Engineering water-tolerant core/shell upconversion nanoparticles for optical temperature sensing

Preparation and Characterization of Uniform and Controlled Silica Encapsulating on Lithium Yttrium Fluoride-Based Upconversion Nanoparticles

In this work, we present an advancement in the encapsulation of lithium yttrium fluoride-based (YLiF4:Yb,Er) upconversion nanocrystals (UCNPs) with silica (SiO2) shells through a reverse microemulsion technique, achieving UCNPs@SiO2 core/shell structures. Key parameters of this approach were optimized to eliminate the occurrence of core-free silica particles and ensure a controlled silica shell thickness growth on the UCNPs. The optimal conditions for this method were using 6 mg of UCNPs, 1.5 mL of Igepal CO-520, 0.25 mL of ammonia, and 50 μL of tetraethyl orthosilicate (TEOS), resulting in a uniform silica shell around UCNPs with a thickness of 8 nm. The optical characteristics of the silica-encased UCNPs were examined, confirming the retention of their intrinsic upconversion luminescence (UC). Furthermore, we developed a reliable strategy to avoid the coencapsulation of multiple UCNPs within a single silica shell. This approach led to a tenfold increase in the UC luminescence of the annealed particles compared to their nonannealed counterparts, under identical silica shell thickness and excitation conditions. This significant improvement addresses a critical challenge and amplifies the applicability of the resulting UCNPs@SiO2 core/shell structures in various fields.

Efficient Lithium-Based Upconversion Nanoparticles for Single-Particle Imaging and Temperature Sensing

Upconversion Nanoparticles (UCNPs) have attracted exceptional attention due to their great potential in high-contrast, free-background biofluorescence deep tissue imaging and quantum sensing. Most of these interesting studies have been performed using an ensemble of UCNPs as fluorescent probes in bioapplications. Here, we report a synthesis of small and efficient YLiF₄:Yb,Er UCNPs for single-particle imaging as well as sensitive optical temperature sensing. The reported particles demonstrated a bright and photostable upconversion emission at a single particle level under a low laser intensity excitation of 20 W/cm². Furthermore, the synthesized UCNPs were tested and compared to the commonly used two-photon excitation QDs and organic dyes and showed a nine times better performance at a single particle level under the same experimental conditions. In addition, the synthesized UCNPs demonstrated sensitive optical temperature sensing at a single particle level within the biological temperature range. The good optical properties of single YLiF₄:Yb,Er UCNPs open an avenue for small and efficient fluorescent markers in imaging and sensing applications.

A dual-ratiometric optical thermometry based on Sr2LaF7:Er3+ crystal-implanted pliable fibers

Sr2(La1-xErx)F7/polyacrylonitrile composite fibers with special pliability and excellent crystal dispersibility have been fabricated, which provide the smaller size and appropriate temperature sensitivity. Up-conversion emission shows quadratic dependence of the photoluminescence...

Photostable and Small YVO4:Yb,Er Upconversion Nanoparticles in Water

In this work, we report a simple method of silica coating of upconversion nanoparticles (UCNPs) to obtain well-crystalline particles that remain small and not agglomerated after high-temperature post-annealing, and produce bright visible emission when pumped with near-infrared light. This enables many interesting biological applications, including high-contrast and deep tissue imaging, quantum sensing and super-resolution microscopy. These VO₄-based UNCPs are an attractive alternative to fluoride-based crystals for water-based biosensing applications.

In vivo single-cell lineage tracing in zebrafish using high-resolution infrared laser-mediated gene induction microscopy

Heterogeneity broadly exists in various cell types both during development and at homeostasis. Investigating heterogeneity is crucial for comprehensively understanding the complexity of ontogeny, dynamics, and function of specific cell types. Traditional bulk-labeling techniques are incompetent to dissect heterogeneity within cell population, while the new single-cell lineage tracing methodologies invented in the last decade can hardly achieve high-fidelity single-cell labeling and long-term in-vivo observation simultaneously. In this work, we developed a high-precision infrared laser-evoked gene operator heat-shock system, which uses laser-induced CreERT2 combined with loxP-DsRedx-loxP-GFP reporter to achieve precise single-cell labeling and tracing. In vivo study indicated that this system can precisely label single cell in brain, muscle and hematopoietic system in zebrafish embryo. Using this system, we traced the hematopoietic potential of hemogenic endothelium (HE) in the posterior blood island (PBI) of zebrafish embryo and found that HEs in the PBI are heterogeneous, which contains at least myeloid unipotent and myeloid-lymphoid bipotent subtypes.

Improved Red Emission and Short-Wavelength Infrared Luminescence under 808 nm Laser for Tumor Theranostics

In this research, a multimodal imaging platform guided photodynamic theranostics under 808 nm was designed using a NaErF₄:Tm@NaYF₄:Yb@NaLuF₄:Nd,Yb-ZnPc structure. Unlike conventional codoped Yb³⁺/Er³⁺ system, Er³⁺ ions as activator and sensitizer were used to improve the up-conversion energy transfer processes. Furthermore, higher energy transfer processes between Er³⁺ ions could be obtained through doped 1% Tm³⁺ ions as an energy trapping center in the NaErF₄. This platform could emit much brighter upconversion luminescence (UCL) (124-fold enhancement for red emission) and short wavelength infrared (SWIR) emission under single 808 nm laser excitation. Importantly, the SWIR imaging with higher resolution and better signal-to-noise ratio can pass the blood-brain barrier to see the brain vessels. Because of the enhanced red emission, the UCL nanoparticles were combined with ZnPc agent to exhibit photodynamic therapy (PDT) effect, and its distribution and excretion could be detected by the photoacoustic (PA) imaging under single near-infrared (NIR) laser. Thus, this platform could be used as multimodal imaging (SWIR, PA, CT, and UCL) guided PDT agent under single 808 nm laser.

Anti-Stokes excitation of solid-state quantum emitters for nanoscale thermometry

Color centers in solids are the fundamental constituents of a plethora of applications such as lasers, light-emitting diodes, and sensors, as well as the foundation of advanced quantum information and communication technologies. Their photoluminescence properties are usually studied under Stokes excitation, in which the emitted photons are at a lower energy than the excitation ones. In this work, we explore the opposite anti-Stokes process, where excitation is performed with lower-energy photons. We report that the process is sufficiently efficient to excite even a single quantum system-namely, the germanium-vacancy center in diamond. Consequently, we leverage the temperature-dependent, phonon-assisted mechanism to realize an all-optical nanoscale thermometry scheme that outperforms any homologous optical method used to date. Our results frame a promising approach for exploring fundamental light-matter interactions in isolated quantum systems and harness it toward the realization of practical nanoscale thermometry and sensing.

Time-resolved universal temperature measurements using NaYF4:Er3+,Yb3+ upconverting nanoparticles in an electrospray jet

Hexagonal upconverting nanoparticles (UCNPs) of NaYF₄:Er³⁺,Yb³⁺ (ca. 300 nm) have been widely used to measure the temperature at the nanoscale using luminescence ratio thermometry. However, several factors limit their applications. For example, changes in the peak shape, mainly is the S-band emission, hinders their ability to be used as a universal temperature sensor. Herein, we introduce a universal calibration protocol for NaYF₄:Er³⁺,Yb³⁺ upconverting nanoparticles that is robust to environmental changes and gives a precise temperature measurement. We used this new procedure to calculate the temperature profile inside a Taylor cone generated with an electrospray jet. Inside the Taylor cone the fluid velocity increases toward the tip of the cone. A constant acquisition length leads to a decrease in excitation and acquisition time. This decrease in excitation time causes a peak shape change that corrupts the temperature measurement if the entire peak shape is integrated in the calibration. Our universal calibration circumvents this problem and can be used for time-resolved applications. The temperature at the end of the Taylor cone increases due to the creation of a whispering gallery mode cavity with 980 nm excitation. We use time-resolved energy balance equations to support our optical temperature measurements inside the Taylor cone. We believe that the findings of this paper provide a foundation for time-resolved temperature measurements using NaYF₄:Er³⁺,Yb³⁺ upconverting nanoparticles and can be used to understand temperature-dependent reactions such as protein unfolding inside microjet/microdroplets and microfluidic systems.

Nanometer-scale luminescent thermometry in bovine embryos

Luminescent nanothermometry is a powerful tool that can precisely monitor temperature changes in animal embryos. Among the most sensitive nanoluminescent temperature sensors are fluorescent nanodiamonds (FNDs), having nitrogen-vacancy color centers, and lanthanide-ion-doped upconversion nanoparticles (UCNPs). Here, we investigate their use as nanothermometers inside bovine embryos. The motivation for using both FNDs and UCNPs to measure temperature is to avoid the question of sensor confusion by the local cellular environment. Specifically, by simultaneously measuring temperature using two different modalities having different physics, it is possible to greatly improve the measurement confidence, thereby directly addressing the recent controversy surrounding temperature measurements in living organisms.

Advanced sensing, imaging, and therapy nanoplatforms based on Nd3+-doped nanoparticle composites exhibiting upconversion induced by 808 nm near-infrared light

Malignant tumors are currently the leading cause of death worldwide, followed by cardiovascular and cerebrovascular diseases. Although various methods, such as blood examination, tissue biopsy, and radiography, for tumor detection, exist, these techniques still require further refinement. Researchers have recently explored the use of novel adjuvant methods, specifically luminescence imaging detection, for the detection of tumors. The light-triggered approach is less invasive and induces fewer side effects than traditional detection methods. This paper highlights recent advances in the design, property tuning, and applications of nanoparticles that exhibit upconversion under 808 nm excitation. When doped with neodymium ions, upconverted nanoparticles gain the ability to absorb 808 nm light. The advantageous unique features of 808 nm light include deep tissue penetration and limited thermal side effects. The 808 nm-excited upconverted nanoparticles exhibit superior potential for use in biosensing, bioimaging, therapy, and three-dimensional display. Thus, innovative theranostic nanoplatforms can be developed by incorporating 808 nm-excited upconverted nanoparticles with phototherapy agents. Such a composite technique is expected to possess the individual advantages of each material.