OptiChem® Bio-Coatings

Summary Points

• OptiChem® surface coatings provide a versatile interface between synthetic or non-biological materials and biological materials.
• OptiChem has an exceptional ability to prevent or delay non-specific adsorption of bio-materials to surfaces.
• It also has high capacity for ligand binding when prepared in chemically activated form, allowing convenient molecular modification to suit different applications.
• Examples of potential applications include biosensors, analytical assay surfaces, pharmaceutical packaging, and invasive medical devices.
• OptiChem can be readily applied to a wide variety of base materials, including glass, silicon, metals and metal oxides, ceramics, and polymers.
• OptiChem coatings withstand a wide range of physical-chemical exposure conditions including pH, temperature, and solvents.
• In a production process, OptiChem offers highly consistent performance and eliminates the variations inherent to adsorptive coating chemistries.

Download a survey of potential OptiChem® applications in bio-coatings and anti-fouling coatings.

Active, Passive, and Hybrid Surface Coatings

OptiChem® surface coatings provide both a protective and functional interface between non-biological and biological materials. As a protective coating, OptiChem has an exceptional ability to prevent adsorption or fouling by sticky biomolecules. As a functional coating, OptiChem offers flexibility for chemical activation and high capacity for selective ligand binding.

Gene and protein microarrays, immunodiagnostics, biosensors, and biomolecule containers exemplify devices that rely on controlled interactions between non-biological and biological materials. Most synthetic materials that come into contact with biological materials quickly become coated with sticky biomolecules. Such adsorption or “fouling” can have serious consequences. A few examples –

• Blood components can cover a biosensor surface, interfere with target analyte binding, and gradually destroy sensing performance.
• Foreign materials implanted or inserted into the body provide attachment surfaces for bacteria, potentially becoming a nidus for infection and biofilm growth.
• Containers for biotech protein drugs can adsorb the active ingredient, accelerating product degradation and shortening shelf life.

Since device designers have limited choices for base materials, they use surface modification to reduce fouling. Modifications include direct action on the surface itself (as with plasma etching) and coating with an appropriate barrier film.

OptiChem has unique properties as an anti-fouling barrier coating. It has micro-porosity that lets small ions pass freely and small biomolecules to diffuse. But it prevents mid- to large-size biomolecules from making contact with the underlying base material. As an example, our BACcelr8r™ analytical cassette uses OptiChem on its assay surfaces, where it provides a very low electrical resistance for ionic electrophoresis buffers.

It has heterogeneous physical-chemical surface properties. It presents a relatively hydrophobic surface to aqueous solutions. Formulations can be adjusted to provide consistent water contact angles up to approximately 70°. But it also provides a hydrophilic molecular environment that reduces protein denaturation.

OptiChem thus offers mutual protection between device surfaces and biomolecules.

Other devices require selective biomolecule binding to a surface, such as biosensors or other assay surfaces. For example, microarrays require chemical binding of molecular probes to discrete spots on a surface. But they need a passivated anti-fouling surface between the active spots. The immobilized probes or ligands are designed to bind selectively to targets of interest in a test sample. When a target molecule binds to a cognate probe molecule, a detectable event occurs and provides the assay signal.

Interfering materials often exist in a sample. They may be native to the sample, such as the cells and sticky molecules in blood. Or they may enter the sample during preparation, such as excess dyes. Their presence may interfere either to reduce sensitivity or introduce unacceptable variability. In both examples the interfering material raises the noise level (or “background”) through non-specific binding (adsorption or fouling) to the detection component. In severe cases, such as glucose sensors inserted into the bloodstream, this can even eliminate the signal.

Compared with alternative surface treatments, OptiChem can maximize the signal-to-noise ratio and maximize sensitivity when used as the assay surface. Its combination of exceptional anti-fouling and high probe density act in concert to deliver superior assay performance.

OptiChem's Engineering Properties

OptiChem coatings are a family of proprietary, multicomponent thin organic films prepared by solvent casting. The films are chemically and physically robust over a wide range of conditions of pH, temperature, and solvents. Formulations adjustments support application by spin-coating, ultrasonic spraying, dip-coating, and other methods according to substrate form factor.

OptiChem adheres tightly to a variety of substrate materials. Examples include glass, metals and metal oxides, silicon, ceramics, and polymers. Polymers tested successfully with OptiChem include polystyrene, polycarbonate, polypropylene, and others. The BACcelr8r™ uses OptiChem applied to polymer fluidic channels (to prevent bacterial adsorption) and ITO (indium tin oxide) assay surfaces where they bind to a bacterial capture agent. Our OptArray™ microarraying slides are coated on specialty glass, as another example.

Chemical activation is also highly flexible. Standard microarraying slides use amine reactivity, and we have produced other types of chemical binding. Post-coating modifications are straightforward. For example, certain commercial protein array suppliers use standard OptiChem that has streptavidin covalently bound to the surface after coating application. The production process has a step for quenching unreacted binding sites after the final probe attachment or modification. This eliminates the need for a separate blocking step by the end-user.