MicrofluidicsControl chipDefinition
Microfluidic chip technology integrates the basic operation units of sample preparation, reaction, separation, and detection in the biological, chemical, and medical analysis processes into a micron-scale chip to automatically complete the whole process of analysis. Due to the huge potential in the fields of biology, chemistry and medicine, microfluidic chips have developed into a new research field at the intersection of biology, chemistry, medicine, fluids, electronics, materials, machinery and other disciplines.
Microfluidic chips have the advantages of high degree of automation, high efficiency, high yield, miniaturization, low cost and ultra-low reagent consumption. Especially in the precise operation of microfluids, which can reach nanoliters or even femtoseconds, there is great potential for research in many interdisciplinary fields such as biology, medicine, physics, and chemistry.
Microfluidic chips can be divided into manyCategory
Continuous-flow microfluidic chips
Continuous flow is a constant, regular, and continuous flow. Thanks to devices such as external pressure pumps or integrated mechanical micropumps, the continuous flow microfluidic chip allows the manipulation of the continuous flow of liquids through microchannels. Continuous flow processes are widely used in bioanalytical, chemical, energy, and environmental applications.
Digital microfluidic chips
Digital microfluidic chips, also known as droplet microfluidics or emulsion science, are one of the main application areas of microfluidic chips. It is capable of using electrowetting to manipulate the own droplets on the substrate. This allows for the generation and control of homogeneous, reproducible droplets within the range of experimental parameters.
Droplet microfluidic chips can be used in a wide range of applications, such as the synthesis of nanoparticles, single-cell analysis, and encapsulation of biological entities. Providing new solutions for diagnostics and **, this technology could become an important tool for drug delivery and biosensing.
Optical fluidics and microfluidic chips
Optical fluidics is an emerging and rapidly developing science that converges three scientific fields: microphotonics, optics, and microfluidics. Microoptics, or light control at the micron level, involves the sequential transmission of photons normally emitted from lasers.
Optical fluidics fuses light and liquid into miniature optical devices, taking advantage of the fluid's properties to provide high precision and flexibility.
Optofluidic applications include lab-on-a-chip equipment, fluid waveguides, deformable lenses, droplet lasers, displays, biosensors, optical switches, or molecular imaging tools and energies.
Acoustic fluidics and microfluidic chips
Acoustic fluidics involves the use of acoustic fields, mainly the sonication of fluids within the channels of microfluidic chips to manipulate cells and particles. It refers to the study and manipulation of sound waves in a fluid environment at the microscale to the nanoscale. These mechanical waves are exerted on the fluid by the action of the actuator on the walls of the microchannel.
Acoustics provides strong support for the manipulation of fluids and particles in fluids at the micro-nano scale.
This has proven to be a cell-gentle approach that can be used in many applications, such as biomedical applications: lab-on-a-chip functionalization, particle movement, cell separation, acoustic capture.
Electrophoresis and microfluidic chips
Electrophoresis is a technique used in clinical and research laboratories to separate molecules based on their size, charge, and shape. Electrophoresis relies on the movement of ions in an electric field. An electric current flows through a medium that holds the mixture of molecules. Positively charged ions (cations) travel towards the negative electrode, while negatively charged cations (anions) travel towards the positive electrode. Ions have a unique mobility and they can be separated.
This method can be used for both DNA and RNA analysis.
Microfabrication and microfluidic chips
Microfabrication technology can study and fabricate microstructures in the micrometer scale and smaller, and integrate them into microfluidic devices. It is used in a wide range of aspects, such as replication molding or micro-contact printing, and to precisely control the shape and function of cells by creating a suitable microstructure.
Microelectronics and microfluidic chips
Microelectronics is the engineering that studies the design of miniature electronic components. It allows the precise fabrication of miniature structures using techniques such as lithography, etching. Although the integration of electrical components can be challenging at times, it can be used in a variety of applications, such as medical sensing systems and ergonomic units.
Electrochemical and microfluidic chips
Electrochemistry is the study of the relationship between current flow and chemical reactions. Electrochemical detection elements can be integrated within microfluidic devices, making them reliable and highly sensitive. With the development of electrochemical sensors, lab-on-a-chip, and biosensors, electrochemistry has many applications, especially in analytical chemistry.
Early microsystems used silicon microfabrication, using complex and expensive processes such as chemical etching. Materials like glass and silicon require a lot of time, effort, and money. To overcome these problems, scientists have introduced microfluidic chips in polymers. Choose the most suitable material through experimentation and budgeting, as there are pros and cons to all of them. Paper-based microfluidic chips are increasingly seen as a possible key technology in the future. For some applications, several materials used in the manufacture of microfluidic chips are described next.
Silicon
Silicon was one of the first materials chosen for the manufacture of microfluidic chips.
Nowadays, silicon is used less and less because of its high cost and its opacity makes it impossible to detect optically other than infrared. In addition, it requires real expertise in micromanufacturing and cleanrooms. However, it enables high-precision silicon processing. Silicon materials have good surface stability, chemical compatibility, and electrical conductivity, which allows the integration of electronics on microfluidic chips, but is not possible for microfluidic chip applications that require high voltages, such as electrophoresis.
Glass
Glass is another material that was used in the early days for the manufacture of microfluidic chips. It benefits from the same surface stability, thermal conductivity, and solvent compatibility as silicon. In addition, glass is biocompatible, chemically inert, hydrophilic, and allows for effective coatings. Its surface chemistry, excellent optical clarity, and high pressure resistance make it the best choice for many applications. The main disadvantage of glass in microfluidic chips is its high cost.
Polymers
Polymers are widely used in the manufacture of microfluidic chips because they are strong, inexpensive, and maintain strong biochemical properties. Due to the wide variety of polymer materials and the convenience of chemical modification, polymers have been used in the manufacture of microfluidic chips.
Polymers can be used to rapidly fabricate microfluidic chips. We can divide them into two categories: thermoplastics and thermoset resins. Some of the thermoplastic polymers that can be used to make microfluidic chips are polystyrene (PS), polyetheretherketone (PEEK), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polymethyl methacrylate (PMMA), cyclic olefin copolymer (COC), polycarbonate (PC), PEI (polyetherimide), and polydimethylsiloxane (PDMS).
Dimethicone
Polydimethylsiloxane (PDMS) is widely used to quickly and easily fabricate microfluidic chips. PDMS has the advantages of optical transparency, elasticity, low toxicity, chemical inertness, low cost, and abundant air permeability. PDMS can also be easily operated, and PDMS devices require very little equipment. These properties make it particularly suitable for the fabrication of microdevices for cell or tissue culture.
However, PDMS is limited by material aging and poor chemical compatibility with many organic solvents. In addition, it is not possible to implement the electrode inside the microfluidic chip unless the electrode is mounted in a glass cover slide instead of the chip. In addition, the PDMS chip is not suitable for high-voltage operation because it can change the geometry of the microchannels.
Thermosettingresin
Thermoset resins are polymers that are held together by irreversible chemical bonds during the curing process. They are optically clear, inexpensive, and easy and quick to make. They don't melt, they don't swell in some solvents, they are insoluble. Polymer structures with highly cross-linked thermosets have high mechanical and physical strength but poor elasticity compared to elastomers. Also, when heated, they turn into hard materials, and as a result, they require fluid interconnectors. In addition, thermoset materials are not breathable, which makes them poor materials for battery-based long-term applications. One of the most commonly used thermoset materials in microfluidic chip manufacturing is thermoset polyester (TPE), but other materials such as epoxy resins can also be found.
Paper-based chips
Paper is a very cheap and promising material for microfluidic chips. In fact, paper is easy to store, use, and transport. It is compatible with biological samples and can be chemically processed to bind to molecules or proteins. On top of that, the paper used to make microfluidic chips is environmentally friendly.
The main disadvantage of using a paper base for making microfluidic chips is that the formation of channel patterns on the chip is very complex.
Hydrogel
The hydrogel is very soft and can be molded on it in a variety of characteristic designs and sizes. Hydrogels are non-toxic to cells and cost-effective. Most cellular nutrients and growth factors are diffusible in hydrogels. The diffusivity of most solutes in agarose gels, a common hydrogel used in microfluidic chips, is thought to be very close to the diffusivity in water.
The above content is the classification of microfluidic chips and the manufacturing materials of common microfluidic chips.