In a standard synthesis, 5 mL ethylene glycol (EG, J. T. Baker, lot no. G32B27) was added into a 100-mL round bottom flask (ACE Glass) and heated under magnetic stirring in an oil bath pre-set to 150 °C. 0.06 mL NaHS (3 mM in EG, Aldrich, 02326AH) was quickly injected into the heated solution after its temperature had reached 150 °C. Two minutes later, 0.5 mL of a 3 mM HCl solution was injected into the heated reaction solution, followed by the addition of 1.25 mL of poly(vinyl pyrrolidone) (PVP, 20 mg/mL in EG, MW≈55,000, Aldrich). The HCl solution was prepared by adding 2.5 μL HCl (38% by weight) into 10.30 mL EG. After another 2 min, 0.4 mL silver trifluoroacetate (CF3COOAg, 282 mM in EG, Aldrich, 04514TH) was added into the mixture. During the entire process, the flask was capped with a glass stopper except during the addition of reagents. After the addition of CF3COOAg, the transparent reaction solution took a whitish color and quickly became slightly yellow in 1 min, indicating the formation of the Ag seeds. The reaction was allowed to proceed for different periods of time and its color went through three stages of dark red, reddish grey, and brown as the edge length of the Ag nanocubes increased. The reaction solution was quenched by placing the reaction flask in an ice-water bath. All the samples were collected by centrifugation and then washed with acetone once to remove the remaining precursor and EG, and then DI water four times to remove excess PVP. We controlled the sizes of the Ag nanocubes monitoring their main LSPR peak positions using a UV-vis spectrometer from 15 to 90 min with an interval of 15 min. Briefly, a small amount (a few drops) of the reaction solution was taken out from the flask using a glass pipette and diluted with 1 mL DI water in a cuvette, followed by recording its extinction spectrum and compared with the calibration curve for wavelength versus edge length.