Interaction between a cationic porphyrin and ctDNA investigated by SPR, CV and UV–vis spectroscopy

The interaction between ctDNA and a cationic porphyrin was studied in this work. The binding process was monitored by surface plasmon resonance (SPR) spectroscopy in detail. The association, dissociation rate constants and the binding constants calculated by global analysis were 2.4 × 102 ± 26.4 M−1 s−1, 0.011 ± 0.0000056 s−1 and 2.18 × 104 M−1, respectively. And the results were confirmed by cyclic voltammetry and UV–vis absorption spectroscopy. The binding constants obtained from cyclic voltammetry and UV–vis absorption spectroscopy were 8.28 × 104 M−1 and 6.73 × 104 M−1 at 298 K, respectively. The covalent immobilization methodology of ctDNA onto gold surface modified with three different compounds was also investigated by SPR. These compounds all contain sulfydryl but with different terminated functional groups. The results indicated that the 11-MUA (HS(CH2)10COOH)-modified gold film is more suitable for studying the DNA–drug interaction.