A detailed investigation on the effect of preparation method on the structural, magnetic, and acidic properties of cobalt ferrite nanoparticles prepared by sol-gel and co-precipitation is presented. Citric acid and ethylene glycol were used as gelling agents, while sodium hydroxide and aqueous ammonia were used as precipitating agents. The resulting ferrites were calcined at 450 ℃ and 750 ℃. Sharper X-ray diffraction (XRD) peaks were observed for the samples calcined at 750 ℃, indicating greater crystallinity of the samples calcined at higher temperature. Average crystallite sizes fell in the ranges of 7.1-21.1 nm and 30.4-42.1 nm for the samples calcined at 450 ℃ and 750 ℃, respectively. The infrared spectra revealed two main absorption bands, the high frequency band ν 1 around 600 cm 1 and the low frequency band ν 2 around 400 cm 1 arising from stretching vibrations of the oxygen bond with the metal in the tetrahedral (A) and octahedral (B) sites in the spinel lattice. Agglomeration of particles was observed in the scanning electron microscopy (SEM) images. Magnetic parameters of CoFe 2 O 4 nanoparticles greatly depended on calcination temperature and preparation techniques. Ammonia temperature programmed desorption (TPD) measurements indicated that weak acid sites predominate medium strength sites, while the number of strong acid sites is the least. Cumulative acidity decreased for the samples calcined at higher temperature. The results underline the effect of preparation conditions on the morphology, crystallite size, and magnetic properties of nano ferrites.

In this work, we report a one-step green synthesis of gold nanoparticles (AuNPs) by microwave irradiation using nontoxic and biodegradable polysaccharide chitosan as a reducing and stabilizing agent. The interaction between gold nanoparticles with the amine group of chitosan was confirmed by Fourier transform infrared spectroscopy analysis, and the stability of the nanoparticle is ascertained by zeta potential measurements. Transmission electron microscopy photograph and dynamic light scattering measurements confirmed the average size of gold nanoparticles as 25 nm. The ability of the synthesised gold nanoparticles as a catalyst for the reduction of eosin dye in the presence of NaBH 4 was monitored by means of spectrofluorometry and spectrophotometry. It is found that the NaBH 4 -induced reduction of eosin is enhanced in the presence of AuNPs even without a catalyst. Time-resolved fluorescence decay studies also confirmed the reduction of eosin in the presence of AuNPs.

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Gold nanoclusters (AuNCs) are an intensely pursued class of fluorophores with excellent biocompatibility, high water solubility, and ease of further conjugation. However, their low quantum yield limits their applications, such as ultra-sensitive chemical or molecular sensing. To address this problem, various strategies have been adopted for augmenting their fluorescence intensity. Herein, we report a facile and scalable approach for the fluorescence enhancement of bovine serum albumin (BSA) capped AuNCs (BSA-AuNCs) using periodic, close-packed polystyrene colloidal photonic crystals (CPCs). The slow photon effect at the bandgap edges is utilized for the increased light-matter interactions and thereby enhancing the fluorescence intensity of the BSA-AuNCs. Compared to the planar polystyrene control sample, the CPC film yielded a 14-fold enhancement in fluorescence intensity. Further, we demonstrated the as-prepared BSA-AuNCs-CPC as a solid-state platform for the highly sensitive and selective fluorescence turn-off detection of creatinine at nanomolar level.