Multimodal quantification of amino groups on silica nanoparticles using qNMR, potentiometry, optical assay, and XPS.
Source: BAM
Engineered nanomaterials (NMs) are increasingly utilized in photonic, electronic, medical and pharmaceutical fields, consumer products, and food. To advance NMs from laboratory research to industrial use, reliable methods for measuring key NM physicochemical properties are needed as well as test and reference materials and reference data to establish and validate measurement methods. This ensures a reliable and comparable characterization of application- and safety-relevant NM properties and quality control during NM production.
In addition to, e.g., size and shape, NM function, interaction with the environment, and how safe NMs are, depends on their surface and surface chemistry. The latter, which is largely determined by the chemical nature and density of surface functional groups (FGs) and ligands, plays a crucial role for NM dispersibility, stability, and processability. However, NM surface chemistry is often complex, sensitive to environmental conditions, and difficult to measure. Also, single measurement methods can provide incomplete or method-specific results.
To create versatile tools for quantifying FGs and ligands on NMs, in the project SMURFnano, funded by the European Metrology program, we explored analytical methods, differing in complexity and chemo-selectivity, principle of signal generation, and targeted measurands, and developed workflows that integrate multiple complementary techniques. Methods covered were cost-efficient potentiometric titrations and optical assays and advanced techniques such as quantitative nuclear magnetic resonance (qNMR) spectroscopy and X-ray photoelectron spectroscopy (XPS), measuring chemoselectively the number of FGs or the ratio of NM- and FG-specific elements on the NM surface. This multi-method characterization concept was explored for silica NMs which are amongst the most broadly utilized NMs worldwide, surface functionalized with amino groups, used to attach sensor dyes, recognition structures or biomolecules.
Our results demonstrate the importance of combining multiple analytical methods to reliably evaluate NM functionality and safety. Together with the measurement workflows and protocols developed and validated by BAM, as well as the reference test samples and reference data provided by BAM, this represents a decisive step toward sustainable, high‑performance NMs, their safer use, and the standardized measurement of key NM properties such as surface chemistry.
Quantifying surface groups on aminated silica nanoparticles of different size, surface chemistry, and porosity with solution NMR, XPS, optical assays, and potentiometric titration Check for updates
Isabella Tavernaro, Isabelle Rajotte, Marie-Pier Thibeault, Philipp C. Sander, Oltion Kodra, Gregory Lopinski, Jörg Radnik, Linda J. Johnston, Andreas Brinkmann, Ute Resch-Genger
Nanoscale Advances, 2025