Polymerase chain reaction (PCR) amplifies specific fragments of DNA molecules and is widely used in the fields of pathogenic bacteria and gene mutation detection, food safety and clinical diagnosis, but traditional PCR instruments have disadvantages such as large size and heat dissipation. The combination of microfluidics and PCR technology exhibits integration, automation, miniaturization and portability. The design of various microfluidic chips equipped with multiple PCR technologies (PCR, RT-PCR, mPCR, dPCR) helps to realize the application of PCR in various scenarios.
Microfluidic Chip
A microfluidic chip, also known as a "lab on a chip", is a chip that integrates basic operations such as sample preparation, reaction, sorting and detection on a chip of a few square centimeters with a complex fluidic operating system and functional unit modules. It is characterized by its small size, low composition, high efficiency, automation and integration. Microfluidic chips are mainly made of inorganic rigid materials such as silicon wafers, polymers such as glass, quartz and epoxy resins, and elastic materials such as polyurea and polyurethane. These materials have good biocompatibility, good electrical insulation and heat dissipation, good optical properties and modifiability, a simple production process and low cost.
PCR is one of the most commonly used methods in genetic research, offering creative solutions to biology, medicine, chemistry, agriculture, food and the environment. In conventional PCR, the heating rate will be affected due to the large thermal resistance between the heating block and the reaction tube. Even with high-quality thermal resistance elements used in PCR instruments, the heating rate is limited to 4°C-6°C/s. Microfluidics offers a viable option for enhanced PCR, and incorporation of microfluidics can significantly shorten the amplification time of PCR reactions and reduce the required sample volume. At present, the combination of microfluidic chips and PCR has become a hot spot, and different types of microfluidic PCR chips have been applied in various fields.
Structure Type of Microfluidic PCR Chip
Since microfluidic PCR was reported in the 1990s, almost all PCR microfluidic chips have adopted MEMS technology to fabricate a series of three-dimensional structures, such as microchannels and micro reaction chambers, on the basis of silicon, glass or polymer materials. Microchannels and micro reaction chambers are made of glass micro capillaries, polytetrafluoroethylene (PTFE) capillaries, fused silica, rectangular borosilicate glass blocks and polypropylene (PP). To achieve rapid, autonomous, and high-throughput DNA amplification on a chip, the 3D structure is combined with microvalves, micropumps, microheaters and temperature sensors.
Currently, microfluidic PCR chips can be divided into two different structural types: microchamber PCR chips and continuous-flow PCR chips. In a microchamber PCR chip, after the sample is injected into the wells, the chip is heated and cooled at a specific thermal cycle temperature. The CF-PCR chip transports the sample to a fixed temperature zone to achieve thermal cycling. CF-PCR chips can be further subdivided into serpentine channel devices, spiral microchannel devices, oscillator devices, closed-loop devices, straight channel devices, etc. These types of designs make microfluidic PCR devices widely used in molecular biology fields such as gene detection and molecular sequencing.
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