Polyelectrolyte-Coated Gold Nanoparticles: The Effect of Salt and Polyelectrolyte Concentration on Colloidal Stability.

Melanie Fuller,Ingo Kӧper

doi:10.3390/polym10121336

Abstract

Gold nanoparticles are widely used in biomedical applications. Their ease of surface modification, biocompatibility and the presence of surface plasmons makes them ideal tools for a variety of investigations. Polyelectrolyte-coated gold nanoparticles are employed in areas such as imaging, drug delivery and gene therapy; however, it is not well understood how different factors such as the polyelectrolyte and salt concentration affect the coating on the nanoparticles and hence their performance. Here, these parameters were systematically varied and their effect on the stability of the colloidal nanoparticle suspension was monitored. An increase in the polyelectrolyte concentration from 0 to 30 mg/mL led to a red shift of the surface plasmon peak and an increase in the zeta potential. Concentrations between 5 mg/mL and 30 mg/mL resulted in the most stable systems, with 1 mg/mL being the most unstable. Stable nanoparticle suspensions were formed in salt concentrations below 50 mM, while higher concentrations caused colloidal instability and irreversible aggregation.

Highlights

Surface modified gold nanoparticles (AuNPs) are becoming more frequently used in biomedical applications and being able to understand the effects various surface coatings have on these NPs is becoming more important [1,2]
The type and length of polyelectrolyte remained unchanged for the duration of the experiment and the ionic strength of the medium was controlled to probe the effect of different PE concentrations on the coating of the AuNPs
The specific Mw of polydiallyldimethylammonium chloride (PDADMAC) was chosen as the longer chains can more effectively wrap around the AuNP, providing better surface coverage

Summary

Introduction

Surface modified gold nanoparticles (AuNPs) are becoming more frequently used in biomedical applications and being able to understand the effects various surface coatings have on these NPs is becoming more important [1,2]. The presence of surface plasmons allows changes in the local environment of the particle to be determined, and the ability to functionalise the surface with a range of moieties including polymers, proteins, DNA and polyelectrolytes makes AuNPs suitable for various applications. The layer-by-layer (Lbl) method of coating NPs and planar substrates using polyelectrolytes (PEs) is well established [3,4,5]. Lbl coatings with PEs have distinct advantages over other surface modification methods, the ease of assembly on a wide range of substrates. Polyanions and polycations can be used alternatively to build up multilayer systems which can be used in applications ranging from water treatment to protein immobilisation [7,8]

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Results

Conclusion