Poly ethylene glycol peg

Potassium dihydrogen phosphate and silver nitrate were obtained from Merck (Darmstadt, Germany). Di-sodium hydrogen phosphate, acetone, sodium dodecyl sulfate, tris(hydroxymethyl)aminomethane, acetic acid, sodium carbonate, ammonium persulfate, tetramethylenediamine, sodium chloride, sodium thiosulfate and poly(ethylene glycol) (PEG, M_n = 6000 g mol⁻¹) were obtained from Carl Roth (Karlsruhe, Germany). Uranyl acetate and acrylamide/bis solution, 37.5 : 1 were purchased from Serva (Heidelberg, Germany). Spurr Low Viscosity Embedding Kit was obtained from Polysciences (Washington, USA). Poly(ethylene glycol) diacrylate (PEG-DA, M_n = 700 g mol⁻¹) and formaldehyde were obtained from Sigma-Aldrich (Merck; Darmstadt, Germany). The radical photoinitiator 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propan-1-one (Irgacure 2959) was a kind gift from Bodo Möller Chemie GmbH (Offenbach, Germany). A Micro BCA Protein Assay Kit was obtained from Thermo Scientific (Waltham, USA). All chemicals and reagent were used as received. Stock solutions containing 28 mg Irgacure 2959 in 3.972 g SPP buffer were obtained by gentle heating with a heat gun at 100 °C until all material was dissolved, and subsequent cooling to room temperature. Water was withdrawn from a Barnstead GenPure xCAD water purification system (Thermo Scientific, Waltham, USA).