Sensors have already penetrated into extremely wide fields such as industrial production, space development, ocean exploration, environmental protection, resource investigation, medical diagnosis, biological engineering, and even cultural relics protection. It is no exaggeration to say that from the vast space to the vast ocean, as well as various complex engineering systems, almost every modernization project is inseparable from various sensors.
Reporter: There are many kinds of sensors, what kind of sensors are we making with DNA molecules?
Liu Zhongming: This sensor is called a genetic sensor, it is a kind of biosensor.
DNA biosensor is a sensing device that can convert the presence of target DNA into a detectable electrical signal. It consists of two parts, one is the identification element, namely the DNA probe, and the other is the transducer. The identification element is mainly used to sense whether the sample contains the target DNA to be tested; the transducer converts the signal sensed by the identification element into a signal that can be observed and recorded (such as current size, frequency change, fluorescence and chemiluminescence intensity, and light absorption degree) Wait). Usually a single-stranded DNA is cured on the transducer, and another DNA containing complementary sequences is identified through the hybridization of DNA molecules (base complementary pairing principle) to form a stable double-stranded DNA through sound, light, and electrical signals To detect the target DNA.
Reporter: How does it extend our senses?
Liu Zhongming: The principle is to pass a single-stranded DNA molecule (also called ssDNA probe) of known nucleotide sequence fixed on the surface of the sensor or transducer probe and another complementary ss-DNA molecule (also called Target DNA) hybridization, the resulting double-stranded DNA will show a certain physical signal, and finally reacted by the transducer.
Let me take the DNA electrochemical sensor to detect gene damage as an example, and explain in detail how it works. DNA base complementation is selective and specific, so we often use the complementary strand of the DNA (target DNA) to be detected as a probe. When the probe and the target DNA are complementary to each other, the current through the DNA strand will change accordingly, and the electrical signal will change. This change reminds us that the two have already coincided with each other. From another perspective, if the electrical signal has not changed, it also implies that there may be damage to this DNA.
To put it more bluntly, it's like stacking a bunch of copper coins together, and when properly aligned they can conduct electricity. If one of the piles of coins goes wrong or is not placed well, the conductivity will drop. If the base pair is mismatched, or there is damage that may cause cancer, the circuit will be disrupted and the current will not be smooth.
This is like opening a lock with a key. If the gap between the key and the lock does not match, we know that the two do not match, and the lock may have a problem. If they match in shape, the lock's attributes can be determined based on the label on the key.
Sensitive, fast and accurate, ideal for medical testing
Reporter: The DNA molecule is very tiny and fragile. How can we fix it and use it?
Liu Zhongming: The problem you mentioned is very important. The immobilization technology of bio-sensitive materials is an important part of the research of genetic sensors and the key to the preparation of biosensors. This technology determines the function, performance and quality of the sensor. To be specific, it also relates to the sensitivity, linear range, stability and service life of the sensor. The techniques for immobilizing DNA probes include covalent bond method, self-assembled membrane method, electrical assembly method, and surface enrichment method.
The covalent bonding method is a method in which bioactive molecules are bound to the electrode surface by covalent bonding and fixed. Before the electrode is fixed, the electrode must be pre-treated for activation, and then active bonding groups (such as amino groups, carboxyl groups, etc.) are introduced, and then the surface is covalently bonded to fix the probe molecules containing predetermined functional groups to the electrode surface.
Of course, we also use self-assembly methods to fix DNA. This technique generally uses a DNA fragment with a sulfhydryl group to form a self-assembled monomolecular membrane on the gold electrode surface to immobilize nucleic acid probes.
There are several other commonly used methods, I will not introduce them one by one here.
Reporter: As a kind of biosensor, what are the unique characteristics of DNA sensor?
Liu Zhongming: DNA sensors are a special kind of sensors, which grew up on the basis of the mutual penetration of various disciplines such as biology, chemistry, physics, medicine, and electronic technology. It has strong specificity, and has a very high specific recognition ability between the double strands of DNA molecules; fast analysis speed, which can get the results in 1 minute; high accuracy, minimal error; relatively simple operating system, easy to implement automatic analysis; cost Low, when used continuously, the measurement price is low. Especially it has the characteristics of high automation, miniaturization and integration.
Reporter: Compared with other fields, the application of DNA sensors in clinical medicine is closer to us and more concerned by everyone. Can you talk about the application in this area?
Liu Zhongming: With the development of molecular biology, people gradually realize that except for trauma, all diseases including infectious diseases, inherited diseases and malignant tumors are related to genes, so DNA sensors used in genetic detection appear Very important.
For example, hepatitis B is an infectious disease caused by hepatitis B virus (HBV) that spreads quickly, has a long incubation period, and has a wide range of hazards. China ’s chronic asymptomatic HBV infection or chronic asymptomatic HBV carriers have exceeded 120 million, which is HBV infection There is the largest number of groups among those. If the self-assembled monomolecular membrane technology I introduced above is used, the single-stranded DNA probe of the thiohexyl-modified probe is fixed on the surface of the gold electrode to prepare a DNA electrochemical sensor, which uses an electrically active substance as an indicator. A DNA sensor with good specificity, high sensitivity and short response time can be obtained. It is more ideal for the response of HBV DNA in serum samples. In other words, the DNA sensor can help us detect whether the subject has been infected with chronic asymptomatic HBV or has carried the virus correctly, quickly and with high quality.
Many industries need very broad application prospects
Reporter: In addition to clinical medicine, what other application fields do biosensors have?
Liu Zhongming: Biosensors have achieved gratifying development in recent decades. Especially after the combination of molecular biology with new disciplines and new technologies such as microelectronics, optoelectronics, microfabrication technology and nanotechnology, this development is accelerating and is being implemented in various sectors of the national economy, such as food, pharmaceutical, chemical, clinical Inspection, biomedicine, environmental monitoring and other fields show a wide range of application prospects.
For example, the content of glucose is an important indicator to measure the maturity and storage life of fruits. The biosensors that have been developed can be used to analyze glucose in liquor, apple juice, jam and honey. In the food industry, the detection of food freshness, especially the freshness of fish and meat, is a major indicator for evaluating food quality. Now someone has developed a sensor that measures the concentration of inosine monophosphate and other substances produced during the degradation of fish, and then evaluates the freshness of the fish.
In recent years, the problem of environmental pollution has become more and more serious. People desperately want to have an instrument that can continuously, quickly, and online monitor pollutants. Biosensors meet people's requirements. At present, quite a few biosensors have been used in water environment monitoring, atmospheric environment monitoring and other fields.
In military medicine, the timely and rapid detection of biological toxins is an effective measure to defend against biological weapons. Biosensors have been used to monitor a variety of bacteria, viruses, and toxins, such as Bacillus anthracis, Yersinia pestis, Ebola hemorrhagic fever virus, and botulinum toxoid.
In addition, in forensics, biosensors can be used for DNA identification and parent-child authentication.
Reporter: What do you think is the future development direction of this research field?
Liu Zhongming: Now, the research of sensors needs to seek new breakthroughs in stability and reliability. Only by creating more stable and reliable biosensors, the application of clinical testing will be greatly expanded.
In addition, the sensor will develop towards miniaturization and integration. With the advancement of micro-processing technology and nanotechnology, biosensors will continue to be miniaturized. The emergence of various portable biosensors makes it possible for people to diagnose diseases at home and directly detect foods on the market. Moreover, the future biosensors must be closely integrated with computers to automatically collect data and process data to provide results more scientifically and accurately, realize one-stop sampling, sampling, and results, and form an automated system for detection. With the deepening of research in these two directions, the cost of products has gradually declined. Biosensors that once showed great application prospects in the laboratory will also "fly into the homes of ordinary people."
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