BioRad ProteOn XPR36 System
This is a walk-up instrument or samples can be dropped off to be run for an additional fee. Training on the instrument is also available. Scheduling of this instrument is done through the Faces Scheduling System. See the Calendars and Scheduling page for more information. Visit the Research Store for current pricing.
SPR is a sensitive spectroscopic tool for studying molecular interactions in a label-free state. The system detects binding in real-time by measuring mass changes of a ligand, which is bound to a chip, as analyte is flowed over the chip. Binding association and dissociation rate constants are determined directly from the binding traces. SPR will work on proteins, nucleic acids, lipids, and small molecules. The ProteOn XPR36 system in the core uses a chip with a 6 x 6 interaction array allowing for simultaneous analysis of up to six ligands and six analytes. See the ProteOn XPR36 brochure for more hardware details.
For SPR the ligand (generally proteins) needs to be attached to the chip while the analyte (protein, nucleic acid, lipid, small molecule) is flowed over the chip. Binding the ligand to the chip can occur through His-tags or covalent linkages. Different chip densities exist to help optimize sensitivity and non-specific interactions with the chip. Chips can often be regenerated and used again. His-tagged chips can be stripped and a different protein bound while covalent bound chips can be regererated and re-used to study different analytes. Typical protein samples are around 1 ug/ul in concentration with volumes around 20 ul to 100 ul. PBS buffer is a good choice and TRIS should be avoided. Binding affinities in the 1 uM to 1 nM range can typically be detected. A classic problem with SPR is non-specific binding of the analytes to the chip matrix. Often blocking agents such as BSA, gelatin, and casein are added to the buffers as are non-ionic detergents such as Tween and Triton to reduce non-specific binding. Ionic strength and pH can also have strong influences in non-specific binding and are often varied when optimizing experimental conditions.