Optical properties of dextran-stabilized silicon nanoparticles in aqueous medium

Silicon nanoparticles (Si-NPs) with initial sizes of the order of 100 nm were prepared by femtosecond laser ablation-fragmentation of microcrystalline silicon in water followed by drying and resuspending in water or in aqueous solutions of dextran. The prepared aqueous suspensions of Si-NPs without dextran and with dextran coating were investigated by means of the scanning electron microscopy, dynamic light scattering and optical absorption spectroscopy in the spectral range from 250 to 800 nm. The optical absorption of uncoated Si-NPs in an aqueous medium with different pH-level varied from 4 to 8 was found to decrease with time because of a process of the dissolution of those NPs in water. The dissolution rate depended nonmonotonically on the solution acidity (pH level) and the corresponding times were in the range from 50 to 180 hours. The addition of dextran into the solution was found to significantly decrease the dissolution rate of Si-NPs to 300 hours because of the coating of NPs with a polymer shell. The obtained results can be useful to develop new biomedical technologies involving Si-NPs as stabilized theranostics (therapy and diagnostics) agents. Key words: nanoparticles, dextran, biopolymer, optics, absorbance