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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]

Alkaline zirconium fluorides (AxZryFx+y, A = Li, Na, and K), featuring unique crystallographic structures, have recently emerged as a class of attractive hosts for fabricating lanthanide (Ln3+)‐doped upconversion nanocrystals (UCNCs) that exhibited distinct morphology, upconversion luminescence (UCL) performance, and physicochemical property. In this paper, for the first time the controlled preparation of Yb3+/Er3+‐doped UCNCs is reported based on the trigonal Cs2ZrF6 host, leading to tunable morphology and size of the resulting UCNCs by varying the reaction temperature and time. By further incorporating Na+ ions into the Cs2ZrF6 crystal lattice, sub‐10 nm Yb3+/Er3+/Na+ tridoped UCNCs with highly improved crystallinity and thus greatly enhanced UCL intensity are obtained. Moreover, these resulting UCNCs display abnormal thermal enhancement of UCL over a temperature range from 333 to 493 K, enabling the fabrication of supersensitive luminescent nanothermometers for temperature sensing. Based on the luminescence intensity ratio of two nonthermally coupled levels (i.e., 4F9/2 and 2H11/2) of Er3+, the as‐prepared Cs2ZrF6:Yb/Er/Na UCNCs exhibit an extremely large absolute sensitivity of 177.3% K−1 and a considerably high relative sensitivity of 1.52% K−1 at 333 K. These results unambiguously demonstrate that Cs2ZrF6 is a suitable host material for preparing small‐sized Ln3+‐doped UCNCs as nanothermometer for high‐performance ratiometric temperature sensing. [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]

To be successfully implemented, an efficient conversion, affordable operation and high values of CO2‐derived products by electrochemical conversion of CO2 are yet to be addressed. Inspired by the natural CaO‐CaCO3 cycle, we herein introduce CaO into electrolysis of SnO2 in affordable molten CaCl2‐NaCl to establish an in situ capture and conversion of CO2. In situ capture of anodic CO2 from graphite anode by the added CaO generates CaCO3. The consequent co‐electrolysis of SnO2 and CaCO3 confines Sn in carbon nanotube (Sn@CNT) in cathode and increases current efficiency of O2 evolution in graphite anode to 71.9 %. The intermediated CaC2 is verified as the nuclei to direct a self‐template generation of CNT, ensuring a CO2‐CNT current efficiency and energy efficiency of 85.1 % and 44.8 %, respectively. The Sn@CNT integrates confined responses of Sn cores to external electrochemical or thermal stimuli with robust CNT sheaths, resulting in excellent Li storage performance and intriguing application as nanothermometer. The versatility of the molten salt electrolysis of CO2 in Ca‐based molten salts for template‐free generation of advanced carbon materials is evidenced by the successful generation of pure CNT, Zn@CNT and Fe@CNT. [ABSTRACT FROM AUTHOR]

The accurate determination of the local temperature is one of the most important challenges in the field of nanotechnology and nanomedicine. For this purpose, different techniques and materials have been extensively studied in order to identify both the best-performing materials and the techniques with greatest sensitivity. In this study, the Raman technique was exploited for the determination of the local temperature as a non-contact technique and titania nanoparticles (NPs) were tested as nanothermometer Raman active material. Biocompatible titania NPs were synthesized following a combination of sol-gel and solvothermal green synthesis approaches, with the aim of obtaining pure anatase samples. In particular, the optimization of three different synthesis protocols allowed materials to be obtained with well-defined crystallite dimensions and good control over the final morphology and dispersibility. TiO2 powders were characterized by X-ray diffraction (XRD) analyses and room-temperature Raman measurements, to confirm that the synthesized samples were single-phase anatase titania, and using SEM measurements, which clearly showed the nanometric dimension of the NPs. Stokes and anti-Stokes Raman measurements were collected, with the excitation laser at 514.5 nm (CW Ar/Kr ion laser), in the temperature range of 293–323 K, a range of interest for biological applications. The power of the laser was carefully chosen in order to avoid possible heating due to the laser irradiation. The data support the possibility of evaluating the local temperature and show that TiO2 NPs possess high sensitivity and low uncertainty in the range of a few degrees as a Raman nanothermometer material. [ABSTRACT FROM AUTHOR]

Sensing temperature in biological systems is of great importance, as it is constructive to understanding various physiological and pathological processes. However, the realization of highly sensitive temperature sensing with organic fluorescent nanothermometers remains challenging. In this study, we report a ratiometric fluorescent nanogel thermometer and study its application in the determination of bactericidal temperature. The nanogel is composed of a polarity-sensitive aggregation-induced emission luminogen with dual emissions, a thermoresponsive polymer with a phase transition function, and an ionic surface with net positive charges. During temperature-induced phase transition, the nanogel exhibits a reversible and sensitive spectral change between a red-emissive state and a blue-emissive state by responding to the hydrophilic-to-hydrophobic change in the local environment. The correlation between the emission intensity ratio of the two states and the external temperature is delicately established, and the maximum relative thermal sensitivities of the optimal nanogel are determined to be 128.42 and 68.39% °C−1 in water and a simulated physiological environment, respectively. The nanogel is further applied to indicate the bactericidal temperature in both visual and ratiometric ways, holding great promise in the rapid prediction of photothermal antibacterial effects and other temperature-related biological events. [ABSTRACT FROM AUTHOR]

Nanothermometers that can reflect temperature in real‐time are crucial for photothermal therapy. Near‐infrared (NIR) fluorescent probes that conform to Boltzmann distribution will play an important role if they have the above characteristics. Here, the LiLuF4: Nd3+/Yb3+ nanocrystals were designed and synthesized by control, exhibiting multiple bright near‐infrared emission peaks at 925–1080 nm region at 280–360 K under the excitation of an 808 nm laser. The feasibility of being used as a nanothermometer was confirmed by testing the spectral variation with temperature and analysis. [ABSTRACT FROM AUTHOR]

Abstract Highly sensitive non-contact mode temperature sensing is substantial for studying fundamental chemical reactions, biological processes, and applications in medical diagnostics. Nanoscale-based thermometers are guaranteeing non-invasive probes for sensitive and precise temperature sensing with subcellular resolution. Fluorescence-based temperature sensors have shown great capacity since they operate as “non-contact” mode and offer the dual functions of cellular imaging and sensing the temperature at the molecular level. Advancements in nanomaterials and nanotechnology have led to the development of novel sensors, such as nanothermometers (novel temperature-sensing materials with a high spatial resolution at the nanoscale). Such nanothermometers have been developed using different platforms such as fluorescent proteins, organic compounds, metal nanoparticles, rare-earth-doped nanoparticles, and semiconductor quantum dots. Carbon dots (CDs) have attracted interest in many research fields because of outstanding properties such as strong fluorescence, photobleaching resistance, chemical stability, low-cost precursors, low toxicity, and biocompatibility. Recent reports showed the thermal-sensing behavior of some CDs that make them an alternative to other nanomaterials-based thermometers. This kind of luminescent-based thermometer is promising for nanocavity temperature sensing and thermal mapping to grasp a better understanding of biological processes. With CDs still in its early stages as nanoscale-based material for thermal sensing, in this review, we provide a comprehensive understanding of this novel nanothermometer, methods of functionalization to enhance thermal sensitivity and resolution, and mechanism of the thermal sensing behavior.

The thermal behavior of enzymes in nanoscale is of great significance to life phenomena. This nonequilibrium state real‐time thermal behavior of enzymes at nanoscale cannot be accurately detected by existing methods. Herein, a novel method is developed for the detection of this thermal behavior. The enzyme‐quantum dot (QD) conjugates can be obtained by chemically grafting temperature‐sensitive amino‐AgInS2 QDs to the enzyme, where the QDs act as nanothermometers with a sensitivity of −2.82% °C−1. Detecting the photoluminescence intensity changes of the enzyme‐QD conjugates, the real‐time thermal behavior of enzymes can be obtained. The enzyme‐QD conjugates show a temperature difference as high as 6 °C above ambient temperature in nano‐microregions with good reproducibility (maximum error of 4%) during catalysis, while solution temperature hardly changed. This method has a temperature resolution of ≈0.5 °C with a detection limit of 0.02 mg mL−1 of enzyme, and spatially ensured that the amino‐AgInS2 QDs are quantitatively bound to the enzyme; thus, it can accurately detect the exothermic behavior of the enzyme and can be extended to other organisms' detection. This method has high sensitivity, good stability, and reliability, indicating its great potential application in investigating the thermal behavior of organisms in nanoscale and related life phenomena. [ABSTRACT FROM AUTHOR]

Nitrogen-doped graphene quantum dots (NGQDs) with controlled emission properties are useful materials for fundamental research and applications. However, the scalable and sustainable production of NGQDs with defined nanostructures from biomass precursors remains elusive. Here a bottom-up microplasma synthesis of emission-controlled colloidal NGQDs used as the multifunctional nanosensors for temperature and selective metal ion sensing is demonstrated. The emission-tuneable NGQDs are synthesized by engineering the N-doping configurations and surface functional groups on the NGQDs surfaces by carefully controlling the plasma conditions and electrolyte chemistry. In situ optical emission and UV–Vis absorbance spectroscopy measurement reveals that the plasma-induced hydroxyl radicals and solvated electrons define the N-dopant configuration and surface functionalization of NGQDs, leading to emission-tuneable NGQDs. The emission-tuneable NGQDs are applied as multifunctional nanosensors for selective Fe3+, Cu2+, and Hg2+ detection revealing broad linear detection range (0.5–300 μM) and low limit of detection (LOD) of 47.9 nM for Hg2+ and sensitive temperature detection from 10 to 80 °C. The developed PL sensing method shows high throughput of 5000 detections per hour. Our work demonstrates the possibility of the plasma-enabled nanoengineering of NGQDs with controlled optical properties and a step towards sustainable and scalable synthesis of graphene nanomaterials from renewable bioresources. [Display omitted] [ABSTRACT FROM AUTHOR]

We synthesized Er3+ and Yb3+ co-doped tantalum oxide (Ta 2 O 5) spherical sub-micrometric particles by a facile method involving formation of tantalum glycolates after pouring in acetone. Then, we investigated how the annealing temperature and Yb3+ concentration (0–30 mol %) affect their structural and luminescence properties. Particle sizes ranged from 146 to 258 nm for the samples annealed at 800 °C. XRD analysis revealed the orthorhombic L-Ta 2 O 5 crystalline structure. The different symmetry sites that the rare earth ions can occupy within the Ta 2 O 5 structure led to intense and broad emission bands centered around 1530 nm. Up-conversion measurements and the calculated number of photons for intense green and red emissions obtained with 980 and 1550 nm excitations helped us to elucidate the mechanisms involved at both excitation wavelengths. We investigated how the 0.5 mol % Er3+/1.5 mol % Yb3+ co-doped Ta 2 O 5 sample performs as a primary thermometer by using the Boltzmann distribution law to predict the absolute temperature from the ratio between the Er3+ 2H 11/2 → 4I 15/2 and 4S 3/2 → 4I 15/2 transitions. We obtained a maximum relative thermal sensitivity of 0.97 ± 0.04 % K−1 and a minimum δT of 2.41 K. The calculated repeatability was above 95%. These results show that promising nanothermometer based on Ta 2 O 5 with controlled size and morphology can be designed. • Er3+/Yb3+ co-doped Ta 2 O 5 particles were synthesized by antisolvent precipitation method. • A more hydrolysis-resistant tantalum precursor was an intermediate in this synthesis. • Spherical particles with well-controlled morphology and size were obtained. • Ta 2 O 5 :Er3+/Yb3+ works as a primary thermometer in physiological temperature range. • The maximum relative sensitivity was 0.97 % K−1. [ABSTRACT FROM AUTHOR]

Sensing temperature in biological systems is of great importance, as it is constructive to understanding various physiological and pathological processes. However, the realization of highly sensitive temperature sensing with organic fluorescent nanothermometers remains challenging. In this study, we report a ratiometric fluorescent nanogel thermometer and study its application in the determination of bactericidal temperature. The nanogel is composed of a polarity-sensitive aggregation-induced emission luminogen with dual emissions, a thermoresponsive polymer with a phase transition function, and an ionic surface with net positive charges. During temperature-induced phase transition, the nanogel exhibits a reversible and sensitive spectral change between a red-emissive state and a blue-emissive state by responding to the hydrophilic-to-hydrophobic change in the local environment. The correlation between the emission intensity ratio of the two states and the external temperature is delicately established, and the maximum relative thermal sensitivities of the optimal nanogel are determined to be 128.42 and 68.39% °C−1 in water and a simulated physiological environment, respectively. The nanogel is further applied to indicate the bactericidal temperature in both visual and ratiometric ways, holding great promise in the rapid prediction of photothermal antibacterial effects and other temperature-related biological events.

Nanodiamonds have been studied for several biomedical applications due to their inherent biocompatibility and low cytotoxicity. Recent investigations have shown perspectives in using fluorescent nanodiamonds as nanothermometers because of their optical properties' dependence on temperature. Easy and accurate localized temperature sensing is essential in a wide variety of scientific fields. Our work demonstrated how the fluorescence spectrum of high-pressure high-temperature fluorescent nanodiamonds of three different sizes: 35 nm, 70 nm and 100 nm, changes with temperature within an important biological temperature range (25 °C to 60 °C). Taking advantage of this phenomenon, we obtained nanothermic scales (NS) from the zero phonon lines (ZPL) of the NV0 and NV− colour centres. In particular, the 100 nm-sized features the more intense fluorescence spectra whose linear dependence with temperature achieved 0.98 R2 data representation values for both NV0 and NV−. This model predicts temperature for all used nanodiamonds with sensitivities ranging from 5.73% °C−1 to 6.994% °C−1 (NV0) and from 4.14% °C−1 to 6.475% °C−1 (NV−). Furthermore, the non-cytotoxic interaction with HeLa cells tested in our study enables the potential use of fluorescence nanodiamonds to measure temperatures in similar nano and microcellular aqueous environments with a simple spectroscopic setup. [ABSTRACT FROM AUTHOR]

Noncontact optical nanothermometers operating within the biological transparency windows are required to study temperature-sensitive biological phenomena at the nanoscale. Nanoparticles containing rare-earth ions such as Nd 3+ have been reported to be efficient luminescence-based ratiometric thermometers, however often limited by poor water solubility and concentration-related quenching effects. Herein, we introduce a new type of nanothermometer, obtained by employing low-dimensional carbon nanodots (CNDs) as matrices to host Nd 3+ ions (NdCNDs). By means of a one-pot procedure, small (∼7-12 nm), water-soluble nanoparticles were obtained, with high (15 wt %) Nd 3+ loading. This stable metal-CND system features temperature-dependent photoluminescence in the second biological window (BW II) upon irradiation at 808 nm, thereby allowing accurate and reversible (heating/cooling) temperature measurements with good sensitivity and thermal resolution. The system possesses remarkable biocompatibility in vitro and promising performance at a high penetration depth in tissue models.

One of the challenges currently facing luminescent thermometry is providing an in-depth analysis of thermally dependent processes occurring in the studied type of nanothermometer. By understanding all possible thermal phenomena, the properties of a given kind of nanosensor can be intentionally improved. Verification of the existing theories on a nanometric scale is particularly important. In this work, a comprehensive characterization of the structural and optical properties of nanocrystalline KLaP4O12 doped with different concentrations of Tb3+ ions was performed. It was shown that Tb3+ ions excited using two distinct wavelengths matched to the ground- and excited-state absorption show luminescences of opposite thermal dependencies. This enabled the single-band-ratiometric (SBR) thermometric approach to be implemented. The experimentally obtained results turned out to be consistent with the proposed form of state equations describing the dynamics of populating Tb3+ energy levels as a function of the temperature. As reported here, the first SBR nanothermometer based on Tb3+ ion emission stands out because of its nanometric size and high relative sensitivity, reaching 5%/°C at 0 °C. Finally, on the basis of modeling changes in the individual parameters in the state equations, their impact on the results obtained for SBR thermometers based on Tb3+ ions was widely discussed. [ABSTRACT FROM AUTHOR]

This short review begins with a brief introductory summary of luminescence nanothermometry. Current applications of luminescence nanothermometry are introduced in biological contexts. Then, theoretical bases of the "temperature" that luminescence nanothermometry determines are discussed. This argument is followed by the 105 gap issue between simple calculation and the measurements reported in literatures. The gap issue is challenged by recent literatures reporting single-cell thermometry using non-luminescent probes, as well as a report that determines the thermal conductivity of a single lipid bilayer using luminescence nanothermometry. In the end, we argue if we can be optimistic about the solution of the 105 gap issue. [ABSTRACT FROM AUTHOR]

Biosensors working in the second near-infrared (NIR-II) spectral region have recently gained great attention owning to their deep tissue bioimaging and high spatiotemporal resolution. However, there is still a challenge to develop efficient nanothermometers based on NIR-II luminescence. Herein, we present a pioneering advancement in the field of nanothermometry by synthesizing a novel nanothermometer, a composite of fluoride nanocrystals and quantum dots. This NaYF 4 :1Nd-Ag 2 S QDs@SiO 2 nanocomposite demonstrates exceptional functionality, being excited by a single light irradiation at 808 nm for NIR-II luminescence imaging. Notably, the composite emits at two distinct wavelengths-1064 nm and 1125 nm, attributable to Nd3+ and Ag 2 S QDs, respectively. This unique emission profile enables deeper tissue penetration, mitigating overheating risks compared to conventional excitation sources at 980 nm. Furthermore, the nanomaterials exhibit remarkable temperature-sensing capabilities, with maximum sensitivities of 0.81%K−1 (S R) at 333 K. These superior sensitivities outperform many existing temperature sensors relying on thermally coupled Stark sublevels. The SiO 2 matrix not only encapsulates and protects the fluoride nanocrystals and quantum dots but also shields them from aqueous environments, ensuring outstanding luminescence stability. Our findings highlight the potential of this nanothermometer as a highly efficient temperature sensor with promising applications in cutting-edge bioapplications. This development introduces a new frontier in temperature sensing and bioimaging, showcasing its potential for transformative contributions to the field. [Display omitted] • Successful synthesis of a novel nanothermometer based on a composite comprising fluoride nanocrystals and quantum dots. • The emission intensity of Nd3+ and Ag 2 S QDs serves as a temperature sensing mechanism (0.81%K−1 (S R) at 333 K). • A versatile platform allows the integration of two different luminescent nanomaterials to meet customized requirements. • The SiO 2 matrix shields NCs and Ag 2 S QDs from water environments, ensuring excellent luminescence stability. [ABSTRACT FROM AUTHOR]

Near-infrared fluorescence (NIRF) thermometry is an emerging method for the noncontact measurement of in vivo deep temperatures. Fluorescence-lifetime-based methods are effective because they are unaffected by optical loss due to excitation or detection paths. Moreover, the physiological changes in body temperature in deep tissues and their pharmacological effects are yet to be fully explored. In this study, we investigated the potential application of the NIRF lifetime-based method for temperature measurement of in vivo deep tissues in the abdomen using rare-earth-based particle materials. β-NaYF 4 particles codoped with Nd 3+ and Yb 3+ (excitation: 808 nm, emission: 980 nm) were used as NIRF thermometers, and their fluorescence decay curves were exponential. Slope linearity analysis (SLA), a screening method, was proposed to extract pixels with valid data. This method involves performing a linearity evaluation of the semilogarithmic plot of the decay curve collected at three delay times after cutting off the pulsed laser irradiation. After intragastric administration of the thermometer, the stomach temperature was monitored by using an NIRF time-gated imaging setup. Concurrently, a heater was attached to the lower abdomens of the mice under anesthesia. A decrease in the stomach temperature under anesthesia and its recovery via the heater indicated changes in the fluorescence lifetime of the thermometer placed inside the body. Thus, NaYF 4 :Nd 3+ /Yb 3+ functions as a fluorescence thermometer that can measure in vivo temperature based on the temperature dependence of the fluorescence lifetime at 980 nm under 808 nm excitation. This study demonstrated the ability of a rare-earth-based NIRF thermometer to measure deep tissues in live mice, with the proposed SLA method for excluding the noisy deviations from the analysis for measuring temperature using the NIRF lifetime of a rare-earth-based thermometer.

TiO2 nanoparticles doped with different amounts of Nd3+ (0.5, 1, and 3 wt.%) were synthetized by the sol–gel method, and evaluated as potential temperature nanoprobes using the fluorescence intensity ratio between thermal-sensitive radiative transitions of the Nd3+. XRD characterization identified the anatase phase in all the doped samples. The morphology of the nanoparticles was observed with SEM, TEM and HRTEM microscopies. The relative amount of Nd3+ in TiO2 was obtained by EDXS, and the oxidation state of titanium and neodymium was investigated via XPS and NEXAFS, respectively. Nd3+ was present in all the samples, unlike titanium, where besides Ti4+, a significantly amount of Ti3+ was observed; the relative concentration of Ti3+ increased as the amount of Nd3+ in the TiO2 nanoparticles increased. The photoluminescence of the synthetized nanoparticles was investigated, with excitation wavelengths of 350, 514 and 600 nm. The emission intensity of the broad band that was associated with the presence of defects in the TiO2, increased when the concentration of Nd3+ was increased. Using 600 nm for excitation, the 4F7/2→4I9/2, 4F5/2→4I9/2 and 4F3/2→4I9/2 transitions of Nd3+ ions, centered at 760 nm, 821 nm, and 880 nm, respectively, were observed. Finally, the effect of temperature in the photoluminescence intensity of the synthetized nanoparticles was investigated, with an excitation wavelength of 600 nm. The spectra were collected in the 288–348 K range. For increasing temperatures, the emission intensity of the 4F7/2→4I9/2 and 4F5/2→4I9/2 transitions increased significantly, in contrast to the 4F3/2→4I9/2 transition, in which the intensity emission decreased. The fluorescence intensity ratio between the transitions I821I880=F5/24I49/2F43/2I49/2 and I760I880=F47/2I49/2F43/2I49/2 were used to calculate the relative sensitivity of the sensors. The relative sensitivity was near 3% K−1 for I760I880 and near 1% K−1 for I821I880.

Nanodiamonds have been studied for several biomedical applications due to their inherent biocompatibility and low cytotoxicity. Recent investigations have shown perspectives in using fluorescent nanodiamonds as nanothermometers because of their optical properties’ dependence on temperature. Easy and accurate localized temperature sensing is essential in a wide variety of scientific fields. Our work demonstrated how the fluorescence spectrum of high-pressure high-temperature fluorescent nanodiamonds of three different sizes: 35 nm, 70 nm and 100 nm, changes with temperature within an important biological temperature range (25 °C to 60 °C). Taking advantage of this phenomenon, we obtained nanothermic scales (NS) from the zero phonon lines (ZPL) of the NV0 and NV− colour centres. In particular, the 100 nm-sized features the more intense fluorescence spectra whose linear dependence with temperature achieved 0.98 R2 data representation values for both NV0 and NV−. This model predicts temperature for all used nanodiamonds with sensitivities ranging from 5.73% °C−1 to 6.994% °C−1 (NV0) and from 4.14% °C−1 to 6.475% °C−1 (NV−). Furthermore, the non-cytotoxic interaction with HeLa cells tested in our study enables the potential use of fluorescence nanodiamonds to measure temperatures in similar nano and microcellular aqueous environments with a simple spectroscopic setup.

In luminescence thermometry enabling temperature reading at a distance, an important challenge is to propose new solutions that open measuring and material possibilities. Responding to these needs, in the nanocrystalline phosphors of yttrium oxide Y2O3 and lutetium oxide Lu2O3, temperature-dependent emission of trivalent terbium Tb3+ dopant ions was recorded at the excitation wavelength 266 nm. The signal of intensity decreasing with temperature was monitored in the range corresponding to the 5D4 → 7F6 emission band. On the other hand, defect emission intensity obtained upon 543 nm excitation increases significantly at elevated temperatures. The opposite thermal monotonicity of these two signals in the same spectral range enabled development of the single band ratiometric luminescent thermometer of as high a relative sensitivity as 4.92%/°C and 2%/°C for Y2O3:Tb3+ and Lu2O3:Tb3+ nanocrystals, respectively. This study presents the first report on luminescent thermometry using defect emission in inorganic phosphors.

Graphical abstract PH value increase induces morphology revolution of UCNPs, resulting in higher surface-to-volume ratios, decreasing luminescence intensity and increase nonradiative rates, hence the enhanced thermometric property. Highlights • Morphology of UCNPS has been tuned. • Surface-to-volume ratios and advanced sensitivities has obtained. • A dual-mode thermometric property has been found. Abstract Exploring the thermometric properties of UCNPs is of great importance for non-contact fluoresce thermometers. Ln-doped β-NaGdF 4 :Yb3+,Er3+ upconversion nanoparticles (UCNPs) have been fabricated by varying the ratio of citric ions to molecules in precursor. Morphology of the as-prepared β-NaGdF 4 :Yb3+,Er3+ UCNPs turns from hexagonal prisms to agglomerations of smaller particles with decreased dimension. Luminescence intensity decreases and red-to-green ratio increases with increasing ratio of citric ions to molecules. A dual-mode thermometric property has been found in the as-prepared β-NaGdF 4 :Yb3+,Er3+ UCNPs. The first mode derives from the temperature dependent fluoresce-intensity-ratios of thermally coupled manifolds of Er3+ (2H 11/2) and (4S 3/2) manifolds, of which the maximum relative sensitivity value is 0.0036 K−1. The other mode derives from temperature dependent red-to-green ratios, which is a linear function of temperature and the maximum relative sensitivity value is 0.0238 K−1. The β-NaGdF 4 :Yb3+,Er3+ UCNPs with morphology of agglomerations of smaller particles with high surface-to-volume ratios show advanced sensitivities, which are suitable for noncontact optical thermometer. [ABSTRACT FROM AUTHOR]

Temperature dependence of the photophysical properties of europium(III) complex with the benzoylcetonate ligand were evaluated. The photostability of the complex and the temperature dependence of the 5 D 0 → 7 F 2 transition band area (maximum relative sensitivity of 5.25% K −1 at 303 K) makes this complex promising as temperature probe. The temperature dependence of the 5 D 0 → 7 F 0 transition band indicates that the electron-phonon coupling is probably the main mechanism operating in the temperature dependence of the photophysical properties of the complex. [ABSTRACT FROM AUTHOR]

Temperature measurement in biology and medical diagnostics is of great importance. Herein, a novel carbon nanodot (CND) based fluorescent nanothermometry device for spatially resolved temperature measurements is demonstrated. The fluorescence CNDs are prepared by a simple one-pot solvothermal method using sucrose as carbon source. Resultant CNDs show stable green fluorescence at 520 nm with high quantum yield (≈6%). The fluorescence of resultant CNDs exhibits a reversible linear response to temperature in a wide range of 20-85 °C. Moreover, the temperature resolution better than 0.5 °C and high sensitive variation of ≈1.3% °C−1 are observed in a broad physiological temperature range of 20-40 °C. Therefore, the as-prepared CNDs possess high water solubility, stable fluorescence, small size, and good biocompatibility, which make them promising candidate for thermometry and cell imaging in biological media. [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]

Thermal effect of rare earth (RE) ions doped nanoparticles under near-infrared light irradiation has been underestimated, because main interest and efforts still fall into the distinctive up-converting luminescence property of these particles. In this work, we demonstrate an approach to convert 980 nm light energy to heat energy via a designed nanoheater which is Sm 3+ /Yb 3+ codoped NaY(MoO 4 ) 2 nanorods derived from a microwave-assisted hydrothermal reaction. To inspect the photothermal conversion effect of the nanoheaters, Er 3+ /Yb 3+ codoped NaY(MoO 4 ) 2 nanorods are prepared via the same synthesis route. A convenient strategy, in which NaY(MoO 4 ) 2 :Er 3+ /Yb 3+ nanorods are used as nanothermometer, is proposed to monitor the laser-induced temperature change of the nanoheaters by mixing a small amount of nanothermometer with nanoheater. The influence of Sm 3+ /Yb 3+ concentrations and excitation power density on the final temperature of the nanoheaters is studied. It is found that when Yb 3+ concentration is fixed to be 10 mol%, the influence of increasing Sm 3+ concentration on the photothermal conversion effect is limited; but when Sm 3+ is fixed to be 5 mol%, the photothermal conversion is enhanced greatly with the increase of Yb 3+ concentration. In addition, the temperature for all the NaY(MoO 4 ) 2 :Sm 3+ /Yb 3+ nanoheaters after laser irradiation is linearly dependent on the excitation power density. In order to examine the photothermal conversion effect of the nanoheater in liquid media, the PVP (polyvinyl pyrrolidone) solution is used for accommodating the nanoheaters, and effective photothermal conversion is observed. [ABSTRACT FROM AUTHOR]

Temperature measurement in biology and medical diagnostics, along with sensitive temperature probing in living cells, is of great importance; however, it still faces significant challenges. Metal nanoclusters (NCs) with attractive luminescent properties may be promising candidates to overcome such challenges. Here, a novel one-step synthetic method is presented to prepare highly fluorescent copper NCs (CuNCs) in ambient conditions by using glutathione (GSH) as both the reducing agent and the protective layer preventing the aggregation of the as-formed NCs. The resultant CuNCs, with an average diameter of 2.3 nm, contain 1-3 atoms and exhibit red fluorescence (λ = 610 nm) with high quantum yields (QYs, up to 5.0%). Interestingly, the fluorescence signal of the CuNCs is reversibly responsive to the environmental temperature in the range of 15-80 °C. Furthermore, as the CuNCs exhibit good biocompatibility, they can pervade the MC3T3-E1 cells and enable measurements over the physiological temperature range of 15-45 °C with the use of the confocal fluorescence imaging method. In view of the facile synthesis method and attractive fluorescence properties, the as-prepared CuNCs may be used as photoluminescence thermometers and biosensors. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

• A microwave-transparent thermochromic MOF is synthesized as nano-thermometer. • The thermometer has good thermal stability and dispersity in liquid solution. • A color-temperature relationship of the thermochromic MOF is established. • The temperature distribution is directly visualized during microwave heating. Microwave has been widely used as an efficient and clean method for energy supply in chemical engineering, due to its unique heating characteristics. The industrialization of microwave is obstructed by the problem of uneven heating; the inhomogeneous temperature distribution results in inaccurate prediction of reaction kinetics, uncertain product yields, and unstable energy utilization efficiencies. With the aim to overcome this problem, we use a non-contact nano-thermometer to achieve in situ imaging of liquid temperature distribution during microwave heating. A zinc-based metal organic framework material (ZMOF) is employed as the temperature indicator in microwave field, due to its microwave transparency, thermal stability and good dispersibility in solvents. A case study was conducted by dispersing the ZMOF particles in a 95% ethanol solution, where the color of ZMOF changes from yellow to orange with the increase of temperature in the range of 30–120 °C with the sensitivity of 1.512%/°C. By linearly correlating the hue value of ZMOF suspension with the temperature, the color images of liquid heated in microwave cavity were transformed into temperature distribution maps. ZMOF also has shown the advantages of good dispersion, cyclic temperature measurement, continuous linear discoloration, and visible light excitation. This facile route of temperature field imaging can provide experimental validation for numerical simulation and guide the equipment optimization in microwave-assisted chemical engineering. A zinc-based MOF material is fabricated, whose color is sensitive to temperature. By dispersing the material in solvents, the temperature distribution of liquid samples can be directly observed during microwave irradiation. This facile route can calibrate the results of numerical simulation and provide guidance for equipment optimization of microwave-assisted chemical engineering. [Display omitted]. [ABSTRACT FROM AUTHOR]

Electromechanical nanothermometer based on the interaction and relative motion walls of the (n,n)@(m,m) double-walled carbon nanotubes (DWNTs) is considered. Temperature measurements are carried out through the measurements of the conductivity. The dependence of the interwall interaction energy on the relative displacement of the walls of the DWNTs is computed ab initio using density functional theory. The conductivity of the DWNTs is calculated within the Huckel-Hubbard model. The operational characteristics of the nanothermometer are calculated. [ABSTRACT FROM AUTHOR]

Aims: A carbon-wrapped nanoscaled thermometer for a contactless temperature control in biological systems on the cellular level is presented. Materials & methods: The thermometer is based on multiwalled carbon nanotubes (MWCNTs) filled with materials with strongly temperature-dependent nuclear magnetic resonance (NMR) parameters. The NMR frequency shift and relaxation time were measured in cuprous-iodide-filled CNTs at different temperatures. Results: The experimental data indicate a pronounced temperature dependence of the NMR parameters, thereby realizing the nanoscaled thermometer. Conclusion: This study is a proof-of-concept that the functionalized CNTs can be used as a contactless thermometer in biomedical applications. [ABSTRACT FROM AUTHOR]

Abstract: A new concept of an electromechanical nanothermometer based on the interaction and relative motion of the components of a nanosystem is proposed. The nanothermometer can be used for accurate temperature measurements in spatially localized regions with dimensions of several hundred nanometers. Temperature measurements are carried out through the measurements of the conductivity of the components assuming that the total conductivity of the system depends significantly on the temperature. A model implementation of the nanothermometer based on the double-walled carbon nanotube is suggested. The dependence of the interwall interaction energy on the relative displacement of the walls of the nanotube is computed ab initio using density functional theory. The conductivity of the walls is calculated within the Huckel–Hubbard model. [Copyright &y& Elsevier]

Biocompatible PLNP-GNR composite nanoplatforms were constructed to simultaneously monitor autofluorescence-free bioimaging and temperature change during PTT process in deep tissue case using a single wavelength (635 nm) light exci-tation strategy. [Display omitted] • Near-spherical ZGGO:Cr3+@CTAB nanoparticles were synthesized. • CTAB was successfully modified on the surface of ZGGO:Cr3+ nanoparticles. • Biocompatible PLNP-GNR composite nanoplatforms were fabricated by a simple method. • The nanoplatforms can monitor temperature variation during deep-tissue PTT process. Currently, it is still a challenge to construct an integrated multi-functional nanoplatform with autofluorescence-free bioimaging and temperature sensing and photothermal therapy (PTT) for tumors located at 10 mm below the surface of local tissue (deep tissue) using gold nanorods (GNRs). Herein, through the self-assembly and surface modification of persistent luminescent nanoparticles (PLNPs) and GNRs using hexadecyl trimethyl ammonium bromide (CTAB) and phosphotungstic acid (PW 12) molecules, biocompatible PLNP-GNR composite nanoplatforms were constructed to simultaneously monitor autofluorescence-free bioimaging and temperature change during in vitro and in vivo PTT process using a single wavelength (635 nm) light excitation strategy. Especially, the nanoplatforms demonstrated that the local-tissue temperature can increase by 26 °C under 635 nm excitation (0.8 W·cm−2) and the photothermal conversion efficiency is ~37%. Among them, PLNPs were acted as optical probes for NIR bioimaging and ratiometric nanothermometer and the temperature sensitivity reaches to ~0.064 K−1. This study is helpful for reducing photodamage to normal tissue through the accurate control of excitation light power during deep-tissue PTT process. [ABSTRACT FROM AUTHOR]

TiO2 nanoparticles doped with different amounts of Nd3+ (0.5, 1, and 3 wt.%) were synthetized by the sol–gel method, and evaluated as potential temperature nanoprobes using the fluorescence intensity ratio between thermal-sensitive radiative transitions of the Nd3+. XRD characterization identified the anatase phase in all the doped samples. The morphology of the nanoparticles was observed with SEM, TEM and HRTEM microscopies. The relative amount of Nd3+ in TiO2 was obtained by EDXS, and the oxidation state of titanium and neodymium was investigated via XPS and NEXAFS, respectively. Nd3+ was present in all the samples, unlike titanium, where besides Ti4+, a significantly amount of Ti3+ was observed; the relative concentration of Ti3+ increased as the amount of Nd3+ in the TiO2 nanoparticles increased. The photoluminescence of the synthetized nanoparticles was investigated, with excitation wavelengths of 350, 514 and 600 nm. The emission intensity of the broad band that was associated with the presence of defects in the TiO2, increased when the concentration of Nd3+ was increased. Using 600 nm for excitation, the 4F7/2→4I9/2, 4F5/2→4I9/2 and 4F3/2→4I9/2 transitions of Nd3+ ions, centered at 760 nm, 821 nm, and 880 nm, respectively, were observed. Finally, the effect of temperature in the photoluminescence intensity of the synthetized nanoparticles was investigated, with an excitation wavelength of 600 nm. The spectra were collected in the 288–348 K range. For increasing temperatures, the emission intensity of the 4F7/2→4I9/2 and 4F5/2→4I9/2 transitions increased significantly, in contrast to the 4F3/2→4I9/2 transition, in which the intensity emission decreased. The fluorescence intensity ratio between the transitions I 821 I 880 = F 5 / 2 4 I 4 9 / 2 F 4 3 / 2 I 4 9 / 2 and I 760 I 880 = F 4 7 / 2 I 4 9 / 2 F 4 3 / 2 I 4 9 / 2 were used to calculate the relative sensitivity of the sensors. The relative sensitivity was near 3% K−1 for I 760 I 880 and near 1% K−1 for I 821 I 880 . [ABSTRACT FROM AUTHOR]

Design and synthesis of new fluoride upconversion (UC) luminescent materials with controllable morphologies remains a challenge. Here, novel Ba 4 Bi 3 F 17 :Er3+/Yb3+ UC nanoparticles (UCNPs) were discovered and prepared using a simple one-step solvothermal strategy, and the modulation of the morphology and particle size was investigated in detail. Upon 980 nm excitation, the influence of dosage amounts of Yb3+/Er3+, and the environmental temperatures on the UC luminescent performance were studied in the temperature range of 293–393 K. The maximum relative sensitivities (S r) of Ba 4 Bi 3 F 17 :1 mol%Er, 13 mol%Yb material are calculated to be 0.0122 K-1 and 0.0167 K−1 at 293 K, respectively, based on the two energetic levels of (2H 11/2 , 4S 13/2) and (2H 11/2 , 4F 9/2). In addition, the internal heating performance of the Ba 4 Bi 3 F 17 :Er3+/Yb3+ UCNPs was also evaluated in the pump power range of 112–901 mW, and the internal temperature of the UCNPs increased from 296 to 367 K with the increase of excitation power. This work initiates the discovery of the new bismuth-based fluoride nanothermometers and demonstrates the great potential for bifunctional applications in temperature sensing and optical heater devices. Image 1 • Ba 4 Bi 3 F 17 :Er3+/Yb3+ UC nanoparticles (UCNPs) were discovered and prepared. • The modulation of the morphology and particle size was investigated. • The applications in temperature sensing and optical heater devices were studied. [ABSTRACT FROM AUTHOR]

A novel dual-emission nitrogen doped carbon dots/gold nanohybrid (NCDs-Au) was designed for specific and sensitive ratiometric detection of intracellular temperature and tyrosine. In this probe, a reductive NCDs was successfully prepared with the use of natural biomass Dendrobium officinale as precursor. The new prepared NCDs acted as both reducers and stabilizers to synthesize a novel NCDs-Au nanohybrid by a facile one-step procedure along with a quantum yield of 14.3%. The prepared nanoprobe showed characteristic fluorescence emissions of NCDs and Au NCs with single-wavelength excitation. Notably, the nanoprobe shows an interesting wavelength-dependent dual response to temperature (448 nm) and tyrosine (660 nm), enabling the two targets to be detected proportionally. As an effective temperature sensor, the nanoprobe exhibited good temperature-dependent fluorescence with a sensational linear response from 5 to 75 °C. In addition, the sensor has a linear response toward tyrosine in the range of 0.5–175 μM with a detection limit of 0.19 μM. Moreover, the fluorescent nanoprobe was successfully applied to ratiometricly monitor the variation of temperature or tyrosine level in cells because of the low cytotoxicity, chemical stability and excellent fluorescence properties. These results suggested that the nanoprobe here has provided the possibility for rapidly biosensing with the acceptable selectivity and sensitivity. Image 1 • The NCDs prepared with natural biomass Dendrobium officinale were used as a reducer and stabilizer. • The NCDs-Au possesses two emission peaks at 448 nm (blue) and 660 nm (red) under a single excitation wavelength. • The dual-emission ratiometric fluorescence nanoprobe was employed for sensing of temperature and tyrosine. • The nanoprobe was successfully applied to ratiometricly monitor the variation of temperature and tyrosine in live cells. [ABSTRACT FROM AUTHOR]

Highly sensitive non-contact mode temperature sensing is substantial for studying fundamental chemical reactions, biological processes, and applications in medical diagnostics. Nanoscale-based thermometers are guaranteeing non-invasive probes for sensitive and precise temperature sensing with subcellular resolution. Fluorescence-based temperature sensors have shown great capacity since they operate as "non-contact" mode and offer the dual functions of cellular imaging and sensing the temperature at the molecular level. Advancements in nanomaterials and nanotechnology have led to the development of novel sensors, such as nanothermometers (novel temperature-sensing materials with a high spatial resolution at the nanoscale). Such nanothermometers have been developed using different platforms such as fluorescent proteins, organic compounds, metal nanoparticles, rare-earth-doped nanoparticles, and semiconductor quantum dots. Carbon dots (CDs) have attracted interest in many research fields because of outstanding properties such as strong fluorescence, photobleaching resistance, chemical stability, low-cost precursors, low toxicity, and biocompatibility. Recent reports showed the thermal-sensing behavior of some CDs that make them an alternative to other nanomaterials-based thermometers. This kind of luminescent-based thermometer is promising for nanocavity temperature sensing and thermal mapping to grasp a better understanding of biological processes. With CDs still in its early stages as nanoscale-based material for thermal sensing, in this review, we provide a comprehensive understanding of this novel nanothermometer, methods of functionalization to enhance thermal sensitivity and resolution, and mechanism of the thermal sensing behavior. [ABSTRACT FROM AUTHOR]

In luminescence thermometry enabling temperature reading at a distance, an important challenge is to propose new solutions that open measuring and material possibilities. Responding to these needs, in the nanocrystalline phosphors of yttrium oxide Y2O3 and lutetium oxide Lu2O3, temperature-dependent emission of trivalent terbium Tb3+ dopant ions was recorded at the excitation wavelength 266 nm. The signal of intensity decreasing with temperature was monitored in the range corresponding to the 5D4 → 7F6 emission band. On the other hand, defect emission intensity obtained upon 543 nm excitation increases significantly at elevated temperatures. The opposite thermal monotonicity of these two signals in the same spectral range enabled development of the single band ratiometric luminescent thermometer of as high a relative sensitivity as 4.92%/°C and 2%/°C for Y2O3:Tb3+ and Lu2O3:Tb3+ nanocrystals, respectively. This study presents the first report on luminescent thermometry using defect emission in inorganic phosphors. [ABSTRACT FROM AUTHOR]

In view of many promising applications of gold nanoclusters (AuNCs), nanothermometry is an important field of research in biology and medicine. Here, we demonstrate the temperature dependent photophysical properties of highly luminescent green emitting 6-aza-2-thiothymine/l-arginine-stabilized Au nanosclusters (ATT/Arg Au NCs) by using steady state and time-resolved photoluminescence spectroscopy. Significantly, thermoresponsive properties of these highly photostable and biocompatible Au NCs are reversible, which endow the probe for further bioanalytical applications with great prospects. Additionally, protein-NC interaction mechanism has been elucidated in vitro and in vivo that dictates the complex behavior of the NCs with living organisms. These ultrasmall Au NCs are observed to accumulate in the cellular cytoplasm by translocating through the membrane as evidenced from the confocal laser scanning microscopy (CLSM). In vivo temperature sensing examined with human osteosarcoma cell line (MG-63 cell) by employing fluorescence lifetime imaging microscopy (FLIM) technique reveals the optimistic application of these lifetime-based nanosensors in biomedicine and biotechnology.