**3. Aptamers**

Aptamers are also used as interesting drug carriers; these molecules are composed of short nucleic acid oligomers. Many pieces of literature have reported the use of aptamers as drug carriers and diagnostic's approaches [44–47]. Aptamers are important because they can be designed and predicted to become a drug carrier for even general drugs and theragnostic drugs for specific pathologies such as Alzheimer's disease and cancer, among others. Since they can be designed, they are able to bind to various important targets such as lipids, nucleic acids, proteins, small organic compounds, or entire organisms. Thanks to their binding specificity, these specific drug carriers have shown less toxicity [44].

Kanwar, et al., 2011, discussed that aptamers can bind to a wide range of targets, which are called epitopes, which possess a high affinity and specificity. Aptamers can be used in chemical biology, therapeutic delivery, diagnosis, research, and monitoring therapy in real-time imaging. As mentioned before, aptamers are interesting for their low immunogenic reaction and also can mimic monoclonal antibodies that are proposed for research, diagnostic, and therapeutic [48].

Ganji et al., 2016, mentioned that aptamers can be generated from libraries of single-stranded nucleic acids against different molecules. The authors discussed that aptamers can be used for dendritic cell targeting, in order to improve immunotherapy in the treatment of allergies and cancers. In this scenario, dendritic cells use several receptors to stimulate the adaptive immune response through the antigen presentation route in naïve T cells [49].

Aptamers are single-stranded oligonucleotides that fold into defined architectures and bind to targets such as proteins. In binding proteins, they often inhibit proteinprotein interactions and thereby may produce therapeutic effects (**Figure 3**) [50].
