Fluorescent Thermometers for Dual-Emission-Wavelength Measurements: Molecular Engineering and Application to Thermal Imaging in a Microsystem

• Published in: Analytical chemistry (Washington) Vol. 81; no. 19; pp. 7988 - 8000
• Main Authors: Barilero, T., Le Saux, T., Gosse, C., Jullien, L.
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.10.2009
• Subjects: Analytical chemistry; Aqueous solutions; Chemistry; Exact sciences and technology; Fluorescence; Heat detection; Spectrometric and optical methods; Thermodynamics; Fluid mechanics; Thermometer; Microsecond; Fluorescence spectrometry; Sensitivity; Chemical reaction; Response time; Fluorescent labelling; Imaging; Protonation; Molecular probe; Thermal imaging; Aqueous solution; Reliability; Microfluidics
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/ac901027f

To facilitate thermal imaging, particularly in microdevices, one has to favor molecular thermometers in which the response is independent of the probe concentration and of the observation setup imperfections. Hence, this paper introduces two temperature fluorescent probes for ratiometric dual-emission-wavelength measurements in aqueous solutions. They are based on a nonathermal chemical reaction, either a conformational transition or a protonation, that induces a modification of their emission spectra as the temperature changes. Relying on both a straightforward theoretical analysis and thorough photophysical, thermodynamic, and kinetic investigations, we demonstrate how the flexible design of these two thermometers can be optimized to face applications with various requirements in terms of operating temperature and wavelength ranges as well as temporal resolution. For instance, the present molecules, which can be used between 5 and 35 °C, provide a relative sensitivity up to ∼ 9 × 10−2 K−1 and milli- to microsecond response times. Finally, we utilize a two-color molecular beacon, a probe belonging to the first series of thermometers, to image temperature profiles in a microfluidic cell heated by a resistive strip. The ratiometric analysis of the fluorescence emission at two different wavelengths is performed on a widely available dual-view microscope, illustrating both the simplicity and reliability of the thermal mapping protocol.