Nanosizer ns90

¹H NMR spectra were recorded on a BRUKER AV-500 (Bruker, MA, USA) spectrometer equipped with a 5-mm TXO probe head and nominal frequency of 500 MHz (number of scans: 64). The sample (~10 mg) was prepared and dissolved in 0.8 mL of D₂O or DMSO. The signal of the solvent residue was used as a reference peak for the ¹H NMR chemical shift and was set at δ 4.79 for D₂O and δ 2.5 for DMSO. The particle size and zeta potential of Dex–SS–DCA nanogels were measured at 25°C with Nanosizer NS90 (Malvern Instrument, Malvern, UK). Thermogravimetric analysis of Dex–SS–DCA nanogels was conducted by the TGA/DSC Simultaneous Thermal Analyzer (TGA/DSC 1/1600HT; Mettler-Toledo Co, Zurich, Switzerland). Morphology of the nanogels was observed by transmission electron microscopy (TEM) (JEM-1230; JEOL, Tokyo, Japan). The amount (in picomole) of Cy7 was determined by a UV–vis spectrophotometer (Bruker) at 750 nm wavelength using a calibration curve based on a series of Cy7 solutions at varying concentrations.

The complexes of SSPEI-SPIO nanoparticle/DNA (siRNA) were prepared by mixing SSPEI-SPIO solution (800 μL, 187.5 or 375 μg/mL, HEPES buffer, 20 mM, pH 7.4) with a DNA (siRNA) solution (200 μL, 75 μg/mL, HEPES buffer, 20 mM, pH 7.4), which affords a SSPEI-SPIO/DNA (siRNA) mass ratio of 10:1 and 20:1, respectively, followed by gentle vortexing and standing for 30 minutes at room temperature. Particle size and surface charge of the complexes were measured by a Nanosizer NS90 (Malvern Instruments, Malvern, UK) at 25°C.