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 <tex-math notation="LaTeX">^2+ </tex-math> ) 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 ( <tex-math notation="LaTeX">Δ λ B </tex-math> ) in correspondence to the added Cu <tex-math notation="LaTeX">^2+ </tex-math> concentration. The amino acid L-Cysteine facilitates the formation of core-satellite nano-assemblies of gold in the presence of Cu <tex-math notation="LaTeX">^2+ </tex-math> . A linear wavelength shift is observed in accordance with the mediating Cu <tex-math notation="LaTeX">^2+ </tex-math> 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 <tex-math notation="LaTeX">100 μ M </tex-math> . The sensor is highly sensitive and selective to Cu <tex-math notation="LaTeX">^2+ </tex-math> with a sensitivity of 230 pM <tex-math notation="LaTeX">10^-1 </tex-math> M. The sensor has proven its capability as an ideal probe for onsite, real-time measurement of Cu <tex-math notation="LaTeX">^2+ </tex-math> in drinking water by giving a recovery percentage of <tex-math notation="LaTeX">$>$ </tex-math> 90% in real water samples in addition to good reproducibility (standard error < 20 pM), high sensitivity, portability, and specificity.