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Antonino Ingargiola edited Burst_Variance_Analysis.tex
about 8 years ago
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and has been successfully applied to identify biomolecular processes with
dynamics on the millisecond time-scale~\cite{Torella_2011, Robb_2013}.
The basic idea behind BVA is to subdivide bursts into contiguous burst chunks
(sub-bursts)
comprising a fixed number $n$ of photons,
and to compare the empirical variance of acceptor counts across all sub-bursts in a burst
with the theoretical shot-noise limited variance, as expected from a binomial distribution.
An empirical variance of
burst chunks sub-bursts larger than the shot-noise limited value indicates
the presence of dynamics. Since the estimation of the
burst chunks sub-bursts variance is affected
by uncertainty, BVA analysis provides and indication of an higher or lower probability
of observing dynamics.
In a FRET (sub-)population originating from a single static FRET efficiency,
the
burst chunks sub-bursts acceptor counts
$N_a$ $n_a$ can be modeled as a binomial-distributed random variable
$N_a \sim \operatorname{B}(n, E)$, where $n$ is the number of photons in each burst chunk and
$E$ is the estimated population FRET efficiency.
Note
that, without approximation, that we can replace E with
PR and use the uncorrected counts. This is possible because, regardless of the
molecular FRET efficiency, PR, since the detected counts are partitioned
between donor and acceptor channel according to a binomial distribution with
a $p$ parameter equal to
PR. PR (regardless of the
molecular FRET efficiency).
The only approximation done here is neglecting the presence background
(a reasonable approximation since the backgrounds counts are in general a
very small fraction of the total counts).
We refer the interested reader to~\cite{Torella_2011} for further discussion.
If $N_a$ follows a binomial distribution, the random variable $E = N_a/n$,