The following analyses were performed for characterization of the nanoparticles: powder X-ray diffraction (PXRD), Fourier transforms infrared spectroscopy (FTIR), transmission electron microscopy (TEM), Dynamic light scattering (DLS), and $\zeta$ potential. The materials were purchased from Sigma-Merck merged chemical groups except the stated items.

To prepare the nanoceria, 0.012 mol resveratrol and 0.004 mol cerium nitrate hexahydrate (Ce(NO${}_3$)${}_3$.6H${}_2$O) were dissolved in 100 mL water separately. The resveratrol was sonicated then stirred vigorously. The cerium ion solution was then added dropwise to the first solution under vigorous stirring. After the addition of cerium ion solution, a milky-like appearance of the mixture confirmed the formation of the resveratrol-cerium complex. Then, the complex was separated using centrifugation and put in an oven at 500 °C overnight (8 h). The prepared nanoceria was used without further purifications. Afterwards, 0.5 g of the as-synthesized nanoceria was dispersed in 2.5 mL of a concentrated solution of Chloroauric acid (HAuCl${}_4$, 0.2 M). Then, it was centrifuged and washed one time with 10 mL of distilled water (DW) and dispersed again in 10 mL DW. Eventually, a solution of ascorbic acid (100 mL, 1 M) was prepared and dispersed nanoceria was added to this solution dropwise under vigorous stirring. The CeO${}_2$@Au core-shells were separated and washed several times with DW and applied for characterization and biological tests.

Liver cancer cell line (HepG2) and human foreskin fibroblasts (HFF) were attained from Iran’s Pasteur Institute. Cell developmental was performed in RPMI and DMEM media, supplemented with 100 $\mu$g/mL penicillin plus 10% FBS, and as a final point transferred to the incubator. In each well of a 96-well plate, cells were seeded, incubated 24 h, and after that the viability of cells was assessed in 24, 48, or 72 h to the biosynthesized NCs at the 0.16, 0.31, 0.63, 1.25, 2.50, 5.00 mg/mL concentrations using MTT assay.

The PXRD confirmed the formation of gold coated nanoceria (CeO${}_2$@Au core-shells), where the peaks of CeO${}_2$ and Au core-shells were compatible with the reference codes of 00-001-0800 and 00-001-1172, respectively (Fig. 1). The crystal systems, space groups and their numbers of both nanoceria and gold core-shells were cubic, Fm-3m and 225. The experimental 2tetha values (d-space, intensity) appeared at 38.48 ˚ (3.34 Å, 42.6%), 44.70 ˚ (2.02, 16.0%), 64.88 ˚ (1.44 Å, 11.9%), and 77.87 ˚ (1.23 Å, 16.3%) were related to the gold layer and the peaks observed at 28.88 ˚ (3.09 Å, 100.0%), 33.39 ˚ (2.68 Å, 36.7%), 47.79 ˚ (1.90 Å, 65.6%), 56.68 ˚ (1.62 Å, 53.3%), 59.42 ˚ (1.56 Å, 8.9%), 69.76 ˚ (1.35 Å, 10.0%), 76.99 ˚ (1.24 Å, 18.3%), and 79.43 ˚ (1.21 Å, 12.0%) were associated with the cerium oxide core.

Fig. 1.

The PXRD pattern of CeO${}_{\mathrm{2}}$@Au core-shells. The peaks of CeO${}_{\mathrm{2}}$ and Au core-shells were compatible with the reference codes of 00-001-0800 and 00-001-1172.

The calculated 2theta value (d space, intensity, HKL) of cerium oxide were 28.68 ˚ (3.11 Å, 100.0%, 111), 33.28 ˚ (2.69 Å, 25.0%, 200), 47.83 ˚ (1.90 Å, 80.0%, 220), 56.78 ˚ (1.62 Å, 60.0%, 311), 59.60 ˚ (1.55 Å, 10.0%, 222), 69.58 ˚ (1.35 Å, 10.0%, 400), 76.81 ˚ (1.24 Å, 25.0%, 331), and 79.08 (1.21 Å, 16.0%, 420) and the ones for gold layer were 38.27 ˚ (2.35 Å, 42.6%, 111), 44.60 ˚ (2.03 Å, 22.6%, 200), 64.68 ˚ (1.44 Å, 14.1%, 220), and 77.55 ˚ (1.23 Å, 17.0%, 311). The comparison of the calculated and experimental data indicated the successful synthesis of cerium oxide and the reduction of Au${}^{3+}$. According to the Scherrer equation, the crystallite (grain) size was calculated $\approx$24.2 nm.

The absorption bands of FTIR between $\approx$3200–3500 cm${}^{-1}$ were associated with the hydroxyl groups of the capped ascorbic acid and possibly on the surface of CeO${}_2$ (Fig. 2) [41, 42, 43]. The bands at 3100–2840 cm${}^{-1}$ can be related to the C–H stretching of ascorbic acid. Ascorbic acid usually shows at absorption signal at $\approx$1750–1760, specifically assigned to the carbonyl stretching of the $\gamma$-lactone ring in the ascorbic acid. The band absence after reduction of gold nanoparticle and bounding to the surface of nanoparticle could prove CeO${}_2$@Au core-shells coated by ascorbic acid [44]. The bands corresponded to C–H bending of the methyl group and carbonate species after calcination was appeared at 1454 and 1385 cm${}^{-1}$, respectively. The bands at 1132 and 1002 were also associated with the C–O stretching of the –OH group of the alcohol. The band observed at 500 cm${}^{-1}$ can also be assigned to the Ce–O vibration [45].

Fig. 2.

The FTIR spectrum of CeO${}_{\mathrm{2}}$@Au core-shells. The bands at 1454, 1385, 1132, 1002, and 500 cm${}^{\mathrm{-}\mathrm{1}}$ represents biochemical groups in the formation of NCs.

The TEM analysis was performed to determine the size of CeO${}_2$@Au core-shells in the solid phase. As shown in Fig. 3, the TEM images have revealed spherical, semi-spherical, and oval morphologies with particles sizes in the range of $\approx$20–170 nm. The images revealed that the appearance of larger sizes could possibly be due to the agglomeration of the several particles.

Fig. 3.

The TEM images of CeO${}_{\mathrm{2}}$@Au core-shells. The particles sizes are in the range of 20–170 nm.

The hydrodynamic size and the partial surface charge of the particles were measured using the DLS and $\zeta$ potential analyzer (Fig. 4). The analyses revealed the z-average of 229 nm, where nearly 50 and 90% of the particles showed particle sizes under 282 and 468 nm in order, respectively. The particle size according to intensity and number of size dispersion was 262 and 115 nm, respectively, whereas the partial surface charge was –24 mV. The analyses demonstrated that the information obtained from solid-phase sizes and the hydrodynamic sizes were compatible and acceptable. The PXRD and FTIR also confirmed the synthesis of the nanoparticles. The TEM images further indicated an aura around the particles that could be attributed to the formation of a gold layer around the nanoceria particles.

Fig. 4.

The hydrodynamic size of CeO${}_{\mathrm{2}}$@Au core-shells.

Nanotechnology-mediated delivery can be employed as a beneficial device in increasing the bioavailability of resveratrol. Nanoscience is an emerging part of investigation that operates at the crossways of biology, physico-chemicals, engineering, pharmacology, and medicine [22, 46, 47, 48]. Designing of NPs (nano particles) for an effective and controlled delivery of anticancer factors is being considered as one of the most important applications of nanoscience [24, 49, 50]. Few experiments have attempted to study potency of resveratrol for the synthesis of nanoparticles. It has been shown that the solid lipid NPs loaded with resveratrol can cross the cell membrane, while it can be enhanced via increasing the exposure time of cells to resveratrol [51]. Another study utilizing bovine serum albumin-bound resveratrol NPs in primary ovarian cancer of mice showed that not only the NP-bound resveratrol was easier to work with because of the improved solubility, it had also a greater influence on prevent of tumor growth, compared to pure resveratrol [52]. The anti-cancer effect of gold nanoparticles against breast, testicular, liver, and lung cancer cells has been proven in a concentration-dependent manner [30, 51, 52, 53, 54, 55]. In another study, the produced gold nanoparticles provided a safe and great system for the delivery of gapmers in cancerous cells, which meaningfully down-regulated mutant p53 proteins and changed molecular markers related to cell growth and apoptosis [56].

The anticancer activity of the produced NC was remarkable, whereas it possessed lower toxic effect on normal cells. The results clearly exhibited the toxicity of NC against cancer cells in a concentration and time dependent manner (Fig. 5). Although resveratrol alone was effective against cancer cells, higher efficacy in toxicity against cancer cell lines was observed in combination with nanoparticles.

Fig. 5.

Cellular toxicity effect of biosynthesized NCs and resveratrol against HepG2 as a cancerous cell lines (B and D) and HFF as a normal cell lines (A and C).