## 2 Materials and Methods
### Dynamic Light Scattering (DLS) and \(\zeta\)-Potential (ZP)  
A NanoPartica SZ-100 apparatus equipped with a 514 nm 'green' laser from HORIB-Scientific was used. Reproducibility was verified by collection and comparison of sequential measurements in at least three separate series of experiments. The samples were not filtered before measurements. At least five measurements were made for each sample and data averaged. X-ray Photoelectron Spectroscopy (XPS) and Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) Analysis  
After centrifugation step, the obtained pellets were deposited on silica wafer and dried at the air for the XPS and ToF-SIMS analyses. XPS measurements were performed using a PHI 5000 VersaProbe apparatus equipped with a monochromatic Al Ka line source (1486.7 eV). Typically, the pressure in the analysis chamber was 5 \(\times\) 10\({}^{-9}\) Torr. For high resolution scans, pass energy and energy step of the analyser were fixed to 23.5 eV and 0.2 eV, respectively. Dual beam charge neutralization from an electron gun (1 eV) and the Ar ion gun (\(<\)10 eV) were used for charge compensation on the sample surface during the measurements. From all spectra, a Shirley background was subtracted before the peak fitting and the binding energy (BE) component of the resolved C 1s peak corresponding to carbon in a hydrocarbon environment was set at 285.0 eV. Positive ion ToF-SIMS spectra were acquired with a ToF-SIMS IV (IONTOF) instrument from ION-TOF GmbH. A pulsed 10 keV argon ion beam was used as analysis beam at a current of 1 pA (positive ion mode detection), and rastered over a scan area of 300 \(\times\) 300 \(\mu\)m\({}^{2}\) for an acquisition time of 3 min. These conditions ensure static SIMS acquisitions (ion fluence maintained lower than 1 \(\times\) 10\({}^{12}\) ions/cm\({}^{2}\)). Five different locations on the surface were accounted for the ToF-SIMS analysis of the samples. For each spectrum, the mass scale was calibrated by using well-identified ions, namely H\({}^{+}\), H\({}_{2}\)\({}^{+}\), H\({}_{3}\)\({}^{+}\), C\({}^{+}\), CH\({}^{+}\), CH\({}_{2}\)\({}^{+}\), CH\({}_{3}\)\({}^{+}\), C\({}_{2}\)H\({}_{3}\)\({}^{+}\). For surface spectroscopy operated in the negative ion mode detection, a pulsed Ar\({}^{+}\) 10 keV ion beam at a current of 2 pA was rastered over a scan area of 300 \(\times\) 300 \(\mu\)m\({}^{2}\), and used as analysis beam during \(\approx\) 6 min [35]. ToF-SIMS spectra were interpreted with the help of the PCA method, by using SIMCA-P13 software (Umetrics, Sweden). Before PCA, the peak intensity was normalized to the total ion count, to correct for the differences in total secondary ion yield, then the normalized spectra were exported from the acquisition software (Surface Lab 6.3) to the SIMCA-P13 analysis software that mean-centres and scales the variables. The scaling of all the peaks inside the ToF-SIMS spectra gives them the same statistical weight, independently of their relative intensity in the spectra. From a geometric point of view, the PCA is a projection method that turns the initial swarm of points (the samples) of the multidimensional system with n axes (n is the number of ToF-SIMS peaks considered) into a highly lowered dimensional system (two to three), the new axes being the principal components (PCi). These new PCi components display, inside the initial n-dimensional space, the main directions along which the swarm of points is the most extended (i.e.,maximum variance). Additionally, from an algebraic point of view, the PCA calculation decomposes the initial matrix, constituted from the intensities (\"the variables\") and the samples (\"the observations\"), into a new set of three matrices, the _scores_, coordinates of the samples onto the new principal components, the _loadings_, statistical weights of contribution of the ToF-SIMS peaks to the principal components, and the _residuals_, random and unexplained variation, respectively.