74 Fig. 6 Cellular uptake of MNPs by smooth muscle cell (SMC). All c values are represented the mean ± standard deviation (SD) of three experiments, each performed in triplicate. Control columns mean that SMC was incubated with only DMEM. a SMC was incubated with DMEM containing the indicated concentration of DMSA-MNPs for 24 h. b SMC was incubated with DMEM containing 0.1 mg/mL DMSA-MNPs for the indicated incubation time, and c SMC was incubated with DMEM containing 0.1 mg/mL indicated MNPs for 24 h structure of particles were observed by TEM, and the images indicate that most of the particles are quasi-spher- ical and with an average diameter of 10 nm. The TEM image and size distribution of particles are shown in Fig. 1 The same morphology and size distribution can avoid the difference of size effect. The phase identiﬁcation of the uncoated MNPs was performed by XRD. As shown in Fig. 2, the result shows that the MNPs are inverse cubic spinel structure [28]. Compared with the theoretical values, the reduction of d-spacing obtained experimentally is due to the lattice constrictions for nanosized particles [25]. Fourier transform infrared spectroscopy was used to conﬁrm that the DMSA, APTS, and GLU were success- fully coated on the nanoparticles. The FTIR spectra of MNPs, DMSA-MNPs, APTS-MNPs, and GLU-MNPs are shown in Fig. 3 All samples show broad band at 3400 cm-1 indicative of the presence of –OH groups on nanoparticles surface. Compared with the uncoated MNPs, all the coated MNPs possess absorption bands in 2956 and 2922 cm-1 due to stretching vibration of C–H bond. In addition, for DMSA-MNPs, the band in 1715 cm-1 appears due to stretching vibration of C=O bond, which reveals the existence of DMSA. For APTS-MNPs, bands in 1091 and 1051 cm-1 are attributed to stretching vibration of C–N bond and Si–O bond, band in 932 cm-1 is attrib- uted to bending vibration of –NH2. In the spectrum of GLU-MNPs, the bands in 1091 and in 932 cm-1 are also observed because the existence of C–O and –NH2 group, which is the strong evidence that GLU is bonded to the surface of the nanoparticles. Zeta (n) potential measurement as a function of pH has been performed to conﬁrm the surface charge properties and the presence of DMSA, APTS, and GLU on the surface of MNPs. Figure 4 shows that the DMSA-MNPs have high negative potential at the pH range, while the APTS and GLU-MNPs are positively charged at lower pH and neg- atively at higher pH and their isoelectric points (IEP) are 7.2 and 7.9, respectively. The difference of charge prop- erties of them attribute to the ionization of the functional groups, such as –COOH, –SH and –NH2 at different pH. According to results, we can make sure that the surface charge property is negative for DMSA-MNPs, positive for APTS-MNPs, and nearly neutral for GLU-MNPs in the physicochemical states (pH 7.4). 123 Nanoscale Res Lett (2009) 4:70–77 The magnetic property of the MNPs was measured by VSM. Figure 5 shows the magnetization of the coated MNPs as a function of an external ﬁeld at ambient tem- perature. The three of MNPs possess similar magnetization loops and saturation magnetization (50 emu/g) because of