Inherently Eu2+/Eu3+ Codoped Sc2O3 Nanoparticles as High‐Performance Nanothermometers

Luminescent nanothermometers have shown competitive superiority for contactless and noninvasive temperature probing especially at the nanoscale. Herein, we report the inherently Eu²⁺/Eu³⁺ codoped Sc₂O₃ nanoparticles synthesized via a one‐step and controllable thermolysis reaction where Eu³⁺ is in‐situ reduced to Eu²⁺ by oleylamine. The stable luminescence emission of Eu³⁺ as internal standard and the sensitive response of Eu²⁺ emission to temperature as probe comprise a perfect ratiometric nanothermometer with wide‐range temperature probing (77–267 K), high repeatability (>99.94%), and high relative sensitivity (3.06% K^–1 at 267 K). The in situ reduction of Eu³⁺ to Eu²⁺ ensures both uniform distribution in the crystal lattice and simultaneous response upon light excitation of Eu²⁺/Eu³⁺. To widen this concept, Tb³⁺ is codoped as additional internal reference for tunable temperature probing range.     

Ratiometric Nanothermometer Based on a Radical Excimer for In Vivo Sensing (Small 32/2023)

Ratiometric fluorescent nanothermometers with near-infrared emission play an important role in in vivo sensing since they can be used as intracellular thermal sensing probes with high spatial resolution and high sensitivity, to investigate cellular functions of interest in diagnosis and therapy, where current approaches are not effective. Herein, the temperature-dependent fluorescence of organic nanoparticles is designed, synthesized, and studied based on the dual emission, generated by monomer and excimer species, of the tris(2,4,6-trichlorophenyl)methyl radical (TTM) doping organic nanoparticles (TTMd-ONPs), made of optically neutral tris(2,4,6-trichlorophenyl)methane (TTM-αH), acting as a matrix. The excimer emission intensity of TTMd-ONPs decreases with increasing temperatures whereas the monomer emission is almost independent and can be used as an internal reference. TTMd-ONPs show a great temperature sensitivity (3.4% K⁻¹ at 328 K) and a wide temperature response at ambient conditions with excellent reversibility and high colloidal stability. In addition, TTMd-ONPs are not cytotoxic and their ratiometric outputs are unaffected by changes in the environment. Individual TTMd-ONPs are able to sense temperature changes at the nano-microscale. In vivo thermometry experiments in Caenorhabditis elegans (C. elegans) worms show that TTMd-ONPs can locally monitor internal body temperature changes with spatio-temporal resolution and high sensitivity, offering multiple applications in the biological nanothermometry field.     

Lanthanide–Organic Framework Nanothermometers Prepared by Spray‐Drying

Accurate, noninvasive, and self‐referenced temperature measurements at the submicrometer scale are of great interest, prompted by the ever‐growing demands in the fields of nanotechnology and nanomedicine. The thermal dependence of the phosphor's luminescence provides high detection sensitivity and spatial resolution with short acquisition times in, e.g., biological fluids, strong electromagnetic fields, and fast‐moving objects. Here, it is shown that nanoparticles of [(Tb_0.914Eu_0.086)₂(PDA)₃(H₂O)]·2H₂O (PDA = 1,4‐phenylenediacetic acid), the first lanthanide–organic framework prepared by the spray‐drying method, are excellent nanothermometers operating in the solid state in the 10–325 K range (quantum yield of 0.25 at 370 nm, at room temperature). Intriguingly, this system is the most sensitive cryogenic nanothermometer reported so far, combining high sensitivity (up to 5.96 ± 0.04% K^?1 at 25 K), reproducibility (in excess of 99%), and low‐temperature uncertainty (0.02 K at 25 K).     

Visible‐Light Excited Luminescent Thermometer Based on Single Lanthanide Organic Frameworks

Isostructural lanthanide organic frameworks (Me₂NH₂)₃[Ln₃(FDC)₄(NO₃)₄]·4H₂O (Ln = Eu ( 1 ), Gd ( 2 ), Tb ( 3 ), H₂FDC = 9‐fluorenone‐2,7‐dicarboxylic acid), synthesized under solvothermal conditions, feature a Ln‐O‐C rod‐packing 3D framework. Time‐resolved luminescence studies show that in 1 the energy difference between the H₂FDC triplet excited state (17794 cm^?1) and the ⁵D₀ Eu³⁺ level (17241 cm^?1) is small enough to allow a strong thermally activated ion‐to‐ligand back energy transfer. Whereas the emission of the ligand is essentially constant the ⁵D₀→⁷F₂ intensity is quenched when the temperature increases from 12 to 320 K, rendering 1 the first single‐lanthanide organic framework ratiometric luminescent thermometer based on ion‐to‐ligand back energy transfer. More importantly, this material is also the first example of a metal organic framework thermometer operative over a wide temperature range including the physiological (12‐320 K), upon excitation with visible light (450 nm).     

Light or Heat? The Origin of Cargo Release from Nanoimpeller Particles Containing Upconversion Nanocrystals under IR Irradiation

Nanoimpellers are mesoporous silica nanoparticles that contain azobenzene derivatives bonded inside the pores and rely on the continuous photoisomerization of multiple azobenzenes to release cargo under near UV irradiation. A recent study employs upconversion nanocrystal embedded particles to replace UV light with IR light to stimulate nanoimpellers. However, the photothermal effect of IR irradiation and its likely contribution to the observed release behavior are not examined. It is found that, in the absence of upconversion nanocrystals, the azobenzene co‐condensed silica particles still respond to 980 nm illumination, which increases the nanoparticle temperature by 25 °C in 15 min, experimentally measured by an encapsulated nanothermometer. After suppressing the heating, the IR irradiation does not initiate the release, indicating that optical heating, not upconverted light, is responsible for the triggered cargo release. The results are explained by numerical analyses.     

Silica–Gold Core–Shell Nanosphere for Ultrafast Dynamic Nanothermometer

Effective temperature measurements are of significance for a fundamental understanding of nanosystems and functional applications, requiring ultimate miniaturization of thermometers with reduced size but maintained sensitivity, simplicity, and accuracy of temperature reading. Grand challenges exist for scenarios of thermal shock or combustion where materials may be subjected to extreme thermal flux and drastic temperature variations, and dynamic thermal sensors with an ultrafast response are yet to be developed. Here, an innovative design of silica–gold core–shell (SiO₂@Au) nanospheres is demonstrated as a potential dynamic sensor with a sub‐second response time and accurate temperature determination based on the strong temperature dependence of the thermally induced morphological self‐reorganization and characteristic surface plasmon (SP) absorption of the metal shell. The irreversible thermally induced morphological and optical signatures behave as characteristic “fingerprints” for temperature recordings, allowing the retrieval of thermal history ex‐situ. As compared with current nanothermometer technologies such as metal‐filled nanotubes, the core–shell nanosphere‐based dynamic thermosensor offers synergistic advantages of ultrafast time response, fast readout, permanent recording of thermal history, and ex‐situ capabilities for effective temperature measurements.     

Optical Heating and Temperature Determination of Core–Shell Gold Nanoparticles and Single‐Walled Carbon Nanotube Microparticles

The real‐time temperature measurement of nanostructured materials is particularly attractive in view of increasing needs of local temperature probing with high sensitivity and resolution in nanoelectronics, integrated photonics, and biomedicine. Light‐induced heating and Raman scattering of single‐walled carbon nanotubes with adsorbed gold nanoparticles decorating silica microparticles are reported, by both green and near IR lasers. The plasmonic shell is used as nanoheater, while the single‐walled carbon nanotubes are Raman active and serve as a thermometer. Stokes and Anti‐Stokes Raman spectra of single‐walled carbon nanotubes serve to estimate the effective light‐induced temperature rise on the metal nanoparticles. The temperature rise is constant with time, indicating stability of the adsorption density. The effective temperatures derived from Stokes and Anti‐Stokes intensities are correlated with those measured in a heating stage. The resolution of the thermal experiments in our study was found to be 5–40 K.