Surface Of Upconverting Nanoparticles Research Articles

The Combination of Upconversion Nanoparticles and Photodynamic Therapy for Alzheimer’s Disease Treatment in Real-Time Monitoring

Alzheimer’s Disease (AD) consumes many medical resources in disease caring and delays symptoms. The aggregation of amyloid-beta (Aβ) is regarded as one of the foci of AD. It will form oligomers and polymerize into fibrotic neurofibrillary tangles leading to AD. Many research has focused on the diagnosis and risk factors of Aβ aggregation, trying to reverse the situation of Aβ aggregation by various approaches. However, there are no advantageous solutions that have been developed so far. Establishing a system from monitoring to controlling Aβ aggregation is urgently needed as a new approach for AD treatment. Once Aβ aggregation can be monitored and controlled to oxide and degrade it before forming oligomers. It will bring huge benefits to AD treatment. Therefore, this study combines photodynamic therapy (PDT) and quartz crystal micro-scale (QCM) techniques to realize the degradation of Aβ and monitor whether Aβ is degraded, and establish a complete system.PDT has been applied in the medical field, especially for cancer treatment which induced oxidative stress results in different levels of protein oxidation. However, the limited excitation source limits the application of PDT, for example, the insufficient penetration depth of the excitation source prevents in vivo treatment of AD. Therefore, it needs to be combined with other materials to achieve in-depth treatment. This study proposes to modify photosensitizers on upconverting nanoparticles (UCNPs), and use 980 nm near-infrared to excite and then emit visible light to perform PDT. The combination of PDT and UCNPs generates the reactive oxygen species (ROS) to oxide Aβ and further degrade Aβ aggregation. However, most of the lanthanide metals and photosensitizers doped UCNPs are cytotoxic. Thus, Rose Bengal (RB) was selected as the reactive photosensitizer in this system owing to it being a metal-free, non-toxic, and widely available material. Also, it has been confirmed through research that RB can effectively transfer energy to form 1O2. To further ensure that material can be used in AD treatment, modify the SiO2 shell on the surface of UCNP to improve biocompatibility. The experimental results show that the cell survival rate can be maintained at about 80% when the concentration of UCNP reaches 25mg/mL.The degradation of the Aβ peptide can be monitored using the QCM technique. QCM was applied for monitoring the differences in the oscillation frequency by the degradation of the Aβ peptide attached to UCNPs. Meanwhile, the DCFH-DA ROS assay kit was applied to estimate the Aβ peptide oxidation level. The results of this study show that the combination of UCNPs for PDT can effectively oxidize and degrade Aβ, and utilizing QCM and ROS assay kit can monitor the level of Aβ oxidation and degradation in real-time. The establishment of this system can help more potential AD patients, providing a diagnostic and treatment method. Figure 1

PMVEMA-coated upconverting nanoparticles for upconversion-linked immunoassay of cardiac troponin

Surface engineering of upconverting nanoparticles (UCNPs) is crucial for their bioanalytical applications. Here, an antibody specific to cardiac troponin I (cTnI), an important biomarker for acute myocardial infection, was covalently immobilized on the surface of UCNPs to prepare a label for the detection of cTnI biomarker in an upconversion-linked immunoassay (ULISA). Core-shell UCNPs (NaYF4:Yb,Tm@NaYF4) were first coated with poly(methyl vinyl ether‐alt‐maleic acid) (PMVEMA) and then conjugated to antibodies. The morphology (size and uniformity), hydrodynamic diameter, chemical composition, and amount of coating on the of UCNPs, as well as their upconversion luminescence, colloidal stability, and leaching of Y3+ ions into the surrounding media, were determined. The developed ULISA allowed reaching a limit of detection (LOD) of 0.13 ng/ml and 0.25 ng/ml of cTnI in plasma and serum, respectively, which represents 12- and 2-fold improvement to conventional enzyme-linked immunosorbent based on the same immunoreagents.

Thulium- and Erbium-Doped Nanoparticles with Poly(acrylic acid) Coating for Upconversion Cross-Correlation Spectroscopy-based Sandwich Immunoassays in Plasma

Fluorescence correlation spectroscopy based on upconverting nanoparticles (UCNPs) can detect single particles in strongly autofluorescent samples, such as plasma. Nanoparticle aggregation, however, is a problem in correlation spectroscopy measurements, and biological media are known to induce aggregation. Here we present an improved UCNP surface chemistry and use these UCNPs in an upconversion cross-correlation spectroscopy (UCCS)-based homogeneous immunoassay for thyroid-stimulating hormone, where the simultaneous emission of green- (NaYF4:Yb3+,Er3+) and blue- (NaYF4:Yb3+,Tm3+) emitting UCNPs is detected when they are bound together by the analyte. The improved coating suppresses UCNP aggregation, even in plasma samples. Additionally, increasing the Tm doping of blue-emitting UCNPs enhances their brightness at a high excitation intensity and also results in a significantly shorter luminescence decay time, which improves the probability of detecting coincident blue and green emission from the bound UCNPs in the UCCS immunoassay.

Unmodified Rose Bengal photosensitizer conjugated with NaYF4:Yb,Er upconverting nanoparticles for efficient photodynamic therapy

In photodynamic therapy (PDT), photosensitizer (PS) molecules are irradiated by light to generate reactive oxygen species (ROS), the presence of which subsequently leads to cell death. At present, the modality is limited to the treatment of skin diseases because of the low tissue penetration of visible or ultraviolet light required for producing ROS. To increase tissue penetration and extend the therapeutic possibilities of PDT to the treatment of deep-seated cancer, rare-earth doped nanoparticles capable of up-converting infrared to visible light are investigated. These up-converting nanoparticles (UCNPs) are conjugated with PS molecules to efficiently generate ROS. In this work, we employ hexagonal β-NaYF4:Yb3 + ,Er3 + as UCNPs and Rose Bengal (RB) as PS molecules and demonstrate efficient in vitro PDT using this nanoformulation. Covalent bonding of the RB molecules is accomplished without their functionalization—an approach which is expected to increase the efficiency of ROS generation by 30%. Spectroscopic studies reveal that our approach results in UCNP surface fully covered with RB molecules. The energy transfer from UCNPs to RB is predominantly non-radiative as evidenced by luminescence lifetime measurements. As a result, ROS are generated as efficiently as under visible light illumination. The in vitro PDT is tested on murine breast 4T1 cancer cells incubated with 250 µg ml−1 of the nanoparticles and irradiated with NIR light under power density of 2 W cm−2 for 10 minutes. After 24 hours, the cell viability decreased to 33% demonstrating a very good treatment efficiency. These results are expected to simplify the protocols for preparation of the PDT agents and lead to improved therapeutic effects.

Controlled synthesis and characterization of NaYF4:Yb/Er upconverting nanoparticles produced by laser ablation in liquid.

Upconverting nanoparticles (UCNPs) composed of NaYF4 and doped with photoactive Yb3+ and Er3+ (NaYF4:Yb/Er) are highly desirable for many biological applications, but obtaining stable dispersions of UCNPs is challenging. Traditional synthetic methods often use complicated synthetic steps, produce toxic side products, and require post modifications to make UCNPs more dispersible in aqueous solutions. In this study, we demonstrate that laser ablation in liquid (LAL) is a novel approach to synthesize water-dispersible and -stable UCNPs with advantages of particle-size tuning, in situ coating of UCNPs with capping agents, no use of toxic or high boiling point solvents, and short reaction times. NaYF4:Yb/Er UCNPs were produced through LAL of annealed targets using water as the liquid, and their compositions and properties were investigated at a laser fluence of 0.57 J cm-2-6.22 J cm-2 by direct capping with citric acid and ethylene glycol and by comparing with the UCNPs prepared from the traditional hydrothermal method. Low laser fluences produced polydisperse particles consisting of no photoactive species through a thermal evaporation mechanism, while high laser fluences generated UCNPs with more uniform morphologies and compositions similar to the target material by an explosive ejection mechanism. The inclusion of capping agents during LAL allowed for direct coating of the UCNP surface without the need of post modifications, and the concentrations of capping agents affected the UCNP photoluminescence lifetimes. As compared to the hydrothermal method, the LAL-prepared samples showed better size control and no degradation of the capping agents.

NIR-Light-Driven Generation of Reactive Oxygen Species Using Ru(II)-Decorated Lipid-Encapsulated Upconverting Nanoparticles.

The biological application of ruthenium anticancer prodrugs for photodynamic therapy (PDT) and photoactivated chemotherapy (PACT) is restricted by the need to use poorly penetrating high-energy photons for their activation, i.e., typically blue or green light. Upconverting nanoparticles (UCNPs), which produce high-energy light under near-infrared (NIR) excitation, may solve this issue, provided that the coupling between the UCNP surface and the Ru prodrug is optimized to produce stable nanoconjugates with efficient energy transfer from the UCNP to the ruthenium complex. Herein, we report on the synthesis and photochemistry of the two structurally related ruthenium(II) polypyridyl complexes [Ru(bpy)2(5)](PF6)2 ([1](PF6)2) and [Ru(bpy)2(6)](PF6)2 ([2](PF6)2), where bpy = 2,2-bipyridine, 5 is 5,6-bis(dodecyloxy)-2,9-dimethyl-1,10-phenanthroline, and 6 is 5,6-bis(dodecyloxy)-1,10-phenanthroline. [1](PF6)2 is photolabile as a result of the steric strain induced by ligand 5, but the irradiation of [1](PF6)2 in solution leads to the nonselective and slow photosubstitution of one of its three ligands, making it a poor PACT compound. On the other hand, [2](PF6)2 is an efficient and photostable PDT photosensitizer. The water-dispersible, negatively charged nanoconjugate UCNP@lipid/[2] was prepared by the encapsulation of 44 nm diameter NaYF4:Yb3+,Tm3+ UCNPs in a mixture of 1,2-dioleoyl-sn-glycero-3-phosphate and 1,2-dioleoyl-sn-glycero-3-phosphocholine phospholipids, cholesterol, and the amphiphilic complex [2](PF6)2. A nonradiative energy transfer efficiency of 12% between the Tm3+ ions in the UCNP and the Ru2+ acceptor [2]2+ was found using time-resolved emission spectroscopy. Under irradiation with NIR light (969 nm), UCNP@lipid/[2] was found to produce reactive oxygen species (ROS), as judged by the oxidation of the nonspecific ROS probe 2′,7′-dichlorodihydrofluorescein (DCFH2–). Determination of the type of ROS produced was precluded by the negative surface charge of the nanoconjugate, which resulted in the electrostatic repulsion of the more specific but also negatively charged 1O2 probe tetrasodium 9,10-anthracenediyl-bis(methylene)dimalonate (Na4(ADMBMA)).

A Strategy for Prompt Phase Transfer of Upconverting Nanoparticles Through Surface Oleate-Mediated Supramolecular Assembly of Amino-β-Cyclodextrin.

Lanthanide-doped upconverting nanoparticles (UCNPs) are promising for applications as wide as biosensing, bioimaging, controlled drug release, and cancer therapy. These applications require surface engineering of as-prepared nanocrystals, commonly coated with hydrophobic ligand of oleic acid, to enable an aqueous dispersion. However, literature-reported approaches often require a long time and/or multiple step treatment, along with several fold upconversion luminescence (UCL) intensity decrease. Here, we describe a strategy allowing oleate-capped UCNPs to become water-soluble and open-modified, with almost undiminished UCL, through ultrasonication of minutes. The prompt phase transfer was enabled by oleate-mediated supramolecular self-assembly of amino modified β-cyclodextrin (amino-β-CD) onto UCNPs surface. We showed that this method is valid for a wide range of UCNPs with quite different sizes (6–400 nm), various dopant types (Er, Tm, and Ho), and hierarchical structures (core, core-shell). Importantly, the amino group of amino-β-CD on the surface of treated UCNPs provide possibilities to introduce entities for biotargeting or functionalization, as exemplified here, a carboxylic-containing near infrared dye (Cy 7.5) that sensitizes UCNPs to enhance their UCL by ~4,820 fold when excited at ~808 nm. The described method has implications for all types of oleate-capped inorganic nanocrystals, facilitating their myriad bioapplications.

Spin–Lattice Relaxation and Diffusion Processes in Aqueous Solutions of Gadolinium-Based Upconverting Nanoparticles at Different Magnetic Fields

We investigated the influence of gadolinium (Gd)-based upconverting nanoparticles (UCNPs) on water spin–lattice relaxation (T1) and diffusion at different magnetic field strengths (0.4 T and 9.4 T). Our findings show that smaller NPs (12 nm compared to 19 nm) were more favourable for proton relaxivity. We also demonstrate that using simplified Solomon–Bloembergen–Morgan (SBM) model we can associate two measured diffusion coefficients with processes occurring near the surface of UCNPs and in bulk water. Using the relationship between relaxation and diffusion, we can estimate not only the total impact of NPs on relaxation of water molecules, but also the impact on relaxation of local water molecules, directly connected to paramagnetic Gd3+ ions in NPs. Different magnetic field strengths did not alter the spin–lattice relaxivity of NPs. This suggests that Gd-based UCNPs could be developed into high-performance multimodal magnetic resonance imaging contrast agents working over a broad range of imaging field strengths used in clinical routine.

Photostable and efficient upconverting nanocrystal-based chemical sensors

Chemical sensing in living systems demands optical sensors that are bright, stable, and sensitive to the rapid dynamics of chemical signaling. Lanthanide-doped upconverting nanoparticles (UCNPs) efficiently convert near infrared (NIR) light to higher energy emission and allow biological systems to be imaged with no measurable background or photobleaching, and with reduced scatter for subsurface experiments. Despite their advantages as imaging probes, UCNPs have little innate chemical sensing ability and require pairing with organic fluorophores to act as biosensors, although the design of stable UCNP-fluorophore hybrids with efficient upconverted energy transfer (UET) has remained a challenge. Here, we report Yb3+- and Er3+-doped UCNP-fluorophore conjugates with UET efficiencies up to 88%, and photostabilities 100-fold greater by UET excitation than those of the free fluorophores under direct excitation. Despite adding distance between Er3+ donors and organic acceptors, thin inert shells significantly enhance overall emission without compromising UET efficiency. This can be explained by the large increase in quantum yield of Er3+ donors at the core/shell interface and the large number of fluorophore acceptors at the surface. Sensors excited by UET show increases in photostability well beyond those reported for other methods for increasing the longevity of organic fluorophores, and those covalently attached to UCNP surface polymers show greater chemical stability than those directly coordinated to the nanocrystal surface. By conjugating other fluorescent chemosensors to UCNPs, these hybrids may be extended to a series of NIR-responsive biosensors for quantifying the dynamic chemical populations critical for cell signaling.

Förster Resonance Energy Transfer Distance Dependence from Upconverting Nanoparticles to Quantum Dots

Forster resonant energy transfer (FRET) with upconverting nanoparticles (UCNPs) as donors and quantum dots (QDs) as acceptors has been regarded as a promising tool for biosensing applications. In this work, we use time-resolved luminescence spectroscopy to analyze the UCNP-to-QD FRET and we focus on the most relevant parameter of the FRET phenomenon, UCNP–QD distance. This distance is controlled by a nanometric silica shell around the UCNP surface. We theoretically reproduce the experimental results applying FRET theory to the distribution of emitting erbium ions in the UCNP. This simple model allows us to estimate the contribution of every erbium ion to the final FRET response and to explore different strategies to improve FRET efficiency.

Facile preparation of multifunctionalisable 'stealth' upconverting nanoparticles for biomedical applications.

Pure hexagonal (β-phase) NaYF4-based hydrophobic upconverting nanoparticles (UCNPs) were surface-modified with O-phospho-l-threonine (OPLT), alendronic acid, and PEG-phosphate ligands to generate water-dispersible UCNPs. Fourier-transform infrared (FTIR) spectroscopy was used to establish the presence of the ligands on the UCNP surface. These UCNPs exhibit great colloidal stability and a near-neutral surface at physiological pH, as confirmed by dynamic light scattering (DLS) and zeta potential (ζ) measurements, respectively. The particles also display excellent long-term stability, with no major adverse effect on the size of UCNPs when kept at pH 7.4. Upon exposure to human serum, PEG-phosphate- and alendronate-coated UCNPs showed no formation of biomolecular corona, as confirmed by SDS-PAGE analysis. The photophysical properties of water-dispersible UCNPs were investigated using steady-state as well as time-resolved luminescence spectroscopy, under excitation at ca. 800 nm. The results clearly show that the UCNPs demonstrate bright upconversion (UC) luminescence. Furthermore, the presence of reactive groups on the NPs, such as free amine groups in alendronate-coated UCNPs, enables further functionalisation of UCNPs with, for example, small molecules, peptides, proteins, and antibodies. Overall these protein corona resistant UCNPs show great biocompatibility and are worthy of further investigation as potential new biomaging probes.

Near-infrared-triggered anticancer drug release from upconverting nanoparticles.

Targeted drug delivery using functional nanoparticles has provided new strategies for improving therapeutic efficacy while concurrently minimizing toxicity. Photodynamic therapy is an approach that offers control of drug delivery by use of an external photon source to allow active therapeutic release to a target area. Upconverting nanoparticles (UCNPs) have potential to operate as integral components of photodynamic therapeutic platforms based on the resonant absorption of near-infrared (NIR) radiation and emission at shorter wavelengths. NIR radiation is minimally absorbed and scattered by biological tissues, and the NIR excitation of UCNPs can generate anti-Stokes emission in the ultraviolet-visible wavelength range at intensities that can be used to trigger cleavage of bonds linking therapeutics at the nanoparticle interface. Herein, we describe an investigation of photocleavage at the surface of UCNPs to release the chemotherapeutic 5-fluorouracil (5-FU). Core-shell UCNPs composed of a β-NaYF4: 4.95% Yb, 0.08% Tm core and a β-NaYF4 shell were coated with o-phosphorylethanolamine ligands and coupled to an o-nitrobenzyl (ONB) derivative of 5-FU. NIR excitation of the UCNPs resulted in photoluminescence (PL) emission bands centered at 365, 455, and 485 nm. The UV-blue PL was in resonance with the absorption band of the ONB-FU derivative resulting in photocleavage and subsequent release of the 5-FU drug from the UCNPs for these in vitro studies. The release of 5-FU was complete in <14 min using a NIR laser source centered at 980 nm that operated at a power of <100 mW. The efficiency of triggered release was as high as 77% of the total ONB-FU conjugate, while the rate of drug release could be tuned with the laser power output. This work provides an important first step in the development of a UCNP platform capable of targeted chemotherapy.

Biomimetic Surface Engineering of Lanthanide‐Doped Upconversion Nanoparticles as Versatile Bioprobes

A general and versatile biomimetic approach to synthesize water dispersible and functionalizable upconverting nanoparticles (UCNPs) for selective imaging of live cancer cells is reported. The approach involves coating the surface of UCNPs with a monolayer of phospholipids containing different functional groups, allowing for conjugation of many molecules for a wide range of applications in fields such as bioinspired nanoassembly, biosensing, and bio-medicine.