Environmental pollution with cadmium (Cd) is a major concern worldwide, with prolonged exposure to this toxic heavy metal causing serious health problems, such as kidney damage, cancer, or cardiovascular diseases, only to mention a few. Herein, a gold-coated reflection-type fiber optic–-surface plasmon resonance (Au-coated FO-SPR) sensor is manufactured and functionalized with (i) bovine serum albumin (BSA), (ii) chitosan, and (iii) polyaniline (PANI), respectively, for the sensitive detection of cadmium ions (Cd${}^{2+}$) in water. Then, the three sensor functionalization strategies are evaluated and compared one at a time. Out of these strategies, the BSA-functionalized FO-SPR sensor is found to be highly sensitive, exhibiting a limit of detection (LOD) for Cd${}^{2+}$ detection at nM level. Moreover, the presence of Cd${}^{2+}$ on the FO-SPR sensor surface was confirmed by the X-ray photoelectron spectroscopy (XPS) technique and also quantified consecutively for all the above-mentioned functionalization strategies. Hence, the BSA-functionalized FO-SPR sensor is sensitive, provides a rapid detection time, and is cheap and portable, with potential applicability for monitoring trace-level amounts of Cd within environmental or potable water.

In this study, we report on the synthesis of L-Cysteine (L-Cys)-coated magnetic iron oxide nanoparticles (NPs) loaded with doxorubicin (Dox). The Fe₃O₄-L-Cys-Dox NPs were extensively characterized for their compositional and morpho-structural features using EDS, SAED, XRD, FTIR and TEM. XPS, Mӧssbauer spectroscopy and SQUID measurements were also performed to determine the electronic and magnetic properties of the Fe₃O₄-L-Cys-Dox nanoparticles. Moreover, by means of a FO-SPR sensor, we evidenced and confirmed the binding of Dox to L-Cys. Biological tests on mouse (B16F10) and human (A375) metastatic melanoma cells evidenced the internalization of magnetic nanoparticles delivering Dox. Half maximum inhibitory concentration IC50 values of Fe₃O₄-L-Cys-Dox were determined for both cell lines: 4.26 µg/mL for A375 and 2.74 µg/mL for B16F10, as compared to 60.74 and 98.75 µg/mL, respectively, for unloaded controls. Incubation of cells with Fe₃O₄-L-Cys-Dox modulated MAPK signaling pathway activity 3 h post-treatment and produced cell cycle arrest and increased apoptosis by 48 h. We show that within the first 2 h of incubation in physiological (pH = 7.4) media, ~10–15 µM Dox/h was released from a 200 µg/mL Fe₃O₄-L-Cys-Dox solution, as compared to double upon incubation in citrate solution (pH = 3), which resembles acidic environment conditions. Our results highlight the potential of Fe₃O₄-L-Cys-Dox NPs as efficient drug delivery vehicles in melanoma therapy.

In this work, we report results on the fabrication and characterization of a surface plasmon resonance (SPR) pH sensor using platinum (Pt) and polyaniline (PANI) layers successively coated over an unclad core of an optical fiber (FO). The plasmonic thin Pt layer was deposited using a magnetron sputtering technique, while the pH-sensitive PANI layer was synthesized using an electroless polymerization method. Moreover, the formation of PANI film was confirmed by X-ray photoelectron spectroscopy (XPS) technique and its surface morphology was investigated using scanning electron microscopy (SEM). It was found that the PANI/Pt-coated FO-SPR pH sensor exhibits a fast and linear response in either acid or alkali solutions (pH operational range: 1 to 14). The proposed FO-SPR sensor could be used for biomedical applications, environmental monitoring or any remote, real-time on-site measurements.

This study explores the development of highly sensitive hydrogen sulfide (H₂S) gas sensors employing hierarchical aluminum-doped zinc oxide (AZO) nanostructures. Vertically oriented AZO nanoplatelets with Al/ZnO molar ratios of 4% and 6% were successfully synthesized using an automated successive ionic layer adsorption and reaction (SILAR) technique. The morphological features of the AZO films significantly changed with the Al content. The AZO thin films exhibited a polycrystalline wurtzite structure and an increase in crystallite size with increasing Al concentrations. This work demonstrates that our AZO sensor structures achieved a maximum response at 150 ppm H₂S and 573 K of 23.3%, being characterized by fast response and recovery times of 28 and 464 s, respectively. Notably, the 6% AZO samples exhibited an augmented selective sensitivity to H₂S, demonstrating stable detection performance. Additionally, the significant improvement in detection capabilities can be attributed to the synergistic effects of electronic and chemical sensitization. These effects enhance the formation of active sites and create doping-induced defects while providing shorter and more efficient diffusion paths for the electrons, significantly improving the sensor’s sensitivity and response speed.

Zinc telluride (ZnTe) thin films were deposited by radio-frequency magnetron sputtering (RF-MS) onto optical glass coated by a silver–copper (Ag:Cu) thin film representing the back-electrode, and they were subsequently electrically contacted with an aluminum (Al) layer acting as the top-electrode. The RF-MS procedure was carried out at 50 W in argon (Ar) gas atmosphere kept at 2.5 × 10⁻³ mbar working pressure for 75 min at a substrate temperature of 220 °C kept constant during deposition. Morphological investigations by scanning electron microscopy allowed a first evaluation of the ZnTe film’s thickness. Optical characterization was then performed via absorption and transmission measurements in the spectral range between 300 and 1500 nm at room temperature. Subsequently, the thickness and bandgap energy of the ZnTe thin film were evaluated to be ∼508 nm and ∼2.13 eV, respectively. Moreover, they revealed high transmittance in infrared and near infrared regions of the electromagnetic spectrum. Then, the electrical measurements of Ag:Cu/ZnTe/Al “sandwich” structure (current–voltage characteristics) at six temperatures ranging from 303 to 354 K were performed, allowing the identification of the charge transport mechanisms through the structure along with their corresponding parameters. Based on the excellent optical and electrical properties, these ZnTe thin films show great potential as candidates for performant small-wavelength photodetectors.

High-quality convex colloidal photonic crystals can be grown on the tip of an optical fiber by self-assembly using the hanging drop method. They are convex-shaped, produce the diffraction of reflecting light with high efficiency (blazing colors), and have a high curvature. The convex colloidal crystals are easily detachable and, as free-standing objects, they are mechanically robust, allowing their manipulation and use as convex reflective diffraction devices in imaging spectrometers. Currently, the same characteristics are obtained by using gratings-based structures. The optical fiber/colloidal crystal interface is disordered; thus, no light diffraction can be registered. The ordering at this interface was highly increased by forming a polystyrene spacer on the optical fiber tip, which served as a self-assembly substrate for silica colloid, as a mechanical bond between the fiber and the crystal, and as a filler reservoir for an inverse-opal synthesis. The silica opal-like grown on the optical fiber tip can be transformed into a high-quality polystyrene (blazing colors) inverse-opal by using the polystyrene spacer as a filler. We found that the colloidal crystal axisymmetric self-assembles onto the optical fiber tip only if a maximum volume of the colloid drop is settled on a flat end of the polystyrene spacer.