Effect of Surface–Molecule Interactions on Molecular Loading Capacity of Nanoporous Gold Thin Films

Abstract

Surface-molecule interactions play an essential role in loading capacity and release kinetics in nanostructured materials with high surface area-to-volume ratio. Engineering the surfaces via immobilizing functional moieties is therefore a versatile means to enhance the performance of drug delivery platforms with nanostructured components. Nanoporous gold (np-Au), with its high effective surface area, well established gold-thiol chemistry, and tunable pore morphology, is an emerging material not only for drug delivery applications but also as a model system to study the influence of physicochemical surface properties on molecular loading capacity and release kinetics. Here, we functionalize np-Au with self-assembled monolayers (SAMs) of alkanethiols with varying functional groups and chain lengths, and use fluorescein (a small-molecule drug surrogate) to provide insight into the relationship between surface properties and molecular release. The results revealed that electrostatic interactions dominate the loading capacity for short SAMs (two carbons). As SAM length increases the loading capacity displays a nonmonotonic dependence on chain length, where for medium-length SAMs (six carbons) allow for higher loading plausibly due to denser SAM surface packing. For longer SAMs (11 carbons), the steric hindrance due to long chains crowds the pores, thereby hampering fluorescein access to the deeper pore layers, consequently reducing loading capacity.

Mutated Human P-Selectin Glycoprotein Ligand-1 and Viral Protein-1 of Enterovirus 71 Interactions on Au Nanoplasmonic Substrate for Specific Recognition by Surface-Enhanced Raman Spectroscopy

“…Various kinds of nanoporous surface have been fabricated in previous studies [33][34][35][36][37]. The high density and uniformity of Au nanoporous substrates make them suitable as SERS substrates.…”

Configurable microfluidic platform for investigating therapeutic delivery from biomedical device coatings

“…The morphology of np-Au is typically described by features such as ligaments and pores as described in Figure S2. The pore size was typically between 20 and 120 nm and the pore density was uniform across the entire np-Au sample [21][22][23][24] . The pore morphology of np-Au can be easily modified by thermal treatment, where enhanced gold surface diffusion leads to coarser ligaments yet reduced pore density 22 .…”

“…The pore morphology of np-Au can be easily modified by thermal treatment, where enhanced gold surface diffusion leads to coarser ligaments yet reduced pore density 22 . Specifically, the average pore sizes (extracted by digital image processing as described previously [21][22][23][24] ) for the np-Au samples displayed in Figure 3 are 65 nm, 70 nm, and 125 nm respectively for standard np-Au to that treated at 400 °C. The pores follow an interconnected tortuous path into thickness of the porous film (~600 nm).…”

“…Alternatively, the coating can be synthesized while doping it with drug molecules 17 . The drug molecules are adsorbed on the material surface either physically through weak intermolecular interactions (e.g., electrostatic, van der Waals) 18,19 or via chemical linkers 20,21 . After the loading step, the drug-loaded coating is rinsed, and immersed in deionized water or a physiology-relevant buffer (typically referred to as the elution medium) to initiate the drug release.…”

“…The microfluidic device and the schematics in two different modes are shown in Figure 1. The operation of the microfluidic platform is demonstrated with nanoporous gold (np-Au) as a model drug delivery coating, since it allows for a wide range of release kinetics due to its tunable morphology and surface chemistry [21][22][23][24] -two important factors that influence loading capacity and release kinetics.…”