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. 2014 Aug 11;20(33):10292-7.
doi: 10.1002/chem.201402828. Epub 2014 Jul 13.

Design of fluorescent nanocapsules as ratiometric nanothermometers

Natalia G Zhegalova  1 , Sergey A Dergunov, Steven T Wang, Eugene Pinkhassik, Mikhail Y Berezin
Affiliations

Design of fluorescent nanocapsules as ratiometric nanothermometers

Natalia G Zhegalova et al. Chemistry. .

Abstract

We have developed a novel design of optical nanothermometers that can measure the surrounding temperature in the range of 20-85 °C. The nanothermometers comprise two organic fluorophores encapsulated in a crosslinked polymethacrylate nanoshell. The role of the nanocapsule shell around the fluorophores is to form a well-defined and stable microenvironment to prevent other factors besides temperature from affecting the dyes' fluorescence. The two fluorophores feature different temperature-dependent emission profiles; a fluorophore with relatively insensitive fluorescence (rhodamine 640) serves as a reference whereas a sensitive fluorophore (indocyanine green) serves as a sensor. The sensitivity of the nanothermometers depends on the type of nanocapsule-forming lipid and is affected by the phase transition temperature. Both the fluorescence intensity and the fluorescence lifetime can be utilized to measure the temperature.

Keywords: fluorescence lifetime; indocyanine green; nanocapsules; thermometers; vesicles.

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Figures

Figure 1
Figure 1
Structures of rhodamine 640 (Rho640) and ICG used to construct nanothermometers.
Figure 2
Figure 2
Structures of lipids DLPC (12:0) and DMPC (14:0)
Figure 3
Figure 3
Fluorescence lifetime thermal sensitivity of ICG/DMPC and Rho640/DMPC in 1x PBS at ex/em. 560/605 nm for Rho640 and 740/815 nm for ICG. Sensitivities SRho640= 0 %·K−1, SICG= 0.58%·K−1
Figure 4
Figure 4
A: Thermal sensitivity of Rho640/DLPC. B: Thermal sensitivity of ICG/DMPC-NC and ICG/DLPC-NC. Fluorescence intensities (S, counts per second) were normalized to the intensity of light (R, microamp) (S/R) C: temperature ramp. Three heating-cooling cycles are shown.
Figure 4
Figure 4
A: Thermal sensitivity of Rho640/DLPC. B: Thermal sensitivity of ICG/DMPC-NC and ICG/DLPC-NC. Fluorescence intensities (S, counts per second) were normalized to the intensity of light (R, microamp) (S/R) C: temperature ramp. Three heating-cooling cycles are shown.
Figure 4
Figure 4
A: Thermal sensitivity of Rho640/DLPC. B: Thermal sensitivity of ICG/DMPC-NC and ICG/DLPC-NC. Fluorescence intensities (S, counts per second) were normalized to the intensity of light (R, microamp) (S/R) C: temperature ramp. Three heating-cooling cycles are shown.
Figure 5
Figure 5
Temperature-dependent emission of Rho640-ICG/DLPC emission: ratiometric dependence of the nanoconstructs’ emission intensity as a function of temperature (Heating/cooling cycle from 20 to 85 °C, one cycle out of three is shown). S=1.7%·K−1
Figure 6
Figure 6
Electron micrograph and DLS of nanocapsules. (a) and (c) TEM images and DLS of polymer nanocapsules made from DLPC and DMPC, respectively. DLS data showed objects with an intensity weighted average size of about 190±20 nm (DLPC) and 180±20 nm (DMPC), with PDI about 0.15–0.19 for both types of nanocapsules. (b) and (d) SEM image of polymer nanocapsules made from DLPC and DMPC, respectively. The average size of nanocapsules isolated after the polymerization of monomers and measured by SEM and TEM was identical to the average size of vesicles observed by DLS.
See this image and copyright information in PMC

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