L-Cysteine Modified Gold Nanoparticles for Copper (II) Ion Detection Using Etched Fiber Bragg Grating Sensor

A highly sensitive and selective optical detection of copper (II) (Cu
$^{{2}+}$
) concentration in water has been proposed using L-cysteine functionalized gold nanoparticles (AuNPs) using an etched Fiber Bragg grating (eFBG) sensor. The eFBG sensor produces a Bragg wavelength shift (
$\Delta \lambda _{B}$
) in correspondence to the added Cu
$^{{2}+}$
concentration. The amino acid L-Cysteine facilitates the formation of core-satellite nano-assemblies of gold in the presence of Cu
$^{{2}+}$
. A linear wavelength shift is observed in accordance with the mediating Cu
$^{{2}+}$
concentration. The sensor’s detection limit is found to be 1 pM which is well within the World Health Organization (WHO) acceptable limit for safe drinking water and the dynamic range of the sensor lies between 1 pM and
$100 \mu \text{M}$
. The sensor is highly sensitive and selective to Cu
$^{{2}+}$
with a sensitivity of 230 pM
$10^{-{1}}$
M. The sensor has proven its capability as an ideal probe for onsite, real-time measurement of Cu
$^{{2}+}$
in drinking water by giving a recovery percentage of
$>$
90% in real water samples in addition to good reproducibility (standard error < 20 pM), high sensitivity, portability, and specificity.