Detection of copper ions in an aqueous solution by a dual-peak long period fiber grating functionalized with a polypyrrole-chitosan composite.

A dual-peak long period fiber grating (DP-LPFG) sensor functionalized by polypyrrole-chitosan composite was proposed for sensitive detection of Cu2+ ions in aqueous solution. The nitrogen atom on the polypyrrole ring and the amino group on the chitosan chain in the complex matrix can chelate the Cu2+ ions. Thus, the refractive index of the overlay changed and further modulated the transmission spectrum of DP-LPFG. After special design, the double peaks can move in opposite directions with the increase of Cu2+ ion concentration, thereby greatly improving detection sensitivity. The linear sensitivity of the fabricated sensor was measured to be 9.12 and 2.14 nm/ppm (0.61 and 0.14 nm/µM) for concentrations of 0.1-0.5 (1.5 µM-7.5 µM) and 0.5-2 ppm (7.5 µM-30 µM), respectively. In addition, the Langmuir isothermal model was used to evaluate the overall response of the sensor to Cu2+ ions quantitatively, and the detection limit was determined to be 0.05 ppb (0.75 nM). This ingenious sensor offers a new solution for sensitive detection of heavy metal ions in environmental water.

Rapid and sensitive detection of ammonia in water by a long period fiber grating sensor coated with sol-gel silica.

A sensitive ammonia sensor based on long-period fiber grating (LPFG) is designed and manufactured for the detection of ammonia concentration in water. Femtosecond laser direct writing technology is used to write LPFGs on standard single-mode silica fiber. A thin layer doped with basic dyes is coated on the optical fiber for sensing by using the sol-gel method. The thicknesses of sol-gel layers, which play a key role in the sensitivity of the LPFG sensor, were carefully studied. Experimental results show that LPFG with a functional layer of ∼340 nm has the best sensing performance, and the detection limit is 0.08 ppm. The response time of the sensor is less than one minute, and the sensor has good repeatability with a short recovery time. Compared with other organic molecules and ions in water, the proposed LPFG sensor has not only good reusability, but also selectivity for the detection of ammonia.

Rapid and sensitive detection of Staphylococcus aureus by using a long-period fiber grating immunosensor coated with egg yolk antibody.

The rapid and reliable detection of bacteria plays an important role in clinical and veterinary practice. A stable, label free, compact, and sensitive long-period fiber grating (LPFG) sensor based on egg yolk antibody (IgY) was proposed for the detection of Staphylococcus aureus (S. aureus). LPFG was fabricated with laser writing technology, and specific IgY was further immobilized on the grating region and then combined with the corresponding bacteria. S. aureus was detected by tracking the change of resonance wavelength in the LPFG transmission spectrum caused by bacteria-antibody interaction induced by the increase of biological cover thickness and density after the immune reaction. The testing results showed that the proposed sensor was selective and sensitive to S. aureus measurement, and the detection limit is approximately 33 CFU/ml. The proposed antibody immobilization method is very simple, and the optical fiber can be manufactured in batch to reduce the cost. The detection time of the sensor is around 20 min, which is fast and suitable for detection. The assay was successfully applied for the quantitative analysis of S. aureus in natural waters and met the needs of on-site screening trace pathogenic bacteria in food safety control.