2.1.4. Efficiency of Functionalization Reaction

The efficient functionalization of SiNPs with both amino and carboxy groups was confirmed by FTIR, Schiff base reaction and zeta potential measurement. The aqueous NP dispersions were dried overnight at 80 ◦C, and the dried samples were used for FTIR measurements. The FTIR spectra were recorded using an FTIR spectrometer (Tensor 27, Bruker Optics, Ettlingen, Germany) equipped with an ATR (MIRacle ATR, Pike technologies, Fitchburg, WI, USA) accessory and Opus Software (Bruker Optics Version 6.5, Billerica, MA, USA). The Schiff base reaction was performed with salicylaldehyde to prove the presence of NH<sup>2</sup> groups with modified concentrations from Cuoq et al. (2012) [26]. Hereby, 10 µg of functionalized particles was added to 1 mL of absolute ethanol and 16 µL salicylaldehyde.
