Fluorescence and photocatalytic properties of hybrid nanostructures that comprise inorganic nanoparticles and biomolecules

Abstract

Hybrid nanostructures were prepared by functionalization of gold and silver nanoparticles with tryptophan and/or riboflavin biomolecules. The obtained bioconjugates were investigated by TEM and HRTEM and various spectroscopy methods (XPS, FTIR, UVvis and photoluminescence). The biomolecule functionalized nanoparticles were introduced in different cells (bacteria, Escherichia coli, fungi Candida albicans and HuH- 7 wt human cancer cells). The process of accumulation of the nanoparticles within the cells was followed by means of synchrotron excitation deep ultraviolet (DUV) fluorescence imaging. The DUV imaging showed that it was possible to distinguish the fluorescent signal pertaining to functionalized nanostructures from the autofluorescence of the cells. Also, a high spatial resolution of the deep UV fluorescence images (one pixel ∼154 nm) enabled us to probe nanoparticle accumulation with single cell resolution. Photocatalytic properties were studied on ZnO/Ag heterostructures. ZnO nanocubes were prepared using alginate biopolymer as a controlled environment for the particle growth. ZnO/Ag heterostructures were prepared by reduction of silver salts in the presence of nanocubes. High resolution scanning electron microscopy showed that the spherical silver nanoparticles were formed at nanocubes edges and vertices. UV–vis and photoluminescence spectroscopy measurements revealed that the surface plasmon resonance peak of the silver nanoparticles dominates the absorption spectra of the ZnO/Ag hybrid particles, while at the same time the Ag nanoparticles quench the ZnO emission. The photocatalytic activity of the ZnO/Ag heterostructure was faster than that of the pure ZnO and further improved with increasing the concentration of silver. Both the alginate-ZnO and alginate-ZnO/Ag nanostructures showed strong antimicrobial activities against gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) bacteria.