**3. Conclusion**

Therefore, this chapter showed nanocrystals inserted in biosensors and their use in drug delivery tools or biomaterials. Graphene and magic-sized quantum dots into biosensors enable an increase in sensitivity and specificity, making the development of nanotechnological platforms in biological diagnosis possible. In theranostic applications, magic-sized quantum dots, magnetic nanoparticles, and TiO2 nanocrystals can be innovative drug delivery tools and dental and orthopedic applications. Thus, the fabrication of nanomaterials with interesting properties makes it possible to generate several potential tools to improve electrochemical sensors and in theranostic applications.
