Multiimage 2 alphaimager hp

The size and ζ-potential of plasmid laden 4-arm PRX were measured by a ZETAPALS instrument (Brookhaven Instruments Corporation), with an equivalent plasmid concentration of 1 μg/mL. The morphology of plasmid laden 4-arm PRX was visualized by atomic force microscope (AFM). Plasmid laden 4-arm PRX was directly added to mica substrate (1 cm ×1 cm), and free plasmid was premixed with 5 mM MgCl₂-HEPES buffer before addition to mica substrate. The equivalent concentration of plasmid was 0.2 μg/mL. The samples were dried with nitrogen gas and imaged on Bruker Dimension FastScan AFM. DNA gel retardation assay was performed with Precast agarose gel (Sigma Aldrich). Plasmid DNA was complexed with 4-arm PRX analogues in multiple N/P ratio. Samples were loaded in gel loading buffer (Sigma Aldrich), running in TBE buffer at 150 V for 30 min, followed by visualization on gel imaging system (MultiImage II AlphaImager HP, Alpha Innotech).