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.

NiCr composite coatings on stainless steel were obtained by the simultaneous deposition of Cr and Ni, using thermionic vacuum arc (TVA) technology. The main aim of this paper is to study the influence of graphite and oxygen incorporation on the structural, mechanical, and tribological properties of the resulting coatings. The deposition geometry was designed to maintain a relative constant Cr/Ni ratio while inducing a controlled compositional gradient in carbon content. An additional batch of samples was synthesized under reactive conditions by introducing a controlled O₂ flow while maintaining the same plasma parameters during deposition. The coatings were deposited on both Si wafers and AISI 304 stainless steel substrates. The elemental composition and phase structure were analyzed by scanning electron microscopy- energy dispersive spectroscopy (SEM-EDS) and grazing-incidence X-ray diffraction (GIXRD), revealing the formation of mixed CrNi intermetallic phases, nickel carbide (Ni₃C), and, under reactive conditions, chromium and nickel oxides. Increasing the oxygen content led to a progressive structural transition from metallic–carbide mixtures to predominantly crystalline oxide phases. Tribological performance was evaluated using a ball-on-disk tribometer, and the results demonstrated a significant reduction and stabilization of the friction coefficient for oxygen-containing coatings, together with enhanced wear resistance. SEM and EDS analyses of the wear tracks confirmed the formation of protective oxide layers that effectively reduced coating removal during sliding. Nanoindentation measurements revealed a substantial increase in hardness from ~4 GPa for binary Cr–Ni coatings to ~9 GPa for ternary Cr–Ni–C films, with the highest hardness values obtained for oxygen-enriched coatings. The results highlight the synergistic role of carbon and oxygen in tailoring the microstructure and enhancing the mechanical and tribological performance of Cr–Ni-based composite coatings deposited by TVA, demonstrating their potential for protective applications under demanding operating conditions. This work demonstrates that controlled oxygen incorporation during TVA deposition can be used as an effective tool to tailor simultaneously the phase composition, surface chemistry, mechanical response, and tribological behavior of Cr–Ni–C coatings without compromising coating integrity.

Carbon–metal composite NiCrFeC coatings, prepared with and without controlled oxygen addition, were investigated to evaluate the influence of oxygen on the structure, mechanical response, and tribological performance. X-ray diffraction revealed that oxygen-containing films (NiCrFeC + O₂) exhibit a mixed metallic–oxide microstructure with CrNi, CrO, and NiO phases, whereas oxygen-free coatings show only CrNi crystalline peaks. The incorporation of oxygen led to a substantial increase in nano-hardness, from 0.84 GPa for NiCrFeC to 1.59 GPa for NiCrFeC + O₂. Scratch testing up to 100 N indicated improved adhesion and higher critical loads for the oxygen-rich coatings. Tribological measurements performed under dry sliding conditions using a sapphire ball showed a significant reduction in friction: NiCrFeC + O₂ stabilized at ~0.20, while NiCrFeC exhibited values between 0.25 and 0.35 at 0.5 N and 0.4–0.5 at 1 N, accompanied by non-uniform sliding due to coating failure. Wear-track analysis confirmed shallower penetration depths and narrower wear scars for NiCrFeC + O₂, despite similar initial roughness (~35 nm). These findings demonstrate that oxygen incorporation enhances hardness, adhesion, and wear resistance while substantially lowering friction, making NiCrFeC + O₂ coatings promising for low-friction dry-sliding applications.