Colloids and Surfaces A: Physicochemical and Engineering Aspects
The influence of agglomeration of nanoparticles on their superoxide dismutase-mimetic activity
Graphical abstract
Highlights
► Three types of nanoparticles CeO2, GdYVO4:Eu and CePO4:Tb are compared in this work. ► Colloidal systems are in a dynamic equilibrium of agglomerization-peptization. ► Superoxide dismutase mimetic activity of NP increases during the decay of agglomerates.
Introduction
In recent years, there has been a dramatic increase in research, technology, and production of nanoparticles. Some of these nanoparticles are widely used in a diverse array of applications including material science and biology. Nanoparticles of metals, semiconductors and dielectric materials have useful properties such as fluorescence, optoelectronic and magnetic behavior [1]. Nanoparticles possess unique properties with potentially wide-ranging therapeutic applications [2]. The development of inorganic luminescent nanoparticles offers a unique opportunity for biologists to use their high photostability for the dynamic tracking of individual species during in vitro or in vivo experiments [3]. These unusual properties depend on individual as well as collective properties of nanoparticles and their sizes and shapes [4], [5], [6]. On the one hand, nanoparticles can exhibit antibacterial and antioxidant properties; on the other hand, there is potential hazard of nanoparticles on human health [7], [8], [9]. It has become important to determine the influence of nanomaterial on biological objects. Results of toxic action studies for various nanoparticles seem to be contradictory. In particular, some sources indicate that the fullerene, cerium oxide and yttrium oxide nanoparticles have an antioxidant effect [10], [11], [12], [13], [14], according to other sources, the effect is prooxidant [16], [17], [18]. The ability of nanoparticles to protect or destroy cells depends not only on their elemental composition, but also on their geometric parameters, the environment, the crystal structure and agglomeration of primary particles in the investigated systems [9], [18], [19], [20], [21]. The concentration of nanoparticles also affects the investigated biological systems. For example, in [10] was shown that OH removing efficiency of hydrated C60 fullerene was in inverse correlation with fullerene concentration. It was conjectured that the antiradical action of fullerene in water medium is generally due to a “nonstoichiometric” mechanism, supposedly to a hydrated free radical recombination (self-neutralization), which is catalyzed by specific water structures ordered by fullerene. One of the factors for increased antioxidant activity together with a decrease in the concentration of nanoparticles may be the agglomeration of particles at higher concentrations [11]. The size growth of a nanoparticle can occur by aggregation and agglomeration. Small particles have larger surface area and higher particle number than bigger particles at the same mass concentration. Thus, extremely small nanoparticles (diameter <3 nm) could not be easily stabilized and aggregated rapidly [19], [20]. A study of small nanoparticles’ aggregation and agglomeration influence on an experimental model is of particular importance for a correct interpretation of results of biological research. Recent studies have provided evidence that cerium oxide nanoparticles act as direct antioxidants to protect cells from various forms of lethal stress in vitro and exhibit SOD mimetic activity [14], [15], [16], [17], [22], [23], [24].
Previously, we have reported that spherical luminescent particles of GdYVO4:Eu3+ were accumulated in the nuclei of liver cells [25]. In this paper, we carry out a comparative study of CeO2−x, GdYVO4:Eu3+ and CePO4:Tb3+colloidal solutions with nanoparticles’ size <3 nm.
Section snippets
Materials
Lanthanide chlorides 99.9% and anhydrous sodium metavanadate (NaVO3, 96%) (“Acros Organics” company) were all used without further purification. Sodium tripolyphosphate (Na5P3O10, 98%), sodium citrate (Na3C6H5O7, 99%), hexamethylenetetramine ((CH2)6N4, 99%), H2O2, 35%, NH4OH, 25% from “Macrochem” Co. Ltd. were used. The inorganic salts and isopropanol (coagulants) were commercial products of reagent grade. Na3VO4 solution with pH value of 13 was obtained by adding solution NaOH (1 mol/L) to NaVO3
Results and discussion
GdYVO4:Eu3+, CeO2−x and CePO4:Tb3+ nanoparticles (NPs) with diameter of 1.9 ± 0.3 nm were stabilized by sodium citrate and had identical concentration of solid phase in water (Fig. 1A–C). Nanoparticles of size less than 3 nm possess high surface activity and diffuse mobility that defines their aspiration to aggregation. Only stabilization of such particles (by surface-active agents) can be used to preserve the stability of sols [13]. The hydrosols which were obtained under our conditions and stored
Conclusion
This work is devoted to a comparative analysis of colloidal solutions, with the varied nature of a solid phase (CeO2−x, GdYVO4:Eu3+ and CePO4:Tb3+). The nanoparticles of the diameter 1.9 ± 0.3 nm stabilized by sodium citrate were used. The ultramicroheterogeneous dispersion in water was found to be a typical hydrophobic colloidal system with negatively charged particles surface. The coagulation by inorganic electrolytes occurs according to the DLVO theory.
It was found that nanoparticles of the
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Comparative analysis of photocatalytic activity of aqueous colloidal solutions of ReVO<inf>4</inf>:Eu<sup>3+</sup>(Re = La, Gd, Y), CePO<inf>4</inf>:Tb, CeO<inf>2</inf> and C<inf>60</inf>
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