BODIPY-Conjugated Thermoresponsive Copolymer as a Fluorescent Thermometer Based on Polymer Microviscosity
Research Center for Solar Energy Chemistry and Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University, Toyonaka 560-8531, Japan. Langmuir
(Impact Factor: 4.46).
10/2009; 25(22):13176-82. DOI: 10.1021/la901860x
A simple copolymer, poly(NIPAM-co-BODIPY), consisting of N-isopropylacrylamide (NIPAM) and boradiazaindacene (BODIPY) units, behaves as a fluorescent thermometer in water. The copolymer exhibits weak fluorescence at <23 degrees C, but the intensity increases with a rise in temperature up to 35 degrees C, enabling an accurate indication of the solution temperature at 23-35 degrees C. The heat-induced fluorescence enhancement is driven by an increase in the polymer microviscosity, associated with a phase transition of the polymer from the coil to globule state. The viscous domain formed inside the globule-state polymer suppresses the rotation of the meso-pyridinium group of the excited-state BODIPY units, resulting in heat-induced fluorescence enhancement. The polymer shows reversible fluorescence enhancement/quenching regardless of the heating/cooling process and displays high reusability with a simple recovery process.
Available from: Kytai Nguyen
- "Accordingly, the ICG molecules inside the NPs are exposed to a polymer-rich microenvironment, which has a relatively lower polarity and higher viscosity compared with the water-rich microenvironment. This type of microenvironment can suppress the nonradiative decay rate of the excited fluorophores2425, and therefore the fluorescence intensity from the ICG increases dramatically. This phase transition caused by the environment's temperature crossing LCST is reversible. "
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ABSTRACT: Fluorescence imaging in deep tissue with high spatial resolution is highly desirable because it can provide details about tissue's structural, functional, and molecular information. Unfortunately, current fluorescence imaging techniques are limited either in penetration depth (microscopy) or spatial resolution (diffuse light based imaging) as a result of strong light scattering in deep tissue. To overcome this limitation, we developed an ultrasound-switchable fluorescence (USF) imaging technique whereby ultrasound was used to switch on/off the emission of near infrared (NIR) fluorophores. We synthesized and characterized unique NIR USF contrast agents. The excellent switching properties of these agents, combined with the sensitive USF imaging system developed in this study, enabled us to image fluorescent targets in deep tissue with spatial resolution beyond the acoustic diffraction limit.
Available from: PubMed Central
- "This relationship has been experimentally shown to be valid in a wide range of viscosities and in both polar and nonpolar fluids [15,34,40,54,55], although deviations exist particularly in the low-viscosity regime that need additional interpretation. Equation 1 has become so popular that in some instances the existence of this power-law relationship has been used to purport TICT behavior of specific molecules [56-59]. "
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ABSTRACT: Molecular rotors are a group of fluorescent molecules that form twisted intramolecular charge transfer (TICT) states upon photoexcitation. When intramolecular twisting occurs, the molecular rotor returns to the ground state either by emission of a red-shifted emission band or by nonradiative relaxation. The emission properties are strongly solvent-dependent, and the solvent viscosity is the primary determinant of the fluorescent quantum yield from the planar (non-twisted) conformation. This viscosity-sensitive behavior gives rise to applications in, for example, fluid mechanics, polymer chemistry, cell physiology, and the food sciences. However, the relationship between bulk viscosity and the molecular-scale interaction of a molecular rotor with its environment are not fully understood. This review presents the pertinent theories of the rotor-solvent interaction on the molecular level and how this interaction leads to the viscosity-sensitive behavior. Furthermore, current applications of molecular rotors as microviscosity sensors are reviewed, and engineering aspects are presented on how measurement accuracy and precision can be improved.
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