Accurate sensing of intracellular temperature is crucial for understanding and monitoring cell metabolism, serving as an initial step toward diagnosing conditions such as mitochondria-related diseases. However, thermal monitoring of cell metabolism is challenging due to the minimal temperature variations caused by intracellular metabolic activity (typically approximate to 1 degrees C) and by the risk of crosstalk in intracellular sensors. A novel type of intracellular thermal sensor is presented, based on silica nanocapsules filled with a thermo-responsive fluorescent medium. This medium undergoes a reversible phase transition from solid to liquid at temperatures approximate to 37 degrees C, inducing a chromatic switch that facilitates remote thermal sensing. The chromatic switchers exhibit a thermal sensitivity of approximate to 13% degrees C--(1) at 37 degrees C, one of the highest reported for intracellular thermal sensing. Notably, the thermal response is unaffected by external factors such as pH, ionic strength, and viscosity. Moreover, it is confirmed that the response of the sensors is not affected by the cellular activity, underscoring their reliability for cytoplasmic temperature measurements. The potential of these sensors is demonstrated by measuring intracellular heating during the metabolic switch from mitochondrial to glycolytic activity, showcasing their potential for real-time, precise thermal monitoring (<1 degrees C) of cell metabolism.

Nanotechnology has revolutionized biomedical applications through the development of nanomaterials with tailored properties, particularly in disease diagnosis and treatment. However, challenges remain regarding the pharmacokinetics of nanomaterials, which influence their biodistribution, targeting efficiency, clearance, and potential toxicity. Near-infrared (NIR) imaging has emerged as a promising tool to study the in vivo behavior of nanomaterials, offering noninvasive, real-time analysis of drug delivery and nanocarrier distribution. Despite its potential, the lack of robust analytical models for precise biodistribution and excretion measurements limits its clinical translation. This study investigates the biodistribution and pharmacokinetics of fluorescent Ag2S nanoparticles (NPs) with varying surface charges and capping agent size. These NPs, emitting light at ∼1200 nm in the NIR-II biological window, allow real-time tracking of their distribution. We explored the effects of polyethylene glycol functionalization with different molecular weights on NP behavior. A novel analytical model was developed to assess pharmacokinetic parameters and the influence of surface chemistry on protein-NP interactions. In vitro experiments confirmed that protein binding alters the surface charge and colloidal properties of NPs, which impacts their pharmacokinetics. This work advances our understanding of how nanoparticle surface modifications affect their in vivo performance and interactions with biological systems.

Melanoma is a highly aggressive skin cancer that often develops resistance to chemotherapy, underscoring the need for new treatment strategies. Here we evaluate plasmonic gold nanocapsules (AuNCs) as photoresponsive agents for two-photon luminescence-assisted photothermal therapy in chemoresistant melanoma models. The performance of the AuNCs was assessed in two-dimensional cell cultures, three-dimensional paclitaxel-resistant B16-F10 melanoma spheroids, and a subcutaneous melanoma mouse model under near-infrared excitation. In vitro, AuNCs alone exhibited no cytotoxicity, but under 830 nm two-photon excitation, they produced strong two-photon luminescence and thermal effects that increased with nanocapsule concentration and laser power. This led to transient oxidative stress, apoptosis induction, and effective melanoma cell ablation under optimal conditions (80 μg mL-1 AuNCs, 12 mW laser power). In vivo, the route of nanoparticle administration proved decisive. A single 4-min 806 nm irradiation after intratumoral injection uniformly heated the lesion (≈45-50 °C), yielded durable tumour eradication, and sequestered >99% of detected gold in the necrotic scab, with only trace renal clearance. In contrast, the same laser fluence after peritumoral injection generated a superficial hot rim, spared the tumour core, allowing eventual regrowth, and left ∼65% of the injected gold systemically redistributed, mainly in the spleen and liver. These findings highlight the potential of AuNCs as potent, image-guided photothermal agents for chemoresistant melanoma, offering targeted tumor destruction with limited systemic exposure. They reveal the injection route is a critical determinant of both therapeutic success and nanoparticle biodistribution.

Intracoronary stents have revolutionized the treatment of coronary obstructions, allowing for minimally invasive procedures and significantly enhancing both therapeutic efficacy and patient quality of life. Despite their clinical success, once implanted, stents act as passive elements, incapable of providing real-time data on the treated artery, thereby limiting early diagnosis of post-implantation complications such as inflammation, restenosis, or recurrence of atheromatous plaques. In this study, we introduce stents with deep tissue sensing capabilities through the incorporation of near-infrared emitting lanthanide-doped nanoparticles. Using 3D printed stent prototypes, we demonstrate that the luminescence emitted by neodymium and ytterbium ions in core/shell/shell NaYF₄ nanoparticles facilitates both deep tissue visualization and tracking of the stent position. Additionally, the temperature-dependent fluorescence lifetime of Nd,Yb:NaYF₄ nanoparticles provides thermal sensitivity, allowing precise deep tissue thermal monitoring of catheter-induced heating with sub-degree accuracy. This work highlights the potential of infrared-emitting nanoparticles to drive the next generation of coronary stents, paving the way for advanced light-based diagnostics and therapeutic procedures.

Gold nanoclusters emitting in the second biological window (NIR-II-AuNCs) have gained significant interest for their potential in deep-tissue bioimaging and biosensing applications due to the partial transparency and reduced autofluorescence of tissues in this spectral range. However, the limited understanding of how the biological environment affects their luminescent properties might hinder their use in bioimaging and biosensing. In this study, we investigated the emission properties of NIR-II-AuNCs when interacting and internalizing into live cells including macrophages, fibroblasts, and cancer cell lines, revealing substantial alterations in their luminescence. A systematic comparison between control and in vitro experiments concluded that the disruption of surface ligands is the main factor responsible for these alterations. NIR-II-AuNCs within cellular environments may also be influenced by other interactions, including aggregation or complexation with proteins. Furthermore, we also corroborated these spectroscopic modifications at the in vivo level, providing additional evidence of the environmental sensitivity of NIR-II-AuNCs. The results obtained in this study contribute to a deeper understanding of the luminescence mechanisms of NIR-II-AuNCs in biological environments in cells and in living tissues and are crucial for their optimization as reliable tools in biological environment for in vitro and in vivo imaging and diagnostics.

Fluorescence imaging using antibody-functionalized luminescent nanoparticles has shown promise for in vivo imaging of infarcted tissues; however, challenges such as suboptimal antibody orientation, increased hydrodynamic size, and reduced circulation times affect their targeting efficiency, hindering their clinical application. In this study, we propose to address these limitations by combining a pretargeting strategy with the overexpression of intercellular adhesion molecule 1 (ICAM-I) in infarcted myocardium, the sharp emission lines of infrared-emitting neodymium/ytterbium co-doped nanoparticles, and hyperspectral imaging technology. The feasibility of the method is demonstrated through ex vivo experiments and autofluorescence-free imaging of beating hearts, highlighting its potential as a high-contrast, non-invasive tool for myocardial infarction diagnosis.

Breast cancer remains a leading cause of mortality among women globally, underscoring the critical need for effective theranostic strategies. MicroRNA-21 (miR-21) imaging-guided photodynamic therapy (PDT) has attracted significant attention in recent years due to its selectivity and sensitivity toward breast cancer. However, key challenges remain, particularly regarding the low abundance of miR-21 caused by low-quality imaging at the tumor site and the low efficiency of PDT. To address these issues, we developed theranostic Ce6-DNAzyme@ZIF-8@PEG nanoparticles (CDZP NPs) for breast cancer, which integrates dual-cycling signal amplification for miR-21 detection and enhanced PDT through GPX4-DNAzyme-mediated gene editing to inhibit reactive oxygen species (ROS) scavenging. The CDZP NPs are based on a dodecahedral metal-organic framework (MOF) ZIF-8, encapsulating a dual-cycling miR-21 imaging system and Ce6-DNAzyme therapeutic system via one-pot synthesis. CDZP NPs exhibit excellent biocompatibility, acid-responsive release behavior, and a high loading capacity. These properties enable the control release of Zn2+, Ce6, and dual-cycling signal magnification system for miR-21 detection and enhanced PDT. In vivo studies with tumor-bearing mice demonstrated that intravenous injection of CDZP NPs could effectively target tumors. The dual-cycling signal amplification system, comprising three hairpin probes (H1, H2, and H3), achieved a detection limit for miR-21 as low as 3.4 pM. Moreover, Zn2+-activated GPX4-DNAzyme significantly inhibited GPX4 protein expression, reducing ROS scavenging and further enhancing PDT efficiency with a high tumor inhibition rate of 72.3%. This proposed theranostic strategy holds promise for advancing precision theranostics in breast cancer treatment.

Fluorescent probes operating within the near-infrared second window (NIR-II, 1000–1700 nm), characterized by high tissue transparency and minimal tissue-induced photon scattering/absorption, have been widely applied for early-stage disease diagnosis. However, the capability of NIR-II emitters for deep-tissue imaging is limited by relatively low brightness, which hinders the acquisition of images at low excitation intensity and administration dose. Herein, we introduce a novel in situ strategy to fabricate ultrabright Ag2S nanoparticles (Ag2S super NPs) via aftertreatment of chemically synthesized Ag2S NPs, where a protective shell grown by a 2-minutes rapid microwave irradiation. This shell effectively reduces the surface and structural defects, resulting in a 25-fold promotion of the quantum yield and 38-times increment of the fluorescence lifetime. The nontoxic PEGylated Ag2S super NPs enable in vivo deep-tissue imaging under low excitation laser (1 mW/cm2) and administration dose (0.5 mg/kg). Furthermore, after the modification with targeting peptide, Ag2S super NPs exhibit outstanding imaging performance by achieving an over 90

Optically bistable materials respond to a single input with two possible optical outputs, contingent on excitation history. Such materials would be ideal for optical switching and memory, but the limited understanding of intrinsic optical bistability (IOB) prevents the development of nanoscale IOB materials suitable for devices. Here we demonstrate IOB in Nd3+-doped KPb2Cl5 avalanching nanoparticles, which switch with high contrast between luminescent and non-luminescent states, with hysteresis characteristic of bistability. We elucidate a non-thermal mechanism in which IOB originates from suppressed non-radiative relaxation in Nd3+ ions and from the positive feedback of photon avalanching, resulting in extreme, >200th-order optical nonlinearities. The modulation of laser pulsing tunes the hysteresis widths, and dual-laser excitation enables transistor-like optical switching. This control over nanoscale IOB establishes avalanching nanoparticles for photonic devices in which light is used to manipulate light. Intrinsic optical bistability in Nd3+-doped KPb2Cl5 avalanching nanoparticles enables high-contrast switching between luminescent and non-luminescent states and transistor-like optical responses. A non-thermal mechanism is discussed and >200th-order optical nonlinearities are shown to be possible.

Multi-functional TLNs were fabricated for magnetically triggered hyperthermic release to enhance cytotoxicity against breast tumour cells.

Luminescence thermometry affords remote thermal readouts with high spatial resolution in a minimally invasive way. This technology has advanced our understanding of biological mechanisms and physical processes from the macro- to the submicrometric scale. Yet, current approaches only allow obtaining 2D thermal images. This aspect limits the potential of this technology, given the inherent three-dimensional nature of heat diffusion processes. Despite initial attempts, a credible method that allows extracting 3D thermal images via luminescence is missing. Here, we design such a method combining Ag2S nanothermometers and machine learning algorithms. The approach leverages the distortions in the emission spectra of luminescent nanothermometers caused by changes in temperature and tissue-induced photon extinction. The optimized neural network-based algorithm can extract this information and provide 3D thermal images of complex nanothermometer patterns. Although tested for luminescence thermometry at the in vivo level, this method has far-reaching implications for luminescence-supported 3D sensing in biological systems in general.

Bright near-infrared-emitting Ag2S nanocrystals (NCs) are used for in vivo temperature sensing relying on a reversible variation in intensity and photoluminescence lifetime within the physiological temperature range. Here, to gain insights into the luminescence and quenching mechanisms, we investigated the temperature-dependent luminescence of Ag2S NCs from 300 to 10 K. Interestingly, both emission and lifetime measurements reveal similar and strong thermal quenching from 200 to 300 K, indicating an intrinsic quenching process that limits the photoluminescence quantum yield at room temperature, even for perfectly passivated NCs. The low thermal quenching temperature, broadband emission, and multiexponential microsecond decay behavior suggest the optical transition involves strong lattice relaxation, which is consistent with the recombination of a Ag+-trapped hole with a delocalized conduction band electron. Our findings offer valuable insights for understanding the optical properties of Ag2S NCs and the thermal quenching mechanism underlying their temperature-sensing capabilities.

Fluorescence imaging in the second near-infrared (NIR-II) window enables deep-tissue imaging with high resolution and improved contrast by taking advantage of the reduced light scattering and tissue autofluorescence in this region of the spectrum. NIR-II fluorescence imaging uses photoluminescent contrast agents - including carbon nanotubes, quantum dots, rare earth-doped nanocrystals, gold nanoclusters, small molecules and their aggregates - and fluorescent proteins, which all exhibit fluorescence in the 1,000-3,000 nm range. After administration of these fluorophores in vivo, live animals can be imaged with specialized detectors and optical instruments, yielding images with contrast and resolution unparalleled by conventional visible and near-infrared fluorescence imaging. This powerful approach enables dynamic imaging of vascular structures and haemodynamics; molecular imaging and image-guided surgery of tumours; and visualization of deep-seated structures, such as the gastrointestinal system. NIR-II fluorescence imaging has revolutionized biomedical imaging over the past 15 years and is poised to make comparable advancements in cardiology, neurobiology and gastroenterology. This Primer describes the principles of NIR-II fluorescence imaging, reviews the most used fluorophores, outlines implementation approaches and discusses specific scientific and clinical applications. Furthermore, the limitations of NIR-II fluorescence imaging are addressed and future opportunities across various scientific domains are explored. Deep tissues can be imaged with high resolution and greater contrast by performing fluorescence imaging in the second near-infrared (NIR-II) window. This Primer summarizes how NIR-II fluorescence imaging can be used in animal models, exploring commonly used fluorophores and implementation approaches across a range of scientific and clinical applications.

The use of plasmonic nanoparticles in performing photothermal treatments in cancer cells requires a full knowledge about their optical properties. The surface plasmon resonance is easily foreseen and measurable in colloidal suspensions, however it can be strongly modified when located inside cells. Assessing the optical behavior of plasmonic nanoparticles in cells is essential for an efficient and controlled treatment. This requires the combination of experimental data and computational models to understand the mechanisms that cause the change in their optical response. In this work, we investigate the plasmonic response of Au nanospheres (AuNSs) internalized into cancer cells (MCF-7). Experimental data are compared to the simulations provided by a 3D model based on a finite element method. We demonstrate the impact of physical parameters such as the type of NS assembly, the surrounding medium and the interparticle gap, in the photothermal efficiency of AuNSs. Results open the avenue to predict, by numerical calculations, the optical properties of plasmonic nanoparticles inside cells to minimize treatment costs and times in photothermal therapies.

Upconverting nanoparticles are essential in modern photonics due to their ability to convert infrared light to visible light. Despite their significance, they exhibit limited brightness, a key drawback that can be addressed by combining them with plasmonic nanoparticles. Plasmon-enhanced upconversion has been widely demonstrated in dry environments, where upconverting nanoparticles are immobilized, but constitutes a challenge in liquid media where Brownian motion competes against immobilization. This study employs optical tweezers for the three-dimensional manipulation of an individual upconverting nanoparticle, enabling the exploration of plasmon-enhanced upconversion luminescence in water. Contrary to expectation, experiments reveal a long-range (micrometer scale) and moderate (20%) enhancement in upconversion luminescence due to the plasmonic resonances of gold nanostructures. Comparison between experiments and numerical simulations evidences the key role of Brownian motion. It is demonstrated how the three-dimensional Brownian fluctuations of the upconverting nanoparticle lead to an "average effect" that explains the magnitude and spatial extension of luminescence enhancement.

Upconverting particles (UCPs), renowned for their capability to convert infrared to visible light, serve as invaluable imaging probes. Furthermore, their responsiveness to diverse external stimuli holds promise for leveraging UCPs as remote multiparametric sensors, capable of characterizing medium properties in a single assessment. However, the utility of UCPs in multiparametric sensing is impeded by crosstalk, wherein distinct external stimuli induce identical alterations in UCP luminescence, hindering accurate interpretation, and yielding erroneous outputs. Overcoming crosstalk requires alternative strategies in upconverting luminescence analysis. In this study, it is shown how a single spinning NaYF4:Er3+, Yb3+ upconverting particle enables simultaneous and independent readings of temperature and viscosity. This is achieved by decoupling thermal and rehological measurements-employing the luminescence of thermally-coupled energy levels of Er3+ ions for thermal sensing, while leveraging the polarization of luminescence from non-thermally coupled levels of Er3+ ions to determine viscosity. Through simple proof-of-concept experiments, the study validates the capability of a single spinning UCP to perform unbiased, simultaneous temperature, and viscosity sensing, thereby opening new avenues for advanced sensing in microenvironments.

In this work, a hypoxia-sensitive nanoprobe is developed by coating the surface of upconverting core/shell nanoparticles (NaGdF4: 2%Yb3+, 3%Nd3+, 0.2%Tm3+/NaYF4) with a non-fluorescent azo-dye based on a boron-dipyrromethene functionalized azo compound. Azo-dyes are able to quench fluorescence emissions due to their N 00000000 00000000 00000000 00000000 11111111 00000000 11111111 00000000 00000000 00000000 N azo bond, which results in the absorption of most visible emissions of the nanoparticles. However, in a biological environment suffering hypoxia, the azo bond is reduced, which allows the recovery of the nanoparticles' upconversion emissions. Thereby a near-infrared excitable sensor with an azo-dye is created and for the first time not only enables excitation via NIR at biocompatible 808 nm but also continuous imaging and tracking of the probe in the infrared due to NIR-emissions enabled by the dopant combination since quenching only occurs in the visible. These multifunctional (imaging and sensing) nanoparticles are characterized, their behaviour in reductive and hypoxic environments is determined and the detection of reducing conditions in a hypoxic environment is demonstrated in cells.

Nanoparticles engineered to combat cancer and other life-threatening diseases may significantly improve patient outcomes. However, inefficient nanoparticle delivery to tumors limits their use and necessitates the development of complex delivery approaches. Here, we examine this issue by harnessing the tumor-homing abilities of human mesenchymal stem cells (MSCs) to deliver a decoupled theranostic complex of rare earth-doped nanoparticles (dNPs) and photosensitizer chlorin e6 (Ce6) to tumors. We show that both bone-marrow- and skin-derived MSCs can transport the dNP-Ce6 complex inside tumor spheroids, which is challenging to accomplish by passive delivery alone. MSCs deliver the dNP-Ce6 complex across the tumor spheroid, facilitating more effective photodynamic damage and tumor destruction than passively accumulated dNP-Ce6. The dNP-Ce6 complex also provides the built-in ability to monitor the MSC migration without causing undesired phototoxicity, which is essential for maximal and side-effect-free delivery of nanoparticles. Our results demonstrate how MSCs can be used as delivery vehicles for the transportation of the dNP-Ce6 complex, addressing the limitations of passive nanoparticle delivery and providing light-based theranostics.

There is a continuous vivid search for biocompatible hybrid magneto-optical nanoprobes with high heating and photoluminescence efficiencies for photothermal theranostics. Herein, two tailored multipurpose hybrid PEGylated gold (Au) and silver sulfide (Ag2S) magnetic iron oxide nanoparticle formulations (Au-PEG-MNPs and Ag2S-PEG-MNPs) with unique opto-magnetic properties for simultaneous photothermal therapy were prepared. The physiochemical properties of the hybrid MNPs were fully characterized using various electronic and spectroscopic techniques, showing colloidal stabilized small-sized nanoparticles (core sizes = 10 nm, D-H = 200 nm) with high saturation magnetizations (M-s up to 85 emu/g) and superparamagnetic behavior. Thermal effects in response to an alternating magnetic field (AMF) at different frequencies (f = 25-300 kHz) and field intensities (H = 12 and 24 kA/m) were assessed using an ultrafast magnetometric method, revealing high heating efficiencies with distinctive heating responses. The "optothermal" efficacies were then evaluated using a unique experimental setup equipped with a highly sensitive thermal camera for recording temperatures in real time, along with a simultaneous clinically safe near-infrared (NIR) laser (lambda = 808 nm and power = 0.5 W cm(-2)) and AMF (H = 12 kA/m, f = 180 kHz) dual effect. Remarkably, when irradiated with an NIR laser and AMF, both hybrid Au- and Ag2S-PEG-MNPs displayed superior heat induction power (SAR = 384 and 441 W/g), rapidly reaching hyperthermia temperatures of 42 degrees C in only a few seconds. Temperatures could reach up to 75 degrees C for Au-PEG-MNPs and 90 degrees C for Ag2S-PEG-MNPs in only 5 min. Such superior heating efficiencies for the hybrid MNPs increased similar to 1.5-2 times under concurrent irradiation compared to the action by laser alone. Finally, cytotoxicity assays against cancerous and normal cells confirmed the safety profiles and low toxicities of the hybrid nanoformulations. This unique synergistic platform has great potential to be utilized for multimodal photothermal therapy with reduced field strengths, laser intensities, and short irradiation times in the unceasing search for tangible hyperthermal clinical nanoprobes.

This study aimed to develop multifunctional nanoplatforms for both cancer imaging and therapy using superparamagnetic iron oxide nanoparticles (SPIONs). Two distinct synthetic methods, reduction–precipitation (MR/P) and co-precipitation at controlled pH (MpH), were explored, including the assessment of the coating’s influence, namely dextran and gold, on their magnetic properties. These SPIONs were further functionalized with gadolinium to act as dual T1/T2 contrast agents for magnetic resonance imaging (MRI). Parameters such as size, stability, morphology, and magnetic behavior were evaluated by a detailed characterization analysis. To assess their efficacy in imaging and therapy, relaxivity and hyperthermia experiments were performed, respectively. The results revealed that both synthetic methods lead to SPIONs with similar average size, 9 nm. Mössbauer spectroscopy indicated that samples obtained from MR/P consist of approximately 11–13% of Fe present in magnetite, while samples obtained from MpH have higher contents of 33–45%. Despite coating and functionalization, all samples exhibited superparamagnetic behavior at room temperature. Hyperthermia experiments showed increased SAR values with higher magnetic field intensity and frequency. Moreover, the relaxivity studies suggested potential dual T1/T2 contrast agent capabilities for the coated SPpH-Dx-Au-Gd sample, thus demonstrating its potential in cancer diagnosis.