A microfluidic chip is a panel of microchannels that can be molded and engraved into various kinds of materials, such as glass, silicon, metal, as well as polymer. Normally, these microchannels can be linked through different sizes of holes to perform the desired functions, including chip mixing, chip pumping, or chip sorting. Pilot studies have demonstrated that microfluidic chips are rapid, automation, and high-throughput analysis tools that can be broadly used for detecting pathogens, analyzing cell patterning, isolating exosomes, and diagnose diseases.
In the past few years, a variety of sample types, like gas or liquid, can be injected and removed from the microfluidic chip by using the external active system (e.g., a simple tube, a syringe pump) or the passive system (e.g. hydrostatic pressure). The channels of microfluidics are usually in the range of one micron or tens of microns. The fabrication of microfluidic chips began with lithography, a process used in the semiconductor industry. With the development of specific processes, including electrodeposition, injection molding, or soft lithography (PDMS), microfluidic chips have been generated using novel materials, polymers (PDMS), and metals (gold).
Fig.1 Schematic illustration of the integrated microfluidic device. (Jiang, 2017)
Nowadays, there are many types of microfluidic chips. Here, we list a few popular chips based on their features and capabilities.
Liquid metals have been broadly used in the generation of microfluidic chips in the past few decades. Many advantages, such as low cost, high integration, as well as high scalability, of liquid metals have been confirmed in different types of microfluidic chips. Moreover, gallium-based liquid metals have been applied to produce microchannels or microfluidic devices.
Pressure sensing inside microfluidic channels is designed by adding an oxygen-sensitive luminescence sensor layer in the inflatable cavity. This chip can precisely detect gas pressures and the backpressure caused by the liquid flowing along the channel. Till now, the flexibility, stability, and reproducibility of pressure sensor-based microfluidic chips have been evaluated by a large number of assays. The data have suggested that the sensitivity of on-chip pressure can be up to 9 mbar and atmospheric pressure can up to 5 bar.
Electrochemical sensors have been selected and integrated into microfluidic chips for improving electrode surface fluid control. Many progress has been made to develop electric and electrochemical microfluidic chips for a battery of applications, such as cell imaging, cell analysis, and DNA detection.
Microfluidics has a very high surface area to volume ratio and is capable of rapid heat and mass transfer, making them ideal tools for efficient and safe detection of chemical reactions. As a result, a range of microfluidic chips based on different nanomaterial reactors or microfluidic droplet reactors, have been developed for protein analysis. Numerous data have shown that this chip can avoid the autolysis of proteases and enhance their activity, reduce the digestion time and improve the enzyme kinetics, so it can be used for large-scale protein mass spectrometry analysis.
Microfluidic fuel cell technology has become an attractive strategy for optimizing electrode structures of microfluidic channels in the development of novel microfluidic chips. Microfluidic fuel cells usually operate in a co-laminar flow structure without physical barriers, such as a diaphragm, to distinguish between anode and cathode. Therefore, this new chip can carry out multi-channel sensing, thus providing multiple analyses and electrochemical imaging.
Separation and sorting of micron-sized particles are essential for the efficacy of microfluidic chips. This micro/nanofluid filter chip has been considered as an innovative way for disease diagnosis, biochemical analyses, and environmental assessment. For example, several integrated micro/nanofluid filter microfluidic chips have been designed for quickly and cost-effectively screening particles.
For Research Use Only. Not For Clinical Use.