Temperature and Phase Transition Sensing in Liquids with Fluorescent Probes
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Temperature and Phase Transition Sensing in Liquids with Fluorescent Probes I. Shishkin1,2, T. Alon1, R. Dagan1, P. Ginzburg1,2 1 School of Electrical Engineering, Tel Aviv University, Ramat-Aviv, 69978, Israel 2 ITMO University, St. Petersburg 197101, Russia ABSTRACT Local environment of fluorescent dyes could strongly affects emission dynamics of the latter. In particular, both signal intensities and emission lifetimes are highly sensitive to solvent temperatures. Here, temperature-dependent behavior Rhodamine B fluorescence in water and ethanol solutions was experimentally investigated. Phase transition point between liquid water and ice was shown to have a dramatic impact on both in intensity (30-fold drop) and in lifetime (from 2.68 ns down to 0.13 ns) of the dye luminescence along with the shift of spectral maxima from 590 to 625 nm. At the same time, use of ethanol as solvent does not lead to any similar behavior. The reported results and approaches enable further investigations of dye-solvent interactions and studies of physical properties at phase transition points. INTRODUCTION Temperature is one of the most important macroscopic measures, characterizing properties of surrounding environment. The ability to control and monitor the temperature at real time and with high precision is required in vast number of applications. Several techniques of micro- and nanothermometry [1] have been developed in order to monitor properties of very small objects. In particular, inapplicability of conventional methods, such as thermocouple measurements or infrared thermography for temperature studies on micro- and nano- scales, has led to search for alternative probes. Recently, the methods basing on the change of fluorescent properties of the quantum emitters have been implemented. Generally, luminescent techniques can be divided in two broad categories: the methods, which are based on relative change of emission intensity of quantum tags [2, 3, 4, 5] and the ones, relying on the change of the lifetimes [6, 7, 8]. The lifetime-based techniques generally require more complex diagnostic equipment compared to intensity-based measurements, though they are less sensitive to environmental effects. Besides the temperature measurements, the fluorescent techniques also were employed in studies of flows inside micro channels in lab-on-chip applications [9, 10], in microviscosity investigations [11, 12], air flow sensing [13, 14], and as pressure measurements [15]. In order to achieve stable and reliable results, the certain balance between isolation and overlap of the probe with the environment is desired. This could be achieved, for example, by embedding dyes in polymer or inorganic host matrix to control their interaction with surrounding environment [16, 17]. Phase transitions sensing in a host media is one among other interesting applications of molecular probes. It has been demonstrated earlier, that phase transitions can be detected by photoluminescence of embedded ions in crystalline solids [18, 19] and with dyes in liquid cr
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