Fig. 10: Photogeneration of superoxide radical (O2•−) and electron-transfer behavior in TG-containing oligo-DNA systems.
a–e: Detection of the photogenerated O2●− using nitro blue tetrazolium (NBT). a Schematic of O2•− detection using NBT as a detection probe to form the UV-detectable formazan compound. UV–Vis spectra showing the absorption intensity at approximately 500–600 nm (corresponding to formazan) for different samples: b negative control (buffer solution containing NBT without ODN), c duplex solution, d single-stranded ODN, and e crosslinked product solution (10 s preirradiated duplex). All samples were photoirradiated in the presence of NBT. Conditions: single-stranded ODN, duplex, or CL product (40 µM, 4.0 µL) was irradiated with NBT (600 µM) in 20 mM phosphate buffer (pH 7.0, containing 100 mM NaCl) at 0 °C using a 365 nm UV LED (UV light intensity: 34.1 W/m²) for 10 s or 1 min. Formazan formation was analyzed by UV–Vis (400–800 nm) spectroscopy after dilution with DMSO. f, g: SET kinetics in duplex vs. Single-stranded oligo-DNA systems. f In-duplex SET: The duplex structure facilitates faster O2•− generation by promoting efficient SET kinetics through a proximity effect, which aligns the donor (0TG) and acceptor (³TG) in a favorable geometry. g Interstrand SET: The single-stranded system exhibits inefficient SET kinetics, leading to slower electron transfer and undetectable O2•− levels under short photoirradiation time.
