**3.7 Silicon and glass Lab-on-a-Chip**

*Contemporary Developments and Perspectives in International Health Security - Volume 1*

**Property Characteristic Consequence**

Breakdown voltage = 2 × 107

Young's modulus typically

Thermal conductivity 0.2 W/(m K)

310 μm/(m°C) Can withstand 200°C

Permeability Impermeable to liquid water

Thermal expansion coeff.

Permeable to gases and nonpolar solvents

Oxidized by plasma exposure

Toxicity Nontoxic Can be implanted in vivo

UV cut-off = 240 nm

Optical Transparent

Electrical Insulating

Mechanical Elastomeric

Thermal Insulator

Reactivity Inert

*Physical properties of PDMS [36].*

**Table 4.**

v/m

750 kPa

**Polymers Glass**

Fabrication complexity Simple fabrication process Time-consuming and expensive,

Clean room facilities Cleanroom environment is necessary Cleanroom facilities are required

Permeability to gases Higher gas permeability relative to glass Does not met the gas permeability

Higher autofluorescence in the UV end of the spectrum and lower transparency

Generally not compatible with most

with a wide selection of different crosssections; high aspect ratio and arbitrary

*Comparison between polymer and glass as the substrate of microfluidic LoC systems for biomedical and* 

More expensive to manufacture as fabrication process is more

and usually wet chemistry is used

Wider range of operation temperature than polymer

Superior optical property than

Excellent resistance to solvents

requirements for some biological

Limited to two-dimensional design due to isotropic nature of etching process. Less flexibility in crosssections than polymer

complex

Optical detection from 240 to 1100 nm

Does not allow the dissipation of optical absorption heating or electrophoretic resistive heating Can be autoclaved for sterilization

Contain aqueous solutions in channels; allow gas

Unreactive toward most reagents, including ethanol

Can be modified to be hydrophilic and also reactive

transport through material bulk Incompatible with many organic solvent

Surface can be etched

Can be permanently bonded

Supports mammalian cell cultures

toward silanes

Allows embedded electrical circuits Electrophoresis possible on contained fluid

Conforms to surfaces Facilitates release from molds

glass

and acids

applications

Manufacturing costs Lower costs than glass, especially in mass volume

Operation temperature Narrow range due to the low glass

than glass

Geometrical flexibility More flexibility for geometrical designs

wall angle

organic solvents

Optical properties and fluorescence detection

Compatibility with organic solvents or strong acids

*chemical applications [36].*

transition temperature

**202**

**Table 5.**

The earliest LoCs were fabricated in silicon, and it appears like a significant characteristic decision since smaller scale innovations depend on the micromachining of silicon [35]. These days' scientists do not frequently utilize silicon for LoC, for the most part since silicon is costly, not optically nontransparent, and requires a spotless room. Moreover, the electrical conductivity of silicon makes it difficult to use for LoC operations. Still, silicon is relevant choice for the industrialization of some LoC applications. Analogous to silicon, glass is also the earliest fabrication material for LoCs. Glass is a hard material to fabricate chip but a useful material due to its inertness and transmutability of wavelengths in UV, IR, and visible regions [40]. However, fabricating LoCs in glass requires hazardous chemicals and lengthy time intervals, expensive facilities. From an exploration perspective, the creation of glass LoCs requires clean rooms and specialists with solid information of microfabrication techniques.
