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My ACF is fit, now what?
Remember that the specific algorithm to fit the ACF varies depending on the
instrument and so ware you are using, but a crucial part of evaluating data is
the amplitude.
1
1.1
1.2
1.3
1.4
3E-7 1E-6 3E-6 1E-5 3E-5 1E-4 3E-4 1E-3 3E-3 1E-2 3E-2
Tau [s]
Autocorrelation
Baseline
Amplitude
The amplitude is the height of the signal
above the baseline as tau approaches 0.
The theoretical maximum amplitude of
the ACF is 1; however, biological solutions
are not ideal systems, and in general
anything from 0.2 to 0.9 is considered
acceptable for evaluation. Many
measurements have an amplitude in the
0.4 to 0.5 range.
Likewise, when screening the ACF data,
it's important to also look at the baseline.
Because the ACF fit is a decay function,
we expect the data to become linear at
a certain baseline value. That specific
value will depend again on the so ware
you are using, but poorly fit data will be
evident when it does not normalize at
the baseline. Understanding the values
expected for amplitude and baseline,
and how the ACF data should fit these,
will enable you to critically evaluate
your DLS data.
