A hydrogel network includes a hydrogel polymer having a coupling site, an oligonucleotide conjugated at a terminal end to the hydrogel polymer at the coupling site, and a functional moiety coupled between the terminal end of the oligonucleotide and the coupling site. Such a hydrogel network can be formed by a method including activating a coupling site of a substrate and binding a linker moiety coupled to a terminal end of an oligonucleotide to the activated coupling site, a functional moiety coupled between the terminal end of the oligonucleotide and the linker moiety.