Selective ultrasensitive FBG-SBL chemosensor for detection of copper ions in water resources based on plasmon resonance energy transfer

In this study, the gold (Au) coated fiber Bragg grating (FBG) probe decorated with Schiff base ligands (SBL) with variable denticity is proposed as a susceptible sensor for monitoring the copper ions (Cu2+) concentration in an aqueous solution. The sensing principle can be attributed to the interaction of the SBL coated on Au/FBG, which serves as anionic chelates with Cu2+, altering the environment refractive index and changing the surface plasmon resonance (SPR) condition. The sensitivity and limit of detection (LOD) through a Bragg wavelength shift are measured to be 23.1 pm/µM and 0.07 µM respectively, with a dynamic range of up to 4  µM (µM, 2.5 ppm), which is within the acceptable limit specified by the World Health Organization (WHO) for safe drinking water (1.3 ppm). The probe shows an assertive coordination behaviour towards Cu2+ for selective detection compared to other heavy metals. Excellent reusability (6 trial times) and specificity and portability make FBG-SBL chemosensor suitable for online monitoring of water resources.