Surface modification
A low-pressure gas discharge (oxygen, air or argon) bombards a surface with ions, radicals and UV, breaking bonds and forming polar, oxygen-containing groups. It cleans, activates and enables bonding within seconds to minutes, but the effect is temporary on mobile polymers like PDMS.
Our ruleSimulations prepare you for the bench but don't replace hands-on practice.
Plasma treatment
A low-pressure gas discharge (oxygen, air or argon) bombards a surface with ions, radicals and UV, breaking bonds and forming polar, oxygen-containing groups. It cleans, activates and enables bonding within seconds to minutes, but the effect is temporary on mobile polymers like PDMS.
How it differs from the standard method
- Oxygen plasma activates most efficiently; argon mostly creates radicals that oxidise afterwards in air.
- Use the surface promptly or keep it wet; recovery begins within minutes in air.
- Too high a dose cracks PDMS and can etch thin films.
1Cells and proteins only meet the top few nanometres
Everything that touches a material in the body or in a dish interacts with its outermost molecular layer. Within seconds of contact with medium or blood, proteins adsorb onto that layer, and what cells later see is that adsorbed protein, not the bulk material.
Plasma treatment
Ionised gas breaks surface bonds and adds oxygen-containing, polar groups. Fast and solvent-free, but the effect fades as the surface reorganises.
Protein coating
Adsorbing fibronectin, collagen, laminin or similar gives cells integrin ligands to grip. Simple, but the protein's orientation and folding decide whether it works.
PEGylation
Dense, hydrated PEG chains resist protein adsorption because compressing them costs energy. Density matters more than anything else.
Silanization
Organosilanes such as APTES react with surface hydroxyls on glass or oxides, leaving amines or other groups for coupling.
2Measuring a surface: contact angle and surface energy
The quickest readout is the water contact angle: a drop beads up on a hydrophobic surface (above 90°) and spreads on a hydrophilic one (towards 0°). Measuring with two liquids, one polar (water) and one purely dispersive (diiodomethane), lets the Owens–Wendt equation split the surface energy into dispersive and polar parts.
3How surface treatments fail
- Hydrophobic recovery: plasma-treated PDMS and many polymers return towards their original contact angle within hours as polar groups bury themselves and uncured chains migrate up.
- Over-treatment: long, high-power plasma on PDMS builds a brittle silica-like skin that cracks.
- Contamination: fingerprints, mould release and airborne hydrocarbons block a treatment that only acts on the outermost layer.
- Protein coatings that dry out or are adsorbed onto very hydrophobic surfaces unfold and lose activity even though the protein is still there.
- PEG layers grafted too sparsely leave gaps between the coils, so proteins still reach the surface.
- Silanes that see too much water polymerise in solution and deposit thick, rough, unstable multilayers.
Key terms
Practise these as flashcards →The angle a liquid drop makes with a surface at the three-phase line; lower means more wettable.
The energy per area of a surface, split by Owens–Wendt into dispersive and polar components.
The return of a treated surface towards its original hydrophobicity over time.
Exchange of adsorbed proteins over time, as abundant early proteins are displaced by ones with higher affinity.
Chains attached per unit area; compared with the coil size it decides mushroom or brush.
Sparse grafted chains are separate coils (mushrooms); dense ones overlap and stretch away from the surface (brush).
Grafting PEG from a buffer near its precipitation point, so coils shrink and more of them fit on the surface.
Surface Si–OH groups on glass and oxidised PDMS, the anchor points for silanes and the source of hydrophilicity.
When to use it
- Making PDMS microfluidic channels or culture substrates wettable and bondable.
- Getting cells to attach to synthetic polymers or glass that carry no adhesive ligands.
- Preventing protein fouling on sensors, nanoparticles, implants or low-binding labware.
- Introducing reactive groups (amines, thiols, maleimides) for covalent coupling of peptides, antibodies or drugs.
Compared with alternatives
XPS and FTIR confirm what chemistry is really on the surface, beyond what a contact angle can say.
The downstream test that a modified surface actually supports the cells you care about.
Measures protein adsorption and binding to a surface in real time, label-free.
When the whole material, not just its surface, has to resist proteins or present ligands.
Where plasma bonding and channel coatings are part of building the device.
Sub-techniques
Choosing one here switches the whole page, including the protocol and the lab, to it.
A low-pressure gas discharge (oxygen, air or argon) bombards a surface with ions, radicals and UV, breaking bonds and forming polar, oxygen-containing groups. It cleans, activates and enables bonding within seconds to minutes, but the effect is temporary on mobile polymers like PDMS.
- Oxygen plasma activates most efficiently; argon mostly creates radicals that oxidise afterwards in air.
- Use the surface promptly or keep it wet; recovery begins within minutes in air.
- Too high a dose cracks PDMS and can etch thin films.