Teruyuki Hayashi

Cationic nanogels of N-isopropylacrylamide (NIPAM), including NIPAM-based cationic fluorescent nanogel thermometers, were synthesized with a cationic radical initiator previously developed in our laboratory. These cationic nanogels were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), zeta potential measurements and fluorescence spectroscopy, as summarized in the temperature-dependent fluorescence response based on the structural change in polyNIPAM units in aqueous solutions. Cellular experiments using HeLa (human epithelial carcinoma) cells demonstrated that NIPAM-based cationic fluorescent nanogel thermometers can spontaneously enter the cells under mild conditions (at 25 °C for 20 min) and can show significant fluorescence enhancement without cytotoxicity with increasing culture medium temperature. The combination of the ability to enter cells and non-cytotoxicity is the most important advantage of cationic fluorescent nanogel thermometers compared with other types of fluorescent polymeric thermometers, i.e., anionic nanogel thermometers and cationic/anionic linear polymeric thermometers.

Temperature is one of the most important of the physiological parameters that determine the biological status of living organisms. However, intracellular temperature was not imaged at the single-cell level until recently because of the lack of a molecular thermometer that can be applied to living cells. We have recently developed a method for imaging intracellular temperature using a cationic linear fluorescent polymeric thermometer (FPT) and fluorescence lifetime imaging microscopy (FLIM). The cationic linear FPT exhibits cell permeability in various mammalian cell lines and yeast cells, entering live cells within 10 min of incubation. Intracellular thermometry using the cationic linear FPT and FLIM can be used to image temperature with high temperature resolution (0.3–1.29 °C within a temperature range of 25–35 °C). The diffuse intracellular localization of the cationic linear FPT allows a high spatial resolution (i.e., the light microscope’s diffraction limit, 200 nm), enabling the detection of temperature distributions at the subcellular level. This protocol, including the construction of a calibration curve and intracellular temperature imaging, requires ~14 h. Experience in handling cultured mammalian cells and use of a confocal laser-scanning microscope (CLSM) is required.

A cationic fluorescent nanogel thermometer based on thermo‐responsive N‐isopropylacrylamide and environment‐sensitive benzothiadiazole was developed with a new azo compound bearing imidazolium rings as the first cationic radical initiator. This cationic fluorescent nanogel thermometer showed an excellent ability to enter live mammalian cells in a short incubation period (10 min), a high sensitivity to temperature variations in live cells (temperature resolution of 0.02–0.84 °C in the range 20–40 °C), and remarkable non‐cytotoxicity, which permitted ordinary cell proliferation and even differentiation of primary cultured cells.

A cationic fluorescent nanogel thermometer based on thermo‐responsive N‐isopropylacrylamide and environment‐sensitive benzothiadiazole was developed with a new azo compound bearing imidazolium rings as the first cationic radical initiator. This cationic fluorescent nanogel thermometer showed an excellent ability to enter live mammalian cells in a short incubation period (10 min), a high sensitivity to temperature variations in live cells (temperature resolution of 0.02–0.84 °C in the range 20–40 °C), and remarkable non‐cytotoxicity, which permitted ordinary cell proliferation and even differentiation of primary cultured cells.

Alkenes react with disilanes in the presence of platinum phosphine complex catalysts to give alk-1-enylsilanes.