Optical Ammonia-Sensing Probe Based on Surface-Plasmon Resonance of Silver-Nanoparticle-Decorated Superparamagnetic Dendritic Nanoparticles

Ammonia is a serious contaminant of aquaculture water due to its continuous release into the water environment during the biological processes of aquatic animals. Ammonia accumulation in water has negative environmental impacts, including eutrophication and the death of aquatic organisms. Therefore, sensitive and accurate determination of ammonia is an urgent need, especially in pisciculture systems. Here, we report the fabrication of a novel magnetic-hyperbranched nanomaterial-based ammonia-sensing probe for the fast and sensitive determination of ammonia in water. The proposed probe is composed of poly(amidoamine) (PAMAM)-coated superparamagnetic iron oxide nanoparticles (SPIONs) decorated with silver nanoparticles. Changing the ammonia concentration is associated with a corresponding change in the surface plasmon resonance property of silver nanoparticles. The proposed nanosystem was characterized with FTIR spectroscopy, SEM imaging, energy-dispersive X-ray (EDX) analysis, TEM imaging, X-ray diffractometry (XRD), and vibrating sample magnetometry (VSM). The TEM images showed a homogenous and uniform distribution of the nanoparticles with an average nanoparticle size of 200 nm, while the surface silver nanoparticles have an average particle size of 10-50 nm. The proposed optical ammonia sensor was successfully used to determine the concentration of ammonia in water samples by measuring the change in the solution absorbance at 428 nm. The obtained results revealed high recovery values (96.3-104.7%) and very low detection (LOD = 5.69 mg/L) and quantification (LOQ = 18.96 mg/L) limits. The standard plot is linear in the concentration range of 10-50 mg/L with an r(2) value of 0.9980. Sandell's sensitivity of the most promising sensor (NP-III) among the investigated systems was found to be 0.15 mu g/cm(2), which indicates high sensitivity.