Design of Fluorescent Nanocapsules as Ratiometric Nanothermometers

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 of 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 where a fluorophore with relatively insensitive fluorescence (rhodamine 640) serves as a reference while a sensitive fluorophore (indocyanine green) serves as a sensor. The sensitivity of the nanothermometers depends on the type of nanocapsules-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.

Nanothermometry: From Microscopy to Thermal Treatments

“…[37] As compared to the ratiometric molecular thermometers, FL-based constructs require only one fluorophore, simplifyingt he thermometer design. [31] Okabe et al [36b] reported ah ighly sensitivep olymeric nanothermometer suitable for FL temperature mapping. For example, the encapsulated NIR dye ICG showedF Lt hermal sensitivity of only 0.58 %K À1 ,a sc ompared to % 1.7 %K À1 in the intensity measurements.…”

“…The ratio of the two emissions provided the basis for temperature measurement. The overall responseo ft he construct, however, showed only am arginal thermals ensitivity of 0.5 %K À1 .I na nother design,Z hegalova et al [31] combined two fluorophores trapped in ah ollow polymethacrylate nanocapsule ( Figure 3).…”

“…For example, the encapsulated NIR dye ICG showedF Lt hermal sensitivity of only 0.58 %K À1 ,a sc ompared to % 1.7 %K À1 in the intensity measurements. [31] Okabe et al [36b] reported ah ighly sensitivep olymeric nanothermometer suitable for FL temperature mapping. This thermometer has two major components,apolymericb ackbone whosec onfirmationi ss ensitivet ot emperature and af luorescent unit containing aw ater-sensitivef luorophore, benzofurazan, which can be quenched by neighboring water molecules at low temperatures, when the thermo-responsive polymer assumesa ne xtended structure.…”

Fluorescence anisotropy (polarization): from drug screening to precision medicine

“…An opposite effect of temperature on dyes is decreasing the fluorescence lifetime, especially in molecules with strong thermal sensitivity such as certain coumarines 50 or cyanine dyes. 51 Overall, the role of temperature is difficult predict, 52 but needs to be controlled in order to generate reproducible results.…”

Size‐Selective Yolk‐Shell Nanoreactors with Nanometer‐Thin Porous Polymer Shells

“…The templating scaffold can be removed and recycled. This directed assembly approach allowed us to create a variety of capsule‐based nanodevices 9e–h. The permeability of the polymer nanocapsule shells can be controlled by imprinting uniform molecular size nanopores using different pore‐forming templates, as well as by pore functionalization 9a,f,i,j.…”