Nano gold particles play an important role in many fields such as molecular detection, photothermal therapy, tumor diagnosis, and green catalysis. Below, I will mainly give a detailed overview of their applications in the field of food safety testing.

1. Detection of pesticide residues
At present, the world produces millions of tons of chemical pesticides every year, and more than a thousand synthetic compounds are used in agricultural production. The pesticide pollution problems caused by this are threatening human health all the time. However, the general gas-liquid chromatography analysis method is not only cumbersome and time-consuming, but also the detection results are not accurate enough. Using nano-gold as an immunolabel to detect the surface antigen of Salmonella can solve the above-mentioned problems. This method has reached the stage of practical application so far, such as carbofuran pesticide residue test paper.

The immunochromatographic test strips used to detect the residual herbicide atrazine use gold nanoparticles as immunolabels, and the color change caused by the agglomeration of gold nanoparticles is used to detect residual atrazine, which can greatly improve the detection sensitivity. , The detection limit can reach 1.0 μg/mL.

Visual detection of organophosphorus pesticides represented by methamidophos was carried out using nano-gold colorimetric probes. The principle is that thioacetylcholine generated by acetylcholinesterase catalyzed by acetylcholinesterase can be combined with nano-gold to cause agglomeration of gold nanoparticles. , The color of the solution changes from wine red to blue, and organophosphorus pesticides can control the color change of nano-gold solution by inhibiting the activity of acetylcholinesterase. The content of organophosphorus pesticides can be known through the color change. Through experiments, it is found that the detection sensitivity of this method reaches 1.40ng/mL.

With the advancement of science and technology, the methods and techniques of using nano-gold to detect pesticide residues are constantly improving and developing. I believe that the detection of pesticide residues will become fast, convenient and accurate in the near future.
2. Detection of veterinary drug residues
Veterinary drug residue is not only the original drug residue as we understand it, but it also includes the metabolites produced by the reaction of the drug in the body. Veterinary drug residues are extremely harmful and generally do not cause disease immediately. However, long-term consumption of meat products containing residual veterinary drugs will cause residues to accumulate in the body, which will eventually lead to a series of toxic reactions such as allergies. Therefore, it is urgent for people to find a fast, sensitive and simple method for detecting veterinary drug residues.
For the first time, the nano-gold immunotechnology was used to simultaneously detect kanamycin and tobramycin in pork tissue. The detection limit of the total amount of kanamycin and tobramycin in pork tissue reached 50 μg/ kg, the detection process is between 5 to 10 minutes, and the result is visible to the naked eye. This method has low detection limit, high sensitivity and short detection time, so it can play an important role in the rapid screening of samples on site.

The same method was used to detect 19-nortestosterone residues in beef and pork samples. The experimental results show that when the linear range is between 0.03 and 38 ng/mL, the detection limit can reach 0.52 ng in phosphate buffer. /mL. It is also suitable for on-site rapid detection.

An earlier report using nano-gold colorimetry to successfully detect β-agonists in pig body fluids, chloroauric acid will be reduced by β-agonists to gold atoms to form a red nano-gold solution. This phenomenon is visible to the naked eye. The detection accuracy is high. With this method, people can detect β-stimulants or other similar substances through the detection of urine, serum and other liquid samples, which has very good application prospects in sports competitions and other aspects.
3. Detection of biological toxins
Biotoxins are essentially toxic chemical substances, which are mainly produced by biological organisms and are not self-replicating. There are many types of biological toxins and their distribution is wide. At present, human beings are still not fully aware of biological toxins. The prevention and treatment of biological toxins is also a worldwide problem. Finding a simple, fast and accurate method for detecting biological toxins is the direction of all researchers' efforts.

The content of aflatoxin B1 in the system was detected using gold nanoparticles as the immunolabeling probe (Figure 3.3). The method is to first add the test antigen, gold-labeled antigen, and aflatoxin B1 antibody to the system to cause the three to have a competitive immune response, and then use silver as an enhanced solution to deposit silver with nano-gold. The aflatoxin in the system The B1 content can be determined by detecting the optical density, and its sensitivity reaches 0.01 ng/mL. Subsequently, they improved this method. On the basis of the above method, silver was dissolved, and then the amount of deposited silver was detected by the luminescence method to determine the aflatoxin B1 content in the system. Compared with the previous method, its sensitivity Up to 0.002 ng/ml, the detection effect is better.


4. Detection of pathogenic microorganisms
Food production is a very complex process. In the whole process, there is the possibility of contamination by pathogenic microorganisms in any link. Including the raw material itself may carry pathogenic microorganisms, or be infected by pathogenic microorganisms during transportation or sales. There are many types of pathogenic microorganisms, among which the most contact with people and the most threatening to people are: avian influenza virus, salmonella, foot-and-mouth disease virus, Staphylococcus aureus, etc.
The rapid detection technology using gold nanoparticles as immunolabels has more applications in pathogenic microorganisms, and the types of detection are also more extensive. The monoclonal antibody of Salmonella is immobilized on a glass electrode modified with ethylenediamine by nano-gold, thereby preparing a capacitive immunosensor, which can directly detect Salmonella.
The DNA complementary to the target sequence to be detected is modified onto gold nanoparticles, and the principle of DNA molecular hybridization is used. As long as the target sequence of Staphylococcus aureus exists in the sample, the DNA sequence complementary to the target sequence will hybridize to it and serve as a carrier. Nano-gold will also be close to each other, causing agglomeration between the nano-gold, causing the color of the nano-gold to change. The difference in the concentration of the target sequence will also cause the color of the gold nanoparticles to show different changes.

5. Detection of heavy metal ions
According to chemical classification, metals with a density greater than 4.5 g/cm3 are generally called heavy metals. For example, copper, lead, mercury, nickel, cadmium, etc. are all heavy metals, and the most harmful heavy metals to the human body are mainly lead, mercury, and chromium.

The use of nano-gold colorimetry to detect heavy metals is currently a more commonly used and mature method. Compared with detection methods such as fluorescence and electrochemistry, the colorimetric method has always been a hot research direction in the field of analytical chemistry because of its advantages that it does not require complicated instrument measurement, the result is visible to the naked eye, and is suitable for real-time and on-site measurement.

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