Kinetics of reaction of gold nanoparticles following partial removal of stabilizers

Abstract

Citrate-stabilized gold nanoparticles (Au NPs) of 17-nm diameter were allowed to react following partial depletion of the stabilizer using dialysis. Kinetics of the reaction was investigated by following time-dependent changes in the visible extinction spectrum. Thus, surface plasmon resonance peak (SPR) of isolated Au NPs (reactant) at 522 nm decreased, while SPR peak due to product-which was agglomerated Au NPs-occurring at 600 nm increased with time. The reaction followed first-order kinetics with respect to concentration of reactant (Au NP) with a rate constant on the order of (2.10 ± 0.34) 9 10 -3 min -1 . Further, product concentration correspondingly increased with time. Transmission electron microscopy investigation indicated the presence of individual NPs, along with agglomerated structures in the beginning of reaction-the extent of which increased with time, rather than the formation of smaller agglomerates. A model has been proposed based on reaction of individual NPs with agglomerated structures which accounted for the observed kinetics.

Control of Primary Particle Spacing in Gold Nanoparticle Clusters for Both High NIR Extinction and Full Reversibility

“…Notably, the shifts were very small for the sample with 500% excess citrate, indicating large spacings from the highly negative ζ (electrostatic repulsion) and the steric stabilization with the multilayers of citrate without any sintering. Similar behavior was reported by Dutta et al With the large excess free citrate, bi- and multilayers form via H-bonds, producing greater repulsion and spacings of the primary particles within the nanoclusters …”

“…Notably, the shifts were very small for the sample with 500% excess citrate, indicating large spacings from the highly negative ζ (electrostatic repulsion) and the steric stabilization with the multilayers of citrate without any sintering. Similar behavior was reported by Dutta et al 44 With the large excess free citrate, bi-and multilayers form via H-bonds, producing greater repulsion and spacings of the primary particles within the nanoclusters. 45 Despite extensive in situ studies of nanoparticle aggregation by DLS, 33,46 relatively few studies have quenched and recovered the Au nanoclusters, particularly for sub-10-nm primary particles and/or for nanoclusters smaller than 70 nm.…”

Glucosamine Phosphate Induces AuNPs Aggregation and Fusion into Easily Functionalizable Nanowires

“…The AuNPs we prepared are stable under the preparation conditions ([sodium citrate] = 6.8 × 10 −3 M) for prolonged times. However, when most of the citrate is removed (citrate-depleted AuNPS, see Section 2.3) they start very slowly to cluster [40,41] as can be seen in the absorbance spectrum (slight increase of absorbance >600 nm in Figure 2B) and increase in size (increase in absorbance at 525 nm in Figure 2B and TEM image in Figure 2C). Clearly, under these low passivation conditions, Ostwald ripening cannot be prevented.…”

Nanoparticle Clusters: Assembly and Control Over Internal Order, Current Capabilities, and Future Potential

“…In a recent example, Chattopadhyay and co-workers [58] describe the use of partial depletion of the stabilizer by dialysis to drive assembly of clusters from 17 nm citrate-stabilized Au NPs. Individual NPs and NPCs were observed initially and a model was proposed based on reaction of individual NPs with agglomerated structures, which accounted for the observed kinetics.…”