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[Display omitted] The effective measurement of temperature in living systems at the nano and microscopic scales continues to be a challenge to this day. Here, we study the use of 2-(anthracen-2-yl)-1,3-diisopropylguanidine, 1 , as a nanothermometer based on fluorescence lifetime measurements and its bioimaging applications. In aqueous solution, 1 is shown in aggregated form and the equilibrium between the two main aggregate types (T -shaped and π-π) is highly sensitive to the temperature. The heating of the medium shifts the equilibrium toward the formation of highly emissive T -shaped aggregates. This species shows a high fluorescence emission and a long lifetime in comparison with the π-π aggregates and the freé monomer. A linear relationship between the fluorescence lifetime and the temperature both in aqueous solution and in a synthetic intracellular buffer was found. Fluorescence lifetime imaging microscopy (FLIM) also showed a linear relationship between lifetime and temperature with an excellent sensitivity in MCF7 breast cancer cells, which opens the door for its potential use as FLIM nanothermometer in the biomedical field. [ABSTRACT FROM AUTHOR]

[Display omitted] • A fast and simple synthesis of Carbon Dots from lemon bagasse (CD-L) • Chemical, morphological and optical properties for CD-L was investigated. • CD-L revealed significant anti-oxidant potential. • A methodology for obtaining carbon dots film (Film-L) was developed. • Film-L has been evaluated as an efficient luminescent thermometer. The design of luminescent nanomaterials for the development of nanothermometers with high sensitivity and free of potentially toxic metals has developed in several fields, such as optoelectronics, sensors, and bioimaging. In addition, luminescent nanothermometers have advantages related to non-invasive measurement, with their wide detection range and high spatial resolution at the nano/microscale. Our study is the first, to our knowledge, to demonstrate a detailed study of a fluorescent film (Film-L) thermal sensor based on carbon dots derived from lemon bagasse extract (CD-L). The CD-L properties were explored as an antioxidant agent; their cytotoxicity was evaluated by using a human non-tumoral skin fibroblast (HFF-1) cell line from an MTT assay. The CD-L were characterized by HRTEM, DLS, FTIR, UV–VIS, and fluorescence spectroscopy. These confirmed their particle size distribution below 10 nm, graphitic structure in the core and surface organic groups, and strong blue emission. The CD-L showed cytocompatibility behavior and scavenging potential reactive species of biological importance: O 2 •− and HOCl, with IC 50 of 276.8 ± 4.0 and 21.6 ± 0.7, respectively. The Film-L emission intensities (I 425 nm) are temperature-dependent in the 298 to 333 K range. The Film-L luminescent thermometer shows a maximum relative thermal sensitivity of 2.69 % K−1 at 333 K. [ABSTRACT FROM AUTHOR]

In this work, tris(phenantroline)ruthenium(II) chloride (Ru(phen) 3 ) was immobilized in silica nanoparticles prepared according to the Stöber method. Efforts were devoted on the optimization of the nano-thermometer in terms of size, polydispersity, intensity of the emission and temperature sensitivity. In particular, the immobilization of the luminophore in an external thin shell made of silica grown in a second step on bare silica nanoparticles allowed producing fluorescent monodisperse silica nanoparticles (420 ± 20 nm). A systematic study was addressed to maximize the intensity of the emission of the fluorescent nanoparticles by adjusting the concentration of Ru(phen) 3 2+ in the shell from 0.2 to 24 wt.%, whereas the thickness of the shell is affected by the amount of silica precursor employed. The luminescent activity of the doped nanoparticles was found to be sensitive to the temperature. In fact, the intensity of the emission linearly decreased by increasing the temperature from 20 °C to 65 °C. The thermoresponsive nanoparticles were functionalized with long aliphatic chains in order to obtain hydrophobic nanoparticles. The developed nanoparticles were immobilized via dip-coating procedure on the surface of hydrophobic porous membranes, such as Polyvinylidene fluoride (PVDF) prepared via Non-Solvent Induced Phase Separation (NIPS), providing local information about the membrane surface temperature. [ABSTRACT FROM AUTHOR]