Upconversion Luminescent Nanoparticles Research Articles

Miniaturized Biosensors Based on Lanthanide-Doped Upconversion Polymeric Nanofibers.

Electrospun nanofibers possess a large surface area and a three-dimensional porous network that makes them a perfect material for embedding functional nanoparticles for diverse applications. Herein, we report the trends in embedding upconversion nanoparticles (UCNPs) in polymeric nanofibers for making an advanced miniaturized (bio)analytical device. UCNPs have the benefits of several optical properties, like near-infrared excitation, anti-Stokes emission over a wide range from UV to NIR, narrow emission bands, an extended lifespan, and photostability. The luminescence of UCNPs can be regulated using different lanthanide elements and can be used for sensing and tracking physical processes in biological systems. We foresee that a UCNP-based nanofiber sensing platform will open opportunities in developing cost-effective, miniaturized, portable and user-friendly point-of-care sensing device for monitoring (bio)analytical processes. Major challenges in developing microfluidic (bio)analytical systems based on UCNPs@nanofibers have been reviewed and presented.

Synthesis of NaYF4:Yb3+, Tm3+ Nanocrystals Via the Thermal Decomposition Method Using Refined Sunflower Oil

Abstract In recent years, up-conversion luminescence nanoparticles have attracted significant attention from researchers in fields such as analytical chemistry (for example qualitative and quantitative analysis of metal and non-metal ions) and biomedicine (cancer imaging, drug delivery, treatment, etc.) due to their high rate of emission efficiency, easy surface functionalization, great chemical and thermal and photostability and other favorable properties. NaYF4 in particular has attracted interest of researchers as a host material due to its low phonon energy, thus increasing the efficiency of emission. In this study, the synthesis of NaYF4:Yb3+,Tm3+ nanocrystals using the hydrothermal method was successfully carried out. Refined sunflower oil containing oleic acid was used as a solvent instead of analytical grade oleic acid and octadecene-1, reducing the cost of the synthesis. Using semi-quantitative XRD measurement analysis, it was determined that 25.3 % hexagonal β-NaYF4:Yb3+,Tm3+ as well as 23.8 % cubic α-NaYF4 nanocrystal crystalline phases were found in the synthesized sample. The sample showed mainly luminescent characteristics typical of hexagonal NaYF4:Yb3+,Tm3+ lattice nanoparticles.

Enhancing Up-Conversion Luminescence Using Dielectric Metasurfaces: Role of the Quality Factor of Resonance at a Pumping Wavelength.

Photonic applications of up-conversion luminescence (UCL) suffer from poor external quantum yield owing to a low absorption cross-section of UCL nanoparticles (UCNPs) doped with lanthanide ions. In this regard, plasmonic nanostructures have been proposed for enhancing UCL intensity through strong electromagnetic local-field enhancement; however, their intrinsic ohmic loss opens additional nonradiative decay channels. Herein, we demonstrate that dielectric metasurfaces can overcome this disadvantage. A periodic array of amorphous-silicon nanodisks serves as a metasurface on which a layer of UCNPs is self-assembled. Sharp resonances supported by the metasurface overlap the absorption wavelength (λ = 980 nm) of UCNPs to excite them, resulting in the enhancement of UCL intensity. We further sharpen the resonances through rapid thermal annealing (RTA) of the metasurface, crystallizing silicon to reduce intrinsic optical losses. By optimizing the RTA condition (at 1000 °C for 20 min in N2/H2 (3 vol %) atmosphere), the resonance quality factor improves from 17.2 to 32.9, accompanied by an increase in the enhancement factor of the UCL intensity from 86- to over 600-fold. Moreover, a reduction in the intrinsic optical losses mitigates the UCL thermal quenching under a high excitation density. These findings provide a strategy for increasing light-matter interactions in nanophotonic composite systems and promote UCNP applications.

Indocyanine green-equipped upconversion nanoparticles/CeO2 trigger mutually reinforced dual photodynamic therapy

Although photodynamic-based tumor therapy has attracted considerable attention, the antitumor effect is limited due to the low reactive oxygen species (ROS) generation of photosensitizers. Therefore, it is an urgent need for improving ROS production and promoting therapeutic outcome of tumor. We developed a nanoplatform of indocyanine green (ICG)-equipped upconversion nanoparticles (UCNPs)/CeO2 modified with NH2-PEG1000-cRGDfK (UICCIP). This nanoplatform has two pathways of ROS production for mutually enhanced dual photodynamic therapy (PDT) of tumors. The ultraviolet (UV) emission of UCNPs could trigger CeO2 to produce ROS for PDT under 808 nm laser irradiation, and ICG can also produce singlet oxygen (1O2) at the meantime. Importantly, ICG can enhance the luminescence of UCNPs through energy transfer, thus promoting the PDT effect of CeO2. For another, CeO2 could catalyze endogenous H2O2 to provide O2 then overcome the hypoxic environment of tumor to enhance the PDT effect. By highlighting the full use of the various components of the nanoplatform and establishing interrelationships, ROS production can be increased significantly, resulting in efficient PDT of tumor. It is believed that UICCIP will become a potential ROS producer, which will broaden the thought of exploring new antitumor nanoplatforms.

Silica Coated Upconversion Nanoplatform for Ag-Based Chemo-/Photodynamic Therapy against Drug-Resistant Bacteria

Near-infrared (NIR) driven photodynamic therapy based on upconversion luminescent nanoparticles (UCNPs) is promising for fighting drug-resistant bacteria infections in deep tissues due to its good noninvasive, nonspecific, and non-drug-resistant properties, but is greatly limited by its low efficacy. Herein, honeycomb-silica-coated upconversion nanoparticles (UCNP@mSiO2) with a size of less than 100 nm were successfully prepared by a typical silica sol–gel reaction assisted with an expanding agent (p-xylene). The honeycomb silica shell has large pores with an average diameter of about 10 nm and large pore volume of 0.82 cm3/g and exhibits a MC540 loading as high as 9% in weight. The UCNP nanoparticle core can effectively capture NIR photons and activate the merocyanine 540 photosensitizer (MC540), generating reactive oxygen species to kill the drug-resistant bacteria of deep tissues. To avoid the drug prerelease, Ag nanoparticles in diameter close to that of the silica hole were covalently grafted onto the aminated UCNP@MC540@mSiO2 (UMS-NH2) nanoparticle. The Ag-decorated UMS-NH2 nanoparticles (UMSAg) showed synergistic antibacterial effects of Ag chemotherapy and photodynamic therapy and are more stable than undecorated UMS nanoparticles in an aqueous medium. The UMSAg with unreacted amino groups enhanced the binding of Ag to the bacterial membrane, effectively exerting the antibacterial effect of Ag+ and ROS. In in vitro antibacterial experiments, the killing rates of the UMSAg composite (150 μg/mL) against drug-resistant Staphylococcus aureus and drug-resistant Pseudomonas aeruginosa under NIR irradiation were 100% and 99.6%, respectively. In addition, the antibacterial activity of the UMSAg group was significantly higher than that of the sole Ag nanoparticles without irradiation. This work provides good insight for the design of efficient antibacterial agents and has a potential application for the bacterial infection of deep tissues.

Upconversion nanoparticles anchored MnO2 nanosheets for luminescence “turn on” detecting hydrogen peroxide

The sensitively and reliably detecting hydrogen peroxide (H2O2) is of significant for biology and environment protection fields. Herein, we reported a high sensitive H2O2 nanoprobe based on upconversion nanoparticles (UCNPs) anchored MnO2 nanosheets. In which, DNA modified NaYF4@NaYF4:Yb,Tm core–shell nanoparticles were anchored onto the MnO2 nanosheets surface via π-π stacking. Owing to the luminescence resonance energy transfer, the blue luminescence of UCNPs was effectively quenched by MnO2 nanosheets, then the luminescence could be restored by adding H2O2 for reducing MnO2 to Mn2+, and achieving a H2O2 concentration-dependent luminescence change, the detection limit could reach to 0.23 nM (S/N = 3). The proposed method could detect H2O2 in serum, lake water and real samples. Thus, a desired upconversion luminescence sensing strategy for detection H2O2 in life and environmental analysis was successfully constructed. It may be provide a potential tool in disease diagnosis and environmental monitoring fields.

A ratiometric aptasensor for simultaneous determination of two estrogens based on multicolor upconversion nanoparticles

Different environmental estrogens (EEs) may coexist in the same foodstuff, necessitating the establishment of a simultaneous detection method. Although there are numerous studies on the detection of EEs, few was reported on the determination of two or more estrogens at the same time except HPLC. Our efforts have been made to develop a ratiometric aptasensor based on multicolor lanthanide-doped upconversion luminescence nanoparticles (UCNPs) to realize simultaneous and sensitive detection of two EEs (bisphenol A and 17β-estradiol). Three types of core-shell UCNPs with excellent luminous properties and distinct emitting colors were successfully synthesized via doping with various lanthanide ions, two of which were conjugated with specific aptamers and act as energy donors, while another one served as a reference. Because of their excellent luminescence quenching performance, ultra-thin metallic MoS2 nanosheets were selected as the energy acceptor. Thus, a ratiometric luminescence aptasensor was established and successfully used for the simultaneous detection of two estrogens in tap water and milk samples, demonstrating its considerable practical application value.

Frequency-Domain Method for Characterization of Upconversion Luminescence Kinetics.

The frequency-domain (FD) method provides an alternative to the commonly used time-domain (TD) approach in characterizing the luminescence kinetics of luminophores, with its own strengths, e.g., the capability to decouple multiple lifetime components with higher reliability and accuracy. While extensively explored for characterizing luminophores with down-shifted emission, this method has not been investigated for studying nonlinear luminescent materials such as lanthanide-doped upconversion nanoparticles (UCNPs), featuring more complicated kinetics. In this work, employing a simplified rate-equation model representing a standard two-photon energy-transfer upconversion process, we thoroughly analyzed the response of the luminescence of UCNPs in the FD method. We found that the FD method can potentially obtain from a single experiment the effective decay rates of three critical energy states of the sensitizer/activator ions involved in the upconversion process. The validity of the FD method is demonstrated by experimental data, agreeing reasonably well with the results obtained by TD methods.

Synthesis and surface modification of ultrasmall monodisperse NaYF4:Yb3+/Tm3+ upconversion nanoparticles

The emerging upconversion nanoparticles (UCNP) have gained substantial consideration in the field of bioanalytical as well as diagnostic applications. Therefore, great progress has been made in the synthesis and surface modification of luminescent UCNPs over the last two decades. In this paper, we have reported monodispersed and high luminescent upconversion nanoparticles NaYF4: 20%Yb3+, 2%Tm3+ have been synthesized using a solvothermal method, followed by a coating of the NaYF4 shell with a thin layer of SiO2 on the surface to afford the core-shell NaYF4:Yb3+, Tm3+@SiO2 nanoparticles (NP@SiO2). The prepared nanoparticles were of strong upconversion fluorescent emission intensity, hexagonal phase, and with an average size of about 8 ± 1 nm, which have been characterized by luminescence spectroscopy, powder X-ray diffraction (P-XRD), Dynamic light scattering (DLS), and Transmission electron microscopy (TEM). The results indicate that the NP@SiO2 can be used for the conjugation of fluorescent probes for various biomolecules and can find applications in cancer cell imaging and disease diagnosis.

3D Printable Hybrid Gel Made of Polymer Surface-Modified Cellulose Nanofibrils Prepared by Surface-Initiated Controlled Radical Polymerization (SI-SET-LRP) and Upconversion Luminescent Nanoparticles.

A cellulose nanofibril-based hybrid gel material was developed by grafting the polymerized stearyl acrylate (PSA) and upconversion nanoparticles (UCNPs) onto cellulose nanofibrils (CNFs) via Cu0-mediated radical polymerization (SET-LRP) to create a highly cross-linked CNF system. A two-step strategy was exploited to surface-exchange the ligand of the UCNPs from a hydrophobic ligand (oleic acid) to a hydrophilic small-molecule ligand (2-acrylamido-2-methyl-1-propanesulfonic acid, AMPS) and therefore be suitable for SET-LRP. The characteristics and properties of the hybrid material (UCNP-PSA-CNF) were monitored by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), rheology, X-ray diffraction (XRD), and microscopic analysis. Those characterization techniques prove the efficient modification of the CNF, with the presence of 1.8% UCNPs. The luminescence measurement was carried out using a homebuilt confocal microscope with a 980 nm laser source. The nanostructure of UCNPs and their incorporated CNF species were measured by small-angle X-ray scattering (SAXS). In addition, this CNF-based hybrid gel has decisive rheological properties, such as good viscoelasticity (loss tangent was below 0.35 for the UCNP-PSA-CNF gel, while the PSA-CNF gel reached the highest value of 0.42), shear-thinning behavior, and shape retention, and was successfully applied to three-dimensional (3D) gel printing throughout various 3D print models.

Construction of self-sensitized NaErF4@NaYF4 nanoparticles with multiple red upconversion luminescence for highly-sensitive optical temperature sensing

Efficient deep-penetrating red upconversion luminescent nanoparticles with ultra-small size are promising biological temperature probes. Herein, bright red upconversion luminescence are achieved in NaErF4@NaYF4 core-shell nanoparticles under multi-wavelength excitation of 808 nm, 980 nm, and 1550 nm. The core-shell structure engineering is constructed to minimize energy dissipation by surface quenchers. Furthermore, the established model explains the temperature dependence of thermally coupled energy levels in detail, confirming that the non-radiative relaxation is responsible for the quenching processes. Based on the luminescence intensity ratio technique, optical temperature sensing characteristics of thermally coupled (2H11/2/4S3/2) and non-thermally coupled energy levels (4F9/2/4S3/2) are investigated under the excitation of a relatively safe near-infrared wavelength for 1550 nm. The thermometer can maintain a maximum sensitivity of 35 × 10−3 K−1 over the entire temperature measurement region by fitting the non-thermally coupled energy levels, which is conducive to temperature monitoring in vivo due to high sensitivity and relatively safe excitation wavelength.

Enhancing optical thermometric sensitivity through controlling particle size in LaNbO4: Yb3+, Tm3+ up-converting luminescent nanoparticles

Enhancing optical thermometric sensitivity through controlling particle size in LaNbO4: Yb3+, Tm3+ up-converting luminescent nanoparticles

Activation of Tomato Growth Under Photoconversion Coatings with Nanoluminophor Sr0.76Ba0.20Yb0.02Er0.02F2.04

The effect of coatings containing upconversion luminescent nanoparticles on the cultivation of Solanum lycopersicum has been studied. Sr0.76Ba0.20Yb0.02Er0.02F2.04 particles capable of converting infrared radiation into visible light (λem = 660 nm, 545 nm, and 525 nm) were used as the phosphor. It was shown that the cultivation of tomatoes under photoconversion coatings accelerated the adaptation of plants to ultraviolet radiation. A more efficient distribution of the energy of absorbed light between the processes of photosynthesis and thermal dissipation under upconversion coatings was revealed. As a result, plants grown under photoconversion coatings increased the number and total leaf area, stem length, and leaf chlorophyll content.

A dye-quenched/sensitized switching upconversion nanoprobe for high-contrast mapping of the pH-related tumor microenvironment.

Nanoprobes based on lanthanide-doped upconversion nanoparticles (UCNPs) exhibit promising potential in bioimaging and biosensing due to their unique optical properties. However, conventional UCNP nanoprobes based on the dye quenching effect are still limited in biosensing due to their low upconversion efficiency. The advent of dye-sensitized upconversion has resulted in nanoprobes with significantly enhanced efficiency; however, these still suffer from a high initial emissive background. In view of this, herein, we have constructed a dye-quenched/sensitized switching upconversion nanoprobe for high-contrast imaging of the pH-related tumor microenvironment. Under normal conditions, the luminescence of the nanoprobe at 540 nm (UCL540) was significantly quenched by the employed dye. Upon being triggered by an acid, the dye would switch to its fluorescent form to sensitize the luminescence of UCNPs, affording a significant enhancement of UCL540. The switching from dye-quenched UCL to dye-sensitized UCL jointly enables the detection of a high signal-to-background ratio (high up to 50), allowing for high-contrast mapping of the tumor specific acidic microenvironment in vivo. We believe that this nanoplatform holds considerable promise for acid-related sensing.

Cerium fluoride nanoparticles as a theranostic material for optical imaging of vulnerable atherosclerosis plaques

AbstractAtherosclerosis (AS) is a chronic progressive vascular disease, which can bring on a threat against the health. The eruption of unstable arteriosclerosis plaques has been linked to heart attacks and strokes. The accumulation of foamy macrophages initiates and evolves atherosclerotic plaques, which can be a good target for identifying vulnerable plaques. CD36 and OPN overexpress in foamy macrophages surface, which have a preferable relation with plaque disruption. Furthermore, we choose Yb ions and Tm ions as doping ions and Ce fluoride as matrix of luminescent materials and prepare upconversion luminescent nanoparticles. With the modification of CD36 antibody and OPN antibody, this material can target macrophages in arteriosclerosis plaques. As‐prepared nanoparticles (CeF3:Yb,Tm@SiO2–CD36/OPN) can be excited by near‐infrared light with deep tissue penetration, while emitting strong blue light to image arteriosclerosis plaques. In brief, this study provides a new upconversion luminescent material for the identification and detection of vulnerable atherosclerosis plaques.

Understanding the efficiency enhancement of perovskite solar cells with NaGdF4: Er3+/Yb3+ nanorods

Perovskite solar cells have drawn significant attention due to their excellent photovoltaic characteristics. Upconversion luminescence material modification is a good strategy to extend the device response to the near-infrared region, which can further increase device efficiency. By adding NaGdF 4 :Er 3+ /Yb 3+ nanorods into chlorobenzene as an additive in the antisolvent to modify the perovskite layer, we found that upconversion luminescence nanoparticles can effectively improve the perovskite solar cell performance. However, unexpectedly, the photocurrent contributed by the infrared part is lower. The efficiency increase of perovskite solar cells is contributed by defect passivation. Further research shows that nanoparticles can effectively fill the holes and gaps at the grain boundaries, eliminate surface defects of the perovskite, and modify the perovskite film, which reduces carrier recombination and effectively improves the device's performance. Finally, the power conversion efficiency of the champion device can reach 21.1%. This research demonstrates the function of upconversion luminescence nanoparticles in PSCs and provides a simple way to improve the device's efficiency. • The up-conversion luminescence NaGdF 4 :Er 3+ /Yb 3+ is introduced into the perovskite layer via anti-solvent chlorobenzene. • The champion device achieved an efficiency of 21.1% by passivating perovskite grain defects through NaGdF 4 nanocrystals. • The reason for the efficiency enhancement is the increase of carrier lifetime rather than spectrum broadening to infrared field.

Excitation Pulse Duration Response of Upconversion Nanoparticles and Its Applications.

Lanthanide-doped upconversion nanoparticles (UCNPs) have rich photophysics exhibiting complex luminescence kinetics. In this work, we thoroughly investigated the luminescence response of UCNPs to excitation pulse durations. Analyzing this response opens new opportunities in optical encoding/decoding and the assignment of transitions to emission peaks and provides advantages in applications of UCNPs, e.g., for better optical sectioning and improved luminescence nanothermometry. Our work shows that monitoring the UCNP luminescence response to excitation pulse durations (while keeping the duty cycle constant) by recording the average luminescence intensity using a low-time resolution detector such as a spectrometer offers a powerful approach for significantly extending the utility of UCNPs.

Multiplexed detection of SARS-CoV-2 based on upconversion luminescence nanoprobe/MXene biosensing platform for COVID-19 point-of-care diagnostics

Multiplexed detection is essential in biomedical sciences since it is more efficient and accurate than single-analyte detection. For an accurate early diagnosis of COVID-19, a multiplexed detection strategy is required to avoid false negatives with the existing gold standard assay. Nb2CTx nanosheets were found to efficiently quench the fluorescence emission of lanthanide-doped upconversion luminescence nanoparticles at wavelengths ranging from visible to near-infrared spectrum. Using this broad-spectrum quencher, we developed a label-free FRET-based biosensor for rapid and accurate detection of SARS-CoV-2 RNA. To target ORF and N genes, two types of oligo-modified lanthanide-doped upconversion nanoparticles can be used simultaneously to identify-two sites in one assay via upconversion fluorescence enhancement intensity measurement with detection limits of 15 pM and 914 pM, respectively. Moreover, with multisite cross-validation, this multiplexed and sensitive biosensor is capable of simultaneous and multicolor analysis of two gene fragments of SARS-CoV-2 Omicron variant within minutes in a single homogeneous solution, which significantly improves the detection efficiency. The diagnosis result via our assay is consistent with the PCR result, demonstrating its application in the rapid and accurate screening of multiple genes of SARS-CoV-2 and other infectious diseases.

Photoswitchable lanthanide-doped core-multishell nanoparticles for tunable triple-mode information encryption and dynamic anti-counterfeiting patterns

Photoresponsive luminescent materials with high-capacity information storage and multilevel anti-counterfeiting capability are attracting much interest in many fields including information encryption and anti-counterfeiting. Herein, a class of novel photoswitchable upconversion luminescent nanoparticles (PUCNPs) with core-multishell structure that shows switchable dual-colored emission is described. The PUCNPs is successively built up from lanthanide-doped NaYF4 nanoparticles and a photochromic spiropyrane (SP) monomer by grafting of poly(glycidyl methacrylate-co-SPMA) on the nanoparticles via surface reversible addition-fragmentation chain transfer (RAFT) polymerization. The as-prepared PUCNPs with triple-mode optical features displayed green upconversion luminescence under a 980 nm laser, red downconervsion fluorescence and purple color under a 365 nm UV light irradiation and turning off, respectively. Furthermore, they enable dynamic reversible changes in color between colorless and purple states with 365 nm UV and white light stimuli. Their potential in complex information encryption and dynamic anti-counterfeiting patterns is described and its great potential in data storage, and rewritable optical materials is foreseen.

Luminescent upconversion nanoparticles evaluating temperature-induced stress experienced by aquatic organisms owing to environmental variations

SummaryGrowing anthropogenic activities are significantly influencing the environment and especially aquatic ecosystems. Therefore, there is an increasing demand to develop techniques for monitoring and assessing freshwater habitat changes so that interventions can prevent irrevocable damage. We explore an approach for screening the temperature-induced stress experienced by aquatic organisms owing to environmental variations. Luminescent spectra of upconversion [Y2O3: Yb, Er] particles embedded within Caridina multidentata shrimps are measured, while ambient temperature gradient is inducing stress conditions. The inverse linear dependence of the logarithmic ratio of the luminescence intensity provides an effective means for temperature evaluation inside aquatic species in vivo. The measured luminescence shows high photostability on the background of the complete absence of biotissues’ autofluorescence, as well as no obscuration of the luminescence signal from upconversion particles. Current approach of hybrid sensing has a great potential for monitoring variations in aquatic ecosystems driven by climate changes and pollution.