The surface of a sensor chip is where the biomolecular interaction takes place and although dimensionally extremely small (the coatings measure in nm), the composition and structure of the coating have a tremendous influence on the performance of a biosensor and the quality of the data obtained.
In brief, a good sensor chip surface should:
The coating material should not affect surface plasmon resonance (SPR) and should interfere as little as possible with the interaction to be analyzed.
Because of the innumerable possible combinations of ligands, analytes and sample matrices, XanTec has developed a variety of different coatings to best meet the above requirements.
Sensor chip surfaces can generally be divided into two categories: planar or 2-dimensional coatings, and 3-dimensional hydrogels.
Planar coatings are <5 nm thick and can immobilize up to a monolayer of ligand, typically reaching protein densities of approximately 1 ng/mm². Their primary application is in kinetic analysis, biological interaction analysis (BIA) of/with high molecular weight or particulate analytes or ligands, and capture of viruses, cells and particles.
Three-dimensional (3D) coatings, typically hydrogels, allow multilayer ligand immobilization, which results in significant signal amplification. As an additional benefit, they are an excellent means to screen the surface against non-specific interactions. The thinner versions are the coatings of choice for experiments into protein–protein interactions, while thicker hydrogels are employed for qualitative screening and detection, concentration determination, and kinetic analysis of low molecular weight compounds. As a rule of thumb, the smaller the analyte, the thicker and denser the hydrogel structure should be.