Two competitive fiber optic sensors for the rapid, sensitive, and highly selective detection of mercury in water are designed, fabricated, and evaluated. A wavelength-modulated sensor based on an etched single-mode–multimode–single-mode (E-SMS) optical fiber structure and an intensity-modulated sensor based on fiber optics with a slanted end were fabricated by readily reproducible methods. The sensors were activated with a nanostructured chitosan/maghemite (
CS
/
Fe
2
O
3
) composite thin film for the selective detection of mercury ions (
Hg
2
+
) in water. The functionalized sensors were implemented to experimentally validate the potential of
CS
/
Fe
2
O
3
thin film for optical sensing of
Hg
2
+
in drinking water. The sensor based on the E-SMS structure exhibited a wavelength-modulated response with a sensitivity of up to 290 pm/(µg/mL), and the sensor based on the slanted end structure showed an intensity-modulated response with a sensitivity of
−
0.07
dBm/
(
µ
g/mL
)
. Validation of the experimental assay method proves the ability to selectively detect chemical interactions as low as 1 ng/mL (one part per billion) of
Hg
2
+
in water for both sensors. The high specificity of the two sensors was demonstrated by evaluating their responses to a number of potentially interfering metal ions in water. These sensors are cost-effective, simple to construct, and easy to implement, which makes them very promising for the on-site detection and monitoring of mercury in bodies of water.
Etched singlemode-multimode-singlemode (E-SMS) optical fiber structures are evaluated through the immobilization of a chitosan/Fe2O3 absorption layer for the detection of Hg2+ ions in water at concentrations as low as 0.001 µg/mL (1 ppb).
A cost-effective refractive index sensor based on optical fibers with 45° slanted surface at the distal end is presented. The sensors are used to measure refractive index of saline solutions with sensitivities of -136 dBm/RIU.
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