Table 2.

Representative materials used for the fabrication of microchips.

Materials		Process	Advantages	Disadvantages
Inorganic materials	Silicon [68]	Standard photolithography	Resistance to organic solvents, high thermoconductivity, simple metal deposition, stable electroosmotic mobility.	Fragile, opaque, poor electrical insulation, hardness, high cost, time-consuming, labor-intensive, the bonding is difficult and requires a sterile environment.
	Glass [69]	Standard photolithography	Optically transparent and electrically insulating, resistance to organic solvents, high thermoconductivity, simple metal deposition, stable electroosmotic mobility, easy surface modification.	Fragile, high cost, time-consuming, labor-intensive, bonding is difficult and requires a sterile environment.
Elastomeric polymers	PDMS [70]	Cast molding	Optically transparent, high elasticity, low cost, easy and reversible binding, non-toxicity, permeability, compatible for cell culture, could integrate with the micropump and microvalve.	Could not withstand high temperatures, low thermoconductivity, strong nonspecific adsorption, poor organic solvent compatibility.
Rigid plastic polymers	PMMA [71]	Thermal molding	Organic solvent compatibility better than PDMS, low cost, can produce thousands of replicas at a high rate, the thermal bonding does not require a sterile environment.	Poor permeability and heat conductivity, high rigidity, difficult surface modification, cannot withstand high temperatures.
	PI [72]
	PC [73]
	PS [74]
	PET [75]
	PVC [76]
	COC [77]
	Teflon PFA [78]		Extremely inert to chemical solvents, optically transparent, moderate permeability, antifouling, proper mechanical strength, low nonspecific absorption, no leaching of residue molecules from the material bulk into the solution in the channel.	Melting temperatures are high (over 280 °C).
	Teflon FEP [78]
Hydrogel polymers	PEG [79,80]	UV-induced polymerization	Highly porous with controllable pore sizes, allowing small molecules or even bio-nanoparticles to diffuse through, compatible for cell culture, short preparation time.	The bonding is difficult.
Photosensitive polymer	SU-8 photoresist [81]	Photolithography	Stable even at high temperatures, resistant to most solvents, and optically transparent.	High cost, high stiffness, poor permeability, and non-uniform thickness.
	NOA81 [82]		Transparent, rapid, solvent-resistant, lower auto-fluorescence, and the thickness can be easily manipulated.
	pCLLA [83]		Non-toxicity, biocompatibility, biodegradability, rapidness, and flexibility in materials processing.
Paper	Paper [84]	Lithographic methods and printing (cutting) methods	Portable and low-cost analysis, without the need for power or external components; large surface-to-volume ratio, the cheapest materials.	Liquids may not be well confined in the channel due to hydrophobicity, the applicable detection methods are relatively limited, low detection sensitivity, evaporation of liquid.