Full Citation: Fluorescence Analysis of Thermoresponsive Polymers. A.G. Ryder and C. Morris, Reviews in Fluorescence 2015 ,
Annual Volumes, Vol. 8, pp. 97-126, (2015). ISBN: 978-3-319-24607-9 (Hardcover), 978-3-319-24609-3 (ebook) Springer.
Page 20 of 31
that solutions heated within the 31–36 °C temperature range consisted of fluid-like particles which
were able to merge and grow in size. At higher temperatures (36–45 °C) the PNIPAm mesoglobules
behaved like more rigid spheres that were unable to merge by collision into larger, slower rotating
globules. This study also employed FRET measurements using pyrene (Py) and naphthalene (Np)
labeled PNIPAm. Monitoring the changes in Py and Np fluorescence shows the expected spike in
the IPy/INp fluorescence intensity ratio near the LCST. The authors ascribed this change as arising
from two factors: (a) chain motion increased upon heating, enhancing the probability of a close
encounter between the two different fluorophores, and (ii) the local fluorophore concentration
increased as a result of solution demixing. However, at temperatures above ~33.5 °C, the IPy/INp
fluorescence intensity ratio decreased once more which was ascribed to the increased micro-viscosity
within the mesoglobule. This restricted the motion of the polymer chains, which caused a reduction
in the frequency of the Py-Np encounters.
The study of Quantum dot (QD)-PNIPAm hybrid particles by FCS has also been recently reported
[131]. This straightforward study described how FCS can be used to monitor changes in
hydrodynamic radii near the LCST for particles having different length PNIPAm chains attached. It
also indicated that there were substantial decreases in the QD lifetime as the temperature increased
through the LCST caused by PNIPAm chain collapse. This alteration in average lifetimes was caused
by large changes in the fast lifetime component, which is generally assigned to trapping processes
caused by surface defects or impurities.
5.6
SWELLING AND ASSEMBLY.
Dansyl is a versatile probe for characterizing PNIPAm as it can provide information via steadystate and time-resolved measurements about the polarity and viscosity of the local environment
[67,132,133]. Some of the advantages of the dansyl probe are that it is relatively insensitive to
oxygen quenching, its absorption maximum is relatively independent of the medium and variation in
the wavelength of maximum emission is directly related to changes in local polarity and/or viscosity.
The mechanism of shrinking in PNIPAm derived materials can be elucidated by measuring changes
in the wavelength of the fluorescence emission maximum of a covalently attached dansyl fluorophore
[133]. The rate of shrinkage of different PNIPAm gels in aqueous solution (normal, with grafted side
chains, and semi-interpenetrating polymer network) was investigated by measuring the change in the
position of the peak emission wavelength. These fluorescence measurements showed clearly that the
grafted chains underwent the coil-to-globule transition at lower temperature (~25 °C) than the main
polymer chains (~33 °C). Dansyl (covalently labeled) has also been used as a probe to look at the
changes due to cross-linking PNIPAm [134]. In this case, cross-linking with glutaraldehyde caused
an increase in hydrophobicity which could be evaluated by measuring the blue shift in the fluorescence
emission spectra.
Dansyl labeled PNIPAm (PNIPAm-Da label content, 0.06 molar %) was also used to investigate
Annual Volumes, Vol. 8, pp. 97-126, (2015). ISBN: 978-3-319-24607-9 (Hardcover), 978-3-319-24609-3 (ebook) Springer.
Page 20 of 31
that solutions heated within the 31–36 °C temperature range consisted of fluid-like particles which
were able to merge and grow in size. At higher temperatures (36–45 °C) the PNIPAm mesoglobules
behaved like more rigid spheres that were unable to merge by collision into larger, slower rotating
globules. This study also employed FRET measurements using pyrene (Py) and naphthalene (Np)
labeled PNIPAm. Monitoring the changes in Py and Np fluorescence shows the expected spike in
the IPy/INp fluorescence intensity ratio near the LCST. The authors ascribed this change as arising
from two factors: (a) chain motion increased upon heating, enhancing the probability of a close
encounter between the two different fluorophores, and (ii) the local fluorophore concentration
increased as a result of solution demixing. However, at temperatures above ~33.5 °C, the IPy/INp
fluorescence intensity ratio decreased once more which was ascribed to the increased micro-viscosity
within the mesoglobule. This restricted the motion of the polymer chains, which caused a reduction
in the frequency of the Py-Np encounters.
The study of Quantum dot (QD)-PNIPAm hybrid particles by FCS has also been recently reported
[131]. This straightforward study described how FCS can be used to monitor changes in
hydrodynamic radii near the LCST for particles having different length PNIPAm chains attached. It
also indicated that there were substantial decreases in the QD lifetime as the temperature increased
through the LCST caused by PNIPAm chain collapse. This alteration in average lifetimes was caused
by large changes in the fast lifetime component, which is generally assigned to trapping processes
caused by surface defects or impurities.
5.6
SWELLING AND ASSEMBLY.
Dansyl is a versatile probe for characterizing PNIPAm as it can provide information via steadystate and time-resolved measurements about the polarity and viscosity of the local environment
[67,132,133]. Some of the advantages of the dansyl probe are that it is relatively insensitive to
oxygen quenching, its absorption maximum is relatively independent of the medium and variation in
the wavelength of maximum emission is directly related to changes in local polarity and/or viscosity.
The mechanism of shrinking in PNIPAm derived materials can be elucidated by measuring changes
in the wavelength of the fluorescence emission maximum of a covalently attached dansyl fluorophore
[133]. The rate of shrinkage of different PNIPAm gels in aqueous solution (normal, with grafted side
chains, and semi-interpenetrating polymer network) was investigated by measuring the change in the
position of the peak emission wavelength. These fluorescence measurements showed clearly that the
grafted chains underwent the coil-to-globule transition at lower temperature (~25 °C) than the main
polymer chains (~33 °C). Dansyl (covalently labeled) has also been used as a probe to look at the
changes due to cross-linking PNIPAm [134]. In this case, cross-linking with glutaraldehyde caused
an increase in hydrophobicity which could be evaluated by measuring the blue shift in the fluorescence
emission spectra.
Dansyl labeled PNIPAm (PNIPAm-Da label content, 0.06 molar %) was also used to investigate