In this study, hydroxyapatite was synthesized using a microwave-assisted hydrothermal method. Calcium nitrate tetrahydrate (Ca(NO₃)₂·4H₂O) and ammonium phosphate ((NH₄)₂HPO₄) served as precursors in a pH 10 ammonium hydroxide (NH₄OH) solution. Polyvinylpyrrolidone (PVP) was employed as a surfactant at varying concentrations of 0 (M0), 0.1% (M1), 0.2% (M2), and 0.3%wt (M3) to control particle size and morphology. The synthesized samples were characterized using Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). The addition of PVP during synthesis resulted in Ca/P ratios ranging from 0.93 to 1.37, and promoted predominantly rod-like morphologies. Samples M1 and M3 exhibited average diameters of 11.23–104.24 nm and lengths of 47.21–222.32 nm. XRD analysis confirmed the presence of both hexagonal and monoclinic phases, with crystallite sizes varying from 18.66 to 22.49 nm. FTIR spectra of sample M1 revealed an elongation at 3432 cm⁻¹ corresponding to OH⁻ groups, indicative of water absorption within the material structure. Vibrational bands at 2950–2300, 1090, and 975 cm⁻¹, attributed to C–H bonds in PVP were also identified. These findings highlight the influence of PVP concentration on the structural and morphological properties of hydroxyapatite, providing insights into its potential applications in various fields.

In the present paper, we show the experimental measurement of the growth of a microbubble created on the tip of a single mode optical fiber, in which zinc nanoparticles were photodeposited on its core by using a single laser source to carry out both the generation of the microbubble by photothermal effect and the monitoring of the microbubble diameter. The photodeposition technique, as well as the formation of the microbubble, was carried out by using a single-mode pigtailed laser diode with emission at a wavelength of 658 nm. The microbubble’s growth was analyzed in the time domain by the analysis of the Fabry–Perot cavity, whose diameter was calculated with the number of interference fringes visualized in an oscilloscope. The results obtained with this technique were compared with images obtained from a CCD camera, in order to verify the diameter of the microbubble. Therefore, by counting the interference fringes, it was possible to quantify the temporal evolution of the microbubble. As a practical demonstration, we proposed a vibrometer sensor using microbubbles with sizes of 83 and 175 µm as a Fabry–Perot cavity; through the time period of a full oscillation cycle of an interferogram observed in the oscilloscope, it was possible to know the frequency vibration (500 and 1500 Hz) for a cuvette where the microbubble was created.

In this work, an analysis was made of the microstructural effects derived from the incorporation of silver (Ag) at different concentrations (0.5, 1, 2, 3, and 8% wt) to obtain ZnO-Ag nanocomposites. The results show an increase in the particle size of Ag in relation to the increase in the weight percentage of the precursor. ZnO-Ag is obtained through an infusion of Origanum vulgare as a reducing agent for Ag in the first stage. Subsequently, the solid-state method was used, resulting in the formation of Zinc Oxide (ZnO) and the ZnO-Ag nanoparticles (NPs). The physicochemical characterization was carried out using X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Transmission Electron Microscopy (TEM), and High-Resolution Transmission Electron Microscopy (HRTEM). The XRD results confirm the presence of Ag and ZnO. Ag shows a preferred orientation of [111] with a crystallite size ranging from 28.46 to 44.92 nm, which increases with the percentage of Ag in the system over ZnO. The wurtzite ZnO presents a preferential orientation of [101] with an increasing crystallite size from 24.9 to 29.84 nm. In the FTIR analysis, a stretching band at 682 cm⁻¹, characteristic of the Zn-O bond, as well as a strain vibration band at 457 cm⁻¹ of ZnO, were observed. The nanoparticle size is attributed to the phytochemical composition of Origanum vulgare, which includes secondary metabolites such as phenolic acids, flavonoids, terpenoids, and flavonoid-based reducing compounds. These compounds help reduce the agglomeration of the particles.