or fluorescence signal intensity of the miRNA-21 in each cell. The above experimental procedure was used to detect the expression of miRNA-21 in MCF-7 treated with different transfectants and the expression level of miRNA-21 in different cells.

The characterization results of the composite probe prepared in this example were analyzed as follows:

as shown in figure 1, the high-symmetry Gold Nanostars (GNS) and gold nanoparticles (AuNP) are characterized by using ultraviolet-visible absorption spectroscopy, electron transmission/scanning electron microscopy and particle size analysis. As shown in FIG. 1(A), the transmission electron micrograph shows that the GNS is highly symmetrical and has uniform size and good dispersibility in PBS buffer solution, and the average diameter is about 200 nm; as shown in fig. 1(B), the scanning electron microscope results show that GNS is highly symmetric and sharp; as shown in fig. 1(C), the scanning electron microscopy results show that GNS can be stably synthesized in bulk; as shown in fig. 1(D), it was shown that AuNP is uniformly spherical, arranged and dispersed, with an average diameter of about 13 nm; in addition, as shown in FIGS. 1(G) and (H), the particle size distribution of AuNP/GNS was substantially the same as the size exhibited by the transmission electron microscopy images.

As shown in FIG. 1(J), the maximum UV-visible absorption peak of the DNA-modified GNS probe is slightly red-shifted compared to GNS, and a UV absorption peak appears at 619 nm. This is due to the DNA modified on the surface of the nanoparticle causing a change in the outer medium of the nanoparticle, resulting in an increase in the dielectric constant. Similarly, the maximum ultraviolet-visible absorption peak of the AuNP probe is slightly red-shifted compared with that of AuNP, and an ultraviolet absorption peak appears at 517 nm.

As shown in FIG. 1(I), the Zeta potential of GNS is-6.3. + -. 2.1, that of GNS machine is-23.5. + -. 3.3, that of AuNP is-7.6. + -. 1.9, and that of AuNPprobe is-32.3. + -. 4.3, which is attributed to the fact that the DNA chain contains a large amount of negative charges. The results of the Zeta potential, which further indicate successful ligation of the DNA strand to the nanoparticle, show that GNS machine and AuNP probe have been successfully prepared.

MnO functionalized by transmission electron microscope, XPS, ultraviolet absorption spectrum and Zeta potential pair₂And (5) performing characterization on the nanosheets. As shown in FIG. 1(E), MnO₂The nano-sheet is in a two-dimensional single-layer sheet structure, and the average diameter of the nano-sheet is about 200 nm. As shown in FIG. 1(F), the XPS method further demonstrates MnO₂Successful synthesis of the nanoplatelets, the curve shows characteristic peaks corresponding to Mn 2p 1/2(641.7eV), Mn 2p 3/2(653.3eV) and O1s (curve a).

MnO as shown in FIG. 1(I)₂The Zeta potential of the nanosheet is-28.7 +/-2.2, and the Zeta potential after the Fuel is adsorbed is-43.7 +/-3.3, so that successful adsorption of the Fuel DNA is further verified. The above results indicate that the composite probe was successfully prepared in this example.

The generation of raman signals is dependent on the assembly of the nuclear satellite structure, and therefore the successfully assembled nuclear satellite structure needs to be verified. As shown in fig. 2(B), the nuclear satellite structure was successfully assembled in the presence of the target; as shown in fig. 2(a), GNS and AuNP are evenly distributed when no target is present. As shown in FIG. 3, after the composite probe is incubated with miRNA-21 at a series of concentrations, the composite probe shows excellent fluorescence/Raman dual-signal responsiveness. As shown in FIG. 3(A), the fluorescence intensity of the composite probe in response to miRNA-21 depends on the target concentration, and the fluorescence intensity increases with increasing target concentration, as shown in FIG. 3(B), an almost linear relationship is obtained between 0.2-2 nM. A calibration curve was obtained between fluorescence intensity and miRNA-21 concentration with a regression equation of y 242.940+242.335x, a limit of detection (LOD) formula, a LOD for the fluorescence response of 47.38pM, R²0.977, which makes the composite probe potential for in vivo tumor imaging. As shown in fig. 3(C), in accordance with the fluorescence signal, the SERS signal also shows a good correlation with the target concentration. As shown in FIG. 3(D), between the Raman intensity and the logarithm of the miRNA-21 concentrationObtaining a calibration curve, wherein the regression equation is that y is 4321.556+389.313lgC_(miRNA-21)LOD of 9.78pM, R²0.987. Compared to the fluorescence strategy, the SERS strategy has a lower LOD, higher sensitivity and inherently high stability, so it has the ability to quantify miRNA-21 in living cells.

Next, we simulated the intracellular environment in vitro and verified whether the standard curve of SERS analysis can be applied in cells. LO2 cells expressed by low miRNA-21 are prepared into cell lysate, and a series of miRNA-21 and 100 mu M hydrogen peroxide are added for SERS analysis. In fig. 3(D), the in-cell suitability of the in vitro SERS calibration curve was verified. Thus, the established calibration curve can be used for quantification of intracellular targets.

miRNA-21 is upregulated in multiple cancer cell lines, therefore we added tumor cells (hepG2, HeLa) and normal cells (L929, LO2) to validate the ability of DTN to quantify endogenous miRNA-21. As shown in FIG. 4(A), clear fluorescent signals were observed in the tumor cells (HepG2 cell, Hela cell and MCF-7 cell), whereas the fluorescent signals were extremely weak in the normal cells (LO2 cell, L929 cell). As shown in fig. 4(B) and (C), the flow cytometry results were consistent with confocal imaging results, further demonstrating the correlation between fluorescence signal intensity and the expression level of miRNA-21 in different cell lines.

As shown in fig. 4(D) and (E), the raman signal intensity of different cells has an excellent correlation with the concentration of miRNA-21. The Raman intensity of miRNA-21 in normal cells (L929 cells, LO2 cells) was significantly lower than that of the other three tumor cells. The Raman intensities of HeLa cells, HepG2 cells and MCF-7 cells were 945.3. + -. 24.9, 963.0. + -. 12.7 and 1201.9. + -. 28.7, respectively. As shown in FIG. 3(B), the concentrations of miRNA-21 in HeLa cells, HepG2 cells, and MCF-7 cells were 2nM, 2.5nM, and 9.7nM, respectively, according to the standard curve in buffer solution. The concentration of miRNA-21 in the above cell lines is consistent with the results reported in the previous literature, which further confirms the high correlation between dual signal detection and intracellular miRNA-21 concentration and confirms that the proposed dual-mode detection strategy can successfully quantify the expression level of intracellular miRNA-21 in various cell lines.

And (3) comparing the methods: furthermore, LOD of this strategy is similar to other miRNA detection methods.

TABLE 2 SERS and Fluorescence measurements of the invention in comparison with other biosensors (upper label is detection limit of the invention)

As shown in Table 2, the SERS + fluorescence double-signal detection method using the AuNP probe as the satellite component and the GNS probe as the SERS core substrate can better detect the miRNA-21 content in the tumor cells.