The properties of most nanocrystals are strongly connected with their size, shape, and surface structure. Recently, the fabrication of nanoparticles enclosed by high-index facets is becoming a hotspot in nano-research area. Generally speaking, the high density of low-coordinated atoms in the forms of atomic steps and kinks, high-index facets, are easy to be more active toward specific reactions than low-index planes which are composed of closely packed surface atoms [
47]. In this work, we also studied the difference between the two kinds of PtPd nanocubes with highindex or low-index facets. The total antioxidant activity of PtPd nanocubes were measured with the ABTS assay kits. With the interaction between ABTS and oxidant, ABTS solution will be converted into a green ABTS
·+ solution, while the production of ABTS
·+ can be inhibited in the presence of antioxidants. By measuring the absorbance of ABTS
·+ at 414 nm or 734 nm, we can indirectly calculate out the total antioxidant activity of PtPd samples. In
Fig. 2a, we found that both the absorbance of PtPd nanocubes with high-index facets at 414 nm and 734 nm were increased with elevated concentrations, and the absorbance at 414nm was higher than the one at 734 nm. In
Fig. 2b, by selecting 734 nm as the measurement wavelength, and 0.1 mg/mL as the measurement concentration, we found that the absorbance had a continuous increase in the first 750 min and the changes of absorbance value were becoming gentle gradually thereafter. These results revealed that our PtPd nanocubes with high-index facets had obvious antioxidant capacities, and such activities could last for 10 min at least. We also performed the same series of tests on the PtPd nanocubes with low-index facets samples. The results were displayed in Supporting information. We can notice that the highest absorbance value of PtPd nanocubes with low-index facets at 414 nm and 734 nm are 1.3 and 0.7, respectively, which are evidently lower than the PtPd nanocubes with high-index facets (Fig. S1a in Suporting information). Besides, we can see from Fig. S1b (Supporting information) that the relative total absorbance of low-index group is only about 1/6 of high-index group, although the trend of absorbance value change seemed to be no differences. Based on these evidences above, we considered that the asprepared PtPd nanocubes with high-index facets have better antioxidant activities than the low-index facets ones. In order to further explore the stability of PtPd nanocubes with high or lowindex facets, we detected the absorbance of the same samples at the first time and a week later. As shown in
Figs. 2c and
d, the value nearly had no obvious changes, which indicated that as-prepared PtPd nanocubes show high stability. In this part, we cleared that the crystal facet will influence the catalytic properties of PtPd nanocubes, and the high-index facets will exhibit more active antioxidant effects than the low-index facets. To explore the biological activities of the PtPd nanocubes with high-index facets on cells or mice, we carried on the biological experiments in the next parts.