Real-time and high-sensitivity monitoring of heavy metal ions in solution is of great significance in environmental monitoring. Traditional electrochemical methods suffer from electrochemical noise and environmental interferences for heavy metal trace detection. To address these issues, we propose a novel electrochemical surface plasmon resonance (EC-SPR) optical fiber sensor. The sensor comprises a tilted fiber Bragg grating imprinted in a commercial single-mode fiber and coated with a nanoscale gold film for high-efficiency SPR excitation. The gold coated optical fiber serves as working electrode, performing the dual functions of anodic stripping voltammetry and SPR optical sensing. We demonstrate detection of Pb2+ as an example of a typical heavy metal ion. We show a stable and reproducible correlation between the real-time ion deposition-stripping cycles and the optical transmission of the optical fiber, with a limit of detection of 10-10 M and a dynamic range of nearly five orders of magnitude. Moreover, by taking derivative of the SPR amplitude change, we can clearly identify the peak stripping potential of the detected ions and therefore realize specific ion identification. The method proposed is inherently immune to temperature cross-talk because the core mode is temperature-dependent but insensitive to surrounding media. The proposed EC-SPR fiber-optic sensor has the advantages of compact size, flexible shape and remote operation capability, thereby opening the way for other opportunities for electrochemical monitoring in various hard-to-reach locations and remote environments.

Environmental monitoring and potable water control are key applications where optical fiber sensing solutions can outperform other technologies. In this work, we report a highly sensitive plasmonic fiber-optic probe that has been developed to determine the concentration of cadmium ions (Cd²⁺) in solution. This original sensor was fabricated by immobilizing the Acinetobacter sp. around gold-coated tilted fiber Bragg gratings (TFBGs). To this aim, the immobilization conditions of bacteria on the gold-coated optical fiber surface were first experimentally determined. Then, the coated sensors were tested in vitro. The relative intensity of the sensor response experienced a change of 1.1 dB for a Cd²⁺ concentration increase from 0.1 to 1000 ppb. According to our test procedure, we estimate the experimental limit of detection to be close to 1 ppb. Cadmium ions strongly bind to the sensing surface, so the sensor exhibits a much higher sensitivity to Cd²⁺ than to other heavy metal ions such as Pb²⁺, Zn²⁺ and CrO₄²⁻ found in contaminated water, which ensures a good selectivity.

Oxygen sensor is an important technique in various applications including industrial process control, medical equipment, biological fabrication, etc. The reported optical fiber‐based configurations so far, using gas‐sensitive coating do not meet the stringent performance targets, such as fast response time and low limit of detection (LOD). Tin‐based halide perovskites are sensitive to oxygen with potential use for sensor applications. Here, the halide perovskite‐based oxygen optical fiber sensor by combining phenylethylammonium tin iodide (PEA₂SnI₄) and tilted fiber Bragg grating (TFBG) is demonstrated. The PEA₂SnI₄‐based oxygen optical fiber sensor is reversible at room temperature with a response time of about 10 s, and the experimental LOD approaches to an extremely low oxygen concentration of about 50 ppm. The as‐fabricated oxygen sensor shows a relative response change of 0.6 dB for an oxygen concentration increase from 50 ppm to 5% with good gas selection against NO₂, CO, CO₂, H₂. This work extends the sensor applications of halide perovskites, providing a novel technique for rapid and repeatable oxygen gas detection at a low level.

Surface plasmon resonance excitation with tilted fiber Bragg gratings has been typically studied using gold films to target biochemical sensing applications. However, surface plasmons can be excited on other metal coatings as well. In this work, plasmonic optical fiber grating platforms are developed using palladium films. Since the optical properties of this metal differ from the ones of gold, simulations are carried out to define the optimal thickness. Due to the phase transition of palladium in the presence of hydrogen, intensity changes in the optical transmission of the devices are produced. It is demonstrated that these platforms can be used for hydrogen detection at concentrations way below the lower explosive limit.