**2.1 Materials**

Glass substrates were microscope coverslips (12 mm diameter, Menzel-Gläzer, Germany). Polyethyleneimine solution (PEI, Mw = 750 000), polyallylamine hydrochloride (PAH, Mw~70 000), poly-l-lysine hydrobromide (PLL, Mw = 70 000 to 150 000), poly(diallyldimethylammonium chloride) solution (lPDDA, Mw < 100 000; hPPDA, Mw = 400 000 to 500 000) were purchased from Sigma-Aldrich (St. Louis, MO, USA). Negatively charged polystyrene particles with two different sizes (sulfate latex, 65±6nm, 470±12nm) were purchased from Interfacial Dynamic Corporation (IDC, Tualatin, OR, USA). The composition of the phosphate buffer saline solution (PBS) was as follows: 137 mM NaCl, 6.4 mM KH2PO4, 2.68 mM KCl, 8 mM Na2HPO4; adjusted to pH 7.4 with 1M NaOH.

## **2.2 Sample preparation**

Figure 1 presents the different steps of sample preparation, from the glass substrate to surfaces with bimodal roughness.
