Surface properties of polystyrene strips for immunological assays


AFM image of the bottom of a Polystyrene well

The quality and the chemical properties of the surface play a major role in the behaviour of strip for immunological analyses.
Indeed surface properties control the main point of the interaction between synthetic and biological phases:


the adsorption of biological molecules on the surface.

The binding capacity of a strip mirrors the suitability of its surface to adsorb biological molecules.
The target of research efforts is to engineer the surface so that the biological molecules of the coating prefer to bind to the solid surface (adsorb) instead of remaining within the liquid phase.
The main thermodynamic force available to induce the adsorption of biological molecules to a solid surface from an aqueous environment is the hydrophobic effect.
The origin of the latter is the relatively ordered structure of water molecules, induced by intramolecular hydrogen bonding:

the presence of a hydrophobic surface, such that of Polystyrene, disturbs the molecular order of water and forces water molecules to assume thermodynamically unfavourable positions.

The most visible consequence is the low wettability of Polystyrene due to the macroscopic thrust to the minimisation of the water/polystyrene interface.
The same behaviour pushes the surface-active biological molecules within the aqueous phase contained in a well to cluster at the water-polystyrene interface:
the crowding of the biological molecules at the two phases boundary prevents the unfavourable water/polystyrene contact. Obviously, to enhance this effect, the well surface must be in the best molecular conditions :
without contamination and defects which could hinder its hydrophobic character.
This means that much skill and accuracy must be used in manufacturing, since even very small amounts (ng) of contaminants can affect the performances of a surface.
Another effect can be used to increase the binding capacity of the strip:

the ionic or the dipole-dipole bonding.

Indeed when surfactants (the detergents used in rinsing) or biological molecules which contain a high percentage of polar groups, and hence are partly hydrophilic, are used, the driving force for adsorption through hydrophobic effect is reduced.
In these cases it is necessary to introduce polar groups on the Polystyrene surface.
These polar groups interacting with biological molecules via ionic or dipole-dipole bonding, increase the binding capacity and improve the stability of surface-adsorbed molecules during washings.

biomat strips with increased binding capacity have polar groups introduced on their surface.

biomat has developed a specific treatment for Polystyrene, resulting in surfaces which couple the hydrophobic effect and the polar groups performances.
The plasma-based treatment was designed to properly engineer the surface, by the specific introduction of the most effective ( in terms of surface-protein interaction) polar groups.
The coupling of high quality Polystyrene to the chemistry of selected polar groups results in surface properties which cannot be matched by more conventional materials.
An important additional feature of this treatment is that it can be applied to different items extending the application of customer's own device.