## 3 Solid-Supported Eosin Y
### Functionalized Eosin Y Materials in Biomedical Imaging  
High interest of scientists in the synthesis of materials that can provide high selectivity for tumor cells and low toxicity to normal cells has led to major breakthroughs in the field of biomedical imaging. Many types of materials have been studied for biomedical imaging applications; for example, it is known that Eosin Y can be used as photoinitiator both in the photo-crosslinking of hydrogels, which act as matrices for tissue engineering and biosensing [39], and in the realization of new promising shear thinning/self-healing hydrogels for drug delivery purposes [40].  
Other studies have indicated significant applications of metal nanoparticles as a suitable material for the early disclosure of diseases [41]. As shown before, Eosin Y has been supported on iron nanoparticles, but examples of Eosin Y-functionalized gold nanoparticles are also known [42]. Unfortunately, one of the major issues of the limited use of nanoparticles in biomedicine relates to their sizes, which have been proved to play a critical role in the exploitation of their biological activity [43]. Unfunctionalized nanoparticles exhibit hydrophobic surfaces and tend to agglomerate and form large clusters, which are not suitable for biological purposes.  
In order to develop more stable, specific and biocompatible derivatized materials, [PERSON] and co-workers investigated the possibility of combining the advantages of nanoparticles and hydrogels for the development of thin, biocompatible and biofunctional hydrogel-coated small-sized nanoparticles for specific cell targeting in biomedical imaging and cancer therapy [43]. In this particular approach, magnetic iron oxide nanoparticles were first derivatized with Eosin Y to form nanoparticles (**24**) and then coated with a biofunctional polyethylene glycol (PEG) hydrogel by photopolymerization to generate (**26**). Biological activity was ensured by the presence of the peptide sequence arginine-glycine-aspartic acid-serine (RGDS sequence), which showed great ability to bind HeLa cancer cell receptors (Scheme 15). [PERSON], for the first time, employed the surface-initiated photopolymerization technique to encapsulate a single magnetic nanoparticle (or its small cluster) within a biofunctional polyethylene glycol (PEG) hydrogel. Eosin Y, as a photosensitizer, had a great impact on the coating of the biofunctional PEG hydrogel through a photopolymerization process on the nanoparticle surface.  
Nanoparticles were first coated with 3-aminopropyltrimethoxysilane (**23**) (APTMS); then, the free amino groups introduced were used to covalently bond Eosin Y onto the nanoparticle core. A solution of these nanoparticles was then mixed with the RGDS-PEG derivative (**25**) and irradiated under green light in order to create the hydrogel shell around the nanoparticles. Different exposure times were evaluated in order to tune the hydrogel thickness around the magnetic core, and the best results were obtained with 60 s of green laser illumination. After biological investigations, it was shown that RGDS-functionalized polyethylene glycol hydrogel-coated magnetic iron oxide nanoparticles enhanced specific intracellular uptake by HeLa cells and increased the viability of cells compared to the uptake and viability measured in control groups.  
Although more studies are needed, it could be stated that the use of nanoparticles as an inorganic material with organic molecules can serve as a platform for preparing biomedical building blocks that can enhance stability in physiological media and transportation to target cells. The formation of biologically acceptable PEG hydrogel nanocomposites via the photopolymerization technique is a good way to perfect the biocompatibility of the molecules used in biomedical imaging.