Relative Surface Density and Stability of the Amines on the Biochip

The surface of a quartz or glass wafer (SiO2/Si (100)) was treated with different aminosilanes in solution. The aminosilane layer was allowed to react with aromatic aldehyde to form an imine, the imine was hydrolyzed in a known volume of water to produce the aromatic aldehyde, and subsequently its absorbance was measured by UV-vis spectroscopy. Thus, the observed number of the aldehyde molecules was equivalent to the number of the imine molecules on the surface. With the known surface area of the substrates and the volume of water, the absolute surface density of the imine, that is, the reactive amine groups on the surface, was calculated. The 9-anthracecarboxaldehyde with high molar extinction coefficient improved the amino detection limitation of the wafers greatly. By this method the amine groups on the 1 cm2 surface of saturated monolayer for (3-aminopropyl)ethoxydimethylsilane and (3-aminopropyl)methoxydimethylsilane were detected. A surface density of 2.1 amine nm−2 was measured. It was also observed that (3-aminopropyl)triethoxysilane and (3-aminopropyl)diethoxymethylsilane produced a multilayer, where surface density increased sharply with the reaction time and produced the multilayer. The aminosilylated substrates were more stable in the deionized water than in the CH3COOH (0.8%) aq and KOH (5%) aq.