Application of sensor technology in environmental detection.
Abstract: Sensors can be divided into gas sensors and liquid sensors in environmental detection, in which gas sensors mainly detect nitrogen oxides and sulfur oxides; The liquid sensor mainly detects heavy metal ions, polycyclic aromatic hydrocarbons, pesticides and biological sources. The application of sensor technology in environmental detection is expounded.
Keywords: gas sensor, liquid sensor, environmental detection
China Library Classification. : O659 document identification code: a commodity number:
With people paying more and more attention to environmental quality, in actual environmental detection, people usually need instruments and analytical equipment that can be carried conveniently and realize continuous and dynamic monitoring of various substances to be detected. The new sensor technology can meet the above requirements well.
Sensor technology mainly includes two parts: the part that can react with the measured object and the signal conversion part. The function of the signal converter is to express the changes after reacting with the measured object with electrical or optical signals. According to the different detection methods, we divide the sensors into optical sensors and electrochemical sensors. According to the different reaction principles, it can be divided into immunosensor, enzyme biosensor and chemical sensor. According to the different detection objects, it can be divided into liquid sensor and gas sensor.
1 gas sensor
Gas sensors can detect indoor air quality, especially in polluted houses or corridors; It can also detect pollutants in the atmospheric environment, such as sulfur oxides and nitrogen oxides, and the detection process is fast and convenient.
Take nitrogen oxides (nitrogen oxides) as an example. Automobile exhaust is the main source of nitrogen oxides, but with the development of the times and the improvement of domestic consumption level, automobile exhaust emissions increase year by year. Nitrogen oxides in automobile exhaust and factory exhaust are directly detected by metal oxide semiconductors. For example, the sensor designed by Dutta, with platinum as electrode and yttrium oxide and zirconium oxide as oxygen ion converters, can detect NO with the content of 10-4~ 10-3. Sulfur-containing oxides are the main substances that cause acid rain, and are also the key items of environmental testing at present. Because the content in the atmospheric environment is lower than 10-6, a sensor with higher sensitivity is needed. Such as a surface acoustic wave device with high detection sensitivity.
Starke et al. used tin oxide, indium oxide and tungsten oxide nanoparticles with a diameter of 8~ 16nm to fabricate a nanoparticle sensor. The detection limits of NO and NO2 can reach 10-8, which increases the specific surface area and sensitivity of the reaction, and the working temperature is much lower than that of conventional sensors, thus reducing energy consumption.
2 liquid sensor
In actual environmental detection, liquid sensors are mostly used for water detection. Because there are many kinds of pollutants in water environment, the application of liquid sensor is more extensive and important than gas sensor. Except for a small amount of natural pollutants, most of the pollutants in the water are inorganic and organic substances dumped artificially. Among inorganic substances, heavy metal ions are the key detection objects; Organic pollutants include pesticides, hormone metabolites and polycyclic aromatic hydrocarbons. These pollutants exceeding the standard will seriously affect the health and safety of all living things.
2. 1 heavy metal ion detection
The main sources of heavy metal ions in water include wastewater discharged from mining, metallurgy and printing and dyeing enterprises. These production wastewater are often mixed with all kinds of wastewater, containing a variety of heavy metal ions, such as mercury, manganese, lead, cadmium, chromium and so on. Heavy metal ions will constantly change their forms and transfer between different phases. If not handled properly, it is easy to form secondary pollution. Heavy metal ions absorbed by organisms from the environment are gradually enriched in advanced organisms through the food chain, which eventually leads to biological poisoning. Therefore, if the metal ions in fish for human consumption exceed the standard, it will have a serious impact on human body, so the detection of heavy metal ions is particularly important.
The sensor invented by Burge et al. can detect whether the concentration of heavy metal chromium in groundwater exceeds the standard by using 1, 2,2 biphenyl carbazide and spectrophotometer.
In addition to chemical reaction detection, heavy metal ions can also be detected conveniently and sensitively by using special biological substances. For example, there is a protein in E.coli that can bind nickel ions, and someone inserted a fluorescent group near the nickel ion binding site of this protein. When protein binds to nickel ions, the fluorescent group will be quenched. Because the intensity of fluorescence is inversely proportional to the concentration of nickel ions, the quantitative detection of nickel ions is realized, and the detection range is not10-8 ~10-2 mol/L. The daily method can also be used to detect several ions such as Cu2+, Co2+, Fe2+ and Cd2+. They also combined with microfluidic technology, which can detect Pb2+ below 100nmol/L only by consuming tens of nanoliters of liquid to be detected. Song Yong fixed TPPS in porous silicon matrix. When Hg2+ exists in the environment, with the change of Hg2+ concentration, the color of TPPS will gradually change from orange to green. The detection limit of the sensor is17.5 nmol/L. Interference ions Ni2+ and Zn2+ are removed by adding aluminosilicate.
Using sensor technology can not only accurately determine the concentration of the object to be measured, but also detect many indexes through the coupling of sensors due to the miniaturization of sensors. Lau et al. designed a sensor based on LED principle, which can detect Cd2+ and Pb2+ simultaneously. The detection limits of this sensor are 10-6 and 10-8 respectively.
2.2 Detection of pesticide residues
Pesticide is a special chemical, which can not only control agricultural and forestry diseases and insect pests, but also cause serious harm to people and livestock. China is a big agricultural country, and the annual use of pesticides is huge, so it is necessary to monitor it. Triazine herbicides can be easily detected by using cobalt-phthalonitrile dye and galvanometer, and the lower limit of direct detection is 50 LG/L. If the sample is pretreated and concentrated, the detection limit can reach 200 ng/L.
Optical fiber infrared spectrum sensor can be used for rapid detection of pesticides. After coating the aerosol material modified by nonpolar organic matter on the inner wall of optical fiber, the signal dissipation effect of water molecules in optical fiber can be significantly improved, and organophosphorus pesticides in solution can be extracted for spectral analysis. The detection limit of this sensor for organic solvents such as benzene, toluene and xylene can reach 10-8~8* 10-8.
2.3 Detection of polycyclic aromatic hydrocarbons
Polycyclic aromatic hydrocarbons (PAHs) are another harmful pollutant with carcinogenicity, but they are used or produced in many industrial production processes. The content of polycyclic aromatic hydrocarbons in water is very low, generally in the range of 10-9, so it is necessary to use a highly sensitive detection sensor. Schechter's team invented an optical fiber fluorescence sensor. In the process of direct detection, there may be some interfering substances such as soil in the sample to be detected, which will reduce the detection signal value. If nonpolar PAH is enriched by polymer membrane first, and then the substances on the membrane are detected by fluorescence, the signal interference problem can be solved. It is reported that the sensor technology enriched in this membrane can detect pyrene as high as 6* 10- 1 1. Stanley et al. used a microbalance of a timely crystal oscillator as a sensor, and fixed an anthracene-carbonic acid monolayer on the surface of the chip, with a detection limit of 2* 10-9.
Based on the principle of immunoassay, antibody molecules that can bind different substances to be detected are printed on the surface of the sensor by molecular imprinting method, which can realize the detection of many different substances. The micro-contact printing technology developed in recent years can also be applied to this field, which makes the volume of the prepared sensor more miniaturized.
2.4 biological pollutants
In addition to the above-mentioned inorganic and organic synthetic pollutants, there are also some potential biological pollutants. For example, the pollution of hormone molecules and their metabolites often leads to abnormal growth, development and reproduction of organisms. The research team led by Gauglitz uses total internal reflection fluorescence biosensor and testosterone antibody to directly and instantly detect testosterone in rivers, and the detection limit is 0.2 ng/L. This technology can directly detect testosterone in natural water in different regions without sample pretreatment, and the detection range is 9 ~ 90 ng/L.
In addition, pathogenic bacteria and viruses are also the objects to be detected. The appearance of some specific strains in the water body can indicate that the water body has been polluted. It is very easy to detect the existence of these biological samples by sensor technology, and the selectivity is very high. For example, the plant virus tobacco mosaic virus can be quickly found from tobacco leaves, and the number of yeast cells can be directly detected by QCM.
3 Conclusion and prospect
At present, sensor technology has been applied to emergency detection of various environmental monitoring institutions, but there are many limitations in practical application. For example, when detecting some harmful substances in the atmosphere, because its content is often lower than the minimum detection limit of the sensor, it is necessary to concentrate the gas in the practical application process, which makes it difficult to miniaturize the sensor or requires the sensor to have higher sensitivity; Similarly, in the field water detection, it often appears that the water to be detected contains a variety of complex interference components, which can not be compared with the standardized conditions in the laboratory; In some sensors based on membrane separation and analysis technology, the service life of membrane is often short, and it is expensive to replace it frequently, so it is still not widely used.
Nevertheless, with the continuous development and improvement of sensor technology, it is still expected to be applied to the on-site direct detection of waste gas and pollution emissions of factories and enterprises and the dynamic unmanned monitoring of outdoor environment in the future, and the results can be consistent with those of conventional instruments in the laboratory, which will greatly accelerate the pace of environmental monitoring and governance.
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Exploration on teaching reform of sensor and automatic detection technology
Sensor and automatic detection technology is an important major course for electrical information specialty. Traditional teaching methods focus on imparting theoretical knowledge, but ignore the cultivation of application level. In order to solve this problem, this paper attempts to analyze the teaching purpose, teaching content, teaching form and teaching effect, and discusses the reform of the teaching scheme of this course, and puts forward an effective teaching scheme combining skills with theoretical knowledge.
Key words: sensor and automatic detection technology; Teaching content; Teaching mode; Engineering thinking
? Sensors and automatic detection technology? It is an important main specialized course of electrical information specialty, a compulsory course, and a comprehensive technology involving many basic theories and technologies such as electrical and electronic technology, sensor technology, photoelectric detection technology, control technology, computer technology, data processing technology, precision mechanical design technology, etc. Modern detection system usually integrates optics, mechanics and electricity, and combines software and hardware.
? Sensors and automatic detection technology? This course began to be offered in the undergraduate and postgraduate stages of Chinese universities in the 1980s. This course focuses on the teaching of sensor and automatic detection technology theory, emphasizing knowledge over skills; Teachers also lack communication, teaching resources are not fully utilized, teaching effect is not ideal, and students' interest in learning is not high.
First, the problems found in the teaching process and the necessity of reform analysis
I teach in an independent college? Sensors and automatic detection technology? This course has been taught for four years. At the beginning, I followed the teaching plan and syllabus of research universities. Because research universities mainly train research-oriented talents, while independent colleges mainly train applied talents, there are great differences in training objectives. In the process of gradual deepening, it is found that the traditional scheme is not in line with the orientation of cultivating applied talents in colleges and universities, and there are the following problems.
1. Pay more attention to theory than practice.
This course is an applied course, which also contains a lot of theoretical knowledge and mathematical derivation. However, traditional research-oriented teaching methods generally focus on theoretical teaching. In class, the principle of the sensor is explained in detail, and the mathematical formula is deduced. In contrast, the application of the sensor is usually briefly introduced through an example, which leads to most students only knowing the structure of the sensor roughly, but not knowing how to use it and where to use it.
2. The teaching mode is single
Traditionally, the teaching method of this course is mainly lectures, telling students ready-made conclusions, formulas and theorems. Students can't actively think and explore, and the process is boring, which leads to students' weariness of learning. At the same time, theoretical teaching is seriously out of touch with practical training and practice teaching.
3. The arrangement of teaching experiment is unreasonable.
In the traditional experimental course arrangement, the proportion of confirmatory experiments is as high as 80%, and there are few comprehensive designed experiments, lacking training and practice links. However, the cultivation of applied talents should focus on practical teaching, focusing on cultivating students' engineering thinking, practical ability and practical ability, so as to meet the requirements of enterprises for technical level and ability when students graduate, and make students adapt to their jobs as soon as possible after graduation.
The second is the reform of teaching plan suitable for independent colleges to train applied talents.
The traditional course of sensor and automatic detection technology pays more attention to theory than practice, and the teaching mode is single, and the teaching experiment is mainly confirmatory experiment. This scheme can train research-oriented talents, but it can't train qualified applied talents. In the teaching process, the author studied hard and practiced repeatedly, and summed up the following aspects that can be reformed.
1. Optimize teaching content and pay attention to engineering thinking.
A very important content of this course is the principle of various types of sensors. Traditional teaching should explain the ins and outs clearly, but I think it is enough to explain all the basic concepts, principles and methods for the cultivation of applied talents. You can choose the important ones to explain a large number of mathematical formulas, and the others can be used as students' self-study content, so that students can learn by themselves after class. At the same time, we should pay attention to the engineering application examples of sensors. On the other hand, it should be explained in combination with the latest actual projects. Only in this way can we stimulate students' interest in learning and cultivate their applied engineering thinking.
2. Reform the teaching method and change the teaching mode.
What is traditional teaching? Instill? The new method tells students all the contents directly whether they accept it or not, which also goes against the starting point and destination of cultivating students' ability to analyze and solve problems and innovate. The author thinks that engineering case teaching should be applied, and heuristic, discussion, research and other teaching methods combined with practice should be implemented to give full play to students' dominant position in teaching activities.
3. Combining engineering practice with other courses.
In the teaching process, we should extract typical engineering application examples from different industries and explain them as examples after streamlining. In teaching, it is necessary to cultivate students' systematic view and make them understand that this course is not an independent course, but is integrated with courses such as automatic control principle and intelligent control theory to achieve the effect of comprehensive learning.
4. Experimental link reform
Experimental teaching is mainly to improve students' practical ability, ability to analyze and solve problems, and deepen students' perceptual knowledge of theories and concepts. In the past, the experimental contents of this course were mostly principled and confirmatory experiments, and students were easily bored and had no enthusiasm for learning. Few students think independently and find problems, and the experimental results are extremely unsatisfactory. In order to change this mode of education, the author changed the experimental content from the traditional verification experiment to the design and development experiment. In experimental teaching, according to objective conditions, on the basis of appropriately reducing confirmatory experiments, pioneering experimental items and designed comprehensive experiments are added.
5. Reform teaching evaluation methods to improve classroom teaching efficiency.
Efficient feedback mechanism of academic performance is a necessary means to promote teaching and learning. At present, this course feeds back the learning effect through course assignments. Each chapter can arrange a design topic, so that students can consult the materials more widely, analyze the content used in the topic in depth on the basis of a certain breadth of knowledge, and then analyze and solve the problem from a deeper level, so as to achieve the effect of combining depth and breadth.
Aiming at the scheme of the traditional research university of sensor and automatic detection technology, this paper puts forward three questions, and based on four years' teaching accumulation, discusses and analyzes the teaching content, teaching mode, experimental link, teaching evaluation and feedback, and puts forward a set of reform methods and measures. This scheme focuses on practical engineering application examples, pays attention to the explanation of sensor application in teaching content, arouses students' learning enthusiasm and initiative by proposing, analyzing and solving problems, cultivates students' engineering thinking and ability, attaches importance to experimental links, replaces confirmatory experiments with designed and comprehensive experiments, trains students to concretize abstract knowledge, and cultivates students' practical application ability, hands-on ability and innovation ability.
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