Nanoparticles (NPs) are increasingly used in consumer products, which have aroused many concerns and debates regarding their fate in biological systems from a point of their safety/toxicity. Although a number of studies on the biological effects of NPs have been published, these are often complicated by the possible toxicity of conventional NPs, caused by contamination with chemical precursors or additives during their synthesis and/or purification procedures. To explicitly understand the toxicity basis of NPs, it is necessary to directly address a main problem related to their intrinsic/inherent toxicity and/or incompatibility with biological objects. The present study is designed to take advantage of a novel laser-assisted method called laser ablation to generate Ag, Au, Co, and Cu NPs in biocompatible aqueous solution, and to evaluate the toxicity of the resulting ultra-pure NPs. Our results show that the ultra-pure NPs with nascent surfaces possess moderate cytotoxicity to human cells in a cell-dependent manner.
We have investigated the effects of formalin on the assembly of colloidal gold nanoparticles (AuNPs) prepared by laser ablation of a solid gold target in deionized water. Upon addition of formalin, the surface plasmon resonance (SPR) band at 519 nm for pure AuNPs decreases and shifts to red while a new broad SPR band appears at ~700 nm. The red-shift is prominent with increase in the incubation time. The average size of the initial AuNPs is around 12 nm but it increases to 23 nm after addition of formalin. It turns out that formalin acts as a cationic surfactant for AuNPs with negative surface charge in the colloidal solutions. Furthermore, through analysis of the Raman spectrum of formalin and the density functional theory calculations, we confirm that methanediol is the main species in formalin which is in charge of the aggregation of AuNPs.
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