Table 2.
Typical techniques for enzyme-immobilization on microchannel surfaces.
| Media | Immobilization method | Enzyme | Advantage and disadvantage | Ref. |
|---|---|---|---|---|
| SiO2 surface | Physical adsorption of biotinylated poly-lysine /biotin-avidin | Alkaline phosphatase | Ease in preparation Requirement for avidin-conjugation Possible occurrence of detachment |
[40] |
| PDMS (O2 Plasma treated) | Physical adsorption of lipid bilayer/biotin-avidin | Alkaline phosphatase | Enable immobilization of enzyme on plastic surface Possible occurrence of detachment Expensive reagents Requirement for avidin-conjugation |
[41] |
| PDMS | Physical adsorption of fibrinogen/Photochemical reaction of Fluorescein- biotin | Alkaline phosphatase | Enable partial modification of microchannel Special equipment is required |
[42] |
| Silicon | Cross-linking (3-aminopropylsilane/ glutaraldehyde) |
Trypsin | Simple operation Difficulty in channel preparation Poor reproducibility |
[43] |
| Fused silica (Sol-gel modified) | Cross-linking (3-aminopropylsilane/ glutaraldehyde) |
Cucumisin Lipase l-Lactic dehydrogenase |
Simple operation Immobilize ~10 times more enzymes than single layer immobilization and therefore, performs with higher reaction efficiency Several chemistry is available (amide, disulfide, His-tag) Needs several steps for immobilization Reproducibility strongly affected by characteristics of silica surface |
[44,45,46,47] |
| PMMA | Cross-linking (Si-O bond between modified surface and silica monolith) | Trypsin | Stabilize enzyme under denaturation condition Complicated preparation method |
[48] |
| PDMS (O2 Plasma treated) | Cross-linking (Si-O-Ti or Si-O-Al bond between titania or alumina monolith) | Trypsin | Stabilizes enzyme under denaturation condition Complicated preparation method |
[49] |
| PET microchip | Entrapment within nanozeolite-assembled network | Trypsin | Large surface/volume network by layer-by-layer technique | [50] |
| Silicon rubber | Cross-linking (3-aminopropyltrieth-oxysilane and glutaraldehyde) | Thermophilic β- glycosidase | Reaction can be performed at 80 °C Complicated preparation method Reaction is slow because not much enzyme can be immobilized |
[51] |
| Fused silica | Cross-linking between physically-immobilized Silica particle (3-aminopropylsilane/succinate) | Lipase | Much larger surface area (1.5 times greater than sol-gel modified surface) and higher efficiency Complicated preparation method Unstable withed physical force (bending etc.) |
[52] |
| SiO2 nanospring | Disulfide bond | β-galactosidase | High solvent-accessible surface area permeability and mechanical stability Repeatability of re-immobilization was poor |
[53] |
| Photopatterning onto PEG-grafted surface | Cross-linking by photo-patterned vinylazlactone | Horseradish peroxidase Glucose oxidase |
Reduced non-specific absorption Sequentially multistep reaction could be achieved Requires special equipment |
[54] |
| PDMS | Entrapment within hydrogel formed on surface | Alkaline phosphatase Urease |
Quite fast reaction (90% conversion at 10 min reaction) Immobilization of multiple enzyme Complicated preparation method Not applicable for higher flow rate |
[55] |