Cary elipse fluorescence spectrophotometer

Competitive triazole orange (TO) displacement experiments were carried out with chelerythrine on a Cary Elipse Fluorescence Spectrophotometer (Agilent Technologies) according to the method described in the literature45 (link). Aliquots of the chelerythrine (2.0 × 10⁻⁴ M) solutions containing 22 nt DNA G-quadruplex d[AGGG(TTAGGG)₃] or 27 nt RNA G-quadruplex (0.25 × 10⁻⁶ M) and TO (0.5 × 10⁻⁶ M) were added into 400 μL solution of G-quadruplex (0.25 × 10⁻⁶ M) and TO (0.5 × 10⁻⁶ M) in 25 mM Tris-HCl buffer (pH7.43) containing 100 mM KCl. This operation ensured that the concentrations of chelerythrine increased gradually from 0 to 0.40 and 0.80 μM, while the concentrations of DNA/RNA and TO were kept constant. An equilibrium period of 5 minute for constant stirring of the mixed solution was allowed before measuring each spectrum. The fluorescence spectra were recorded with an excitation wavelength at 501 nm at room temperature, and the fluorescence intensities of maximum emission of bound TO at 530 nm were used to calculate the percent fluorescence decrease induced by competitive binding of chelerythrine.

All the fluorescence measurement in this paper was performed by a Cary Elipse Fluorescence Spectrophotometer (Agilent Technologies, Santa Clara, CA, USA). The sample cell was a 350 μL quartz cuvette. The excitation wavelength and emission wavelength were 495 nm and 520 nm respectively. Both the excitation and emission slits were set at 5 nm. Atomic force microscopy (AFM) images were obtained on a Bruker Multimode 8 SPM (Bruker Corporation, Billerica, MA, USA) system in tapping mode.