DOI: 10.1002/chem.200900683 A Near-Infrared Fluorescence-Based Optical Thermosensor Seung-Young Lee, [a] Seulki Lee, [a] In-Chan Youn, [a] Dong Kee Yi, [b] Yong Taik Lim, [c] Bong Hyun Chung, [c] James F. Leary, [d] Ick Chan Kwon, [a] Kwangmeyung Kim,* [a] and Kuiwon Choi* [a] Fluorescence-based sensors have attracted a great deal of attention because they allow for the specific, rapid and sen- sitive detection of nonfluorescent analytes by simple emis- sion enhancement or quenching without special instrumen- tation. [1] Various fluorescent sensors have been developed to more accurately detect and image various types of analytes, including biomolecules, organic molecules, pH and ions. However, fluorescent sensors capable of detecting changes in environmental conditions such as temperature have rarely been described, even though the development of a fluores- cence-based thermosensor is desired in industrial testing and manufacturing and also in many biomedical diagnostic and treatment processes, such as measuring induced hyperther- mia around tumors and inflammation. [2] Especially, fluores- cence-based optical thermosensors are advantageous com- pared to contact temperature sensors in monitoring temper- ature within micro/nanometer range (e.g., biological cells or nano/micro devices), where it is physically difficult to con- nect, since there is no contact with the medium in the mea- surement process. [3] Recently, fluorescent thermosensors de- rived from temperature-responsive organic molecules and polymers, such as poly(N-isopropyl acrylamide), have been studied and provide easy solutions for temperature monitor- ing on the basis of fluorescence emission intensity. [4, 5] How- ever, there are no reports of fluorescent thermosensors ca- pable of providing selective fluorescence visualization at a broad temperature range in real-time. This application is limited because these sensors only display fluorescence ra- tiometry of emissions, show modest fluorescence changes at a narrow temperature range, and therefore provide insuffi- cient resolution. [5] Here, we describe the development of a fluorescent poly- meric thermosensor, exhibiting selective near-infrared (NIR) emission throughout a broad range of temperatures (1–80 8C) based on the fluorescent signal activation method. [6, 7, 8] This NIR fluorescent thermosensor also has the advantage to be applied in biological and medical field be- cause, in NIR region, it is possible to image tissues at differ- ent resolutions and depth penetrations with minimizing tissue autofluorescence. [9] As shown in Scheme 1, we designed a thermosensor by using a combination of a thermo-responsive polymer and an NIR dye, Pluronic F127 (PF127) and Cy5.5, respectively. PF127 is an FDA-approved biocompatible triblock copoly- mer consisting of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) blocks. Plur- onic tri-block copolymers are of considerable interest in widespread industries because of their unique temperature responsibilities. [10] At low temperature or below the critical micelle concentration (CMC), block copolymers exist as a linear state in solution as dissolved monomers. Above the CMC or the critical micelle temperature (CMT), block co- polymers gradually self-assemble into micelles with increas- ing temperatures, owing to increases in the hydrophobic nature of PPO in PF127. Further increases in temperature or concentration of PF127 can lead to a sol–gel transition by micelle packing. [11, 12, 13] These temperature responsibilities are depended on the composition and molecular weight of [a] S.-Y. Lee, Dr. S. Lee, Dr. I.-C. Youn, Dr. I.C. Kwon, Dr. K. Kim, Dr. K. Choi Biomedical Research Center Korea Institute of Science and Technology 39-1 Hawolgok-dong, Seongbuk-gu, Seoul, 136-791 (Korea) Fax: (+ 82) 2-958-5909 E-mail: kim@kist.re.kr choi@kist.re.kr [b] Dr. D. K. Yi Division of Bionanotechnology Kyungwon University Sung Nam City (Korea) [c] Dr. Y. T. Lim, Dr. B. H. Chung Bionanotechnology Research Center Korea Research Institute of Bioscience and Biotechnology Daejeon (Korea) [d] Dr. J. F. Leary Weldon School of Biomedical Engineering Purdue University West Lafayette, Indiana (USA) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.200900683. Chem. Eur. J. 2009, 00,0–0  2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim These are not the final page numbers! ÞÞ &1& COMMUNICATION