The Dynamic Response (DR) is a parameter that characterizes the switching speed of DNA nanolevers. It is automatically calculated from the raw data by the switchSENSE software package. For every recorded data point, the software evaluates typically the upward motion of the DNA nanolevers as indicated in Figure 9. Integration of the normalized time-resolved fluorescence intensity traces that reflect the upward motion, yields the Dynamic Response value for a certain time interval. Changes of the hydrodynamic friction, such as the interaction with an analyte molecule, will affect the progression of the fluorescence intensity curve, reflecting the altered switching dynamics. As indicated in Figure 9, such an event will yield a different integrated area (=DR) under the fluorescence intensity curve, compared to the initial state. Generally, small DR values can be attributed to slow switching motion and large values indicate fast switching.
Figure 9: The Dynamic Response is calculated by integration from normalized fluorescence intensity data, typically of the upward motion of the DNA nanolevers. Events, such as the binding of an analyte, which change the hydrodynamic friction, affect the steepness and shape of the normalized fluorescence intensity progression, resulting in a different Dynamic Response level.
Depending on the interaction to be investigated, it is advisable to select different integration time intervals for optimal signal to noise ratio. Hence, the Dynamic Response is provided for several integration intervals. For the respective interval, the time at which the potential is reversed from an attractive (positive) to a repulsive (negative) potential, is defined as 0 .
Additional parameter of the Dynamic Response is the Dynamic Response downward (DRdown), which is used to characterize the downward motion of the DNA nanolevers. Corresponding to the upward motion of the DNA nanolevers, also their downward motion is affected by changes in the hydrodynamic drag resulting in high DR levels for fast switching, and low levels for slow switching.