Temperature-Dependent Fluorescence Lifetime of a Fluorescent Polymeric Thermometer, Poly(N-isopropylacrylamide), Labeled by Polarity and Hydrogen Bonding Sensitive 4-Sulfamoyl-7-aminobenzofurazan

Abstract

Fluorescent molecular thermometers showing temperature-dependent fluorescence lifetimes enable thermal mapping of small spaces such as a microchannel and a living cell. We report the temperature-dependent fluorescence lifetimes of poly(NIPAM-co-DBD-AA), which is a random copolymer of N-isopropylacrylamide (NIPAM) and an environment-sensitive fluorescent monomer (DBD-AA) containing a 4-sulfamoyl-7-aminobenzofurazan structure. The average fluorescence lifetime of poly(NIPAM-co-DBD-AA) in aqueous solution increased from 4.22 to 14.1 ns with increasing temperature from 30 to 35 degrees C. This drastic change in fluorescence lifetime (27% increase per 1 degrees C) is the sharpest ever reported. Concentration independency, one of the advantages of fluorescence lifetime measurements, was seen in average fluorescence lifetime (13.7 +/- 0.18 ns) of poly(NIPAM-co-DBD-AA) at 33 degrees C over a wide concentration range (0.005-1 w/v%). With increasing temperature, polyNIPAM units in poly(NIPAM-co-DBD-AA) change their structure from an extended form to a globular form, providing apolar and aprotic environments to the fluorescent DBD-AA units. Consequently, the environment-sensitive DBD-AA units translate the local environmental changes into the extension of the fluorescence lifetime. This role of the DBD-AA units was revealed by a study of solvent effects on fluorescence lifetime of a model environment-sensitive fluorophore.

Thermometry at the nanoscale

“…The most explored polymers are PNIPAM, which has a lower critical solution transition at 305 K, 6,20,78,[127][128][129][130][131][132][133][134][135][136][137][138][139] together with others polymers of the same family, such as NNPAM or NIP-MAM. 134 Other examples include PEG-based polymers, Table 2 and Fig.…”

High-resolution imaging in a deep turbid medium based on an ultrasound-switchable fluorescence technique

“…16 Although its peak excitation light is in the visible light region, as a proof-ofconcept study, it provides a good opportunity to investigate the feasibility of the USF technique. It has been found that a)…”

“…The underlying mechanism of temperature-induced change in fluorescence intensity for these polymers has been discussed previously. 16 A high intensity focused ultrasound (HIFU) transducer can be used to externally and rapidly increase the tissue temperature above the threshold to switch on the fluorophores only in its focal volume (due to tissue absorption of acoustic energy). After ultrasound exposure and USF data acquisition, thermal energy is diffused and temperature recovers back to background temperature.…”

Temperature‐Dependent Fluorescence of Cu5 Metal Clusters: A Molecular Thermometer

“…These characteristics, together with the almost total independence of the measured values on other experimental conditions, including oxygen concentration, make this system one of the most versatile molecular thermometers reported to date. [21][22][23] To demonstrate the potential of 1 to measure temperature changes in real systems, we investigated its emission changes when spotted on different surfaces. We used a very simple (and inexpensive) apparatus made up of a plastic container filled with water, a UV lamp for excitation (365 nm), and a standard webcam for image collection (see the Supporting Information for the details on the experimental setup).…”