The Synthesis and Analysis of the Cytotoxicity of Al2O3-Supported Silver Nanoparticles Prepared by the Plasma Chemical Process Initiated by Pulsed MW Radiation in the Al2O3-Ag Powder Mixtures

Abstract

An original plasma chemical process initiated by microwave discharge in a mixture of metal and dielectric powders was applied to prepare specific materials, which consisted of microsized spherical particles of aluminum oxide covered with silver nanoparticles. The prepared materials are highly uniform in shape, size distribution, and composition. Their cytotoxicity was investigated using the human cell lines MCF7, HEK293T, A549, and VA-13 and the bacterial strains E. coli JW5503 (ΔtolC) and E. coli K12. Their cytotoxicity was found not to exceed the cytotoxicity of the starting materials. Thus, the prepared materials can be considered highly promising for catalysis and biotechnology applications.

Keywords: aluminum oxide; cytotoxicity; microwave radiation; plasma chemical process; silver.

Figure 1

(a) SEM image of the starting aluminum oxide powder; (b) SEM image of the starting silver powder.

Figure 2

The typical optical emission spectra obtained from the free volume of the reactor ((a), spectrometer 11) and the bottom side of the powder ((b), spectrometer 10) for the Al₂O₃ + 20 wt.% Ag mixture.

Figure 3

SEM image (a) and elemental maps (b–d) of the particles collected from the wall of the quartz cylinder after the treatment of the Al₂O₃ + 5 wt.% Ag mixture.

Figure 4

Detailed SEM image (a) and elemental maps (b–d) of the particles collected from the wall of the quartz cylinder after the treatment of the Al₂O₃ + 5 wt.% Ag mixture.

Figure 5

Concentration–viability dependencies for cells treated by studied substances. Doxorubicin is given for comparison. Results for the initial Al₂O₃ and Ag powders are shown in the top row. Middle row: starting mixtures containing 2 wt.%, 5 wt.%, and 20 wt.% of silver. Bottom row: the mixtures treated with MW radiation, and samples collected from the walls of the quartz tube (marked as ‘wall’) and from the surface of the powder in the reactor (marked as ‘powder’).

Figure 6

Evaluation of the bacterial toxicity of the particles toward (a) the hypersensitive strain of E. coli JW5503 (ΔtolC, with impaired efflux) and (b) the standard strain of E. coli K-12. The figure shows the starting mixtures containing 2 wt.%, 5 wt.%, and 20 wt.% of silver and the mixtures treated with MW radiation, the samples collected from the walls of the quartz tube (marked as ‘wall’) and from the surface of the powder in the reactor (marked as ‘powder’), and the control antibiotics («ery» is erythromycin, and «lev» is levofloxacin).

Figure 7

(a) General scheme of the plasma chemical setup for the treatment of the mixtures of powders with pulses of microwave radiation: 1—high-power gyrotron (0.8 MW/75 GHz), 2—quasi-optical pathway, and 3—plasma chemical reactor; (b) 1—quartz plate, 2—isolating layer of dielectric powder (optional), 3—reaction mixture, 4—gas phase, 5—plasma phase, 6 and 7—bottom- and side-view windows, 8—high-speed camera, 9—regular optical camera, 10 and 11—AvaSpec optical emission spectrometers (operating in the range of 370 ÷ 920 nm with a 0.7 nm resolution, and in the range 250 ÷ 800 nm with a 0.8 nm resolution, respectively, obtaining 100 spectra at 4 ms intervals), and 12—quartz cylinder; and (c) image of the initiator (stainless-steel sponge) on the quartz cylinder.