Greetings.

this is PEG(polyethylene glycol) particle with COOH, that photo is when I run experiment, conjugate NH2-modified oligonucleotides and hybridized with FAM-DNA. but DNA was spotted. (image above)

Nowadays I run experiment, conjugate streptavidin in PEG particle first, and reaction with biotinylated DNA, and run DNA-DNA hybridization woth FAM-DNA, fluorescence show even, like image below.

Streptavidin have a positive charge in acidic condition, so it conjugates easily with COOH particle, but there are many protocols how conjugates NH2-oligonucleotide directly(Not PEG but surface is COOH). then, can I conjugate amine modified DNA directly with even fluorescence?

What affects for even conjugation? (charge or density of PEG?)