Environmental pollution problems are becoming more and more prominent, and simple, fast, sensitive and portable environmental monitoring technologies are favored. The traditional monitoring method requires sampling, storage, transportation and measurement. The monitoring cost is high, and the operator needs to have high skill and rich experience. The existing sensor monitoring and analysis has a relatively small sample range and many interference factors. It is far from meeting the needs of modern environmental monitoring. In the 1990s, the MicroTotal Analysis Systems (μTAS) proposed by Widmer and Manz of the Ciba-Geigy Analytical Laboratory in Switzerland provided a new technology platform for the development of modern environmental monitoring technology. The goal of μTAS is to integrate the functions of the entire laboratory, including sampling, dilution, reagent addition, reaction, separation, detection, etc. on a few cm2 of microchips for fast, real-time, online and portable analysis of analytes.
The following are a few examples of environmental monitoring applications based on microfluidic chips:
Capillary electrophoresis microfluidic chip system was used to detect perchlorate content in drinking water. The device is capable of detecting perchlorate content over a large linear range with a minimum concentration of 5.6 μg/L. In addition, the detection time is shortened to 1/15 to 1/30 of ion chromatography (IC), conductivity detection, and mass spectrometry.
Gold nanoparticle probes can be used for the detection of heavy metal ions such as mercury, lead and copper. Using a combination of a microfluidic chip and optical detection, the detection limit of arsenic ions can be as low as 10 to 50 μg/L. Microfluidic chips based on fluorescent gold nano-ions (AuNPs) can detect pesticides in real time and quickly. By measuring the fluorescence intensity, the pesticide content in the tested substance is analyzed. For example, the detection concentration of the dithiocarbamate pesticide thiram can be as low as 6 μg/L.
Another platform based on electrochemical detection method that combines a microfluidic device with a sample injection system (FIA) can achieve rapid, high sensitivity and selective detection of ethinyl estradiol (EE2) in river water samples. . The system employs a direct competitive immunoassay in which the EE2 polyclonal antibody is immobilized on 3-aminopropyl-modified magnetic microspheres, and the use of the microspheres not only increases the surface area of ​​the reaction but also reduces the diffusion distance.
Some devices based on microfluidic paper chip detection are used for the detection of environmental pollutants, which can better reflect their fast and simple characteristics, such as various chemical pollutants and heavy metals. According to the colorimetric mechanism, a microfluidic paper chip based polydiacetylene (PDA) colorimetric sensor can be used to detect volatile organic compounds (VOCs).
Up to 18 volatile organic compounds can be resolved by measuring changes in RGB color values ​​under gas phase conditions. The immunochromatographic electrochemical strip test biosensor (IEB) can achieve a detection concentration of trichloropyridine (TCP) as low as 0.1 ng/mL and a good linearity in the concentration range of 0.1-100 ng/mL. degree.
In the detection of heavy metals, a microfluidic paper chip based on solid phase biological activity can detect the content of each of the following metals by colorimetric detection within 10 min: mercury (II) = 0.001 mg / L; silver (I) = 0.002 mg / L; copper (II) = 0.020 mg / L; cadmium (II) = 0.020 mg / L; lead (II) = 0.140 mg / L; chromium (VI) = 0.150 mg / L; nickel (II) = 0.230 mg / L.
When the microfluidic chip is applied to the analysis of actual environmental samples, although the sampling volume is small and the sample is not representative, the characteristics of its rapid analysis can be used to perform network sampling, so that a large amount of data can be obtained in time and space, and it is avoided. Representative sampling problem. So far, the analysis of microfluidic analysis and detection systems applied to actual environmental samples is very limited, mainly because there are some theoretical and technical problems that have not been solved or yet to be solved: (1) Most microfluidic chips are not yet Ability to analyze complex samples; (2) reliability of separation and analysis of μTAS; (3) reproducibility of microfluidic chip device preparation; (4) microfluidic chip device and real-time online analysis There should be good interface issues between environments and so on.
Therefore, the following aspects will become the research hotspots of environmental monitoring in the future micro-analysis system:
(1) Integrating sample pretreatment units including absorption, purification, concentration, dilution, and derivation, so that the microfluidic chip can gradually have the ability to process and analyze complex samples;
(2) There is a good interface between the microfluidic chip device and the environment, including a good filtering system to avoid the growth of biological organisms caused by sample introduction into the system, and a reproducible automatic sample introduction system to achieve the original Bit real time detection;
(3) The integration of wireless communication and microfluidic chip devices, that is, low-power wireless integrated network sensors, can generate automatic network workstations, provide a large amount of information, and avoid the limitation of cumbersome sampling of environmental detection.
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