TY - JOUR
T1 - Fluorescence correlation spectroscopy
T2 - An efficient tool for measuring size, size-distribution and polydispersity of microemulsion droplets in solution
AU - Pal, Nibedita
AU - Verma, Sachin Dev
AU - Singh, Moirangthem Kiran
AU - Sen, Sobhan
N1 - Copyright:
Copyright 2012 Elsevier B.V., All rights reserved.
PY - 2011/10/15
Y1 - 2011/10/15
N2 - Fluorescence correlation spectroscopy (FCS) is an ideal tool for measuring molecular diffusion and size under extremely dilute conditions. However, the power of FCS has not been utilized to its best to measure diffusion and size parameters of complex chemical systems. Here, we apply FCS to measure the size, and, most importantly, the size distribution and polydispersity of a supramolecular nanostructure (i.e., microemulsion droplets, MEDs) in dilute solution. It is shown how the refractive index mismatch of a solution can be corrected in FCS to obtain accurate size parameters of particles, bypassing the optical matching problem of light scattering techniques that are used often for particle-size measurements. We studied the MEDs of 13 different W 0 values from 2 to 50 prepared in a ternary mixture of water, sodium bis(2-ethylhexyl) sulfosuccinate (AOT), and isooctane, with sulforhodamine-B as a fluorescent marker. We find that, near the optical matching point of MEDs, the dynamic light scattering (DLS) measurements underestimate the droplet sizes while FCS estimates the accurate ones. A Gaussian distribution model (GDM) and a maximum-entropy-based FCS data fitting model (MEMFCS) are used to analyze the fluorescence correlation curves that unfold Gaussian-type size distributions of MEDs in solution. We find the droplet size varies linearly with W 0 up to ∼20, but beyond this W 0 value, the size variation deviates from this linearity. To explain nonlinear variation of droplet size for W 0 values beyond ∼20, we invoke a model (the coated-droplet model) that incorporates the size polydispersity of the droplets.
AB - Fluorescence correlation spectroscopy (FCS) is an ideal tool for measuring molecular diffusion and size under extremely dilute conditions. However, the power of FCS has not been utilized to its best to measure diffusion and size parameters of complex chemical systems. Here, we apply FCS to measure the size, and, most importantly, the size distribution and polydispersity of a supramolecular nanostructure (i.e., microemulsion droplets, MEDs) in dilute solution. It is shown how the refractive index mismatch of a solution can be corrected in FCS to obtain accurate size parameters of particles, bypassing the optical matching problem of light scattering techniques that are used often for particle-size measurements. We studied the MEDs of 13 different W 0 values from 2 to 50 prepared in a ternary mixture of water, sodium bis(2-ethylhexyl) sulfosuccinate (AOT), and isooctane, with sulforhodamine-B as a fluorescent marker. We find that, near the optical matching point of MEDs, the dynamic light scattering (DLS) measurements underestimate the droplet sizes while FCS estimates the accurate ones. A Gaussian distribution model (GDM) and a maximum-entropy-based FCS data fitting model (MEMFCS) are used to analyze the fluorescence correlation curves that unfold Gaussian-type size distributions of MEDs in solution. We find the droplet size varies linearly with W 0 up to ∼20, but beyond this W 0 value, the size variation deviates from this linearity. To explain nonlinear variation of droplet size for W 0 values beyond ∼20, we invoke a model (the coated-droplet model) that incorporates the size polydispersity of the droplets.
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U2 - 10.1021/ac2012637
DO - 10.1021/ac2012637
M3 - Article
C2 - 21899251
AN - SCOPUS:80054708471
SN - 0003-2700
VL - 83
SP - 7736
EP - 7744
JO - Analytical Chemistry
JF - Analytical Chemistry
IS - 20
ER -