[Advances in exosome-targeting aptamer-screening techniques].

Exosomes play crucial intercellular-communication roles and regulate various cellular physiological processes. They are considered potential biomarkers for the early diagnosis of cancers and other diseases. Therefore, detecting and isolating exosomes with specific functions has significant clinical implications. Moreover, the development of low-cost, highly sensitive recognition elements for identifying exosomes is essential for advancing early disease diagnosis and treatment. Nucleic acid aptamers are single-stranded DNA or RNA molecules capable of specifically binding to targets and are produced through the systematic evolution of ligands by exponential enrichment (SELEX) technique. Such aptamers are highly stable, chemically synthesizable, exhibit high affinities and specificities, and are applicable to a broad range of targets, which endow them with unique advantages. Currently, aptamers that target exosomes have been used in a variety of research fields, including cell imaging, drug delivery, and disease diagnosis and treatment. However, selecting aptamers that precisely identify specific exosomes is significantly challenging owing to the complex structures of exosome and their heterogeneity. Consequently, obtaining high-performance aptamers requires efficient screening techniques. This review first summarizes the functions and selection strategies of key targets for exosome-aptamer screening. Furthermore, it outlines the main methods and techniques currently used to screen exosome aptamers, which includes five screening techniques: magnetic bead-SELEX, microfluidic-SELEX, nitrocellulose-SELEX, cell-SELEX, and capillary electrophoresis-SELEX. The separation principles, advantages, limitations, and the latest applications of these techniques are discussed in detail. The review finally addresses current challenges associated with selecting exosome aptamers and provides insight into future research directions.