Scheme 2 illustrates the procedure to assembly carboxylicfunctionalized
silica nanoparticles to silicon wafer surface. Silicon
wafer was cleaned in piranha solution (H2SO4/H2O2 = 7:3
v/v) for 3 h at 90 ◦C, and then rinsed with water and acetone
thoroughly. The cleaned substrates were placed into the APTES
solution of 5.0 × 10−3 M in a mixture solvent of acetone and
ultra-pure water (v/v = 5:1), and kept for 3 h, followed by rinsing
with acetone and ethanol, the target monolayer of APTES
was thus formed on the hydroxylated silicon surface (Si–NH2).