Self-limiting gold nanoparticle surface assemblies through modulation of pH and ionic strength
Techniques to assemble monolayers of nanoparticles on surfaces are crucial for manufacturing devices for applications ranging from bio-sensing to tribology. Electrostatic-mediated assembly has numerous potential attributes, including self-limiting deposition and the ability to tune nanoparticle density and order through solution conditions. Herein, we establish the synergistic role of pH, ionic strength (I), and particle functionalization to identify the conditions for electrostatic assembly that yield maximum process stability and particle coverage. When the particle and surface are oppositely charged, the density of adsorbed 11.4-nm gold nanoparticles (AuNPs) could be tuned with both pH and ionic strength. The resulting monolayer arrays were disordered, in agreement with random sequential adsorption (RSA) theory. Finally, AuNPs stabilized by associated citrate molecules provided a larger processing window (pH 3–9, I = 1–10 mM) than AuNPs capped with a covalently bound mercaptopropanesulfonate (MPS) ligand shell (pH 3–9, I = 0.1–5 mM). These processing regimes provide a standard for predicting structural formations at reduced particle-surface interactions.
KeywordsGold nanoparticles pH Ionic strength APTES Self-assembled monolayers Random sequential adsorption Radial distribution function Voronoi tessellation
The authors would like to thank Jennifer Luna-Singh and Logan Ward for writing MATLAB code for structural analyses as well as Andrey A. Voevodin and Erick S. Vasquez for their technical consultation.
This work was financially supported by the Air Force Research Laboratory Materials & Manufacturing Directorate and the Air Force Office of Scientific Research.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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