# Surface Chemistry-Dependent Binding Interactions between Kraft Lignin and Polyelectrolyte-Encapsulated Gold Nanoparticles

## TL;DR

This study explores how the surface chemistry of gold nanoparticles affects their binding with kraft lignin, revealing that non-electrostatic forces are key.

## Contribution

The study identifies that van der Waals forces, not electrostatics, drive lignin adsorption on polymer-coated gold nanoparticles.

## Key findings

- Lignin binding affinity was highest for PDADMAC-coated AuNPs.
- Electrostatic interactions were not the main factor in lignin adsorption.
- Hydrophobic and hydrogen bonding forces likely mediate lignin–AuNP interactions.

## Abstract

This study investigated the relationship between gold
nanoparticle
(AuNP) surface chemistry and the binding affinity of unfractionated
kraft lignin to polyelectrolyte-coated AuNPs. Specifically, fluorescence
quenching titrations were employed to determine lignin’s binding
affinity (K
a) to different charged polymer
surfaces displayed on 90 nm citrate-stabilized AuNPs, (poly­(allylamine
hydrochloride)) (PAH), polyacrylate (PAA), and poly­(diallyldimethylammonium
chloride) (PDADMAC). AuNP–lignin conjugates were characterized
by UV–vis absorbance spectroscopy, ζ-potential analysis,
and dynamic light scattering (DLS) measurements. The characterization
data showed that the size, surface charge and aggregation state of
the lignin–AuNP conjugates depended on the original surface
chemistry of the AuNP, in conjunction with the lignin concentration.
Fluorescence quenching titrations indicated that lignin’s binding
affinity for the polyelectrolyte-wrapped AuNPs was significantly higher
for PDADMAC-AuNP, while the Cit-, PAH-, and PAA-AuNPs gave statistically
indistinguishable affinity constants (p < 0.05). K
a values for PAA-AuNP, Cit-AuNP, PAH-AuNP, and
PDADMAC-AuNP were determined to be 87 ± 8 nM–1, 92 ± 11 nM–1, 107 ± 13 nM–1, and 240 ± 13 nM–1, respectively. This fluorescence
data indicates that electrostatic interactions are not the primary
driving force in lignin adsorption to these AuNP surfaces. Instead,
van der Waals forces (such as hydrophobic interactions and hydrogen
bonding) are likely more important in mediating lignin–AuNP
adsorption on this length scale. Understanding how the surface chemistry
of polymers mounted on nanoscale surfaces impacts lignin adsorption
will inform the process of eco-corona formation on polymer-coated
nanoscale surfaces.