**4. Conclusions**

Aptamers encounter problems such as lower in vivo stability and fast renal excretion. To address these difficulties, researchers used chemical changes to boost aptamer resistance to nucleases and *in vivo* stability. Modification can be accomplished either during the SELEX procedure (selection process) by adding functional groups to random libraries or after the SELEX methodology has been completed using solid-phase chemical synthesis. The latter approach is especially effective for adding phosphorothioate units that are resistant to nuclease digestion and inhibit fast renal filtration. The limited half-life extension provided by PEG components may require frequent subcutaneous injections, reducing compliance. Developing aptamers with higher proportion of the active aptamer component and employing low molecular weight modification approaches can enhance therapeutic efficacy.
