Influence of Surface Coating on Structural and Photoluminescent Properties of CaMoO4:Pr Nanoparticles

Impact of luminescent-ion doping on the crystallographic and photo-physical properties of the CaMoO4 nanoparticles

Luminescent lanthanide (Ln3+ = Pr, Nd, Sm, Eu, and Tb)-ions doped calcium molybdate(CaMoO4) nanoparticles(NPs) were prepared by the polyol wet-chemical route. X-ray diffraction (XRD) pattern of all samples showed the formation of a single-phase scheelite type tetragonal structure with an average crystalline size over 21.6-33.4 nm. Thermal stability was evaluated to study the surface-anchored functional groups by weight loss measurement. Fourier transform infrared (FTIR) spectra were recorded to identify the adsorbed functional groups. Aqueous dispersibility and colloidal stability were recorded with the help of the UV/visible absorption spectra. These nanocrystals formed semi-transparent colloidal solutions after being evenly disseminated in aqueous media. The doping of the luminescent ions significantly affects the crystal structure and photoluminescence (PL) properties of the CaMoO4:Ln3+ NPs. In a comparative analysis of the absorption spectra, bandgap, Raman-active modes, and luminescent properties, they were greatly influenced by altering the dopant ion due to the variation in the atomic radius of the element. The doping of smaller atomic radius Ln3+-ions distorts the unit cell, and, subsequently, bond angle/length alters the symmetry of the host crystal. The distorted crystal lattice affects the crystalline, size, lattice parameter, band gap values, Raman active vibrational modes, and luminescent efficiency. The distorted crystal structure of the host lattices facilitates the movement of the oxygen vacancies through charge transfer, resulting in efficiently suppressed emission efficiency.Graphical abstract.

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.

Perovskite Nanoparticles as an Electrochemical Sensing Platform for Detection of Warfarin

Chemically prepared PrAlO3 perovskite nanoparticles (NPs) were applied for the electrochemical detection of warfarin, which is commonly utilized for preventing blood clots, such as in deep vein thrombosis. PrAlO3 perovskite NPs were synthesized by the co-precipitation process at environmental conditions. Crystallographic structure, phase purity, morphological structure, thermal stability, optical properties, and electrochemical characteristics were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, UV-visible analysis, and cyclic voltammetry techniques. TEM micrographs showed the highly crystalline structure, smooth surface, irregular shape, and size of nanocrystalline particles with an average size of 20–30 nm. Particularly crystalline perovskite NPs were pasted on glassy carbon electrodes (GCE) to electrochemically detect the warfarin contents in liquid samples. The fabricated electrode was electrochemically characterized by different parameters such as different potential, scan rates, same potential with seven consecutive cycles, time response, real-time sample analysis, and as a function of warfarin concentration in phosphate buffer solution (0.1 M PBS, pH 7.2). The electrochemical electrode was further verified with various potentials of 5, 10, 20, 50, 100, and 150 mV/s, which exhibited sequential enhancements in the potential range. For detecting warfarin over a wide concentration range (19.5 µM–5000 µM), the detection devices offered good sensitivity and a low limit of detection (19.5 µM). The time-dependent influence was examined using chronoamperometry (perovskite NPs/GCE) in the absence and presence of warfarin at four distinct voltages of +0.05 to +1.2 V from 0 to 1000 s. The repeatability and reliability of the constructed electrochemical sensing electrode were also evaluated in terms of cyclic response for 30 days, demonstrating that it is substantially more reliable for a longer period. The fabricated perovskite NPs/GCE electrodes could be employed for the rapid identification of other drugs.

Physiochemical characterization of highly biocompatible, and colloidal LaF3:Yb/Er upconversion nanoparticles

Highly colloidal upconversion nanoparticles (UCNPs) were synthesized at low temperatures by the thermal decomposition process. The structure, morphology, crystallinity, surface chemistry, and optical properties were systematically optimized and studied through various spectroscopic techniques. X-ray diffraction (XRD) patterns have shown the formation of single-phase, highly purified, well-crystalline, hexagonal LaF₃ NPs, while the TEM micrographs show small, irregular sizes, spherically shaped, and aggregated polycrystalline UCNPs with an average crystalline size of about 8-15 nm. The Negative Zeta Potential value exhibits good biocompatibility of the UCNPs, which supports the idea that surface-anchored hydroxyl groups facilitate the stabilization of the NPs in aqueous media, as well as enhance biomolecules' tagging efficiency. The absorption spectrum, Zeta Potential, and hydrodynamic size that were measured in aqueous media illustrate excellent dispersibility, colloidal stability, biocompatibility, and cytotoxicity character of the UCNPs. Zeta potential and MTT assay studies illustrated high biocompatibility, it could be due to the surface-anchored hydroxyl groups. The nanoproduct demonstrates an excellent UC luminescence spectrum (i.e., prominent green emission ⁴S_3/2 → ⁴I/_15/2) upon irradiation by the 980-nm laser diode. TEM micrographs, further, revealed that this optically active material with aqueous sensitivities, porous crystal structure, and excellent UCNPs, could be a favorable candidate for potential photonics-based bio-related applications.

Optically active neodymium hydroxide surface-functionalized mesoporous silica micro-cocoons for biomedical applications

Neodymium hydroxide (Nd(OH)₃)-surface modified mesoporous silica micro-cocoon microstructures were prepared using a facile single-step sol-gel chemical process. XRD revealed the semi-crystalline nature of the as-prepared materials. TEM and SEM micrographs exhibited highly monodisperse, non-aggregated, typical ordered mesoporous, and irregular sized cocoon-shaped micro-structures with a narrow size distribution. Optical properties, that were examined in the aqueous media, revealed a high colloidal stability and the formation of a semi-transparent colloidal solution. The colloidal solution of Nd(OH)₃-surface functionalized micro-structures revealed well characteristics absorption bands of Nd³⁺ ions in the visible region. thus validating the successful coating of SiO₂@Nd(OH)₃ layer over the surface silica forming core-shell structures. Zeta potential, 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium) bromide, and neutral red uptake assays were applied in a dose-dependent manner to investigate the biocompatibility and toxic potential of the designed cocoon-shaped microstructures. Both the assays and the high zeta potential value demonstrated good cell viability even at high concentrations and hydrophilic conditions, indicating excellent biocompatibility and non-toxicity. These highly hydrophilic, optically active, mesoporous, biocompatible, and non-toxic cocoon-shaped microstructures could be potentially suitable candidates for optical bio-probes and drug delivery applications.

Mitigation of acyl-homoserine lactone (AHL) based bacterial quorum sensing, virulence functions, and biofilm formation by yttrium oxide core/shell nanospheres: Novel approach to combat drug resistance

The present study evaluated the efficacy of Y2O3:Tb (core) and Y2O3:Tb@SiO2 nanospheres (core/shell NSs) against virulence functions regulated by quorum sensing (QS) and biofilm formation in pathogenic bacteria. Scanning electron microscope (SEM) images were used to study the size, shape, and morphology. The images clearly displayed spherical shaped, mono-dispersed particles with narrow size distribution and an average grain size of 110-130 nm. The chemical composition of the samples was determined by using energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS). We determined the impact of core and core/shell NSs on QS using sensor strains of Chromobacterium violaceum CVO26 and Pseudomonas aeruginosa PAO1 in a comparative study. Sub-MICs of core and core/shell NSs substantially suppressed QS-controlled violacein production in C. violaceum. Similar concentration-dependent effect of sub-MICs of synthesized core and core/shell NSs was observed in the QS-regulated virulence functions (elastase, total protease, pyocyanin production, swarming motility, and exopolysaccharide production) in PAO1. A concentration-dependent decrease (14-60%) was recorded in the biofilm forming capability of PAO1, upon treatment with core and core/shell NSs. Moreover, core/shell NSs were more effective in inhibiting biofilm at higher tested concentrations as compared to core-NSs. The synthesized NSs demonstrated significantly impaired attachment of cells to the microtiter plate indicating that NSs target biofilm inhibition at the attachment stage. Based on these results, we predict that core and core/shell NSs may be an alternative to combat the threat of drug-resistant pathogenic bacteria.

Synthesis and characterization of luminescent SiO2 @Eu(phen-Si) core-shell nanospheres

Four core-shell structured nanometre luminescent composites with different kernel sizes and different shell layer thicknesses (SiO₂₍₅₀₀₎ @Eu (phen-Si)₍₅₀₎ , SiO₂₍₅₀₀₎ @Eu (phen-Si)₍₁₅₎ , SiO₂₍₂₅₀₎ @Eu (phen-Si)₍₅₎ and SiO₂₍₂₅₀₎ @Eu (phen-Si)₍₁₀₎ ) were made by changing synthesis conditions. Here, initial subscript numbers in parentheses refer to the particle size of the SiO₂ core, whereas the final subscript numbers in parentheses refer to shell layer thickness. In these composites, silica spheres of 500 nm or 250 nm were identified as the core. The shell layer was composited of silicon, 1,10-phenanthroline and europium perchlorate, abbreviated as Eu(phen-Si); the chemical formula of phen-Si was phen-N-(CONH (CH₂ )Si(OCH₂ CH₃ )₃ )₂ . The composites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and infrared spectroscopy. The monodispersed spherical SiO₂ showed characteristics of a regular microstructure and a smooth surface, as well as the advantage of dispersity, shown by SEM. The Eu(phen-Si) complex was able to self-assemble into monodispersed SiO₂ spheres, as seen using TEM. Fluorescence spectra indicated that the four composites had excellent luminescence properties. Furthermore, composites composed of a SiO₂ core and a 250 nm kernel size exhibited stronger fluorescence than 500 nm kernel-sized composites. Fluorescence properties were affected by shell thickness: the thicker the shell, the greater the fluorescence intensity. For the four composites, quantum yield values and fluorescence lifetime corresponded to fluorescence emission intensity data as quantum yield values and fluorescence lifetime were higher, and luminescence properties increased.

Toxicity response of highly colloidal, bioactive, monodisperse SiO2@ Pr(OH)3 hollow microspheres

In a facile synthesis, highly colloidal, bioactive Pr(OH)₃-encapsulated silica microspheres (PSMSs) with an average diameter of 500-700 nm were successfully prepared via a sol-gel process followed by heat treatment. The phase formation, morphology, surface and optical properties of the as-synthesized PSMSs were characterized by various techniques including X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscope (SEM), transmission electron microscope (TEM), N₂-adsorption-desorption, energy dispersive X-ray (EDX) analysis, Fourier transform infrared (FTIR) and UV/vis spectroscopy. The PSMSs were semi-amorphous or ultra-small in size, highly dispersible in water, mesoporous, irregular in size and spherical in shape. The SEM images show a well-ordered broad nanoporous structure which is preserved after coating with Pr(OH)₃ molecules, demonstrating interaction between the optically active Pr³⁺ ion and silanol (Si-OH) groups via hydrogen bonding. Optical spectra show well-resolved weak intensity 4f-4f absorption transitions in the visible region of the Pr³⁺ ion, indicating successful grafting of the Pr(OH)₃ layer. Toxicity was measured by MTT and NRU assays to determine potential toxicity. Cell viability was suppressed with increasing dosage of PSMSs, but showed greater than 55% cell viability at a concentration of 200 μg/mL, resulting in low toxicity. Due to its high aqueous dispersibility, optical activity, excellent biocompatibility and low toxic nature, it could be a favorable material for biomedical and drug delivery applications.

Aqueous dispersible green luminescent yttrium oxide:terbium microspheres with nanosilica shell coating

Tb-doped Y₂O₃ microspheres (MSs) were prepared via a homogeneous thermal degradation process at a low temperature and then coated with a nanosilica shell (Y₂O₃:Tb@SiO₂) using a sol-gel process. The core MSs were highly crystalline and spherical with a porous surface, single cubic phase, and particle size of 100-250 nm. Transmission electron microscopy (TEM) images clearly showed the spherical shape of the as-prepared core MSs, which were fully covered with a thick and mesoporous nanosilica shell. Fourier transform infrared (FTIR) spectra displayed the well-resolved infrared absorption peaks of silica (SiO, SiOSi, etc.), confirming the presence of the silica surface coating. The core MSs retained their spherical shape even after heat treatment and subsequent silica surface coating. It was observed that the core/shell MSs are easily dispersible in aqueous media and form a semi-transparent colloidal solution. Ultraviolet/visible and zeta potential studies were tested to prove the changes in the surface chemistry of the as-designed core/shell MSs and compare with their core counterpart. The growth of the amorphous silica shell not only increased the particle size but also enhanced remarkably the solubility and colloidal stability of the MSs in aqueous media. The strongest emission lines originating from the characteristic intra-shell 4f-4f electronic transitions of Tb ions were quenched after silica layer deposition, but the MSs still showed strong green (⁵D₄ → ⁷F₅ at 530-560 nm as most dominant) emission efficiency, which indicates great potential in fluorescent bio-probes. The emission intensity is discussed in relation to the quenching mechanism induced by surface silanol (Si-OH) groups, particle size, and surface charge.

Physiochemical properties of greatly enhanced photoluminescence of aqueous dispersible upconversion CaF2:Yb/Er nanoparticles

Crystal phase morphological structure and optical properties of the as-prepared upconversion CaF₂:Yb/Er(core) and sequential coating of an inert crystalline material and silica layers surrounding the seed core-nanoparticles (NPs) were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), optical absorption, FTIR spectroscopy and upconversion photoluminescence spectroscopy. Owing to the unique properties of CaF₂ host matrix, we realized their practical applications in biomedical science to improve the upconversion luminescence property and aqueous dispersibility. The surface coating on the seed core particles will significantly influence the structural, optical band gap energy and upconversion luminescence properties. These NPs were well-dispersed in aqueous and non-aqueous solvents to form clear colloidal solutions. The colloidal solutions of three samples show a characteristic optical absorption band in UV/Visible region. As a result, optical band gap gradually decreases after sequential growth of the inert shell and amorphous silica due to an increase in the crystalline size. Comparative upconversion luminescence analysis showed that after inert shell growth, the upconversion intensity was greatly improved, and such an improvement was found to arise from efficient suppression of surface-related deactivation from the core nanocrystals. Interestingly, growth of an inert (CaF₂) shell over the seed core NPs shows intense upconversion emission lines under 980 nm NIR laser excitation, highlighting their promising applications, such as multi-analyte biolabels, staining, displays and other photonic based technological applications.

Influence of Shell Formation on Morphological Structure, Optical and Emission Intensity on Aqueous Dispersible NaYF4:Ce/Tb Nanoparticles

A highly water-dispersible NaYF4:Ce/Tb (core), NaYF4:Ce/Tb@NaYF4(core/shell) and NaYF4:Ce/Tb@NaYF4@SiO2 (core/shell/SiO2) nanoparticles (NPs) were synthesized via a general synthesis approach. The growth of an inert NaYF4 and silica shell (~14 nm) around the core-NPs resulted in an increase of the average size of the nanopaticles as well as broadening of their size distribution. The optical band-gap energy slightly decreases after shell formation due to the increase the crystalline size. To optimize the influence of shell formation a comparative analysis of photoluminescence properties (excitation, emission, and luminescence decay time) of the core, core/shell, and core/shell/SiO2 NPs were measured. The emission intensity was significantly enhanced after inert shell formation around the surface of the core NPs. The Commission International de l'Eclairage chromaticity coordinates of the emission spectrum of core, core/shell, core/shell/SiO2 NPs lie closest to the standard green color emission at 545 nm. By quantitative spectroscopic measurements of surface-modified core-NPs, it was suggested that encapsulation with inert and silica layers was found to be effective in retaining both luminescence intensity and dispersibility in aqueous environment. Considering the high aqueous dispersion and enhanced luminescence efficiency of the core-NPs make them an ideal luminescent material for luminescence bioimaging and optical biosensors.