Supplementary Information
Stability of silver nanoparticles: agglomeration and oxidation in biological relevant conditions.
Laura E. Valenti1,2 and Carla E. Giacomelli*1.
Figure 1SI displays the SPR spectra and particle size distribution measured by DLS of Ag-NP/citrate dispersed in different media at two incubations times. The SPR spectra of Figure 1A-SI compare the results of Ag-NP/citrate dispersed in different media (citrate, SBF and NaNO3) just after the synthesis. The spectral featuresindicate the agglomeration of Ag-NP/citrate dispersed in SBF or NaNO31. Figure 1B-SI shows the particle size distributions for the same dispersions displayedin figure 1A-SI, expressed as intensity (I) and number (N) distributions. Both representations give the same information when measuring monodisperse systems whereas polydispersity, shifts the I-distribution towards the contribution of large particles2. When large particles do not represent a significant population, the hydrodynamic diameter of the particles is more accurately calculated from the N-distribution. Combining both representations gives a proper notion of the particle size and the distribution. In fact, the I-distribution of Ag-NP/citrate dispersed in citratereflects a broad size distribution, whereas the N-distribution gives a 2 nm median hydrodynamic diameter 2. This effect become more evident with Ag-NP/citrate dispersed in either SBF or NaNO3, sincea second population of largeparticles is detected in the I-distribution. However, large particles contributing to these samplesare rather minor compared to smaller ones, as they are not detected in the N-distribution.
The absence of any noticeable changes in the SPR spectrum or DLS measurements (Figure 1C-SI and 1D-SI) indicates that Ag-NP/citrate dispersed in citrate are stable after storing for 24 hours. However, the SPR bands of Ag-NP/citrate incubated in either SBF or NaNO3vanish, and prevail the spectral features related to agglomeration. Moreover, the populations of large particle are evident on both representations of particle size distribution, indicating that their contribution becomes significant in quantity. In short, high ionic content induces the agglomeration of Ag-NP/citrate, mainly under long incubation time.
Figure 1SI: SPR spectra (A and C) and particle size distribution (B and D) of Ag-NP/citrate dispersed in citrate (black), SBF (red) and 0.15 mol L-1 NaNO3 (green) and measured after 15 minutes (A and B) and 24 hours of incubation (C and D).
Figure 2SI displays the SPR spectra (A and C) and particle size distribution measured by DLS (B and D) of Ag-NP/albumin dispersed in different media at two incubations times.A completely different behavior is observed with Ag-NP/albumin (Figure 2-SI); the Ag-NP SPR band at around 418 nm appears as a single and intense peak in the three media and both incubation times (a very slight broadening in the SPR band becomes evident when NPs are incubated in SBF). Furthermore, the normalized SPR spectra highlight the unchanged spectral features of Ag-NP/albumin dispersed in these different media. In addition, I- and N- distributions shows absence of changes in size when albumin coated NPs are dispersed in medium of high ionic content. These results indicate the presence of single Ag-NP/albumindispersed in these media with the same size, shape or coating.
Figure 2SI: Normalized SPR spectra (A and C) and particle size distribution (B and D) of Ag-NP/albumin dispersed in citrate (black), SBF (red) and 0.15 mol L-1 NaNO3 (green) and measured after 15 minutes (A and B) and 24 hours of incubation (C and D).
Figure 3SI displays the normalized SPR spectra shown in figure 1A. The fact that the spectra merge in a master curvehighlight the unchanged spectral features of Ag-NP/albumin dispersed in SBF for 30 minutes.
Figure 3SI: Normalized SPR spectra of Ag-NP/albumindispersed in SBF as a function of time (first 30 minutes of incubation) in the absence of H2O2.
REFERENCES:
1.Chambers, B. A. et al. Effects of chloride and ionic strength on physical morphology, dissolution, and bacterial toxicity of silver nanoparticles. Environ. Sci. Technol.48, 761–769 (2014).
2.Valenti, L. E. & Giacomelli, C. E. Unaffected features of BSA stabilized Ag nanoparticles after storage and reconstitution in biological relevant media. Colloids Surf. B. Biointerfaces132, 71–7 (2015).