How to Choose A Microfluidic Chip

A microfluidic chip is a device that can be used to process or visualize a small amount of liquid. Such a microfluidic chip allows the integration of multiple functions that usually require an entire laboratory in a single microdevice, which is used in many fields, such as medicine, biology, chemistry, and physics.

Materials Used in Microfluidic Devices

The materials used to make the microfluidic chip play an important role and have the appropriate properties required for the application. There are three types of materials commonly used to create microfluidic chips: Silicon and glass are the earliest materials used for microfluidics, but with the passage of time and the development of new technologies, researchers have used polymer substrates and composite materials.

Each material has its specific chemical and physical properties. For a specific experiment, a combination of these three materials will need to be used to create the required microfluidic chip characteristics. The choice of material depends on:

• Requirements and conditions of the application.
• Type of solvent, sample, buffer and its polarity
• Microfluidic chip design.
• Budget.

For research purposes, the materials used usually give priority to the performance of the chip. But in the process of commercialization, its production cost, reliability and ease of use are given top priority.

Why Choose Silicon Microfluidic Chips?

Silicon was the first material used for microfluidics, but it was quickly replaced by glass and then polymers. Silicon was first selected due to: surface stability, excellent thermal conductivity, resistance to organic solvents, and easy metal deposition.

However, due to its high hardness, silicon microfluidic chips are not easy to handle, so it is difficult to manufacture active microfluidic components, such as valves and pumps. When subjected to optical inspection, silicon exhibits significant optical opacity. In addition, combined with its higher price than other materials, silicon microfluidic chips have not been widely used in microfluidic research.

Why Choose Glass Microfluidic Chips?

Glass is an amorphous material, and it is optically transparent and electrically insulating. Standard photolithography or wet/dry etching methods are usually used to process the material. Glass shares with silicon the same advantages, but with additional ones such as: well-defined surface chemistry, excellent high-pressure resistance, excellent optical transparency, biocompatibility, chemical inertness, and allowing effective coating.

Figure 1. Glass microfluidic devices. (Wlodarczyk K. L, et al. 2019)

The glass microfluidic chip is not gas-permeable and has relatively low non-specific adsorption. Therefore, although it is compatible with biological samples, it cannot be used for long-term cell culture. Other typical applications include on-chip reactions, capillary electrophoresis, droplet formation, solvent extraction, and in-situ manufacturing. The main obstacles to this material are still its hardness and relatively high cost.

Why Choose Polymer Microfluidic Chips?

A wide variety of polymers provide great flexibility in choosing suitable materials with specific properties. They are easy to obtain, cheap, sturdy and require a faster manufacturing process. Many polymers such as cyclic olefin copolymer (COC), polymethyl methacrylate (PMMA), polydimethylsiloxane (PDMS), can be used to make chips.

Due to its low cost and ease of manufacturing, PDMS is now the most commonly used microchip material. The main advantages of PDMS microfluidic chips include:

• Elasticity
• Robustness
• Optical transparency
• Non-toxic and biocompatible
• Possibility to create complex microfluidic designs by stacking multiple layers.
• The permeability of oxygen and gas may be beneficial for the transportation of oxygen and carbon dioxide in cell research and long-term experiments.

Figure 2. PDMS microfluidic chips. (Song Q, et al. 2018)

One of the main disadvantages of the PDMS chip is its hydrophobicity. PDMS surface modification technology can avoid problems caused by hydrophobicity. Another problem is that they are not suitable for high-pressure operation because it changes the geometry of the channel and is prone to leakage under high pressure.

Choose The Right Material For Microfluidic Chips

The following are some key information for choosing a microfluidic chip:

• The material must be biocompatible for life science applications.
• Tend to use transparent materials for optical observation/analysis.
• Most chips require surface treatment to adapt their surface properties to the application and limit non-specific adsorption.

Currently, polymeric materials have become the materials of choice in this field. Although PDMS is still the most commonly used microfluidic material substrate, new materials and composites with interesting functions have been created to make it lower price, and more adaptable.

References

• Wlodarczyk K. L, et al. (2019). “Maskless, Rapid Manufacturing of Glass Microfluidic Devices Using a Picosecond Pulsed Laser.” Scientific Reports. 9: 20215.
• Song Q, et al. (2018). “A New Method for Polydimethylsiloxane Microfluidic Chips to Maintain Vacuum-Driven Power Using Parylene C.” Sensors and Actuators B: Chemical. 256: 1122-1130.

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