Measurement of Temperature Distribution at the Nanoscale with Luminescent Probes Based on Lanthanide Nanoparticles and Quantum Dots

Ferrous Fumarate-Encapsulated Nanoformulation Triggering a Domino Effect for Enhanced Ferroptosis Therapy

Fenton-induced ferroptosis has emerged as a promising therapeutic strategy for malignant tumors. However, the therapeutic efficacy of ferroptosis is limited by factors such as suboptimal Fenton efficiency, intracellular antioxidant systems, and insufficient drug accumulation. Here, we report a domino effect triggered by a homologous cancer cell membrane-camouflaged nanoformulation: disrupting intracellular redox homeostasis, inducing enhanced oxidative stress and leading to specific ferroptosis. This strategy involves using pure red-emission upconversion nanoparticles (NaErF4:4%Tm@NaYF4, U NPs), a ferroptosis inducer (ferrous fumarate, an iron-deficiency anemia therapeutic reagent), and glucose oxidase (GOx). The nanoformulation, U@mSiO2/ferrous fumarate/GOx@lecithin/cell membrane (USFGM), enables efficient in vivo deep tissue upconversion luminescence (UCL) imaging by pure red-emission. Lecithin-modified cancer cell membranes are characterized by homologous target "homing" and acid-responsive release. Exogenous GOx depletes intratumoral glucose and generates H+/H2O2, which disrupts the nutrient supply and promotes efficient generation of reactive oxygen species (ROS). Subsequently, Fe2+/fumaric acids (FAs) are acid-responsively released from ferrous fumarate, which synchronously triggers and exacerbates the process of ferroptosis through mechanisms such as lipid ROS generation and glutathione (GSH) depletion. Here, we report for the first time that FA depletes GSH and leads to inactivation of GSH-dependent peroxidase 4 (GPX4). This concept is also confirmed in tumor-bearing mice of salivary adenoid cystic carcinoma (SACC). In summary, this work identifies a systemic, low-toxicity, and highly efficient cancer inhibitory nanoformulation from existing clinical drugs, which provides a promising direction for exploring therapeutic strategies for human malignant tumors.

Intracellular Temperature Sensing with Remarkably High Relative Sensitivity Using Nile Red-Loaded Biocompatible Niosome

Accurate temperature sensing at the nanoscale within biological systems is crucial for understanding various cellular processes, such as gene expression, metabolism, and enzymatic reactions. Current temperature-sensing techniques either lack the temperature resolution and sensitivity necessary for intracellular applications or require invasive procedures that can disrupt cellular activities. In this study, we present Nile Red (NR)-loaded hybrid (span 60-L64) niosomes and Nile Red-loaded L64 niosomes as highly sensitive fluorescent nanothermometers. These niosomes are synthesized via the thin-layer evaporation method, forming thermoresponsive vesicles, and they demonstrate reversible phase transition behavior with temperature. When loaded with polarity-sensitive Nile Red, vesicles exhibit a strong temperature-dependent fluorescence response (change in intensity, emission maximum, and lifetime), suitable for noncontact temperature sensing in the biologically important temperature range of 25 to 50 °C. While NR-hybrid niosomes exhibit a high relative sensitivity of 19% °C-1 at 42 °C, NR-L64 niosomes achieved extraordinary relative sensitivity of 36% °C-1 at 40 °C. Using NR-L64 niosomes, the temperature resolution is found to be 0.0004 °C at 40 °C. The nanothermometers displayed excellent photostability, thermal reversibility, and resistance to variations in ion concentration and pH. Temperature-dependent confocal microscopy using FaDu cells confirmed the biocompatibility and effectiveness of the designed nanothermometers for precise intracellular temperature sensing. The results demonstrate the significant potential of Nile Red-loaded niosomes for temperature monitoring using live cell imaging in biological media.

Time-Resolved Ratiometric Fluorescence Nanothermometer for Real-Time Endoscopic Temperature Guidance during Tumor Ablation

Thermal ablation is a common treatment option for early-stage cancers, but the lack of real-time temperature imaging feedback method increases the risk of incomplete or excessive ablation. Although ratiometric nanothermometer offers a rapid temperature imaging solution, accurate in vivo signal extraction remains challenging due to the autofluorescence and wavelength-dependent tissue absorption and scattering. Herein, a time-resolved ratiometric fluorescence nanothermometer composed of europium and iridium complex with identical working wavelength but distinguishing lifetimes is reported, whose well-designed structures enable 450 nm excitation of both complexes with a high quantum yield (57.8%). Based on the nanothermometer, accurate signal extraction is realized in whole blood, beneath a 2 cm tissue phantom and a 5 mm pork slice through a time-resolved ratiometric method. By leveraging the exceptional thermal sensitivity (6.9% K-1), high temperature resolution (0.02 K), and clinically relevant temperature range (30-96 °C) of the nanothermometer, a fluorescence temperature endoscopy system is further designed with a real-time temperature imaging speed of 10 fps, which is applied to minimally invasive temperature monitoring during microwave ablation of liver tumors in rabbits, realizing precise ablation control through dynamic ablation power adjustment. The real-time and accurate temperature imaging performance of the nanothermometer may offer a new perspective for intraoperative guidance.

A novel Ln3+/Al3+ metallacrown multifunctional material for latent fingerprint detection, luminescent thermometers and luminescent sensors

Lanthanide luminescent complexes are active and thriving in various research fields due to their unique optical properties, while optical materials across a wide spectral range and with multiple functions in one were rarely reported. In this work, a new class of Ln3+/Al3+ metallacrowns (MCs) were constructed with excellent luminescence properties in both the visible and near-infrared regions, and the elaborate luminescence modulation can be achieved by doping with different Ln3+ ions. Strikingly, the powder of LnMC was developed as a luminescent nanomaterial for the detection of latent fingerprints (LFPs), and even the third level details of fingerprints can be clearly recognized, which provides a reference for the identification of fingerprints in the field of criminal investigation. More importantly, TbMC and Tb0.1Sm0.9MC can be successfully used as luminescent thermometers with sensitivities of 2.51% °C-1 and 2.33% °C-1, respectively, higher than most reported values. Meanwhile, TbMC was developed as a luminescent probe for Fe3+ and 2,6-pyridinedicarboxylic acid (DPA) with low limits of detection (LOD) of 0.51 μM and 4.26 μM, respectively, representing the first example of MC with luminescence sensing. Also of note is that SmMC, Tb0.1Sm0.9MC and TbMC can be functionalized as luminescent inks and films due to their clear recognizable colours in the visible range, suggesting a new strategy for high-level anti-counterfeiting. In short, the LnMC luminescent material has wide application prospects in many fields, especially rare for multifunctional applications of small-molecule complexes with non-metal-organic frameworks.

A Nanothermometer with a Microwave Thermal Effect for Sensing Cell Membrane Temperature and Measuring Microwave-Induced Thermal Gradient Distribution

In microwave (MW) thermotherapy, it is challenging to regulate the temporal and spatial distribution of the temperature at the nanoscale. Herein, we report a nanothermometer for simultaneous MW heating and temperature distribution measurement. The nanothermometer was prepared by free radical polymerization with vinylbenzyl trimethylammonium chloride (VBTMACl) as the MW thermosensitizer and isopropylacrylamide (NIPAM) as the thermoresponsive unit, followed by anion exchange with fluorophore sodium 3-(4-(1,2,2-triphenylvinyl)phenoxy)propane-1-sulfonate (TPESO3Na). In aqueous medium, the nanothermometer self-assembles into micelles with TPESO3- as the hydrophobic core and thermoresponsive polymer P(NIPAM-co-VBTMACl) as the hydrophilic shell, thereby to exhibit aggregation-induced emission (AIE). By increasing the temperature, the conformational change of the thermoresponsive polymer drives TPESO3- to transfer from the core to the shell of the micelles, and the nanothermometer converts from an aggregate state to a dispersed state. As a result, the nanothermometer exhibits a superior temperature-dependent emission feature in the temperature range 25-41 °C, with a relative thermal sensitivity of 8.3% °C-1 at 37 °C. In addition, the nanothermometer possesses a positive charge and balanced hydrophilic-hydrophobic feature which prompts its anchoring to the cell membrane. Therefore, it realizes in situ temperature sensing of cell membranes during MW heating, as well as temperature distribution of the cell membrane.

Luminescence Thermometry Beyond the Biological Realm

As the field of luminescence thermometry has matured, practical applications of luminescence thermometry techniques have grown in both frequency and scope. Due to the biocompatibility of most luminescent thermometers, many of these applications fall within the realm of biology. However, luminescence thermometry is increasingly employed beyond the biological realm, with expanding applications in areas such as thermal characterization of microelectronics, catalysis, and plasmonics. Here, we review the motivations, methodologies, and advances linked to nonbiological applications of luminescence thermometry. We begin with a brief overview of luminescence thermometry probes and techniques, focusing on those most commonly used for nonbiological applications. We then address measurement capabilities that are particularly relevant for these applications and provide a detailed survey of results across various application categories. Throughout the review, we highlight measurement challenges and requirements that are distinct from those of biological applications. Finally, we discuss emerging areas and future directions that present opportunities for continued research.

Spotlight on Luminescence Thermometry: Basics, Challenges, and Cutting-Edge Applications

Luminescence (nano)thermometry is a remote sensing technique that relies on the temperature dependency of the luminescence features (e.g., bandshape, peak energy or intensity, and excited state lifetimes and risetimes) of a phosphor to measure temperature. This technique provides precise thermal readouts with superior spatial resolution in short acquisition times. Although luminescence thermometry is just starting to become a more mature subject, it exhibits enormous potential in several areas, e.g., optoelectronics, photonics, micro- and nanofluidics, and nanomedicine. This work reviews the latest trends in the field, including the establishment of a comprehensive theoretical background and standardized practices. The reliability, repeatability, and reproducibility of the technique are also discussed, along with the use of multiparametric analysis and artificial-intelligence algorithms to enhance thermal readouts. In addition, examples are provided to underscore the challenges that luminescence thermometry faces, alongside the need for a continuous search and design of new materials, experimental techniques, and analysis procedures to improve the competitiveness, accessibility, and popularity of the technology.

Photothermal Nanomaterials: A Powerful Light-to-Heat Converter

All forms of energy follow the law of conservation of energy, by which they can be neither created nor destroyed. Light-to-heat conversion as a traditional yet constantly evolving means of converting light into thermal energy has been of enduring appeal to researchers and the public. With the continuous development of advanced nanotechnologies, a variety of photothermal nanomaterials have been endowed with excellent light harvesting and photothermal conversion capabilities for exploring fascinating and prospective applications. Herein we review the latest progresses on photothermal nanomaterials, with a focus on their underlying mechanisms as powerful light-to-heat converters. We present an extensive catalogue of nanostructured photothermal materials, including metallic/semiconductor structures, carbon materials, organic polymers, and two-dimensional materials. The proper material selection and rational structural design for improving the photothermal performance are then discussed. We also provide a representative overview of the latest techniques for probing photothermally generated heat at the nanoscale. We finally review the recent significant developments of photothermal applications and give a brief outlook on the current challenges and future directions of photothermal nanomaterials.

Visible light responsive photoacids for subcellular pH and temperature correlated fluorescence sensing

Liao's photoacids (PAs) are a well-known type of visible light-responsive photoswitches. Here, taking advantage of the temperature-dependent thermal relaxation from the ring-closed to the ring-opened forms, PAs are proposed for the first time as a fluorescent temperature sensor in cells. The logarithmic lifetime (ln τ) of the ring-closed spiro-form exhibited an excellent linear response to the reciprocal of the temperature. In addition, the fluorescent ring-opened PAs were able to highlight lysosomes and responded to lysosomal pH changes. These properties made the PAs promising fluorescent probes in the sensing of subcellular pH and temperature.

A Lanthanide Upconversion Nanothermometer for Precise Temperature Mapping on Immune Cell Membrane

Cell temperature monitoring is of great importance to uncover temperature-dependent intracellular events and regulate cellular functions. However, it remains a great challenge to precisely probe the localized temperature status in living cells. Herein, we report a strategy for in situ temperature mapping on an immune cell membrane for the first time, which was achieved by using the lanthanide-doped upconversion nanoparticles. The nanothermometer was designed to label the cell membrane by combining metabolic labeling and click chemistry and can leverage ratiometric upconversion luminescence signals to in situ sensitively monitor temperature variation (1.4% K^-1). Moreover, a purpose-built upconversion hyperspectral microscope was utilized to synchronously map temperature changes on T cell membrane and visualize intracellular Ca²⁺ influx. This strategy was able to identify a suitable temperature status for facilitating thermally stimulated calcium influx in T cells, thus enabling high-efficiency activation of immune cells. Such findings might advance understandings on thermally dependent biological processes and their regulation methodology.

Challenges for optical nanothermometry in biological environments

Temperature monitoring is useful in medical diagnosis, and essential during hyperthermia treatments to avoid undesired cytotoxic effects. Aiming to control heating doses, different temperature monitoring strategies have been developed, largely based on luminescent materials, a.k.a. nanothermometers. However, for such nanothermometers to work, both excitation and emission light beams must travel through tissue, making its optical properties a relevant aspect to be considered during the measurements. In complex tissues, heterogeneity, and real-time alterations as a result of therapeutic treatment may have an effect on light-tissue interaction, hindering accuracy in the thermal reading. In this Tutorial Review we discuss various methods in which nanothermometers can be used for temperature sensing within heterogeneous environments. We discuss recent developments in optical (nano)thermometry, focusing on the incorporation of luminescent nanoparticles into complex in vitro and in vivo models. Methods formulated to avoid thermal misreading are also discussed, considering their respective advantages and drawbacks.

Er-Based Luminescent Nanothermometer to Explore the Real-Time Temperature of Cells under External Stimuli

Temperature as a typical parameter, which influences the status of living creatures, is essential to life activities and indicates the initial cellular activities. In recent years, the rapid development of nanotechnology provides a new tool for studying temperature variation at the micro- or nano-scales. In this study, an important phenomenon is observed at the cell level using luminescent probes to explore intracellular temperature changes, based on Yb-Er doping nanoparticles with special upconversion readout mode and intensity ratio signals (I₅₂₅ and I₅₄₅ ). Further optimization of this four-layer core-shell ratio nanothermometer endows it with remarkable characteristics: super photostability, sensitivity, and protection owing to the shell. Thus this kind of thermal probe has the property of anti-interference to the complex chemical environment, responding exclusively to temperature, when it is used in liquid and cells to reflect external temperature changes at the nanoscale. The intracellular temperature of living RAW and CAOV3 cells are observed to have a resistance mechanism to external stimuli and approach a more favorable temperature, especially for CAOV3 cells with good heat resistance, with the intracellular temperature 4.8 °C higher than incubated medium under 5 °C environment, and 4.4 °C lower than the medium under 60 °C environment.

Lanthanide-Doped Upconversion Luminescent Nanoparticles-Evolving Role in Bioimaging, Biosensing, and Drug Delivery

Upconverting luminescent nanoparticles (UCNPs) are "new generation fluorophores" with an evolving landscape of applications in diverse industries, especially life sciences and healthcare. The anti-Stokes emission accompanied by long luminescence lifetimes, multiple absorptions, emission bands, and good photostability, enables background-free and multiplexed detection in deep tissues for enhanced imaging contrast. Their properties such as high color purity, high resistance to photobleaching, less photodamage to biological samples, attractive physical and chemical stability, and low toxicity are affected by the chemical composition; nanoparticle crystal structure, size, shape and the route; reagents; and procedure used in their synthesis. A wide range of hosts and lanthanide ion (Ln3+) types have been used to control the luminescent properties of nanosystems. By modification of these properties, the performance of UCNPs can be designed for anticipated end-use applications such as photodynamic therapy (PDT), high-resolution displays, bioimaging, biosensors, and drug delivery. The application landscape of inorganic nanomaterials in biological environments can be expanded by bridging the gap between nanoparticles and biomolecules via surface modifications and appropriate functionalization. This review highlights the synthesis, surface modification, and biomedical applications of UCNPs, such as bioimaging and drug delivery, and presents the scope and future perspective on Ln-doped UCNPs in biomedical applications.

Lanthanide-MOFs as Multifunctional luminescence Sensors

Five isostructural lanthanide metal-organic frameworks, [Ln(BDPO)(H2O)4] (Ln= Eu for CUST-623, Tb for CUST-624, Gd for CUST-625, Dy for CUST-626, Sm for CUST-627, BDPO = N, N' bis (3,5 - dicarboxyphenyl)-oxalamide)...

A Comprehensive Review of Synthesis, Applications and Future Prospects for Silica Nanoparticles (SNPs)

Silica nanoparticles (SNPs) have shown great applicability potential in a number of fields like chemical, biomedical, biotechnology, agriculture, environmental remediation and even wastewater purification. With remarkably instinctive properties like mesoporous structure, high surface area, tunable pore size/diameter, biocompatibility, modifiability and polymeric hybridizability, the SNPs are growing in their applicable potential even further. These particles are shown to be non-toxic in nature, hence safe to be used in biomedical research. Moreover, the molecular mobilizability onto the internal and external surface of the particles makes them excellent carriers for biotic and non-biotic compounds. In this respect, the present study comprehensively reviews the most important and recent applications of SNPs in a number of fields along with synthetic approaches. Moreover, despite versatile contributions, the applicable potential of SNPs is still a tip of the iceberg waiting to be exploited more, hence, the last section of the review presents the future prospects containing only few of the many gaps/research extensions regarding SNPs that need to be addressed in future work.

All near-infrared multiparametric luminescence thermometry using Er3+, Yb3+-doped YAG nanoparticles

This paper presents four new temperature readout approaches to luminescence nanothermometry in spectral regions of biological transparency demonstrated on Yb³⁺/Er³⁺-doped yttrium aluminum garnet nanoparticles. Under the 10 638 cm⁻¹ excitation, down-shifting near infrared emissions (>10 000 cm⁻¹) are identified as those originating from Yb³⁺ ions' ²F_5/2 → ²F_7/2 (∼9709 cm⁻¹) and Er³⁺ ions' ⁴I_13/2 → ⁴I_15/2 (∼6494 cm⁻¹) electronic transitions and used for 4 conceptually different luminescence thermometry approaches. Observed variations in luminescence parameters with temperature offered an exceptional base for studying multiparametric temperature readouts. These include the temperature-dependence of: (i) intensity ratio between emissions from Stark components of Er^{3+ 4}I_13/2 level; (ii) intensity ratio between emissions of Yb³⁺ (²F_5/2 → ²F_7/2 transition) and Er³⁺ (⁴I_13/2 → ⁴I_15/2 transition); (iii) band shift and bandwidth and (iv) lifetime of the Yb³⁺ emission (²F_5/2 → ²F_7/2 transition) with maximal sensitivities of 1% K⁻¹, 0.8% K⁻¹, 0.09 cm⁻¹ K⁻¹, 0.46% K⁻¹ and 0.86% K⁻¹, respectively. The multimodal temperature readout provided by this material enables its application in different luminescence thermometry setups as well as improved the reliability of the temperature sensing by the cross-validation between measurements.

Four completely new NIR luminescence temperature readouts in the second and third biological windows are demonstrated with YAG:Er³⁺, Yb³⁺ nanoparticles.