Ammonium solution

All materials employed in this study were purchased from commercial sources and used without further purification. The ZnO precursor solution was prepared by dissolving ZnO powder (Sigma Aldrich, 99.9%) in an ammonium solution (Sigma Aldrich, 99%) to form a 0.1 M $\text{Zn}{\left({\text{NH}}_3\right)}_4^{2+}$ complex precursor saturated solution. The solution was refrigerated for several tens of hours to promote the ZnO powder dissolution. Then, various molar ratios (3, 5, and 10%) of M₂CO₃ were added to the precursor solution to prepare the M₂CO₃ doped $\text{Zn}{\left({\text{NH}}_3\right)}_4^{2+}$ complex precursor solution. The patterned indium-tin-oxide (ITO) glass substrates with a sheet resistance of 15 Ω/sq were cleaned in ultrasonic bath with detergent, de-ionized water, acetone, and isopropanol consecutively, then they were dried by keeping them in an oven at 80°C for 12 h before usage.

Autoclaved distilled water was used to make dilutions of already sterilized stock chemicals. For solutions, 10% ammonium solution, 2 N sodium hydroxide (NaOH) solution, 5% ferric chloride solution (FeCl₃), ethanol, H₂SO₄ solution, hexane and methanol were purchased from Sigma Aldrich. Chloroform, 10% ferric chloride solution and 10% NaOH solution were purchased from Fischer Scientific. Deionized water, distilled water was purchased locally. Folch solution used for lipid extraction was prepared using chemical grade Chloroform and methanol which were mixed in 2:1 (v/v) ratio in a sterile bottle. The bottle was sealed and kept in the dark, at room temperature.

The SILAC-labeled peptides were pre-fractionated by high-pH reverse phase liquid chromatography using an Agilent 1100 HPLC system with Waters XBridge C18 reverse phase column (4.6 × 250 mm, 3.5 μM, 130 Å) with 10 mM ammonium formate (solvent A, Fluka, #17843) and 10 mM ammonium formate in 90% acetonitrile (solvent B, EMD Millipore, #AX0145) adjusted to pH 10 using ammonium solution (EMD Millipore, #105426). Fractions were collected every 1 min at a flow rate of 700 μl/min using a gradient method (from 0 to 75% solvent B in 60 min). The collected fractions were frozen at −80°C followed by CentriVap lyophilization.