# Polymer@gold Nanoparticles Prepared via RAFT Polymerization for Opto-Biodetection
## 5 Conclusions  
This review highlighted the relevance of surface modification and functionalization methods in achieving functional Au NPs for opto-biodetection methods. Although a large number of publications have reported different approaches aiming at these type of core-shell nanostructures (e.g., small charged molecules, polyelectrolytes or thiolated molecules), polymers offer convenient routes to prepare stable, robust and multifunctional shells while keeping the optical properties of the Au core. In particular, RAFT polymerization has emerged as a powerful tool to obtain coated Au NPs with controlled polymer shells. Furthermore, RAFT polymerization can use functional monomers and mild reactions conditions which is a great advantage of this controlled radical polymerization mechanism. Three strategies were presented and discussed in this review: \"grafting to\" involves the mixture of previously prepared polymers with Au NPs and quasi-covalent interactions such as sulfur-Au, are involved. In this case, full control over the polymer (MW) and the NP (size and shape) are advantageous but polymer graft density can be a challenging issue especially in cases involving small NPs (<10 nm) or polymers with high MW. In the \"in situ\" strategy, NPs are synthesized using an inorganic precursor in the presence of the previously prepared polymer. This one-step nanocomposite synthesis is very interesting however achieving control over the size of the NPs (usually nanospheres) is not straightforward since it depends on many factors, namely the chemical functional groups and the MW of the polymers. As regards the \"_grafting front_\" approach, the Au NPs are previously prepared with the desired optical properties by using size and shape as control parameters. The polymer shells are then prepared and tailored from the NP surface modified with RAFT agents, keeping the control over the MW, although smaller MW are usually obtained, higher grafting densities are also achieved. Even though this is a very promising strategy, the polymerization mechanism can be rather complex thus it requires fine tuning of various reaction parameters. In the last years, a similar strategy (REEP) has been developed for the design of more robust polymer shells. REEP involves chain extension via RAFT emulsion copolymerization from the macroRAFT agent adsorbed onto NP surface. All these strategies are potentially useful for biomedical applications but still present challenges, that include issues regarding toxicity and biosafety assessment.  
This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (FCT Ref. UID/CTM/50011/2013), financed by national funds through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement. [PERSON] thanks FCT for her PhD grant SFRH/BD/80156/2011.  
The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.