Rapid and efficient identification of Cd (II) ions in water with functionalized gold nano particle coated etched FBG Sensors

Cadmium (Cd (II)) is one of the important contributors to global water pollution, due to its prolonged biological half-life and carcinogenic nature. This study presents a selective and sensitive optical sensor based on an etched Fiber Bragg Grating (e-FBG) sensor coated with Mercaptosuccinic Acid (MSA) functionalized gold nanoparticles for the rapid identification of Cd (II). Carboxylic groups present in MSA self-assembles on gold nanoparticles to provide the selective binding sites for Cd (II), thereby inducing a Bragg wavelength shift (Δλ
_B
) with corresponding changes in Cd (II) concentrations. The present study demonstrates a linear dependency of Δλ
_B
with the molar concentration of Cd (II), with a limit of detection (LOD) of 10 × 10
^-15
Molar (fM, 0.00000112 ppb) and a dynamic range up to 100 × 10
^-9
Molar (nM, 11.24 ppb). These values align comfortably within the World health organization (WHO) limits (26 × 10
^-9
M or 3 ppb) for drinking water. The specificity of the sensor has been ascertained in the presence of other interfering metal ions like lead (Pb (II)), mercury (Hg (II)), arsenic (As (III)), sodium (Na (I)) and chromium (Cr (VI)). Further, the accuracy of the sensor (> 93 %), has been cross verified with Inductively Coupled Plasma Mass Spectroscopy (ICPMS). A good recovery percentage of > 95% obtained in drinking water samples, further highlights the sensors efficacy for practical applications. The linear response, good reproducibility (standard error ≤ 15 pm), portability and real-time monitoring capability, make the present sensor a promising candidate for on-site monitoring of Cd (II) in drinking water samples.