Results . Morphological characterization of tungsten atomic clusters . The W-SAs were synthesized according to the previously reported protocols 18 . Briefly, in a typical synthesis, polydopamine (PDA, 3?g), polyethylene oxide-co-polypropylene oxide-co-polyethylene oxide (P 123 , 3?g), 2-amino-2-hydroxymethyl-propane-1, 3-dio (Tris, 0.5?g), Na 2 H 2 PO 4 ·2H 2 O (0.6?g) and 0.04?g Na 2 WO 4 ·2H 2 O (0.04?g) were dissolved in distilled water (30?mg) with continuous stirri...