Tailoring the structure and self-activated photoluminescence of carbonated amorphous calcium phosphate nanoparticles for bioimaging applications.

Self-activated luminescent calcium phosphate (CaP) nanoparticles, including hydroxyapatite (HA) and amorphous calcium phosphate (ACP), are promising for bioimaging and theragnostic applications in nanomedicine, eliminating the need for activator ions or fluorophores. In this study, we developed luminescent and stable citrate-functionalized carbonated ACP nanoparticles for bioimaging purposes. Our findings revealed that both the CO32- content and the posterior heating step at 400 °C significantly influenced the composition and the structural ordering of the chemically precipitated ACP nanoparticles, impacting the intensity, broadness, and position of the defect-related photoluminescence (PL) emission band. The heat-treated samples also exhibited excitation-dependent PL under excitation wavelengths typically used in bioimaging (λexc = 405, 488, 561, and 640 nm). Citrate functionalization improved the PL intensity of the nanoparticles by inhibiting non-radiative deactivation mechanisms in solution. Additionally, it resulted in an increased colloidal stability and reduced aggregation, high stability of the metastable amorphous phase and the PL emission for at least 96 h in water and supplemented culture medium. MTT assay of HepaRG cells, incubated for 24 and 48 h with the nanoparticles in concentrations ranging from 10 to 320 µg mL-1, evidenced their high biocompatibility. Internalization studies using the nanoparticles self-activated luminescence showed that cellular uptake of the nanoparticles is both time (4-24 h) and concentration (160-320 µg mL-1) dependent. Experiments using confocal laser scanning microscopy allowed the successful imaging of the nanoparticles inside cells via their intrinsic PL after 4 h of incubation. Our results highlight the potential use of citrate-functionalized carbonated ACP nanoparticles for use in internalization assays and bioimaging procedures.

Rational Design of W-Doped Ag3PO4 as an Efficient Antibacterial Agent and Photocatalyst for Organic Pollutant Degradation.

Bacterial and organic pollutants are major problems with potential adverse impacts on human health and the environment. A promising strategy to alleviate these impacts consists in designing innovative photocatalysts with a wider spectrum of application. In this paper, we report the improved photocatalytic and antibacterial activities of chemically precipitated Ag3PO4 microcrystals by the incorporation of W at doping levels 0.5, 1, and 2 mol %. The presence of W directly influences the crystallization of Ag3PO4, affecting the morphology, particle size, and surface area of the microcrystals. Also, the characterization via experimental and theoretical approaches evidenced a high density of disordered [AgO4], [PO4], and [WO4] structural clusters due to the substitution of P5+ by W6+ into the Ag3PO4 lattice. This leads to new defect-related energy states, which decreases the band gap energy of the materials (from 2.27 to 2.04 eV) and delays the recombination of e'-h• pairs, leading to an enhanced degradation process. As a result of such behaviors, W-doped Ag3PO4 (Ag3PO4:W) is a better visible-light photocatalyst than Ag3PO4, demonstrated here by the photodegradation of potential environmental pollutants. The degradation of rhodamine B dye was 100% in 4 min for Ag3PO4:W 1%, and for Ag3PO4, the obtained result was 90% of degradation in 15 min of reaction. Ag3PO4:W 1% allowed the total degradation of cephalexin antibiotic in only 4 min, whereas pure Ag3PO4 took 20 min to achieve the same result. For the degradation of imidacloprid insecticide, Ag3PO4:W 1% allowed 90% of degradation, whereas Ag3PO4 allowed 40%, both in 20 min of reaction. Moreover, the presence of W-dopant results in a 16-fold improvement of bactericidal performance against methicillin-resistant Staphylococcus aureus. The outstanding results using the Ag3PO4:W material demonstrated its potential multifunctionality for the control of organic pollutants and bacteria in environmental applications.

α-AgVO3 Decorated by Hydroxyapatite (Ca10(PO4)6(OH)2): Tuning Its Photoluminescence Emissions and Bactericidal Activity.

Defect-related luminescent materials have attracted interest because of their excellent optical properties and are considered as a less expensive and nontoxic alternative to commonly used lanthanide-based optical systems. These materials are fundamentally and technologically important for the next generation of full-color tunable light-emitting diodes as well as in the biomedical field. In this study, we report the preparation of α-silver vanadate (α-AgVO3, AV) decorated by hydroxyapatite (Ca10(PO4)6(OH)2, HA) with intense photoluminescence (PL) emissions at various HA/AV molar ratios (1:1-1:1/32) by a simple route based on chemical precipitation. The well-defined diffraction peaks observed by X-ray diffraction were all indexed to the monoclinic AV and hexagonal HA phases. Analysis of the results obtained by Fourier transform infrared spectroscopy reveals the presence of short-range structural order as deduced by the characteristic vibrational modes assigned to AV and HA systems. Characterization by scanning and transmission electron microscopies confirms the presence of AV and HA micro- and nanorods, respectively. UV-vis spectroscopy renders band gap energies of 5.80 eV for HA and in the range 2.59-2.65 eV for pure AV and HA/AV samples. The PL data reveal the presence of broad-band emission profiles, typical of defect-related optical centers in materials. Depending on the molar ratio, the emission can be completely tunable from the blue to red spectral regions; in addition, pure white color emission was obtained. On the basis of these results, we propose an order-disorder model induced by structural and interface defects to explain the PL emissions in the HA/AV system. Moreover, our results show that HA/AV composites have superior bactericidal activity against Staphylococcus aureus (methicillin-resistant and methicillin-susceptible) and can be used as a novel multifunctional material.

Tailoring the Bactericidal Activity of Ag Nanoparticles/α-Ag2WO4 Composite Induced by Electron Beam and Femtosecond Laser Irradiation: Integration of Experiment and Computational Modeling.

In nanotechnology research, significant effort is devoted to fabricating patterns of metallic nanoparticles on the surfaces of different semiconductors to find innovative materials with favorable characteristics, such as antimicrobial and photocatalytic properties, for novel applications. We present experimental and computational progress, involving a combined approach, on the antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA) of as-synthesized α-Ag2WO4 samples and Ag nanoparticle composites (Ag NPs)/α-Ag2WO4. The former included two morphologies: hexagonal rod-like (α-Ag2WO4-R) and cuboid-like (α-Ag2WO4-C), and the latter included composites formed under electron beam, Ag NPs/α-Ag2WO4-RE and Ag NPs/α-Ag2WO4-CE, and femtosecond (fs) laser irradiation, Ag NPs/α-Ag2WO4-RL and Ag NPs/α-Ag2WO4-CL. Direct observations of the arrangement of Ag NPs on the Ag NPs/α-Ag2WO4 composites irradiated with an electron beam and laser, through transmission electron microscopy (TEM), high-resolution TEM, energy-dispersive X-ray spectroscopy, and field-emission scanning electron microscopy, allow us to investigate the surface morphology, chemical composition, homogeneity, and crystallinity. Therefore, these experimental factors, and in particular, the facet-dependent response of Ag NPs/α-Ag2WO4 composites were discussed and analyzed from the perspective provided by the results obtained by first-principles calculations. On this basis, α-Ag2WO4-R material proved to be a better bactericidal agent than α-Ag2WO4-C with minimum bactericidal concentration (MBC) values of 128 and 256 µg/mL, respectively. However, the Ag NPs/α-Ag2WO4-CL composite is the most efficient bactericidal agent of all tested samples (MBC = 4 µg/mL). This superior performance can be attributed to the cooperative effects of crystal facets and defect engineering. These results on the synthesis and stability of the Ag NPs/α-Ag2WO4 composites can be used for the development of highly efficient bactericidal agents for use in environmental remediation and the potential extension of methods to produce materials with catalytic applications.

From Complex Inorganic Oxides to Ag-Bi Nanoalloy: Synthesis by Femtosecond Laser Irradiation.

Bimetallic nanoalloys with a wide variety of structures and compositions have been fabricated through many diverse techniques. Generally, various steps and chemicals are involved in their fabrication. In this study, the synthesis of Ag-Bi nanoalloys by femtosecond laser irradiation of an inorganic oxide Ag2WO4/NaBiO3 target without any chemicals like reducing agents or solvent is presented. The interaction between these materials and the ultrashort pulse of light allows the migration of Ag and Bi atoms from the crystal lattice to the particles surfaces and then to the plasma plume, where the reduction of the positively charged Ag and Bi species in their respective metallic species takes place. Subsequently, the controlled nucleation and growth of the Ag-Bi alloyed nanoparticles occurs in situ during the irradiation process in air. Although at the bulk level, these elements are highly immiscible, it was experimentally demonstrated that at nanoscale, the Ag-Bi nanoalloy can assume a randomly mixed structure with up to 6 ± 1 atom % of Bi solubilized into the face-centered cubic structure of Ag. Furthermore, the Ag-Bi binary system possesses high antibacterial activity against Staphylococcus aureus (methicillin-resistant and methicilin-susceptible), which is interesting for potential antimicrobial applications, consequently increasing their range of applicability. The present results provide potential insights into the structures formed by the Ag-Bi systems at the nanoscale and reveal a new processing method where complex inorganic oxides can be used as precursors for the controlled synthesis of alloyed bimetallic nanoparticles.