Quantifying Thiol Ligand Density of Self-Assembled Monolayers on Gold Nanoparticles by Inductively Coupled Plasma-Mass Spectrometry

Autor(en)

Helmut Hinterwirth, Stefanie Kappel, Thomas Waitz, Thomas Prohaska, Wolfgang Lindner, Michael Lämmerhofer

Abstrakt

Gold nanoparticles (GNPs) are often used as colloidal carriers in numerous applications owing to their low-cost and size-controlled preparation as well as their straightforward surface functionalization with thiol containing molecules forming self-assembling monolayers (SAM). The quantification of the ligand density of such modified GNPs is technically challenging, yet of utmost importance for quality control in many applications. In this contribution, a new method for the determination of the surface coverage of GNPs with thiol containing ligands is proposed. It makes use of the measurement of the gold-to-sulfur (Au/S) ratio by inductively coupled plasma mass spectrometry (ICP-MS) and its dependence on the nanoparticle diameter. The simultaneous ICP-MS measurement of gold and sulfur was carefully validated and found to be a robust method with a relative standard uncertainty of lower than 10%. A major advantage of this method is the independence from sample preparation; for example, sample loss during the washing steps is not affecting the results. To demonstrate the utility of the straightforward method, GNPs of different diameters were synthesized and derivatized on the surface with bifunctional (lipophilic) omega-mercapto-alkanoic acids and (hydrophilic) mercapto-poly(ethylene glycol) (PEG)(n)-carboxylic acids, respectively, by self-assembling monolayer (SAM) formation. Thereby, a size-independent but ligand-chain length-dependent ligand density was found. The surface coverage increases from 4.3 to 6.3 molecules nm(-2) with a decrease of ligand chain length from 3.52 to 0.68 nm. Furthermore, no significant difference between the surface coverage of hydrophilic and lipophilic ligands with approximately the same ligand length was found, indicating that sterical hindrance is of more importance than, for example, intermolecular strand interactions of Van der Waals forces as claimed in other studies.

Organisation(en)

Institut für Analytische Chemie, Physik Nanostrukturierter Materialien

Externe Organisation(en)

Universität für Bodenkultur Wien, Eberhard Karls Universität Tübingen

Journal

ACS Nano

Band

7

Seiten

1129-1136

Anzahl der Seiten

8

ISSN

1936-0851

DOI

https://doi.org/10.1021/nn306024a

Publikationsdatum

2013

Peer-reviewed

Ja

ÖFOS 2012

210006 Nanotechnologie, 104002 Analytische Chemie, 103018 Materialphysik

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/a4ef8611-8350-48bc-bb81-3441f523e7ee