Rapid and Efficient Identification of Cd (II) Ions in Water With Functionalized Gold Nanoparticle 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 (gnps) for the rapid identification of Cd (II). Carboxylic groups present in MSA self-assembles on gnps to provide the selective binding sites for Cd (II), thereby inducing a Bragg wavelength shift (
$\Delta \lambda _{B}$
) with corresponding changes in Cd (II) concentrations. This study demonstrates a linear dependence of
$\Delta \lambda _{B}$
with the molar concentration of Cd (II), with a limit of detection (LOD) of
$10\times 10^{-{15}}{}$
Molar (fM, 0.00000112 ppb) and a dynamic range up to
$100\times 10^{-{9}}$
Molar (nM, 11.24 ppb). These values align comfortably with the World Health Organization (WHO) limits (
$26\times 10^{-{9}}$
M or 3 ppb) for drinking water. The specificity of the sensor has been ascertained in the presence of other interfering metal ions such as 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
$\le 15$
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.