Design $($i$)$ a process for constructing a hydrophobic surface, $($ii$)$ a process for constructing a surface that can be turned positively$-$charged, $($iii$)$ a process without random cross$-$linking on a silica$-$based surface and $($iv$)$ two different processes for constructing a DNA chip, using the substrate materials and compounds shown below by covalent linkage. $(10\%)$

Substrate materials: gold or glass.

DNA strands: ssDNA$-$NH $2,$ ssDNA$-$SH

Organosilanes

Cross$-$linkers:

Thiol Compounds:

OS