Several parts of the system can give rise to some artefacts in the sensorgrams. Knowing them can help you to avoid these.
SPR is temperature dependent because the refractive index of a liquid is temperature dependent. Since the detection unit is temperature controlled, any influence of temperature is usually negligible. Even injecting a liquid that has a different temperature than the detector, will not affect the data because the small volume of liquid will have the proper temperature before reaching the detector.
When changing the temperature of the system, the detector should be reset to ensure proper functioning (highest sensitivity).
On the other hand, the temperature dependency of kinetics can be exploited. With measurements at different temperatures, it is possible to investigate the influence of the temperature on the thermodynamics of the interaction (1),(2).
Injecting a volume of flow buffer over a new non derivatised surface, ideally should give a flat baseline with low drift.
In general, a slight positive bulk effect is seen (5–10 RU) during injection. In addition, an injection with a solution with a higher salt concentration (e.g. +25 mM NaCl) than the running buffer must give a sharp rise, flat steady state and sharp fall of the curve indicating that the injection system is working properly. If the response between the flow channels is not comparable, it may be an indication that the IFC needs replacement (3)
Matrix effects are changes in the extension of the dextran matrix on the sensor chip surface due to variations in pH or ionic strength (4). The effect of these variations is usually small in terms of absolute response, but may be significant in experiments where the highest sensitivity is required. Matrix effects may have time constants ranging from seconds (for e.g. small changes in pH or ionic strength) to minutes or even hours (for example after regeneration with extreme conditions). Normally, matrix effects are directly related to the mass concentration of the immobilized ligand, with greater effects at higher concentrations (5), (6). When the matrix interferes with the experiments, other matrices or sensor chips without a matrix layer can be used.
Matrix effects can be minimized by matching the injected sample to the flow buffer used, either by dialysing the analyte or by adjusting the flow buffer.
|Solute||dR/dC (RU .(mg/ml)-1)|
|proteins and DNA||~180|
|(1)||Zeder-Lutz, G., E. Zuber, J. Witz, et al. Thermodynamic analysis of antigen-antibody binding using biosensor measurements at different temperatures. Analytical Biochemistry 246: 123-132; (1997).|
|(2)||Navratilova, I., G. A. Papalia, R. L. Rich, et al. Thermodynamic benchmark study using Biacore technology. Analytical Biochemistry 364: 67-77; (2007). Goto reference|
|(3)||Myszka, D. G. Improving biosensor analysis. J.Mol.Recognit. 12: 279-284; (1999). Goto reference|
|(4)||Paynter, S. and D. A. Russell Surface plasmon resonance measurement of pH-induced responses of immobilized biomolecules: conformational change or electrostatic interaction effects? Analytical Biochemistry 309: 85-95; (2002). Goto reference|
|(5)||Biacore AB BIACORE Instrument Handbook. (1998).|
|(6)||Karlsson, R. and A. Falt Experimental design for kinetic analysis of protein-protein interactions with surface plasmon resonance biosensors. Journal of Immunological Methods 200: 121-133; (1997). Goto reference|