OH− ions-controlled synthesis and upconversion luminescence properties of NaYF4:Yb3+,Er3+ nanocrystals via oleic acid-assisted hydrothermal process

A versatile upconversion-based multimode lateral flow platform for rapid and ultrasensitive detection of microRNA towards health monitoring

MicroRNAs are small single-stranded RNA molecules associated with gene expression and immune response, suggesting their potential as biomarkers for health monitoring. Herein, we designed a novel upconversion-based multimode lateral flow assay (LFA) system to detect microRNAs in body fluids by simultaneously producing three unique signals within a detection strip. The core-shell Au-DTNB@Ag nanoparticles act as both the Raman reporters and acceptors, quenching fluorescence from upconversion nanoparticles (UCNPs, NaYF4: Yb3+, Er3+) via the Förster resonance energy transfer mechanism. Using microRNA-21 as a representative analyte, the LFA system offers remarkable detection range from 2 nM to 1 fM, comparable to outcomes from signal amplification methods, due to the successful single-layer self-assembly of UCNPs on the NC membrane, which greatly enhances both the convenience and sensitivity of the LFA technique. Additionally, our proprietary fluorescence-Raman detection platform simplifies result acquisition by reducing procedural intricacies. The biosensor, when evaluated with diverse bodily fluids, showed remarkable selectivity and sustained stability. Importantly, our LFA biosensor effectively identified periodontitis and lung cancer patients from healthy subjects in genuine samples, indicating significant potential for disease prediction, early diagnosis, and progression tracking. This system holds promise as a multifunctional tool for various biomarker assays.

Assessing the reproducibility and up-scaling of the synthesis of Er,Yb-doped NaYF4-based upconverting nanoparticles and control of size, morphology, and optical properties

Lanthanide-based, spectrally shifting, and multi-color luminescent upconverting nanoparticles (UCNPs) have received much attention in the last decades because of their applicability as reporter for bioimaging, super-resolution microscopy, and sensing as well as barcoding and anti-counterfeiting tags. A prerequisite for the broad application of UCNPs in areas such as sensing and encoding are simple, robust, and easily upscalable synthesis protocols that yield large quantities of UCNPs with sizes of 20 nm or more with precisely controlled and tunable physicochemical properties from low-cost reagents with a high reproducibility. In this context, we studied the reproducibility, robustness, and upscalability of the synthesis of β-NaYF₄:Yb, Er UCNPs via thermal decomposition. Reaction parameters included solvent, precursor chemical compositions, ratio, and concentration. The resulting UCNPs were then examined regarding their application-relevant physicochemical properties such as size, size distribution, morphology, crystal phase, chemical composition, and photoluminescence. Based on these screening studies, we propose a small volume and high-concentration synthesis approach that can provide UCNPs with different, yet controlled size, an excellent phase purity and tunable morphology in batch sizes of up to at least 5 g which are well suited for the fabrication of sensors, printable barcodes or authentication and recycling tags.

A Comprehensive Review on Upconversion Nanomaterials-Based Fluorescent Sensor for Environment, Biology, Food and Medicine Applications

Near-infrared-excited upconversion nanoparticles (UCNPs) have multicolor emissions, a low auto-fluorescence background, a high chemical stability, and a long fluorescence lifetime. The fluorescent probes based on UCNPs have achieved great success in the analysis of different samples. Here, we presented the research results of UCNPs probes utilized in analytical applications including environment, biology, food and medicine in the last five years; we also introduced the design and construction of upconversion optical sensing platforms. Future trends and challenges of the UCNPs used in the analytical field have also been discussed with particular emphasis.

Lanthanide-Ion-Doping Effect on the Morphology and the Structure of NaYF4:Ln3+ Nanoparticles

Two series of β-NaYF₄:Ln³⁺ nanoparticles (Ln = La-Nd, Sm-Lu) containing 20 at. % and 40 at. % of Ln³⁺ with well-defined morphology and size were synthesized via a facile citric-acid-assisted hydrothermal method using rare-earth chlorides as the precursors. The materials were composed from the particles that have a shape of uniform hexagonal prisms with an approximate size of 80-1100 nm. The mean diameter of NaYF₄:Ln³⁺ crystals non-monotonically depended on the lanthanide atomic number and the minimum size was observed for Gd³⁺-doped materials. At the same time, the unit cell parameters decreased from La to Lu according to XRD data analysis. The diameter-to-length ratio increased from La to Lu in both studied series. The effect of the doping lanthanide(III) ion nature on particle size and shape was explained in terms of crystal growth dynamics. This study reports the correlation between the nanoparticle morphologies and the type and content of doping lanthanide ions. The obtained results shed light on the understanding of intrinsic factors' effect on structural features of the nanocrystalline materials.

Polymer-Functionalized Upconversion Nanoparticles for Light/Imaging-Guided Drug Delivery

The strong upconversion luminescence (UCL) of upconversion nanoparticles (UCNPs) endows the nanoparticles with attractive features for combined imaging and drug delivery. UCNPs convert near-infrared (NIR) light into light of shorter wavelengths such as light in the ultraviolet (UV) and visible regions, which can be used for light-guided drug delivery. Although light-responsive drug delivery systems as such have been known for many years, their application in medicine is limited, as strong UV-light can be damaging to tissue; moreover, UV light will not penetrate deeply into the skin, an issue that UCNPs can now address. However, UCNPs, as obtained after synthesis, are usually hydrophobic and require further surface functionalization to be stable in plasma. Polymers can serve as versatile surface coatings, as they can provide good colloidal stability, prevent the formation of a protein corona, provide a matrix for drugs, and be stimuli-responsive. In this Review, we provide a brief overview of the most recent progress in the synthesis of UCNPs with different shapes/sizes. We will then discuss the purpose of polymer coating for drug delivery before summarizing the strategies to coat UCNPs with various polymers. We will introduce the different polymers that have so far been used to coat UCNPs with the purpose to create a drug delivery system, focusing in detail on light-responsive polymers. To expand the application of UCNPs to allow photothermal therapy or magnetic resonance imaging (MRI) or to simply enhance the loading capacity of drugs, UCNPs were often combined with other materials to generate multifunctional nanoparticles such as carbon-based NPs and nanoMOFs. We then conclude with a discussion on drug loading and release and summarize the current knowledge on the toxicity of these polymer-coated UCNPs.

Influence of the Sodium Precursor on the Cubic-to-Hexagonal Phase Transformation and Controlled Preparation of Uniform NaNdF4 Nanoparticles

NaLnF₄ nanoparticles (NPs) with lighter lanthanides (where Ln = La, Ce, Nd, or Pr) are more difficult to prepare than those with heavier lanthanides [Naduviledathu et al. Chem Mater., 2014, 26, 5689]. Our knowledge is weakest for NaLnF₄ NPs with the lowest atomic mass lanthanides (Yan's group 1: La to Nd) and more advanced for group 2 (Sm to Tb) NaLnF₄ NPs [Mai et al., J. Am. Chem. Soc., 2006, 128, 6426]. Here we focus on the synthesis of NaNdF₄ NPs. We employed the high-temperature chemical coprecipitation method and explored the influence of a wide range of synthesis parameters (e.g., reaction time and temperature, precursor ratios (Na⁺/Nd³⁺ and F^-/Nd³⁺), choice of a sodium precursor (Na-oleate or NaOH), and the amount of oleic acid) on the size and uniformity of the NPs obtained. We tried to identify "sweet spots" in the reaction space that led to uniform NaNdF₄ NPs with sizes appropriate for mass tag applications in mass cytometry. We were able to obtain NPs with a variety of sizes in the range of 5-38 nm with several different shapes (e.g., polyhedra, spheres, and rods). XRD patterns recorded for aliquots collected at different reaction time intervals revealed that NaNdF₄ nucleated in the cubic phase (α) and then transformed to the hexagonal phase (β) as the reaction progressed up to 2 h. A very striking observation was that the NPs synthesized using NaOH as a reactant preferred to remain in the α-phase, and for a lower reaction temperature (285 °C), did not undergo a phase transformation to the β-phase over 2 h of reaction time. Under similar experimental conditions, NPs prepared using Na-oleate exhibited an α → β phase transformation. Nevertheless, NaNdF₄ NPs prepared at a higher temperature (315 °C) using either of the Na⁺ precursors exhibited the α → β phase transformation over time. This transition, however, appeared to be faster in the case of the NPs synthesized using Na-oleate. We found that, in many instances, syntheses carried out using Na-oleate produced more uniform NPs compared to those synthesized using NaOH. Under the conditions we employed for the Na-oleate precursor, the NPs initially formed were polydisperse spheres that evolved into irregular polyhedra and eventually formed more uniform rod-shaped NPs. The aspect ratio of the final NPs depended on the Na⁺/Nd³⁺ precursor ratio. High-resolution transmission electron micrographs and corresponding fast Fourier transform of the data provided information about the preferred growth direction of the NaNdF₄ nanorods.

Recent Progress of Rare-Earth Doped Upconversion Nanoparticles: Synthesis, Optimization, and Applications

Upconversion is a nonlinear optical phenomenon that involves the emission of high-energy photons by sequential absorption of two or more low-energy excitation photons. Due to their excellent physiochemical properties such as deep penetration depth, little damage to samples, and high chemical stability, upconversion nanoparticles (UCNPs) are extensively applied in bioimaging, biosensing, theranostic, and photochemical reactions. Here, recent achievements in the synthesis, optimization, and applications of UCNP-based nanomaterials are reviewed. The state-of-the-art approaches to synthesize UCNPs in the past few years are introduced first, followed by a summary of several strategies to optimize upconversion emissive properties and various applications of UCNPs. Lastly, the challenges and future perspectives of UCNPs are provided as a conclusion.