**4. Conclusions**

In this study, a method has been developed which can raise the stability of multilayer films made up of polymer and inorganic nanoparticles. The covalently cross-linked super stratum was formed on outermost layer of the multilayer films so that the structure of multilayers can be stabilized. The super stratum acts as a nano-net which prevents the diffusion of the nanoparticles from the substrate. It is worth mentioning that the super stratum possesses permeability for small molecules like FITC-RGD, FITC-RGD-Ad, FITC-(SGGYGGS)4 or FITC-(SGGSGGS)4. The difference in permeability of the super stratum towards nanoparticles and small molecules is utilized to synthesize a functional system for drug delivery incorporating mesoporous silica as the molecule reservoir. The construction of functional multilayer films that incorporate inorganic nanoparticles has potential promotional value benefitting from the mild synthesis conditions of the super stratum.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/1996-1944/12/8/1206/s1.

**Author Contributions:** K.N., X.Y., N.K. and Y.Z. conceived and designed the experiments; K.N. conducted the experiments and analyzed the data; K.N. wrote the draft, and K.N., N.K. and X.Y. improved it.

**Funding:** This research was funded by [National Natural Science Foundation of China] gran<sup>t</sup> number [21303169, 21673209].

**Acknowledgments:** This work was supported by the NSFC (21303169, 21673209) and the National Scholarship Fund of China Scholarship Council (CSC). I am very grateful to Jeffrey I. Zink and Navnita Kumar for helping me to polish and revise the paper. Navnita Kumar is a postdoctoral faculty in the Department of Chemistry and Biochemistry at University of California, Los Angeles (UCLA).

**Conflicts of Interest:** The authors declare no conflict of interest.
