Peptide-Conjugated Fluorescent Silicon Nanoparticles Enabling Simultaneous Tracking and Speciﬁc Destruction of Cancer Cells Chongxi Song,† Yiling Zhong,† Xiangxu Jiang, Fei Peng, Yimei Lu, Xiaoyuan Ji, Yuanyuan Su,* and Yao He* Institute of Functional Nano and Soft Materials (FUNSOM) and Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou, Jiangsu 215123, China S Supporting Information *
ABSTRACT: We herein introduce a kind of ﬂuorescent silicon nanoparticles (SiNPs) bioprobes, that is, peptidesconjugated SiNPs, which simultaneously feature small sizes (60 min) leads to gradual internalization of the SiNPs-RGD (Figure 4a). Typically, during the long-term imaging period, the SiNPs-RGD preserves stable and strong ﬂuorescent signals, with the green signals maintaining consistently strong during 120 min observation (Figure 4a). In contrast, the red ﬂuorescence signals of DiD (a kind of commercial ﬂuorescent molecular probe for membrane tracking) are obviously diminished as time elapses (Figure 4b). The corresponding overlay channels clearly display the photobleaching evolution of the red signals of DiD, while the green ﬂuorescence of SiNPs-RGD maintains stability during 120 min continuous observation. Taken together, these results D
DOI: 10.1021/acs.analchem.5b00853 Anal. Chem. XXXX, XXX, XXX−XXX
Figure 3. Photostability comparison of ﬂuorescent signals of U87MG cells incubated with (a) as-prepared SiNPs-RGD (green) and (b) FITC (green). The cell nucleus is labeling with Hoechst (blue). All ﬂuorescence images are captured under the same condition. Scale bar = 15 μm. (c) Quantitative analysis of changes in ﬂuorescence intensities of SiNPs-RGD (red trace) and FITC (blue trace) according to (a) and (b), respectively. Mean ﬂuorescence intensity is automatically measured by the ImageJ software.
Figure 4. Fluorescence imaging of live U87MG cells by as-prepared SiNPs-RGD (a) and DiD cell membrane tracker (b; 37 °C, 5% CO2). (c) The overlay of SiNPs-RGD channel and DiD tracker channel. All the pictures share the same scale bar (20 μm). In vitro concentrationdependent cellular viability of (d) U87MG and (e) MCF-7 cells. The categorization of 1, 2, 3, 4, and 5 on the x axis represents 0, 30, 60, 120, and 240 μg/mL for SiNPs and 0, 3, 6, 12, and 24 μg/mL for c(RGDyC), respectively. For SiNPs-RGD, the categorization represents the concentrations of SiNPs (0, 30, 60, 120, and 240 μg/ mL). Each bar stands for mean ± SD of four independent experiments. Herein, “mean” stands for the average value of four independent experiments. “SD” is shorted for standard deviation. The analysis of variance is carried out by utilizing a one-way ANOVA. Asterisks (** and *) indicate p < 0.01 and 0.05, respectively.
imply that the SiNPs-RGD could be used for the detection of integrin αvβ3-positive cancer cells and also may serve as a potentially powerful biological probe for real-time and longterm tracking of the integrin αvβ3-mediated endocytosis in vitro. Numerous studies have shown that RGD peptides could induce apoptosis of U87MG cells by binding integrin αvβ3 expressed on their cell surfaces.12 We therefore reason that the as-prepared SiNPs-RGD might feature anticancer ability to some extent. To verify this hypothesis, we systematically test in vitro toxicity of SiNPs, SiNPs-RGD, and c(RGDyC) peptides through an established MTT assay. As shown in Figures 4d,e and S12, cell viabilities of pure SiNPs-treated U87MG, MCF-7 cells, and QSG-7701 human hepatocytes maintain above 90%, indicating that free SiNPs produce feeble cytotoxicity because of favorable biocompatibility of silicon, well in agreement with previous reports.5d,e In sharp contrast, signiﬁcant cell death is observed when U87MG cells are incubated with the SiNPsRGD or free c(RGDyC) peptides instead, with a slightly dosedependent tendency (Figure 4d). Speciﬁcally, cell viability of the SiNPs-RGD or c(RGDyC)-targeted U87MG cells is decreased to almost 50% after 48-h treatment. Moreover, for U87MG cells, the cell viabilities of SiNPs-RGD-treated cells are slightly lower than those of pure c(RGDyC) peptides, which may contribute to the multivalent enhancement of aﬃnity caused by c(RGDyC) peptides.13 In comparison, for MCF-7 cells (Figure 4e) and QSG-7701 human hepatocytes (Figure S12) with low expression of integrin αvβ3, the cell viability maintains nearly 100% since few c(RGDyC) peptides or SiNPsRGD speciﬁcally target to the cells. A corresponding observation of cellular morphology well consists with the above results of MTT assays. Typically, the U87MG cells
(Figure S8) become rounded up with some detaching from the plastic, whereas the MCF-7 cells (Figure S8) and QSG-7701 human hepatocytes (Figure S13) display no signiﬁcant morphological alteration from untreated controls. Collectively, the above investigation indicates that the as-prepared SiNPsRGD display speciﬁc eﬀective anticancer eﬀects to U87MG cells in vitro.
CONCLUSIONS In conclusion, we present the ﬁrst example of multivalent RGDconjugated SiNPs featuring small sizes (