Escherichia coli (E. coli) is a large and diverse bacteria group that inhabits the intestinal tract of many mammals. Most E. coli strains are harmless, however some of them are pathogenic, meaning they can make one sick if ingested. By being in the feces of animals and humans, its presence in water and food is used as indicator of fecal contamination. The main method for this microorganism detection is the bacterial culture medium that is time-consuming and requires a laboratory with specialized personnel. Other sophisticated methods are still not fast enough because they require sending samples to a laboratory and with a high cost of analysis. In this paper, a gold-coated U-shaped plastic optical fiber (POF) biosensor for E. coli bacteria detection is presented. The biosensor works by intensity modulation principle excited by monochromatic light where the power absorption is imposed by predominant effect of either bending loss or surface plasmon resonance (SPR), depending on the gold thickness. Bacterial selectivity is obtained by antibody immobilization on the fiber surface. The biosensor showed a detection limit of 1.5 × 10³ colony-forming units (CFU)/mL, demonstrating that the technology can be a portable, fast response and low-cost alternative to conventional methodologies for quality analysis of water and food.

Most of the dam’s disasters that occurred in the world could be avoided if proper and preventive measures were taken, such as long-term surface or underground monitoring to detect small soil displacements. However, due to the complex operation necessary to monitor underground layer displacements, inclinometers are not used with suitable regularity. To circumvent the logistics of field campaigns necessary in conventional inclinometers, a real-time, remote monitoring system was developed. In this paper, a fiberoptic inclinometer system was designed, consisting of FBGs arrays fixed along a flexible tube to be inserted into conventional boreholes to monitor underground layers displacements. Tests on the bench consisted of applying lateral displacements to curve the tube with the Bragg wavelengths acquired by an FBG interrogator. Then, a specially developed algorithm, applying the Frenet-Serret equations, and the cubic spline interpolation method were used to reconstruct the tube profile. For the first validation of the proposed method, the algorithm was applied to real data obtained in-field by a conventional inclinometer. The results of these tests showed a good agreement between the curve reconstruction and the plotted data of field measurements. The final validation was performed by applying lateral displacements to the instrumented tube and comparing the real tube profile measured by a laser ruler with the calculated profile by the algorithm. The errors found in all tests were less than 1% attesting that the proposed system can be an alternative methodology to the conventional techniques of geotechnical instrumentation, through continuous monitoring with fast response and in real-time, with possible application to quantify the mass movement of soils; movements from earth dams, landfills, and slopes.

A flare system in oil platform is a combustion stack used to burn off excess gases that cannot be processed and gases that have to be eliminated in emergency shutdown to avoid the risk of explosion. Gas flow measurement in flares is still considered challenging because the measurement has to attend many specific demands, quite different from any other flow measurement application. For these types of measurements many sensor technologies are available, however they are all very expensive, and only a few ones can attend all demands. The objective of this paper is to present a flow rate sensor based on Fiber Bragg Grating (FBG), cross-correlation and heatwave travel time techniques. The system was developed with inexpensive components and is little-intrusive, capable of attaining the rangeability of the flare demand and independent of gas composition, pressure and temperature.

In this paper, a compact fiber-optic current sensor (FOCS) based on in-fiber Fabry-Perot interferometer (FPI) and magnetostrictive transducer is presented. The in-fiber FPI sensor employed in the proposed FOCS was fabricated with a 273-μm section of capillary fiber spliced between two pieces of standard single-mode fiber (SMF). The in-fiber FPI sensor and a commercial fiber Bragg grating (FBG), which was used as a reference sensor for sensitivity comparison, were bonded to a small magnetostrictive actuator (Terfenol-D) and assembled in the proposed FOCS for electric current monitoring up to 800 A _rms using a commercial FBG interrogator. The in-fiber FPI sensor presented a sensitivity 84.4% higher than that of the FBG sensor. An alternative interrogation system based on an edge-filter technique with temperature compensation was also developed and employed for characterization of the proposed FOCS under the same range of electric current. Using the edge-filter interrogation system developed, the in-fiber FPI sensor presented a sensitivity 169.8% higher than that shown by the FBG. The results show that the proposed FOCS using an in-fiber FPI sensor presented high sensitivity to electric current sensing and, therefore, is a potential candidate for current monitoring in complement to conventional current transformers (CTs) as well as to conventional optical current transformers (OCTs).

Conventional pathogen detection methods require trained personnel, specialized laboratories and can take days to provide a result. Thus, portable biosensors with rapid detection response are vital for the current needs for in-loco quality assays. In this work the authors analyze the characteristics of an immunosensor based on the evanescent field in plastic optical fibers with macro curvature by comparing experimental with simulated results. The work studies different shapes of evanescent-wave based fiber optic sensors, adopting a computational modeling to evaluate the probes with the best sensitivity. The simulation showed that for a U-Shaped sensor, the best results can be achieved with a sensor of 980 µm diameter by 5.0 mm in curvature for refractive index sensing, whereas the meander-shaped sensor with 250 μm in diameter with radius of curvature of 1.5 mm, showed better sensitivity for either bacteria and refractive index (RI) sensing. Then, an immunosensor was developed, firstly to measure refractive index and after that, functionalized to detect Escherichia coli. Based on the results with the simulation, we conducted studies with a real sensor for RI measurements and for Escherichia coli detection aiming to establish the best diameter and curvature radius in order to obtain an optimized sensor. On comparing the experimental results with predictions made from the modelling, good agreements were obtained. The simulations performed allowed the evaluation of new geometric configurations of biosensors that can be easily constructed and that promise improved sensitivity.