Expanding the Toolbox of Simple, Cost-Efficient, and Automatable Methods for Quantifying Surface Functional Groups on...

Area of Science:

• Nanomaterial Science
• Analytical Chemistry
• Surface Chemistry

Background:

• Accurate measurement of surface functional groups (FGs) on nanomaterials (NMs) is vital for NM dispersibility, stability, and predictable functionality.
• Current methods for FG quantification can be complex or costly, hindering routine application in NM production, quality control, and risk assessment.
• There is a need for simple, cost-efficient, and automatable methods for screening and quantifying broadly utilized FGs on NMs.

Purpose of the Study:

• To develop and validate a simple, cost-efficient pH titration method for measuring total (de)-protonable FGs on aminated silica nanoparticles (SiO2 NPs).
• To assess the accuracy and robustness of the optimized pH titration workflow across different operators and laboratories.
• To compare the titration method with established analytical techniques like quantitative nuclear magnetic resonance (qNMR) and thermogravimetric analysis (TGA) for method validation.

Main Methods:

• Adaptation of pH titration with potentiometric and optical readout for nanomaterial surface analysis.
• Stepwise optimization of titration workflows for aminated silica nanoparticles (SiO2 NPs).
• Validation by cross-comparison with quantitative nuclear magnetic resonance spectroscopy (qNMR) and thermogravimetric analysis (TGA), and the fluorescamine (Fluram) assay.

Main Results:

• The NM-adapted pH titration method successfully measured the total number of (de)-protonable FGs on aminated SiO2 NPs.
• The method demonstrated accuracy and robustness through inter-laboratory assessments and cross-validation with qNMR, TGA, and the Fluram assay.
• Comparison highlighted the importance of measuring both total titratable groups and reporter-specific FGs for comprehensive surface characterization.

Conclusions:

• The developed pH titration method offers a simple, cost-efficient, and robust approach for quantifying surface functional groups on nanomaterials.
• This method can enhance quality control in NM production, improve stability studies, and facilitate large-scale data generation for NM regulation and standardization.
• Combined application of pH titration with optical assays provides a powerful tool for nanomaterial surface analysis and safe-by-design implementation.