First, a premade 400:1 methanol-triton X solution was added to the polystyrene bead solution to create 1.3% polystyrene bead suspension, followed by the addition of 5% volume of ethanol (97%) to the mixture. The suspension was dispersed by shaking for 10 minutes using a vortex. The 30X30 mm dies were thoroughly cleaned with acetone to remove all resist residues, followed by immersing in fresh piranha solution (H2O2 30%:H2SO4, 1:3) for 5 min, and a thorough washed with DIW and drying using an N2 gun. The surface was additionally cleaned and oxidized using an O2 Plasma generator (100 W 10 min).