Computer chip-inspired design of nanocellulose/carbon dots hydrogel as superior intensifier of nano-sized photocatalyst for effective Cr(VI) removal

Hydrogel, a common carrier of photocatalyst that suffers from compromised catalytic efficiency, is still far from practical application. Herein, based on "computer chip-inspired design", a novel nanocellulose/carbon dots hydrogel (NCH) was fabricated as superior intensifier instead of common carrier of sodium titanate nanofibre (STN), where carbon dots (CDs) enhanced amino group-induced adsorption for Cr(VI), promoted photocatalytic properties of STN via transferring the photogenerated electron-hole pairs and improved amino group-induced desorption for reduced product (Cr(III)) via electrostatic repulsion, showing an efficiency of 1 + 1 > 2. Adsorption and photocatalysis experiments demonstrated superior removal performance of the NCH incorporating STN, as shown by theoretical maximum adsorption capacity of 425.74 mg/g and kinetic constant of 0.0374 min^-1 in the photocatalytic process, which was nearly 6.6 and 7.3 times of STN. A series of experiments was conducted to confirm the novel mechanism of CDs-enhanced adsorption-photocatalysis-desorption synergy. This work not only provides new insights into the fabrication of a superior intensifier for nanosized photocatalyst, but also proposes one new mechanism of CDs-enhanced adsorption-photocatalysis-desorption synergy, which is helpful for designing and optimizing nanosized photocatalyst.

Facile synthesized NaGdF4 :Yb, Er peanut-shaped, highly biocompatible, colloidal upconversion nanospheres

A facile method was used for the synthesis of peanut-shaped very emissive NaGdF₄ :Yb, Er upconversion nanospheres (UCNSs) at lower temperatures with uniform size distribution. Crystallographic structure, phase purity, morphology, thermal robustness, biocompatibility, colloidal stability, surface chemistry, optical properties, and luminesce properties were explored by X-ray diffraction (XRD), Scanning electron microscope (SEM), transmission electron microscope (TEM), zeta potential, Thermogravimetric/thermal differential analysis (TGA/DTA), Fourier transform infrared (FTIR), UV/visible and photoluminescence spectroscopic tools. XRD pattern verified the construction of a single-phase, highly-crystalline NaGdF₄ phase with a hexagonal structure. Peanut-shaped morphology of the sample was obtained from SEM micrographs which were validated from high-resolution TEM images, have an equatorial diameter of 170-200 nm and a length of 220-230 nm, with irregular size, monodispersed, porous structure, and rough surface of the particles. The positive zeta potential value exhibited good biocompatibility along with high colloidal stability as observed from the absorption spectrum. The prepared UCNSs revealed high dispersibility, irregular size peanut-shaped morphology, rough surface, good colloidal stability, and excellent biocompatibility in aqueous media. A hexagonal phase NaGdF₄ doped with Yb, and Er UCNSs revealed the characteristics of highly dominant emissions located at 520-525, 538-550, and 659-668 nm are corresponding to the ² H_11/2 →⁴ I_15/2 , ⁴ S_3/2 →⁴ I_15/2 , and ⁴ F_9/2 →⁴ I_15/2 transition of Er³⁺ ions, respectively, as a result of energy transfer from sensitizer Yb³⁺ ion to emitter Er³⁺ ion.

Effect of Excess Ligand on the Reverse Microemulsion Silica Coating of NaLnF4 Nanoparticles

Silica coating of inorganic nanoparticles (NPs) is widely employed as a means of providing colloidal stability in aqueous media and surface functionality for a variety of applications, particularly in biology. When the NPs are synthesized with a surface coating of an organic surfactant like oleic acid, silica coating is performed by using the reverse microemulsion method. There are many reports in the literature of the successful application of this method to NaYF₄ upconversion NPs (doped with Yb and Er), and we have used this method to coat NaHoF₄ NPs designed as a mass cytometry reagent. This method failed when we attempted to apply it to other NaLnF₄ NPs (Ln = Sm, Eu, Tb). In this report we describe an investigation of the problem and show how it can be overcome. To control size in the synthesis of NaLnF₄ NPs and at the same time maintain size uniformity, it is necessary to adjust the Na/F and F/Ln ratios. Problems with silica coating are associated with substoichiometric F/Ln ratios (F/Ln < 4) that leave Ln oleate salts as a byproduct, often as a phase-separated oily layer that could not be purified from the NPs by precipitation with ethanol and redispersion in hexanes. The nature of the oily byproduct was inferred from a combination of TGA, NMR, and FTIR measurements. We explored five different additional purification procedures, and by adopting the appropriate purification method, NaLnF₄ NPs with a variety of compositions and synthesized using different reaction conditions could be coated with a thin shell of silica.

Nanoparticles Determination by Laser Ablation Inductively Coupled Plasma Mass Spectrometry

Quantitatively studying the biodistribution and transformation of nanomaterials is of great importance for nanotoxicological evaluation. Recently, laser ablation inductively coupled plasma mass spectrometry has been employed to distinguish nanoparticles (NPs) with their dissolved ions in biological samples. The principle of the proposal is based on a hypothesis that the intact NPs sampled by laser ablation will generate discrete sharp pulses of signals in ICP-MS measurement, being totally different from the continuous, relatively lower signals generated by ions. However, it is still a controversy whether NPs could maintain their intactness during the laser ablation. This work found a way to exactly determine the number of NPs sampled for each LA-ICP-MS measurement. It made possible to reveal the signal profile of a single NP in LA-ICP-MS analysis. The results suggest that AuNR, AgNP and TIO₂ NP were broken into much smaller secondary NPs during the laser ablation, therefore generating continuous signals in the analyzer. There was a certain probability that the fragmentation of large-sized NP or multiple NPs by laser ablation was not sufficient, leaving some NPs unbroken or some secondary NPs with relatively large sizes to generate discrete pulses of signals in the analyzer. When the intactness of NPs during laser ablation cannot be assured, it is impossible to determine the attribution of mass spectrum signals. These findings compromise the reliability of distinguishing NPs from their dissolved ions by LA-ICP-MS.

PEG-Neridronate-Modified NaYF4:Gd3+,Yb3+,Tm3+/NaGdF4 Core-Shell Upconverting Nanoparticles for Bimodal Magnetic Resonance/Optical Luminescence Imaging

Upconverting nanoparticles are attracting extensive interest as a multimodal imaging tool. In this work, we report on the synthesis and characterization of gadolinium-enriched upconverting nanoparticles for bimodal magnetic resonance and optical luminescence imaging. NaYF4:Gd3+,Yb3+,Tm3+ core upconverting nanoparticles were obtained by a thermal coprecipitation of lanthanide oleate precursors in the presence of oleic acid as a stabilizer. With the aim of improving the upconversion emission and increasing the amount of Gd3+ ions on the nanoparticle surface, a 2.5 nm NaGdF4 shell was grown by the epitaxial layer-by-layer strategy, resulting in the 26 nm core-shell nanoparticles. Both core and core-shell nanoparticles were coated with poly(ethylene glycol) (PEG)-neridronate (PEG-Ner) to have stable and well-dispersed upconverting nanoparticles in a biological medium. FTIR spectroscopy and thermogravimetric analysis indicated the presence of ∼20 wt % of PEG-Ner on the nanoparticle surface. The addition of inert NaGdF4 shell resulted in a total 26-fold enhancement of the emission under 980 nm excitation and also affected the T 1 and T 2 relaxation times. Both r 1 and r 2 relaxivities of PEG-Ner-modified nanoparticles were much higher compared to those of non-PEGylated particles, thus manifesting their potential as a diagnostic tool for magnetic resonance imaging. Together with the enhanced luminescence efficiency, upconverting nanoparticles might represent an efficient probe for bimodal in vitro and in vivo imaging of cells in regenerative medicine, drug delivery, and/or photodynamic therapy.

Lanthanide ion (Ln3+ )-based upconversion sensor for quantification of food contaminants: A review

The food safety issue has gradually become the focus of attention in modern society. The presence of food contaminants poses a threat to human health and there are a number of interesting researches on the detection of food contaminants. Upconversion nanoparticles (UCNPs) are superior to other fluorescence materials, considering the benefits of large anti-Stokes shifts, high chemical stability, non-autofluorescence, good light penetration ability, and low toxicity. These properties render UCNPs promising candidates as luminescent labels in biodetection, which provides opportunities as a sensitive, accurate, and rapid detection method. This paper intended to review the research progress of food contaminants detection by UCNPs-based sensors. We have proposed the key criteria for UCNPs in the detection of food contaminants. Additionally, it highlighted the construction process of the UCNPs-based sensors, which includes the synthesis and modification of UCNPs, selection of the recognition elements, and consideration of the detection principle. Moreover, six kinds of food contaminants detected by UCNPs technology in the past 5 years have been summarized and discussed fairly. Last but not least, it is outlined that UCNPs have great potential to be applied in food safety detection and threw new insight into the challenges ahead.

Effect of different silica coatings on the toxicity of upconversion nanoparticles on RAW 264.7 macrophage cells

Upconversion nanoparticles (UCNPs), consisting of NaYF₄ doped with 18% Yb and 2% Er, were coated with microporous silica shells with thickness values of 7 ± 2 and 21 ± 3 nm. Subsequently, the negatively charged particles were functionalized with N-(6-aminohexyl)-3-aminopropyltrimethoxysilane (AHAPS), which provide a positive charge to the nanoparticle surface. Inductively coupled plasma optical emission spectrometry (ICP-OES) measurements revealed that, over the course of 24h, particles with thicker shells release fewer lanthanide ions than particles with thinner shells. However, even a 21 ± 3 nm thick silica layer does not entirely block the disintegration process of the UCNPs. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays and cell cytometry measurements performed on macrophages (RAW 264.7 cells) indicate that cells treated with amino-functionalized particles with a thicker silica shell have a higher viability than those incubated with UCNPs with a thinner silica shell, even if more particles with a thicker shell are taken up. This effect is less significant for negatively charged particles. Cell cycle analyses with amino-functionalized particles also confirm that thicker silica shells reduce cytotoxicity. Thus, growing silica shells to a sufficient thickness is a simple approach to minimize the cytotoxicity of UCNPs.

Highly colloidally stable trimodal 125I-radiolabeled PEG-neridronate-coated upconversion/magnetic bioimaging nanoprobes

"All-in-one" multifunctional nanomaterials, which can be visualized simultaneously by several imaging techniques, are required for the efficient diagnosis and treatment of many serious diseases. This report addresses the design and synthesis of upconversion magnetic NaGdF4:Yb3+/Er3+(Tm3+) nanoparticles by an oleic acid-stabilized high-temperature coprecipitation of lanthanide precursors in octadec-1-ene. The nanoparticles, which emit visible or UV light under near-infrared (NIR) irradiation, were modified by in-house synthesized PEG-neridronate to facilitate their dispersibility and colloidal stability in water and bioanalytically relevant phosphate buffered saline (PBS). The cytotoxicity of the nanoparticles was determined using HeLa cells and human fibroblasts (HF). Subsequently, the particles were modified by Bolton-Hunter-neridronate and radiolabeled by 125I to monitor their biodistribution in mice using single-photon emission computed tomography (SPECT). The upconversion and the paramagnetic properties of the NaGdF4:Yb3+/Er3+(Tm3+)@PEG nanoparticles were evaluated by photoluminescence, magnetic resonance (MR) relaxometry, and magnetic resonance imaging (MRI) with 1 T and 4.7 T preclinical scanners. MRI data were obtained on phantoms with different particle concentrations and during pilot long-time in vivo observations of a mouse model. The biological and physicochemical properties of the NaGdF4:Yb3+/Er3+(Tm3+)@PEG nanoparticles make them promising as a trimodal optical/MRI/SPECT bioimaging and theranostic nanoprobe for experimental medicine.

Monodisperse Core-Shell NaYF4:Yb3+/Er3+@NaYF4:Nd3+-PEG-GGGRGDSGGGY-NH2 Nanoparticles Excitable at 808 and 980 nm: Design, Surface Engineering, and Application in Life Sciences

Lanthanide-doped upconversion nanoparticles (UCNPs) have a unique capability of upconverting near-infrared (NIR) excitation into ultraviolet, visible, and NIR emission. Conventional UCNPs composed of NaYF₄:Yb³⁺/Er³⁺(Tm³⁺) are excited by NIR light at 980 nm, where undesirable absorption by water can cause overheating or damage of living tissues and reduce nanoparticle luminescence. Incorporation of Nd³⁺ ions into the UCNP lattice shifts the excitation wavelength to 808 nm, where absorption of water is minimal. Herein, core-shell NaYF₄:Yb³⁺/Er³⁺@NaYF₄:Nd³⁺ nanoparticles, which are doubly doped by sensitizers (Yb³⁺ and Nd³⁺) and an activator (Er³⁺) in the host NaYF₄ matrix, were synthesized by high-temperature coprecipitation of lanthanide chlorides in the presence of oleic acid as a stabilizer. Uniform core (24 nm) and core-shell particles with tunable shell thickness (~0.5–4 nm) were thoroughly characterized by transmission electron microscopy (TEM), energy-dispersive analysis, selected area electron diffraction, and photoluminescence emission spectra at 808 and 980 nm excitation. To ensure dispersibility of the particles in biologically relevant media, they were coated by in-house synthesized poly(ethylene glycol) (PEG)-neridronate terminated with an alkyne (Alk). The stability of the NaYF₄:Yb³⁺/Er³⁺@NaYF₄:Nd³⁺-PEG-Alk nanoparticles in water or 0.01 M PBS and the presence of PEG on the surface were determined by dynamic light scattering, ζ-potential measurements, thermogravimetric analysis, and FTIR spectroscopy. Finally, the adhesive azidopentanoyl-modified GGGRGDSGGGY-NH₂ (RGDS) peptide was immobilized on the NaYF₄:Yb³⁺/Er³⁺@NaYF₄:Nd³⁺-PEG-Alk particles via Cu(I)-catalyzed azide-alkyne cycloaddition. The toxicity of the unmodified core-shell NaYF₄:Yb³⁺/Er³⁺@NaYF₄:Nd³⁺, NaYF₄:Yb³⁺/Er³⁺@NaYF₄:Nd³⁺-PEG-Alk, and NaYF₄:Yb³⁺/Er³⁺@NaYF₄:Nd³⁺-PEG-RGDS nanoparticles on both Hep-G2 and HeLa cells was determined, confirming no adverse effect on their survival and proliferation. The interaction of the nanoparticles with Hep-G2 cells was monitored by confocal microscopy at both 808 and 980 nm excitation. The NaYF₄:Yb³⁺/Er³⁺@NaYF₄:Nd³⁺-PEG-RGDS nanoparticles were localized on the cell membranes due to specific binding of the RGDS peptide to integrins, in contrast to the NaYF₄:Yb³⁺/Er³⁺@NaYF₄:Nd³⁺-PEG-Alk particles, which were not engulfed by the cells. The NaYF₄:Yb³⁺/Er³⁺@NaYF₄:Nd³⁺-PEG-RGDS nanoparticles thus appear to be promising as a new non-invasive probe for specific bioimaging of cells and tissues. This development makes the nanoparticles useful for diagnostic and/or, after immobilization of a bioactive compound, even theranostic applications in the treatment of various fatal diseases.