Figure 2: Normalized specific chlorophyll a ( ) as a function of the concentration of the NP. Solid circles are Al2O3 (17.6 nm). Open squares are SiO2 (14.3 nm). Solid triangles are TiO2 (18.7 nm). Error bars are ±1 standard deviation ( ). Lines are 2nd-order polynomial fits to the data. The data was fitted with an empirical 2nd-order polynomial from SigmaPlot ver. 9.01. Experimental conditions: initial algae concentration =  cell/mL, test duration = 4 days, and initial test volume = 200 mL.