Example - Selecting FRET populations

This notebook is part of smFRET burst analysis software FRETBursts.

In this notebook shows two methods to select FRET populations: size filtering and DCBS. For a complete tutorial on burst analysis see FRETBursts - us-ALEX smFRET burst analysis.



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from fretbursts import *



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sns = init_notebook(apionly=True)
print('seaborn version: ', sns.__version__)



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# Tweak here matplotlib style
import matplotlib as mpl
mpl.rcParams['font.sans-serif'].insert(0, 'Arial')
mpl.rcParams['font.size'] = 12
%config InlineBackend.figure_format = 'retina'

Get and process data



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url = 'http://files.figshare.com/2182601/0023uLRpitc_NTP_20dT_0.5GndCl.hdf5'
download_file(url, save_dir='./data')
full_fname = "./data/0023uLRpitc_NTP_20dT_0.5GndCl.hdf5"

d = loader.photon_hdf5(full_fname)
loader.alex_apply_period(d)
d.calc_bg(bg.exp_fit, time_s=1000, tail_min_us=(800, 4000, 1500, 1000, 3000))
d.burst_search(min_rate_cps=8e3)
ds = d.select_bursts(select_bursts.size, add_naa=True, th1=40)

Filtering method

We can select the FRET population (S ~ 0.5) combining these two filters:

Filter out A-only: select bursts with counts during $D_{ex}$ > threshold
Filter out D-only: select bursts with counts in $A_{ex}A_{em}$ > threshold

In code, this becomes:



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ds_no_Aonly = ds.select_bursts(select_bursts.size, th1=30)
ds_fret = ds_no_Aonly.select_bursts(select_bursts.naa, th1=30)

alex_jointplot(ds)
alex_jointplot(ds_fret)

DCBS Method

With Dual-channel Burst Search (DCBS), we define bursts as the intersection of a burst search performed on $D_{ex}$ stream and one performed on $A_{ex}A_{em}$ stream (see (Nir et al. JPC 2006)).

In this way we filter D-only and A-only bursts, but also we reduce the burst duration of FRET bursts to the portion where $D_{ex}$ and $A_{ex}A_{em}$ both give signal. This property allows filtering acceptor photo-blinking, that causes part of a burst to appear as D-only.

To perform DCBS in FRETBursts we use:



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d_fret_2 = bext.burst_search_and_gate(d)

The function bext.burst_search_and_gate() performs two burst searches on the photon streams defined by ph_sel1 and ph_sel2 arguments (by default ph_sel1=Ph_sel(Dex='DAem') and ph_sel2=Ph_sel(Aex='Aem'), i.e. $D_{ex}$ and $A_{ex}A_{em}$). Then, it takes the "intersection in time" (and-gate) for the two sets of bursts.

burst_search_and_gate accepts the same m, F, and min_rate_cps arguments as Data.burst_search(). It is also possible to use different burst search parameters for the two burst searches:



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d_fret_22 = bext.burst_search_and_gate(d, m=(8, 10), F=(5, 12))

Before plotting we still need to select bursts by size:



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ds_fret_2 = d_fret_2.select_bursts(select_bursts.size, th1=30)
alex_jointplot(ds_fret_2)



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ds_fret_22 = d_fret_22.select_bursts(select_bursts.size, th1=30)
alex_jointplot(ds_fret_22)



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