Microfluidic chips are miniaturized laboratory systems for controlling and manipulating tiny liquid fluids. Among other things, the material of the chip is crucial as it can directly affect the performance and stability of the chip.
One of the commonly used materials for microfluidic chips is glass. Glass has many advantages, such as excellent chemical stability, transparency, high temperature stability and corrosion resistance.
In addition, the glass has a flat surface and uniform pore distribution, properties that make fabricating microfluidic chips easier and more controllable.
Among the glass materials, quartz glass, borosilicate glass and hot melt glass are commonly used. Among them, quartz glass is one of the preferred materials for the fabrication of microfluidic chips because of its high transparency, high temperature resistance and corrosion resistance.
Borosilicate glass has high-temperature stability and good optical properties and is commonly used in the manufacture of biochips. Hot melt glasses have high chemical stability and uniform pore distribution and are commonly used to fabricate microfluidic reactors.
In summary, glass is one of the preferred materials for the fabrication of microfluidic chips, and different types of glass materials can be selected according to different application requirements.
Currently the most commonly used glass: BF33, B270, D263
1.BF33 Glass
BF33 glass is a borosilicate glass whose composition mainly consists of SiO2 (68.1%), B2O3 (14.1%), Na2O (9.3%), and Al2O3 (7.1%).BF33 glass has excellent optical properties, good light transmittance, good resistance to acid and alkali corrosion, and can withstand high temperatures and high pressures, and is easy to be processed into complex shapes. Therefore, it is often used to make channels and reaction cells in microfluidic chips.
2.B270 glass
B270 glass is an alkali metal magnesium-aluminum silicate glass, whose composition mainly includes SiO2 (69.2%), Al2O3 (1.3%), MgO (3.3%), K2O (8.8%) and Na2O (16.6%).B270 glass has excellent flatness and optical properties, high surface homogeneity, high resistance to corrosion from acids and alkalis, and high thermal and chemical stability. Therefore, it is often used to make the bottom substrate in microfluidic chips.
3.D263 Glass
D263 glass is a silicate glass whose composition mainly includes SiO2 (64.8%), Na2O (8.6%), Al2O3 (3.9%), MgO (4.2%), and CaO (7.6%).D263 glass is characterized by high transparency, low fluorescence, and low free-ion content, and therefore, it is widely used in optical devices. In microfluidic chips, D263 glass can be used to make micro channels and reaction cells.
A comparison of their differences is shown in the table below:
| characterization | BF33 | B270 | D263 |
| ingredient | SiO2、B2O3、Al2O3 | SiO2、Al2O3、MgO、Na2O、K2O | SiO2、Al2O3、Na2O |
| Chemical resistance | good | Average | bad |
| transparency (of light) | good | good | good |
| heat resistance | good | good | Average |
| processing performance | Average | good | good |
| Price | moderate | moderate | cheaply |
It should be noted that the above only lists some of the main characteristics and advantages and disadvantages of BF33, B270 and D263 glass, and does not mean that in the microfluidic chip manufacturing can only be used in these three materials, there are other types of glass materials are often used in microfluidic chips.
Processing method for microfluidic glass chips
1 Wet corrosion
Wet etching is a common way to process microfluidic glass chips. By plating an acid and alkali resistant chromium layer and photoresist on the surface of the glass chip, and then using the chromium and photoresist layers together as a mask, etching is carried out in an acid or alkaline solution.
By controlling the etching time and etchant formulation, microchannels and microstructures of various shapes can be fabricated.
2 Laser Processing
Laser processing is a high-precision way to process microfluidic glass chips. Laser processing can realize the preparation of microchannels and microstructures of different shapes and sizes by adjusting the laser power and focusing distance. Laser processing can realize high-precision processing and non-contact processing, which can fabricate more complex microfluidic chips.
3 Machining
Machining is a traditional microfabrication technology, which mainly includes methods such as CNC machine processing, glass cutting, and grinding processing. The advantage of machining methods is that highly precise microstructures can be processed, while different shapes can be processed using different processing tools. However, machining methods also have some limitations, such as slower processing speed, higher cost, easy to produce debris and other problems.
Glass models and specifications
Dxfluidics offers the following models of blank glass and etching glass (chrome + photoresist).
| Glass Model | Glass thickness | Glass size | Chromium thickness/,adhesive layer thickness |
| BF33/chrome plate glass | 1mm 2mm | 101.6×101.6mm 127x127mm 152.4×152.4mm | 180nm/500nm |
| D270 | 1mm 2mm 4mm | 101.6×101.6mm 127x127mm 152.4×152.4mm | 180nm/500nm |
| D263 | 0.7mm | 101.6×101.6mm 127x127mm 152.4×152.4mm | 180nm/500nm |
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