How to accurately predict solution-phase gold nanostar stability

Abstract

Unwanted nanoparticle aggregation and/or agglomeration may occur when anisotropic nanoparticles are dispersed in various solvents and matrices. While extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory has been successfully applied to predict nanoparticle stability in solution, this model fails to accurately predict the physical stability of anisotropic nanostructures; thus limiting its applicability in practice. Herein, DLVO theory was used to accurately predict gold nanostar stability in solution by investigating how the choice of the nanostar dimension considered in calculations influences the calculated attractive and repulsive interactions between nanostructures. The use of the average radius of curvature of the nanostar tips instead of the average radius as the nanostar dimension of interest increases the accuracy with which experimentally observed nanoparticle behavior can be modeled theoretically. This prediction was validated by measuring time-dependent localized surface plasmon resonance (LSPR) spectra of gold nanostars suspended in solutions with different ionic strengths. Minimum energy barriers calculated from collision theory as a function of nanoparticle concentration were utilized to make kinetic predictions. All in all, these studies suggest that choosing the appropriate gold nanostar dimension is crucial to fully understanding and accurately predicting the stability of anisotropic nanostructures such as gold nanostars; i.e., whether the nanostructures remain stable and can be used reproducibly, or whether they aggregate and exhibit inconsistent results. Thus, the present work provides a deeper understanding of internanoparticle interactions in solution and is expected to lead to more consistent and efficient analytical and bioanalytical applications of these important materials in the future. Graphical abstract ᅟ.

Facile immobilization of glucose oxidase onto gold nanostars with enhanced binding affinity and optimal function

“…The red-shifting in the GOx-modified AuNSs is plausibly due to growth in size of the AuNSs after attaching to the enzyme. No broadening of the LPSR spectrum for GOx-modified AuNSs was observed which implied the maintenance of the structural integrity of the AuNSs after conjugation [18,44].

Figure 2.Normalized UV–vis spectra of PVP-stabilized AuNSs, cysteine-modified AuNSs and AuNSs–Cys–GOx bioconjugates.

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What Does Nanoparticle Stability Mean?

“…16 The initial metastable state of these materials depends on the synthetic route used to generate the nanomaterials of interest. 6, 17–18 Because of the extensive literature on nanoparticle synthesis, we have focused this feature article on nanomaterial changes post-synthesis, that is, during storage and/or subsequent use.…”

“…17, 21 Both dependencies impact the likelihood of nanostructure aggregation. 17, 22 It is important to note that surface chemistry, which promotes the presence of primary nanoparticles without preventing interactions between reactants and metal atoms, is needed for retention of catalytic activity.…”

“…Common non-native surface chemistries include thin oxide, 24 sulfide, 23 or silica 25 layers, and the thickness and dielectric properties of these materials are tuned to promote a particular size-dependent property while suppressing dissolution or metal release into an environment. 19, 19, 21, 26, 17, 22, 23, 27…”

“…In all of these studies, the term “nanoparticle stability” describes the preservation of nanostructure properties as a function of composition, 6 shape, 17 size, 28 and surface chemistry. 29 Size dependent properties and/or targeted applications have also been considered.…”