Sensor chips are the core of any SPR instrument and their proper choice will help determine whether a biomolecular interaction can be studied effectively with SPR. The base sensor chip is glass coated with a thin layer of metal which has free electrons. Aluminum, copper, silver and gold all have frequencies in the visible range but gold is most frequently used since it is the most chemically inert choice. Additional chemical layers are added to the slide which make how the ligand or target couples to the surface more specific. From gold-plated or nano-structured to membrane associated molecules, sensor technology and development provides new and exciting applications for researchers.

For monitoring biomolecular interactions, sensor chip surfaces can be either a 2D planar surface or a 3D hydrogel. Planar surface thickness is approximately 5nm or less offering a thin coating useful for kinetic analysis of analytes with high molecular weight and capture of particulate analytes such as viruses, cells and particles. This is a good sensor chip for studying protein-protein interactions. Dextran or other hydrogel 3D surfaces can also be used to study protein-protein interactions, but also have added utility for studying interactions between proteins and small molecules. The rule of thumb is that the larger the molecular weight difference between the target and the analyte, the more target you need to couple to the surface. Also, generally speaking, the thicker the coating, the more target you can couple. 3D gels can be from 30 nm to 1000 nm in thickness. Additional modifications can be made to either type of slide to make them specific for the capture of biotinylated molecules (where streptavidin or NeutrAvidin is coupled) or for poly-His tagged proteins (using a Nickel-NTA surface). For antibody capture, a Protein A surface can be prepared to capture IgG, or, a hydrophobic surface, which is used to capture lipids, can be prepared from a plain gold slide.

SPR sensors vary greatly in their construction giving scientists a broad spectrum of options for their research. Scientists have published 52 studies on novel SPR sensor technology in the past six years alone. Companies even now offer blank template sensors and allowed scientists to customize sensor coatings for their particular field of study.

As new materials continue to be developed on a daily basis we can only expect the SPR sensor technology to expand and blossom in the next decade.