Dear Shawana,

   As surely you know, the usual biosensors have three parts: a sensor device employing different physical and/or optical principles, a sample delivery system, and a sensor surface whereby one of the interaction partners is immobilized. Thus the interaction of a binding partner from the soluble phase can be monitored in real-time. And nowdays several biosensor systems employ surface plasmon resonance as the physical mechanism of detection.

   From the physical point of view, the resonance is a result of the interaction between the electromagnetic field acting as incident light and free electron clouds,

which are the plasmons, in the conductor. And the surface plasmon resonance can arise because of a resonant coupling between the incident light energy and surface plasmons in the conducting film at a specific angle of incident light. Absorption of the light energy causes a characteristic drop in the reflected light intensity at that specific angle. y, the angle depends on the refractive index of the medium opposite to the incident light and this is the main physical characteristic to be measured in such process.

  I hope this can helps.

Dear Dr. Behnam and Dr. Daniel,

Thank you so much for your answers. Actually my question was a little different. I know the working principle of SPR. 

I will clarify my question:

I have seen many papers where dynamic measurement of SPR shift is done to understand the binding kinetics of biomolecules (antigen-antibody interaction mechanism) on the sensor surface. But for sensing, is it really necessary to conduct dynamic measurement (Resonance wavelength/angle shift vs. time)? For example, I can simply measure the shift in resonance by looking at the response curve (Reflectance vs. wavelength for example). 

    Dear Shawana,

    You write:

     But for sensing, is it really necessary to conduct dynamic measurement (Resonance wavelength/angle shift vs. time)? For example, I can simply measure the shift in resonance by looking at the response curve (Reflectance vs. wavelength for example). 

    In short, the answer is yes. Obviously the resonance by itself is a dynamic process. In fact, the major advantage of kinetic analysis using Surface Plasmon Resonance for

biosensors is the option of determining separately distinct association and dissociation rate constants exceeding the classical steady-state analysis of biomolecules,