Search Results (94)

Photoacoustic imaging (PAI) merges the high spatial resolution of optical methods with the deep tissue penetration provided by ultrasound, making it a valuable tool in biomedical imaging. In recent years, a diverse array of photoacoustic contrast agents, spanning both organic and inorganic materials, has been developed. Among them, upconversion nanoparticles (UCNPs) stand out as promising candidates due to their unique optical features, tunable absorption in the near-infrared I (NIR-I, 750–1350 nm) region, and strong potential for both imaging and treatment-related uses. This review discusses the growing significance of UCNPs in the field of PAI, focusing on their structural characteristics, strengths, and existing challenges. Then, we talk about an up-to-date account of the current literature on the use of UCNPs as contrast agents for PAI. Lastly, we discuss the challenges and perspectives of UCNPs as a contrast agent for PAI in preclinical research and clinical diagnosis. Full article

Near-infrared (NIR) photoelectric synaptic devices show great potential in studying NIR artificial visual systems integrating excellent optical characteristics and bionic synaptic plasticity. However, NIR synapses based on transition metal dichalcogenides (TMDCs) suffer from low stability and poor environmental performance. Thus, an environmentally friendly NIR synapse was fabricated based on lanthanide-doped upconversion nanoparticles (UCNPs) and two-dimensional (2D) WSe₂ via solution spin coating technology. Biological synaptic functions were simulated successfully through 975 nm laser regulation, including paired-pulse facilitation (PPF), spike rate-dependent plasticity, and spike timing-dependent plasticity. Handwritten digital images were also recognized by an artificial neural network based on device characteristics with a high accuracy of 97.24%. In addition, human and animal identification in foggy and low-visibility surroundings was proposed by the synaptic response of the device combined with an NIR laser and visible simulation. These findings might provide promising strategies for developing a 24/7 visual response of humanoid robots. Full article

Rare-earth nanoparticles (RE-NPs), particularly NaYF₄:Yb³⁺,Er³⁺, have emerged as a promising class of photoluminescent probes for bioimaging and sensing applications. These nanomaterials are characterized by their ability to absorb low-energy photons and emit higher-energy photons through an upconversion luminescence process. This process can be triggered by continuous-wave (CW) light excitation, providing a unique optical feature that is not exhibited by native biomolecules. However, the application of upconversion nanoparticles (UCNPs) in bioimaging requires systematic optimization to maximize the signal and ensure biological compatibility. In this work, we synthesized hexagonal-phase UCNPs (average diameter: 29 ± 3 nm) coated with polyacrylic acid (PAA) and established the optimal conditions for imaging human erythrocytes. The best results were obtained after a 4-h incubation in 100 mM HEPES buffer, using a nanoparticle concentration of 0.01 mg/mL and a laser current intensity of 250–300 mA. Under these conditions, the UCNPs exhibited minimal cytotoxicity and were found to predominantly localize at the erythrocyte membrane periphery, indicating surface adsorption rather than internalization. Additionally, a machine learning model (Random Forest) was implemented that classified the photoluminescent signal with 80% accuracy and 83% precision, with the signal intensity identified as the most relevant feature. This study establishes a quantitative and validated protocol that balances signal strength with cell integrity, enabling robust and automated image analysis. Full article

Rare earth-doped upconversion nanoparticles (UCNPs) can convert low-energy photons (NIRs) into high-energy photons (visible light), offering advantages such as low background signal, good stability, and excellent biocompatibility. However, exploring a strategy to combine the advantages of high efficiency, low cost, and easy fabrication of a plasmonics–UCNPs system is still a challenge. Here, we reported a metal–dielectric–metal (MDM)-type plasmonic platform based on the aluminum metasurface, which can efficiently enhance the luminescence intensity of magnetic and non-magnetic rare earth-doped UCNPs. Attributed to the strong local field effect of the nanocavities formed by the aluminum anti-transmission layer at the bottom, the fluorescence of the two types of UCNPs in such a platform can be enhanced by over 1000 folds compared with that in the conventional substrate. It is found that the deposited UCNPs amount and the aluminum pillar size can both impact the enhancement. We confirmed that the constructed MDM nanocavities could enhance and regulate the local field strength, and the optimum enhancement can be achieved by choosing proper parameters. All these findings provide an efficient way of exploring the plasmon-enhanced UCNPs luminescence system with low cost, high efficiency, and easy fabrication and can be promising in the fields of biosensing and photovoltaic devices. Full article

Rare-earth-doped upconversion nanoparticles (UCNPs) have been widely used in biological detection due to their unique anti-Stokes shift, stable chemical properties, tunable emission wavelengths, and low biotoxicity. However, their low fluorescence quantum yield remains a challenge. Constructing a high-performance detection platform based on UCNPs is therefore a critical consideration. Focusing on the biological detection applications of UCNPs, this paper introduces the fundamental principles of upconversion and the design of upconversion fluorescence probes. It then summarizes common strategies for enhancing upconversion luminescence and three biosensing platform formats: solution-based, strip-based, and plate-based. Finally, future directions for UCNPs in biological detection are discussed. Full article

This study presents an effective strategy to enhance the efficiency and stability of perovskite solar cells (PSCs) by integrating neodymium-doped upconversion nanoparticles (UCNPs) coated with a TiO₂ shell into the mesoporous electron transport layer. The incorporation of neodymium (Nd³⁺) as a novel sensitizer shifts the near-infrared (NIR) absorption band away from the water vapor absorption region in the solar spectrum. This modification enables UCNPs to efficiently convert NIR light into ultraviolet (UV) and blue wavelengths, which are readily absorbed by TiO₂, generating additional charge carriers and improving photovoltaic performance. The optimized PSCs, fabricated by blending 30% UCNPs@TiO₂ with commercial TiO₂ paste, achieved a peak power conversion efficiency (PCE) of 21.71%, representing a 20.4% improvement over the control (18.04%). This enhancement included a 0.9% increase in the open-circuit voltage (V_oc), a 6.6% rise in the short-circuit current density (J_sc), and an 11.9% boost in the fill factor (FF). Additionally, the optimized PSCs exhibited remarkable stability, retaining over 90% of their initial PCE after 900 h in humid conditions, compared to only 70% for the control. These improvements result from enhanced light absorption, reduced moisture infiltration, and lower defect-related recombination. This approach provides a promising pathway for developing highly efficient and durable PSCs. Full article

Thiol–epoxy photopolymerization offers exceptional advantages for high-performance protective coatings, yet efficiently curing thick formulations remains a significant challenge due to the limited penetration depth of conventional UV light. Herein, we report a novel near-infrared (NIR) light-activated photopolymerization system for deep-curing applications, strategically integrating upconversion nanoparticles (UCNPs) as NIR-to-UV converters, isopropylthioxanthone (ITX) as a photosensitizer, and a liquid N-phenylglycine-based photobase generator (NPG-TBD) with enhanced resin solubility. Upon 980 nm NIR irradiation, photogenerated TBD efficiently catalyzes thiol–epoxy polymerization through an anionic mechanism, enabling uniform network formation with epoxy and thiol functional group conversions greater than 90% throughout samples exceeding 2.5 cm in thickness. The resulting coatings exhibit excellent mechanical properties including 3H pencil hardness, strong adhesion (0 grade), and good flexibility (2 mm), significantly outperforming conventional UV systems limited to approximately 1.5 mm. Additionally, the cured materials demonstrate multifunctional characteristics including distinctive upconversion luminescence and dual-responsive shape memory behavior. This approach addresses critical limitations in deep-photocuring technology while offering significant potential for applications in protective coatings for marine infrastructure, chemical storage facilities, and smart materials requiring both substantial barrier properties and programmable responsiveness. Full article

Boosting the accuracy and speed of cancer detection is highly desirous in tumor detection, and sensors capable of detecting carcinoembryonic antigen (CEA) have great application prospects in this field. A highly sensitive sensor is constructed based on the fluorescence resonance energy transfer (FRET) with heavily rare-earth-doped upconversion nanoparticles (UCNPs) as energy donors and polydopamine nanoparticles (PDA NPs) as energy acceptors. This sensor detects the fluctuations in CEA molecules via luminescence quenching and recovery resulting from a competitive binding assay between CEA and PDA NPs. The high-level-doped design of UCNPs (i.e., NaYF₄@NaYbF₄:1%Tm@NaYF₄) is beneficial, providing upconversion luminescence intensity that is more than 10 times higher than that of the conventional low-level-doped UCNPs (i.e., NaYF₄@NaYF₄:20%Yb, 0.2%Tm@NaYF₄). The sensor exhibits impressive sensitivity. Specifically, in diluted fetal bovine serum, the detection limit reaches 0.013 ng/mL in the range of 0–1.5 ng/mL (S/N = 3), while the detection limit is 1.38 ng/mL in the range of 1.5–250 ng/mL (S/N = 3). This method has great potential for future applications in the rapid and early diagnosis and treatment of cancer. Full article

Pathogens and their metabolites in food present significant risks to both human health and economic development. Rising living standards and increasing awareness of food safety have driven the demand for sensitive and rapid detection methods. Lanthanide-doped upconversion nanoparticles (UCNPs), with their exceptional optical properties, have emerged as a promising platform for developing biosensors to detect pathogenic bacteria and their metabolites. The integration of UCNPs with point-of-care testing (POCT) has garnered considerable attention for its portability and immediacy, highlighting a promising future for biosensing, particularly in applications requiring quick and accurate diagnostics. This review explores the recognition elements and design principles commonly used in UCNP-based biosensors and examines various applications, including lateral flow assays, microfluidic systems, photoelectrochemical devices, and smartphone-integrated platforms. Despite significant advancements, challenges remain in the applicability and commercialization of UCNP-based biosensing technology. Future research should focus on enhancing sensitivity and specificity, developing scalable and cost-effective production methods, and integrating with advanced digital technologies to enable broader adoption. Addressing these challenges, establishing regulatory frameworks, and considering sustainability will be crucial to fully realizing the potential of UCNP-based biosensors. Full article

The widespread use of thiamethoxam has led to pesticide residues that have sparked global concerns regarding ecological and human health risks. A pressing requirement exists for a detection method that is both swift and sensitive. Herein, we introduced an innovative fluorescence biosensor constructed from alendronic acid (ADA)-modified upconversion nanoparticles (UCNPs) linked with magnetic nanoparticles (MNPs) via aptamer recognition for the detection of thiamethoxam. Through base pairing, thiamethoxam-specific aptamer-functionalized MNPs (apt-MNPs) were integrated with complementary DNA-functionalized UCNPs (cDNA-UCNPs) to create the MNPs@UCNPs fluorescence biosensor. Thiamethoxam specifically attached to apt-MNPs, leading to their separation from cDNA-UCNPs, which in turn led to a reduction in fluorescence intensity at 544 nm following separation by an external magnetic field. The change in fluorescence intensity (ΔI) was directly correlated with the concentration of thiamethoxam, enabling the quantitative analysis of the pesticide. With optimized detection parameters, the biosensor was capable of quantifying thiamethoxam within a concentration span of 0.4–102.4 ng·mL⁻¹, and it achieved a detection limit as minute as 0.08 ng·mL⁻¹. Moreover, leveraging the swift magnetic concentration properties of MNPs, the assay duration could be abbreviated to 25 min. The research exhibited a swift and precise sensing platform that yielded promising results in samples of cucumber, cabbage, and apple. Full article

The aim of this work is to incorporate lanthanide-cored upconversion nanoparticles (UCNP) into the surface of microengineered biomedical implants to create a spatially controlled and optically releasable model drug delivery device in an integrated fashion. Our approach enables silicone-based microelectrocorticography (ECoG) implants holding platinum/iridium recording sites to serve as a stable host of UCNPs. Nanoparticles excitable in the near-infrared (lower energy) regime and emitting visible (higher energy) light are utilized in a study. With the upconverted higher energy photons, we demonstrate the induction of photochemical (cleaving) reactions that enable the local release of specific dyes as a model system near the implant. The modified ECoG electrodes can be implanted in brain tissue to act as an uncaging system that releases small amounts of substance while simultaneously measuring the evoked neural response upon light activation. In this paper, several technological challenges like the surface modification of UCNPs, the immobilization of particles on the implantable platform, and measuring the stability of integrated UCNPs in in vitro and in vivo conditions are addressed in detail. Besides the chemical, mechanical, and optical characterization of the ready-to-use devices, the effect of nanoparticles on the original electrophysiological function is also evaluated. The results confirm that silicone-based brain–machine interfaces can be efficiently complemented with UCNPs to facilitate local model drug release. Full article

The performance optimization of photoluminescent (PL) materials is a hot topic in the field of applied materials research. There are many different crystal defects in photoluminescent materials, which can have a significant impact on their optical properties. The luminescent properties and chemical stability of materials can be effectively improved by adjusting lattice defects in crystals. We systematically studied the effect of doping ions on the energy transfer upconversion mechanism in different defect crystals by changing the matrix alkali metal ions. Meanwhile, the influence mechanism of crystal defect distribution on luminescence performance is explored by adjusting the ratio of Na–Li. The PL spectra indicate that changing the alkaline ions significantly affects the luminescence performance and efficiency of UCNPs. The change in ion radius leads to substitution or gap changes in the main lattice, which may alter the symmetry and strength of the crystal field around doped RE ions, thereby altering the UCL performance. Additionally, we demonstrated the imaging capabilities of the synthesized upconversion nanoparticles (UCNPs) in cellular environments using fluorescence microscopy. The results revealed that Na_0.9Li_0.1LuF₄–Yb, Er nanoparticles exhibited significantly enhanced fluorescence intensity in cell imaging compared to other compositions. We further investigated the mechanism by which structural defects formed by doping ions in UCNPs with different alkali metals affect energy transfer upconversion (ETU). This work emphasizes the importance of defect regulation in the ETU mechanism to improve the limitations of crystal structure on the luminescence performance and promote the future application of upconversion nanomaterials, which will provide important theoretical references for the exploration of high-performance luminescent materials in the future. Full article

Food safety is of great concern, and food-borne bacterial infections and diseases are a major crisis for health. Therefore, it is necessary to develop rapid detection techniques for the prevention and recognition of food safety hazards caused by food-borne pathogens. In recent years, the fluorescence assay has become a widely utilized detection method due to its good signal amplification effect, high detection sensitivity, high stability, and short detection time. In this review, the different kinds of fluorescence materials were concentrated, including quantum dots (QDs), carbon dots (CDs), metal–organic frameworks (MOFs), and upconversion nanoparticles (UCNPs). The optical properties and applications of different kinds of fluorescent materials were analyzed and compared. Furthermore, according to the biosensing components, different fluorescence biosensors are reviewed, including label-free based fluorescence probes, aptamer-based biosensors, and antibody-based biosensors. Finally, we focused our attention on the discussion of fluorescent detection techniques combined with other techniques and their applications. The review presents future trends in fluorescence sensors, providing new sights for the detection of food-borne pathogens. Full article

Upconversion nanoparticles (UCNPs) are well-reported for bioimaging. However, their applications are limited by low luminescence intensity. To enhance the intensity, often the UCNPs are coated with macromolecules or excited with high laser power, which is detrimental to their long-term biological applications. Herein, we report a novel approach to prepare co-doped CaF₂:Yb³⁺ (20%), Er³⁺ with varying concentrations of Er (2%, 2.5%, 3%, and 5%) at ambient temperature with minimal surfactant and high-pressure homogenization. Strong luminescence and effective red emission of the UCNPs were seen even at low power and without functionalization. X-ray diffraction (XRD) of UCNPs revealed the formation of highly crystalline, single-phase cubic fluorite-type nanostructures, and transmission electron microscopy (TEM) showed co-doped UCNPs are of $~$12 nm. The successful doping of Yb and Er was evident from TEM–energy dispersive X-ray analysis (TEM-EDAX) and X-ray photoelectron spectroscopy (XPS) studies. Photoluminescence studies of UCNPs revealed the effect of phonon coupling between host lattice (CaF₂), sensitizer (Yb³⁺), and activator (Er³⁺). They exhibited tunable upconversion luminescence (UCL) under irradiation of near-infrared (NIR) light (980 nm) at low laser powers (0.28–0.7 W). The UCL properties increased until 3% doping of Er³⁺ ions, after which quenching of UCL was observed with higher Er³⁺ ion concentration, probably due to non-radiative energy transfer and cross-relaxation between Yb³⁺-Er³⁺ and Er³⁺-Er³⁺ ions. The decay studies aligned with the above observation and showed the dependence of UCL on Er³⁺ concentration. Further, the UCNPs exhibited strong red emission under irradiation of 980 nm light and retained their red luminescence upon internalization into cancer cell lines, as evident from confocal microscopic imaging. The present study demonstrated an effective approach to designing UCNPs with tunable luminescence properties and their capability for cellular imaging under low laser power. Full article

Upconversion nanoparticles (UCNPs) and carbon quantum dots (CQDs) have emerged as promising candidates for enhancing both the stability and efficiency of perovskite solar cells (PSCs). Their rising prominence is attributed to their dual capabilities: they effectively passivate the surfaces of perovskite-sensitive materials while simultaneously serving as efficient spectrum converters for sunlight. In this work, we synthesized UCNPs doped with erbium ions as down/upconverting ions for ultraviolet (UV) and near-infrared (NIR) light harvesting. Various percentages of the synthesized UCNPs were integrated into the mesoporous layers of PSCs. The best photovoltaic performance was achieved by a PSC device with 30% UCNPs doped in the mesoporous layer, with PCE = 16.22% and a fill factor (FF) of 74%. In addition, the champion PSCs doped with 30% UCNPs were then passivated with carbon quantum dots at different spin coating speeds to improve their photovoltaic performance. When compared to the pristine PSCs, a fabricated PSC device with 30% UCNPs passivated with CQDs at a spin coating speed of 3000 rpm showed improved power conversion efficiency (PCE), from 16.65% to 18.15%; a higher photocurrent, from 20.44 mA/cm² to 22.25 mA/cm²; and a superior fill factor (FF) of 76%. Furthermore, the PSCs integrated with UCNPs and CQDs showed better stability than the pristine devices. These findings clear the way for the development of effective PSCs for use in renewable energy applications. Full article