The work is devoted to the defining of regularities of formation and stabilization of polyfunctional nanostructured materials based on noble metals in the presence of the essential amino acid tryptophan (Trp) as a biocompatible bifunctional agent for the reduction of metal ions and stabilization of formed nanoparticles (NPs). Experimental approaches for the directed chemical and photochemical synthesis of nanoparticles of silver and gold, their bimetallic compositions, as well as magneto-plasmonic nanocomposites [Fe3O4/M] in an aqueous medium have been developed, and biologically active nanosystems with controlled optical properties and morphology have been obtained.
It was found that the use of Trp during the synthesis of metal NPs eliminates the toxic effects of obtained nanosized systems due to avoiding the use of common reagents such as strong reducing agents and stabilizers like surfactants.
The effect of pH of the medium of the initial components, as the main factor influencing the properties of the formed NPs, in particular optical properties (localized surface plasmon resonance band characteristics), surface charge (zeta-potential) and size distribution, was analyzed (due to the existence of cationic, neutral and anionic states of tryptophan formed at different pH and the formation of metal hydroxocomplexes).
An important problem of stabilization of metal NPs in such systems is solved and long-term stability of solutions (more than 3 years) is achieved. It is shown that in order to obtain the most stable and monodisperse NPs, chemical reduction of metal ions must be carried out in an alkaline medium at boiling temperature.
Nanoscale metal systems have a characteristic yellow (silver) and red (gold) color, which is reflected in the absorption spectra as bands of localized surface plasmon resonance (LSPR) of metals with maxima located in the visible region at 420 and 525 nm, respectively. In the case of bimetallic AgAu NPs of alloy type with different metal ratio (AuAg(3:1), AuAg(1:1) та AuAg(1:3)), the maximum of the LSPR band is located between the maxima of the bands inherent to the individual metals, and depend on their ratio of Ag:Au in the nanoparticle.
It is shown that the use of polimer pluronic F68 used during the synthesis as an additional stabilizer allows to increase the metal content in the nanoscale system up to 40 times (CM = 4·10-3M), which corresponds to the value of 0.4-0.8 mg/ml of metal, when particles do not lose nanoscale and retain the initial optical characteristics.
Bimetallic AgAu nanoparticles of the core-shell type were obtained using the method of sequential reduction of metal ions. Such NPs are characterized by the presence of a single LSPR band in the absorption spectra, and its position depends on the distribution of metals within the NPs. The formation of a metal shell on the surface of another particle is evidenced by the appearance of a new absorption band of LSPR after the disappearance of the absorption band of the pre-formed core. This process occurs for both the Ag core Au shell and Au core Ag shell systems.
It is shown that the composition and topology of NPs are factors that determine their antitumor activity. It was found that in the conditions of in vitro and in vivo experiment (with mouse Lewis lung cancer), the most effective bimetallic NPs where AuAg(3:1) and Ag core Au shell, that can become the basis of effective antitumor nanomaterials.
To obtain low-toxic and highly efficient metal NPs, including nanostructures of the core-shell type, a method of photochemical reduction of metal ions in the presence of tryptophan using ultraviolet irradiation with = 280 nm is proposed, which activates the redox process at lower temperatures due to excitation of photoactive indole moiety of Trp. It is shown that this approach allows to accelerate the process of NPs formation up to 2-10 times (compared to chemical reaction), depending on the experimental conditions (irradiation power, exposure time and temperature), and obtain stable nanosized metal systems with defined particle size (25-50 nm), due to the influence on the initial stage of the process - the reduction of metal ions.
Chemical and photochemical methods for the synthesis of the [Fe3O4/Au] magneto-plasmonic nanocomposites (MPNC) with a core-satellite structure have been developed. The presence of nanosized iron oxide allows magnetic field induced concentration of MPNC with further increase of optical response of obtained systems in longwavelength region (800-1000 nm) due to the formation of MPNC aggregates. It has been demonstrated in vitro that laser irradiation of MPNC attached to the surface of HeLa cancer cells leads to the photothermal effect of gold.
Key words: metal nanoparticles, localized plasmon resonance, nanoscale systems, gold, silver, bimetallic, nanoparticles of the alloy and core-shell type, tryptophan, biological activity, magneto-plasmonic nanocomposites.
