On the use of pH titration to quantitatively characterize colloidal nanoparticles.

Functional nanoparticles (NPs) for bioapplications have been achieved, thanks to synthesis providing high quality nanocrystals, efficient procedures for transfer in water, and further conjugation of (bio)active molecules. However, these nanomaterials are still subjected to batch-to-batch variability and investigations of their physicochemical properties and chemical reactivity are still in their infancy. This may be due to lack of a routine, cost-effective, and readily available quantitative method for characterizing functional NPs. In this work, we show that pH titrations can be a powerful tool for investigating the surface properties of charged NPs and quantifying their surface functionalities. We demonstrate how this method can be useful in characterizing the colloidal and chemical stability, composition, and purity of the nanomaterial. The method also shows potential for the optimization of conjugation conditions.