# Therapeutic Potential of Polymer-Coated Mesoporous Silica Nanoparticles
## 9 Polymer Coated MSNs for Imaging  
The synthesis of mesoporous silica not only allows for the precise control of pore size and structure, as well as particle size and shape, but is also suitable for constructing core@shell composites by coating other nanoparticles with porous silica shells. For imaging purposes, inorganic materials are frequently used as core materials due to their inherent detectability by several (bio)medical imaging techniques, e.g., iron oxide cores for MRI as exemplified above. Amorphous silica itself is optically transparent, so in lieu of a detectable core material, MSNs can be loaded or conjugated to molecular imaging probes for introducing traceability in the physiological environment [73]. Simultaneously, a silica layer does not interfere with the imaging signal of optically active core material and provides better dispersibility to the otherwise most often hydrophobic inorganic cores [74]. Consequently, these core@shell constructs are fully composed of inorganic materials and usually require polymer coatings as well to render them more functional or responsive to the physiological environment, as outlined above for plain MSNs. In one example, fluorescent nanodiamonds (ND) were used as an optically active core material, which were coated with porous silica shells to introduce drug delivery ability to the system. Coating with silica yielded more uniform particles as compared to the irregularly shaped and sized ND cores, and the porous shells could be amply loaded with cargo molecules instead of adsorption to the ND surface, which is otherwise a customary strategy for ND drug delivery [75].  
In an example, gold nanorods coated with mesoporous silica (Au@MSNs) were fabricated by [PERSON] et al. as a theranostic agent for NIR imaging and photothermal cancer therapy. PEG was used to cover the silica pores and to introduce stealth property. PEG was also used as a linker for attaching targeting ligand polypeptide (tLyp-1). This indocyanine green (tracker dye) loaded nano-system offered a promising theranostic system for near-infrared (NIR) light-induced imaging-guided photothermal cancer therapy [54].  
In another study, cisplatin loaded MSNs were prepared using starting material (3-aminopropyl)-trimethoxysilane (APTMS) labelled with fluorescein isothicarate (FITC) for theranostic application in cancer therapy. MSNs were further coated with PDA and graphene oxide (GO) to control the release of drug and for better dispensability of the particles. The thin layer of PDA over the MSN surface was created by oxidative self-polymerization, and later, coated MSNs were double wrapped with GO sheets via electrostatic interaction, followed by the conjugation of epidermal growth factor receptor (EGFR) peptide as a targeting ligand (Figure 14). In addition to pH responsive drug release, NIR light responsive accelerated drug release was also observed due to the higher NIR absorbance of the GO/PDA coating, which in turn produced an excellent photothermal effect. Confocal microscopy demonstrated the localisation of FITC-MSNs in the cytoplasm and the results also suggest that GO promotes the internalization of MSNs in H-SY5H cells through clathrin-mediated endocytosis. As expected, EGFR functionalized MSNs demonstrate more pronounced cytotoxicity due to specific targeting via receptor mediated endocytosis [55].  
In an interesting study, curcumin polymer was prepared and used as a multifunctional material, which provides MSNs with a coating, acts as fluorescent probe and offers stimuli-sensitive drug release. Curcumin polymer was prepared from bis-acrylated curcumin derivative and later coupled to MSNs via thiol-ene coupling reaction in the presence of 3-mercaptoethanolpropyltrimethoxysilane (MPTMS) and dithiothreitol (DTT) to impart a reduction sensitive property. The accelerated release of loaded DOX was observed in the presence of glutathione owing to the degradation of curcumin polymer, and the polymer also demonstrated fluorescence imaging capability as evidenced by confocal microscopy [56].