Dispersions of 15 μL were prepared with AuNRs concentrations from 5 to 15 mM Au 0 and 0.08 mM CTAC for all experiments. An imaging spacer of 0.12 mm in diameter (SecureSeal, Grace Bio-Labs, Bend, OR) was adhered onto glass cover slip without any previous treatment and the 15 μL dispersion was pipetted into the circular well. Another glass cover slip was placed on top, and a slight pressure was applied to ensure adhesion and push out excess liquid. The influence of ethanol on the assembly process could be studied by varying solvent composition up to 20%(v/v) with fixed PVP concentration. In addition, the influence of polymer concentration (from 0.1 to 1 mg/mL) and laser power (8.6 to 14 mW) were studied. To determine the effect of polymer size, PVP with molecular weights of 10, 55 and 360 kDa were studied with a fixed concentration (1 mg/mL) in 20% EtOH. For comparison with AuNRs, the printing of gold nanospheres (diameter = 23 nm) in 20% EtOH was also carried out similar to our previous work .