Since the response time is a vital property in the demonstration of the device performance, so the dynamic sensitivity exmine the response time, which may be much more important than the sensitivity in a static (stationary) response, which detects the final response.
Take a look at this article for instance:
B .Špačková, P. Wrobel, M. Bocková, and J. Homola, "Optical biosensors based on plasmonic nanostructures: a review," Proceedings of the IEEE, vol. 104, no. 12, pp. 2380-2408, 2016.