Microfluidic chip technology and its application in biology

Microfluidic chip technology and its application in biology

In 1990, Manz and Widmer et al. ^[1] first proposed the concept of microfluidic chip. Since then, microfluidic chip technology has been rapidly developed. It has effectively reduced reagent and sample consumption, speeds up analysis, and improves detection sensitivity. The advantages of reducing the cost of analysis ^[2] make it widely used in various fields, including genetic analysis, protein analysis, screening of active ingredients of natural products, and food safety analysis. This paper focuses on the development of microfluidic technology and its application in biology.

1 Development of microfluidic chip technology

The technology of manipulating fluids or gases in a 10~100μm wide channel system is called microfluidic technology. Microfluidics is the core, micro-pipes, micro-pumps, micro-valves, micro-storage through micro-machining technology. Functional components such as liquids, microelectrodes, micro-detection components, windows and connectors are integrated into chip materials like integrated circuits. Micro-flow analysis systems for applications in biology, chemistry, biomedicine, etc. are called microfluidics. Control chip ^[3] . The earliest microfluidic chips were built on silicon wafers. The microfabrication technology of silicon substrates is relatively mature and the materials are relatively cheap. However, the biocompatibility of silicon is not good, and the silicon substrate is not resistant to high voltage and opacity, which limits its application in this field ^[4] . Then quartz glass becomes the main substrate material. The micro-machining technology of quartz substrate is similar to that of silicon wafer. It can withstand high pressure, good biocompatibility, and is completely transparent and easy to detect, but the cost of quartz substrate is high. In recent years, polymer materials have become the most popular materials due to their low cost and simple processing methods. Polydimethylsiloxane (PDMS) is the most widely used polymeric material. At present, the application of biological materials in microfluidic chips has received great attention ^[4] .

In 1990, Swiss researchers Manz and Widmer first proposed the concept of microfluidic chip ^[5] . In 1992, Manz developed a capillary electrophoresis microchip analysis device, which pioneered the microfluidic chip technology. Therefore, the microfluidic chip technology is Developed on the basis of chip capillary electrophoresis technology ^[6] . In the study of the 1990s throughout the 1990s, microfluidic chips were used more as a chemical analysis platform, which was mainly used in chip electrophoresis ^[7-8] . In 1994, Ramsey et al. ^{[9] of} Oak Ridge National Laboratory in the United States improved the injection method of chip capillary electrophoresis based on Manz's work, and improved its performance and practicability. In 1995, Mathies et al. ^{[10] of the} University of California at Berkeley implemented high-speed DNA sequencing on a microfluidic chip, and its commercial value began to appear. In September of the same year, the first microfluidic chip company, Caliper Technologies, was established. In 1996, Mathies et al. integrated polymerase chain reaction (PCR) amplification and capillary electrophoresis, and later realized multi-channel capillary DNA sequencing on microfluidic chips ^[11] . In 1998, the first microfluidic analysis instrument was introduced, and various instruments and chips were springing up. In the same year, Science published an article on microfluidic chips as a miniaturized chemical factory for the first time, which triggered new research hotspots ^[12] . In 1999, Shi et al ^[13] developed 96 capillary separation electrophoresis chips in separate lanes, which can simultaneously separate pBR322 samples within 2 min. In 2000, Anderson et al. ^[14] developed a highly integrated chip for complex molecular processing of multiple samples. It extracts concentrated nucleic acids from milliliter aqueous samples for microcrystalline chemical amplification and enzymatic reactions. , hybridization, mixing and determination, etc., and more than 60 continuous operations of more than a dozen reactants. In 2001, the "Lab on a Chip" magazine was launched as a mainstream publication that influenced the progress of relevant research worldwide. Since then, the development of microfluidic chips has entered a new stage; in 2002, an article entitled "Microscale Bioanalytical Systems" and "Small Integration of Microfluidic Chips" was published on Science, which means micro The value of the flow control chip has been recognized by academics and industry ^[15-16] ; in 2006, Nature published the "Lab on a Chip" album, which included 1 introduction and 8 reviews, and explained the chip from different angles. The research history, current status and application prospects of the laboratory ^[17] . At present, microfluidic chip technology has become an important tool and hotspot in life science, drug synthesis, disease diagnosis, food safety testing and other research.

2 Microfluidic chip technology in the field of biology

2.1 Application of microfluidic chip technology in gene detection

In terms of gene detection, microfluidic chip technology is mainly used for nucleic acid amplification, separation, sequencing and peptide detection. Polymerase chain reaction (PCR) is widely used in molecular biology. It can amplify DNA molecules in vitro. The conventional PCR process takes about 1-2 hours, and requires more reagents, which is time-consuming and labor-intensive. When the microfluidic chip technology is used for PCR amplification and related detection, it can simplify the operation steps and significantly improve the detection efficiency. In 1998, Kopp et al. ^[18] proposed a continuous flow microfluidic PCR amplification chip. The reaction solution was circulated through different temperature zones to complete the PCR amplification reaction. The entire amplification reaction was completed in the flow, shortening the amplification time. , reducing the reagents required for the reaction. Since then, many scientists have further improved the continuous flow PCR technology based on this research, making it more miniaturized ^[19] . With the continuous improvement and development of microfluidic chip technology, the length of DNA fragments that can be separated by microfluidic analysis technology is gradually expanded, and the sequencing of DNA fragments and the separation and analysis of genetic material can be completed, and simultaneous occurrence can occur. Parallel analysis of multi-channel microfluidic chips ^[19] . Mathies ^[20] studied the sequence length of 150-200 bp on a single-channel glass chip with an effective separation length of 3.5 cm. Later, they extended the separation channel to 7.5cm, and switched to a 500bp sequence analysis using a four-color fluorescence detector for 20 minutes, with an accuracy rate of 99.4%. Single nucleotide polymorphism (SNP) is an ideal genetic marker for the physical map of the human genome, which can locate the genes involved in metabolism, growth and disease. The gene polymorphism is in various human heritable variations. A common phenomenon ^[21] . The SNP test method is mainly based on PCR, and the genotyping is performed by electrophoresis to distinguish various differences in DNA fragments caused by base differences. Taylor et al ^[22] designed a cross-type microfluidic chip to analyze and analyze the correlation between various diseases and their variation. The entire analysis process was shortened by a few days from the traditional method to 45 minutes.

2.2 Application of Microfluidic Chip Technology in Protein Analysis

Protein is the most basic biologically active substance in organisms. Separation and determination of proteins can help people understand the role of proteins in biological functions, and it is invaluable in discovering new methods of diagnosis and treatment ^[6] . Traditional protein analysis steps are performed by hand. These methods are too cumbersome, have large sample consumption, and are not sensitive enough to meet the needs of proteomics for rapid, integrated, high-throughput, high-sensitivity analysis systems. The microfluidic analysis chip system was used to analyze the structure, function and protein interaction of protein samples, proteins, and the analysis steps were carried out on a few square centimeters of analytical chips, with fast reaction speed and high sensitivity ^[19] . In addition, the amount of reagents and reactants required for microfluidic chip detection technology is small, which can greatly reduce reagent consumption ^[19] . Hofmann et al ^[23] used isoelectric focusing capillary electrophoresis chip technology to label the peptides with Cy5, and separated 9 protein mixtures such as cytochrome C, ribonuclease A and myoglobin, and completed the whole detection process in 5 min.

2.3 Application of microfluidic chip technology in cell analysis

With the rapid development of life sciences, the analysis and detection of single-cell and intracellular components and morphological changes has become a research hotspot. Due to its microchannel width (10-50 μm) and biological cell size, microfluidic chips are very easy to manipulate, observe and detect in microchannels. Single cell research with microfluidic chips has unique advantages ^{[ 19]} . Shin et al ^[24] constructed an electroporation cell chip, which used an exponential decay pulse generator to perform electroporation experiments on cells in a fluid channel, and measured various parameters of cell electroporation. In recent years, people have also conducted extensive research on the chemical concentration gradient of the cell microenvironment for time and space control, cell culture and the like. It is believed that with the continuous updating of microfluidic technology, this technology is expected to become the main tool for cell research ^[19] .

3 Outlook

After more than 20 years of development, microfluidic chip technology has been maturing from the germination stage. At present, microfluidic chips have been widely used in biological fields such as gene sequencing and protein profiling. The development of life sciences has entered a very important In the historical period, the intersection and combination of life sciences and chemistry, engineering and other fields has become the inevitable development of science. Microfluidic chips have the unique advantages of miniaturization, integration and multidisciplinary crossover. They are also widely used in different research fields such as biomedicine, and have achieved remarkable results, showing broad application prospects ^[25] . With the continuous maturity of microfluidic chip technology and the continuous reduction of production costs, it is necessary to enter the field of routine medical testing on a large scale, replacing those laborious and complicated testing and testing equipment, and thus promote the advancement of medical level ^{[4] ]} .

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