New core–shell hyperbranched chitosan-based nanoparticles as optical sensor for ammonia detection

•New core–shell hyperbranched chitosan (HBCs) nanoparticles (NPs) were synthesized.•The HBCs NPs were investigated as a platform for the controlled synthesis of AgNPs.•Formation of HBCs NPs and the AgNPs was successfully confirmed.•AgNPs (20–50 nm) were formed homogeneously on the HBCs NPs surface.•The newly developed HBCs NPs-AgNPs worked as efficient ammonia optical sensor.

In this paper, preparation of new core–shell amino-terminated hyperbranched chitosan nanoparticles (HBCs-NH2) NPs is described. The synthesized nanoparticles were characterized using ninhydrin assay, FTIR, TGA, and FESEM. The newly prepared (HBCs-NH2) NPs were then used as a platform for facile and controlled synthesis of silver nanoparticles (AgNPs) which was confirmed using FTIR, UV–vis spectrometry, X-ray diffraction, SEM and HRTEM. Formation of the AgNPs was also noted upon changing the color of (HBCs-NH2) NPs suspension from colorless into yellow as well as through the appearance of surface plasmon resonance (SPR) peak at 400 nm. HRTEM showed a uniform and spherical morphology of the resulting HBCs-NH2 NPs with average size 400 nm, and the AgNPs were formed mainly on their surface with average size of 20–50 nm. The newly developed (HBCs-NH2) NPs-AgNPs showed a great potential as optical sensor for efficient detection of the ammonia concentration in solutions based on the change in the SPR.