Cadmium ion aptamer and application and kit thereof

Abstract

The application relates to the technical field of detection, in particular to a cadmium ion aptamer and application and kit thereof. The nucleic acid base sequence of the cadmium ion aptamer provided by the application is shown as SEQ ID NO:1 or SEQ ID NO:2. Compared with the prior art, the nucleic acid aptamer has the advantages of high affinity, strong specificity, easy preparation, high chemical stability, wide range of target substances and the like, and is suitable for rapid detection of heavy metals.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of detection, more particularly to a cadmium ion aptamer and application and kit thereof. BACKGROUND

[0002] Cadmium (Cd) is a non-essential and highly toxic heavy metal element. The International Agency for Research on Cancer (IARC) of the World Health Organization has classified cadmium and cadmium compounds as a class I carcinogen. Cadmium is used as a raw material in industry and agriculture, mainly in industries such as electroplating, nickel-cadmium battery production, plastic stabilizer, alloy corrosion resistance, and phosphate fertilizer application. Cadmium accumulates in the human body through food, drinking water, and inhalation of cadmium-containing dust, and induces osteoporosis, osteomalacia, pulmonary emphysema, renal tubular dysfunction, hypertension, and other diseases, and causes irreversible damage to organ systems such as the respiratory system, immune system, cardiovascular system, nervous system, and reproductive system. Therefore, it is of great significance to accurately detect the content of heavy metal cadmium in food and water to protect human life, health and safety.

[0003] Traditional methods for detecting cadmium ions include atomic absorption spectrometry, atomic emission spectrometry, atomic fluorescence spectrometry, inductively coupled plasma mass spectrometry, inductively coupled plasma atomic emission spectrometry, high-performance liquid chromatography, and spectrophotometry. Although traditional detection methods have high sensitivity and good reproducibility, they are limited in their application in rapid detection due to the need for large instruments, complex operation, and high detection costs. Rapid detection methods for heavy metals, including immunoassay and enzyme analysis, have certain limitations in their scope of application due to high antibody preparation costs and limited types of enzymes. SUMMARY

[0004] Therefore, the present application aims to provide a cadmium ion aptamer and application and kit thereof. The cadmium ion aptamer of the present application has low cost, is easy to synthesize, and has a wide range of targets. The colloidal gold colorimetric method based on the aptamer is used to detect cadmium ions, and has the advantages of simple operation, short time consumption, high sensitivity, and good selectivity.

[0005] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0006] The cadmium ion aptamer has a nucleic acid base sequence as shown in SEQ ID NO: 1 or SEQ ID NO: 2.

[0007] The cadmium ion aptamer provided by the present application is a single-stranded DNA (ssDNA) with a length of 21-mer or 17-mer. The cadmium ion aptamer forms a stem-loop loop structure. The equilibrium dissociation constant Kd of the cadmium ion aptamer is 10-7-10-9 M.D The value is (1.17-1.50)×10 -6 mol / L.

[0008] Among all types of biosensors, those that use nucleic acid aptamers as target substances to recognize molecules and colloidal gold colorimetry as the detection method not only have good specificity, high sensitivity, low detection limit, and fast analysis speed, but are also simple to operate and easy to miniaturize and port.

[0009] This invention also provides the application of the above-mentioned cadmium ion nucleic acid aptamer in the detection of cadmium ions.

[0010] This invention is based on a 21-mer cadmium ion aptamer. By truncating the aptamer while retaining its core region and stem-loop structure, a 17-mer aptamer is obtained. Experiments have confirmed that the truncated optimization does not alter the binding affinity between the aptamer and cadmium ions. This invention establishes a colorimetric detection method for cadmium ions based on the 17-mer aptamer. Compared to the original 21-mer aptamer, the truncated and optimized aptamer improves the sensitivity of cadmium ion detection by 2.5 times. The method has advantages such as simple operation, low cost, short processing time, high sensitivity, and good selectivity, and has high practical application value.

[0011] The present invention also provides the application of the above-mentioned cadmium ion nucleic acid aptamer in the preparation of a kit for detecting cadmium ions.

[0012] The present invention also provides a kit for detecting cadmium ions, comprising the above-mentioned cadmium ion nucleic acid aptamer.

[0013] In this invention, the kit for detecting cadmium ions further includes: colloidal gold and NaCl; the colloidal gold is preferably present in solution form; the NaCl is preferably present in solution form.

[0014] In this invention, the molar ratio of the cadmium ion nucleic acid aptamer to colloidal gold is (2-6):1; the molar ratio of the cadmium ion nucleic acid aptamer to NaCl is (1 / 16-6)×10⁻⁶. -6 :1.

[0015] In this invention, the colloidal gold is gold nanoparticles with a diameter of 13 nm; the colloidal gold is prepared by reducing chloroauric acid with trisodium citrate.

[0016] In this invention, the method for preparing colloidal gold includes: heating a chloroauric acid solution, mixing it with a trisodium citrate solution, and continuing to heat until the color of the system no longer changes;

[0017] The concentration of the chloroauric acid solution is preferably 1%-2%; the chloroauric acid solution is diluted 50 times with water.

[0018] The concentration of the trisodium citrate solution is preferably 1.5%-2%; the volume ratio of the trisodium citrate solution to the diluted chloroauric acid solution is 1:(25-30); the trisodium citrate solution and the chloroauric acid solution are preferably filtered using a 0.22μm ultrafiltration membrane before mixing.

[0019] The preferred method for preparing the colloidal gold includes: taking 1 mL of 1% chloroauric acid solution, diluting it in 50 mL of ultrapure water, and stirring and heating it in a magnetic stirrer; after the solution boils, quickly adding 2 mL of 1.5% trisodium citrate solution filtered through a 0.22 μm ultrafiltration membrane, and observing that the solution color changes from light yellow to wine red; when the system no longer changes, continue heating and stirring for 10 min, then stop heating, and after stirring and cooling to room temperature, colloidal gold is obtained.

[0020] In one embodiment of the present invention, the final concentration of colloidal gold in a 200 μL colloidal gold solution is 14.0 nM.

[0021] In one embodiment of the present invention, the final concentration of colloidal gold in a 500 μL colloidal gold solution is 5.6 nM.

[0022] The present invention also provides a method for detecting cadmium ions, which involves mixing the above-mentioned cadmium ion nucleic acid aptamer with colloidal gold and the sample to be tested, and then reacting it with NaCl; detecting the absorbance values ​​under wavelength conditions of 650 nm and 520 nm, and obtaining the concentration of cadmium ions in the sample to be tested according to the standard curve.

[0023] In this invention, the colloidal gold is gold nanoparticles with a diameter of 13 nm; the colloidal gold is prepared by reducing chloroauric acid with trisodium citrate.

[0024] In this invention, the molar ratio of the cadmium ion nucleic acid aptamer to colloidal gold is (2-6):1; the molar ratio of the cadmium ion nucleic acid aptamer to NaCl is (1 / 16-6)×10⁻⁶. -6 :1.

[0025] In this invention, the colloidal gold is preferably present in solution form; the NaCl is preferably present in solution form; the method for detecting cadmium ions preferably includes: reacting the cadmium ion nucleic acid aptamer solution with the colloidal gold solution, then reacting it with the sample solution to be tested, and finally reacting it with the NaCl solution;

[0026] The volume ratio of the cadmium ion nucleic acid aptamer solution to the colloidal gold solution, the sample solution to be tested, and the NaCl solution is 1:(2-5):(1-2):(0.5-1), preferably 1:2.5:1:0.5;

[0027] The reaction time between the cadmium ion nucleic acid aptamer solution and the colloidal gold solution was 10 min; the reaction time between the test sample solution and the system was 30 min; and the reaction time between the NaCl solution and the system was 10 min.

[0028] The concentration of the cadmium ion nucleic acid aptamer solution is preferably 15-30 nM; the concentration of the NaCl solution is preferably 10-60 mM, and more preferably 40 mM.

[0029] The linear working equation established in this invention uses the logarithm of the concentration of cadmium ion solution as the abscissa, and the corresponding A 650nm / A 520nm The change value is on the ordinate.

[0030] In this invention, the method for preparing colloidal gold includes: heating a chloroauric acid solution, mixing it with a trisodium citrate solution, and continuing to heat until the color of the system no longer changes;

[0031] The concentration of the chloroauric acid solution is preferably 1%-2%; the chloroauric acid solution is diluted 50 times with water.

[0032] The concentration of the trisodium citrate solution is preferably 1.5%-2%; the volume ratio of the trisodium citrate solution to the diluted chloroauric acid solution is 1:(25-30); the trisodium citrate solution and the chloroauric acid solution are preferably filtered using a 0.22μm ultrafiltration membrane before mixing.

[0033] The preferred method for preparing the colloidal gold includes: taking 1 mL of 1% chloroauric acid solution, diluting it in 50 mL of ultrapure water, and stirring and heating it in a magnetic stirrer; after the solution boils, quickly adding 2 mL of 1.5% trisodium citrate solution filtered through a 0.22 μm ultrafiltration membrane, and observing that the solution color changes from light yellow to wine red; when the system no longer changes, continue heating and stirring for 10 min, then stop heating, and after stirring and cooling to room temperature, colloidal gold is obtained.

[0034] A schematic diagram of the present invention for the detection of cadmium ions based on aptamer colloidal gold colorimetric method is shown below. Figure 1 As shown, the original aptamer is the original-length aptamer, and the truncated aptamer is the shortened aptamer. The gold nanoparticles maintain the stability of the solution through electrostatic repulsion. Adding a high concentration of NaCl solution disrupts this stability, causing aggregation and turning the solution from red to blue. However, free ssDNA, by exposing its positively charged bases, directly adsorbs onto the AuNPs surface through electrostatic interaction with the negatively charged surface of the gold nanoparticles. In this case, even with the addition of a high concentration of NaCl, it remains stable, and the solution remains red. When the target substance Cd is present in the reaction system... 2+ At that time, the aptamer and Cd2+ Specific binding to form Cd 2+ In the aptamer complex, the bases of the aptamer are no longer exposed, causing the aptamer to lose its ability to protect AuNPs. Consequently, the free AuNPs aggregate under the influence of NaCl solution, resulting in a color change from red to bluish-gray. (Cd) 2+ Non-essential nucleotides in the original aptamer sequence, excluding the stem-loop region, may interact with AuNPs, inhibiting complete dissociation of the aptamer from AuNPs and preventing AuNP aggregation, thereby affecting the color change and sensitivity of this colorimetric sensor. Therefore, this invention removes redundant bases to improve the colorimetric sensitivity of Cd... 2+ The original long aptamer sequence was truncated (Cd-17), and an AuNP-based Cd-17 sequence was established using the original long aptamer and the truncated aptamer. 2+ Colorimetric detection method.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) The cadmium ion nucleic acid aptamer of the present invention is based on the specific binding of cadmium ion to its aptamer, and has the advantages of high affinity, strong specificity, easy preparation, high chemical stability and wide range of target substances, making it suitable for rapid detection of heavy metals.

[0037] (2) The present invention truncates and optimizes the original cadmium ion sequence. The lowest detection limit of the colloidal gold colorimetric method based on the truncated aptamer is 0.27 nM, which is 2.5 times higher than the original aptamer sensitivity. Furthermore, the recovery rate in actual samples is between 94.68% and 103.8%, indicating that the method can be used for the detection of cadmium ions in actual samples. Moreover, the colloidal gold colorimetric method constructed by truncating the aptamer is beneficial to improving the sensitivity of the colorimetric system.

[0038] (3) The method for detecting cadmium ions by colloidal gold using cadmium ion nucleic acid aptamers established in this invention can detect cadmium ions qualitatively and quantitatively by the ratio of color and absorbance. It has the advantages of simple operation, no labeling required, low cost, low sensitivity, and fast analysis speed, and has good practical application value. Attached Figure Description

[0039] Figure 1 This is a schematic diagram illustrating the use of the cadmium ion aptamer colloidal gold colorimetric method for detecting cadmium ions according to the present invention.

[0040] Figure 2 This is a characterization diagram of the colloidal gold prepared in Example 1 of the present invention, wherein... Figure 2 A is a transmission electron microscope image of the colloidal gold solution; Figure 2 B is a transmission electron microscope image of colloidal gold solution in a high-salt solution; Figure 2C represents the absorption spectra of colloidal gold, colloidal gold + NaCl, colloidal gold + cadmium ion aptamer + NaCl, and colloidal gold + cadmium ion aptamer + cadmium ion + NaCl systems.

[0041] Figure 3 This is a simulation diagram of the secondary structure of the cadmium ion nucleic acid aptamer NUPACK in Example 2 of the present invention, wherein... Figure 3 A is a 21-mer aptamer; Figure 3 B is the 17-mer aptamer;

[0042] Figure 4 This is the ITC titration curve of the interaction between the cadmium ion nucleic acid aptamer and cadmium ions in Example 2 of the present invention, wherein... Figure 4 A is the ITC titration curve of the interaction between the 21-mer aptamer and cadmium ions; Figure 4 B-4D is the ITC titration curve of the interaction between the modified aptamer and cadmium ions; Figure 4 E is the ITC titration curve of the interaction between the 17-mer aptamer and cadmium ions;

[0043] Figure 5 The image shows a circular dichroism chromatogram of the cadmium ion nucleic acid aptamer before and after binding with cadmium ions in Example 2 of this invention.

[0044] Figure 6 This is a standard curve diagram for the detection of cadmium ions based on the 21-mer and 17-mer aptamer colloidal gold colorimetric method in Example 3 of the present invention, wherein... Figure 6 A is a 21-mer aptamer; Figure 6 B is the 17-mer aptamer;

[0045] Figure 7 This is a comparison diagram showing the specificity of cadmium ion detection based on the 21-mer and 17-mer aptamer colloidal gold colorimetric method in Example 3 of the present invention. Detailed Implementation

[0046] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0047] To further illustrate the present invention, the following embodiments are provided for detailed description. All raw materials used in the following embodiments of the present invention are commercially available products.

[0048] Example 1: Synthesis of Colloidal Gold

[0049] (1) Take 1 mL of 1% chloroauric acid solution, dilute it in 50 mL of ultrapure water, and stir and heat it in a magnetic stirrer.

[0050] (2) After the solution boils, 2 mL of 1.5% trisodium citrate solution filtered through a 0.22 μm ultrafiltration membrane is quickly added. The solution color is observed to change from light yellow to wine red.

[0051] (3) When the color no longer changes, continue heating and stirring for 10 minutes, then stop heating, stir and cool to room temperature, and store in a 4°C refrigerator for later use.

[0052] Two drops of the colloidal gold prepared by the above method were added to an ultrathin carbon film and allowed to air dry for at least 2 hours. The prepared colloidal gold solution was characterized by transmission electron microscopy (JEOL 2100F), and the results are as follows. Figure 2 As shown, the average diameter of AuNPs particles is 13 nm. According to the Lambert-Beer law, the extinction coefficient of 13 nm AuNPs is 2.7 × 10⁸ mol. -1 ·cm -1 The final concentration of gold nanoparticles AuNPs in a 200 μL system was calculated to be 14.0 nM.

[0053] Example 2: Modification and Optimization of Cadmium Ion Nucleic Acid Aptamers

[0054] (1) Optimization of aptamer sequence truncation

[0055] Based on the predicted structure of the original cadmium ion aptamer (21-mer), this sequence was modified and optimized by removing redundant bases irrelevant to the binding domain, resulting in a truncated and optimized aptamer (17-mer). The predicted structures of the two aptamers are shown below. Figure 3 As shown.

[0056] (2) Characterization of aptamer affinity

[0057] Isothermal titration calorimetric characterization: This invention mainly uses isothermal titration calorimetric experiments to characterize the heat response and affinity data that occur when cadmium ion solution is titrated with truncated aptamers, and to verify the optimal aptamer and Cd. 2+ The binding strength between them. The titration curve of the interaction between the modified aptamer and cadmium ions is shown in the figure. Figure 4 As shown, K D The value indicates the retention of Cd. 2+ Removing excess bases from the stem-loop region of the aptamer Cd-21 does not affect its affinity for Cd. 2+ The binding strength with cadmium ions is reduced by adding corresponding bases to the original aptamer (21-mer). The truncated aptamer binds to Cd... 2+ The binding ability remains unchanged. Partial modification sequence information and K DThe values ​​are shown in Table 1.

[0058] Table 1. Partial sequence information of cadmium ion aptamers and K D value

[0059]

[0060] Circular dichroism characterization: The detection system was characterized using circular dichroism chromatograms to represent the conformational changes of the aptamer before and after the addition of cadmium ions, further validating the binding of the original nucleic acid aptamer (21-mer) and the truncated optimized aptamer (17-mer) to cadmium ions. Results are as follows... Figure 5 As shown, the positive peaks at 213 nm and 218 nm for the two aptamer chains indicate the presence of random coil sequences in the cadmium ion aptamer chains; the original nucleic acid aptamer (21-mer) and the truncated aptamer (17-mer) have negative and positive peaks at approximately 240 nm and 280 nm, respectively, indicating that Cd... 2+ Nucleic acid aptamers themselves have a B-type DNA structure. Adding Cd... 2+ After solution treatment, the CD values ​​of the nucleic acid aptamer increased near 240 nm and 280 nm, and a new negative peak appeared around 260 nm. Compared with the original sequence (21-mer), the peak intensity of the CD peak changed more significantly after binding to the truncated sequence (17-mer). These changes are presumably due to Cd. 2+ This affected the stacking and helicity of nucleic acid aptamers, resulting in changes in their conformation.

[0061] Example 3: Application of cadmium ion aptamers in the detection of cadmium ions

[0062] (1) Optimization of NaCl concentration: 25 μL of NaCl solutions with final concentrations of 0 mM, 10 mM, 20 mM, 30 mM, 40 mM, 50 mM, 60 mM, 70 mM, and 80 mM were added to 200 μL of AuNPs solution. The system was then replenished with ultrapure water to a final volume of 500 μL. After mixing, the solution was incubated at room temperature in the dark for 10 min. The optimal NaCl solution concentration was selected as the minimum NaCl concentration corresponding to the maximum absorbance ratio when the colloidal gold was completely aggregated.

[0063] (2) Optimization of aptamer concentration: 25 μL of aptamer solutions of different concentrations (21-mer aptamers 5 nM, 10 nM, 15 nM, 20 nM, 25 nM, 30 nM; 17-mer aptamers 10 nM, 20 nM, 30 nM, 40 nM, 50 nM, 60 nM) were added to 200 μL of AuNPs solution. The system was then brought to 450 μL with ultrapure water, vortexed to mix, and incubated at room temperature in the dark for a period of time. Then, 25 μL of 0 nM and 250 nM Cd were added. 2+The solution was incubated at room temperature in the dark for a period of time. Finally, 25 μL of the optimal concentration of NaCl solution was added, mixed well, and incubated at room temperature in the dark for 10 min. The absorbance ratio (A650 / A520) of the blank group and the experimental group at different aptamer concentrations was measured, and the value of ΔA650 / A520 was calculated. 15 nM and 30 nM were selected as the optimal aptamer concentrations for the 21-mer and 17-mer systems, respectively.

[0064] (3) Comparison of the sensitivity of the original aptamer (21-mer) and the truncated aptamer (17-mer) for detecting cadmium ions: Colorimetric detection methods for cadmium ions were established using the original aptamer and the truncated aptamer, as follows:

[0065] 25 μL of nucleic acid aptamer solution (21-mer 15 nM, 17-mer 30 nM) was reacted with 200 μL of 13 nm colloidal gold solution for 10 min. Then, 25 μL of test samples of different concentrations were added and reacted for 30 min. Finally, 25 μL of 40 mM NaCl solution was reacted for 10 min, and the absorbance ratio A650 / A520 was measured using a microplate reader. (The text then abruptly shifts to a seemingly unrelated topic about Cd.) 2+ A standard curve is constructed with the logarithm of concentration on the x-axis and the absorbance ratio on the y-axis.

[0066] Experimental results are as follows Figure 6 As shown in Figures A and B, the standard curves for determining cadmium ions using the original aptamer (21-mer) and the truncated aptamer (17-mer) are respectively: The curves in Figure A correspond to cadmium ion concentrations of 20 nM, 50 nM, 200 nM, 500 nM, 2000 nM, and 5000 nM. It can be seen that the detection sensitivity using the original aptamer is 0.67 nM, and the color does not change significantly with increasing cadmium ion concentration. In contrast, the curves in Figure B, corresponding to cadmium ion concentrations of 2 nM, 10 nM, 20 nM, 100 nM, 200 nM, 1000 nM, 2000 nM, 10000 nM, and 20000 nM, show a detection sensitivity as low as 0.27 nM, and the color changes from red to grayish-blue with increasing cadmium ion concentration. This indicates that the sensitivity using the truncated aptamer is 2.5 times higher than that of the original aptamer.

[0067] (4) Comparison of the specificity of the original aptamer (21-mer) and the truncated aptamer (17-mer) in detecting cadmium ions.

[0068] Using ferrous ions (Fe) 2+ ), potassium ions (K) + ), barium ions (Ba 2+ Nickel ions (Ni) 2+ ), aluminum ions (Al) 3+ ), cobalt ions (Co) 2+), manganese ions (Mn) 2+ ), copper ions (Cu) 2+ ), lead ions (Pb) 2+ A comparative study of the specificity of the original aptamers and truncated aptamers was conducted. The specific methods are as follows:

[0069] After reacting 25 μL of nucleic acid aptamer solution with 200 μL of 13 nm colloidal gold solution for 10 min, 25 μL of 1 μM different metal ion samples were added and reacted for 30 min. Then, the solution was reacted with 25 μL of 40 mM NaCl solution for 10 min. The absorbance ratio A650 / A520 was measured using an ELISA reader.

[0070] Experimental results are as follows Figure 7 As shown, the colorimetric systems constructed from both aptamers have excellent specificity for cadmium ion detection, and the truncated aptamer system exhibits a clear color difference that can be observed with the naked eye.

[0071] (5) Experiment on the recovery rate of cadmium ions in actual samples using truncated aptamers

[0072] Lake water and tap water were filtered through a 0.22 μm microporous membrane and then mixed with ultrapure water at a 1:1 ratio to prepare test samples. The cadmium ion content in the samples was first determined by ICP-MS, followed by standard spiking. After spiking, the colloidal gold colorimetric sensor was used to incubate and detect each spiked sample. The calculated A650 / A520 ratio was substituted into the standard curve to obtain the actual measured cadmium ion concentration results, as shown in Table 2. The detection recoveries ranged from 94.68% to 103.8%, and the RSD values ​​were all below 6.4%. This indicates that the detection method based on the Cd-17 aptamer colorimetric aptamer sensor has good accuracy and can be used for the detection of cadmium ions in actual samples.

[0073] Table 2 Spike Recovery Experiment

[0074]

[0075] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A cadmium ion nucleic acid aptamer, characterized in that, Its nucleic acid base sequence is shown in SEQ ID NO:1 or SEQ ID NO:

2.

2. The application of the cadmium ion nucleic acid aptamer according to claim 1 in the detection of cadmium ions.

3. The application of the cadmium ion nucleic acid aptamer according to claim 1 in the preparation of a kit for detecting cadmium ions.

4. A reagent kit for detecting cadmium ions, characterized in that, Includes the cadmium ion nucleic acid aptamer as described in claim 1.

5. The kit for detecting cadmium ions according to claim 4, characterized in that, Also includes: Colloidal gold and NaCl.

6. The kit for detecting cadmium ions according to claim 5, characterized in that, The molar ratio of the cadmium ion nucleic acid aptamer to colloidal gold is (2~6):1; the molar ratio of the cadmium ion nucleic acid aptamer to NaCl is (1 / 16~6)×10 -6 :

1.

7. The kit for detecting cadmium ions according to claim 5 or 6, characterized in that, The colloidal gold is gold nanoparticle with a diameter of 13 nm; the colloidal gold is prepared by reducing chloroauric acid with trisodium citrate.

8. A method for detecting cadmium ions for non-disease detection purposes, characterized in that, The cadmium ion nucleic acid aptamer described in claim 1 is mixed with colloidal gold and the sample to be tested and reacted, and then reacted with NaCl; the absorbance values ​​are detected under wavelength conditions of 650 nm and 520 nm, and the concentration of cadmium ions in the sample to be tested is obtained according to the standard curve.

9. The method for detecting cadmium ions according to claim 8, characterized in that, The colloidal gold is gold nanoparticle with a diameter of 13 nm; the colloidal gold is prepared by reducing chloroauric acid with trisodium citrate.

10. The method for detecting cadmium ions according to claim 8 or 9, characterized in that, The molar ratio of the cadmium ion nucleic acid aptamer to colloidal gold is (2~6):1; the molar ratio of the cadmium ion nucleic acid aptamer to NaCl is (1 / 16~6)×10 -6 :1.

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