Aptamer-functionalized nanoparticles for drug delivery

Aptamers are artificial single-stranded DNA or RNA sequences, usually 20-60 bases long, that fold into secondary and tertiary structures, which enables their binding to a wide range of targets, including amino acids, drugs, proteins or even entire cells, with high affinity and specificity. Generally synthesized through an in vitro selection and amplification process known as the SELEX (systematic evolution of ligands by exponential enrichment), selected aptamers have dissociation constants ranging from nanomolar to picomolar level. Nanotechnology is the manipulation of matter on an atomic and molecular scale, generally in the 1-100 nm dimension range. The many unique physicochemical properties of nanoparticles include their ultra-small size, large surface area-to-mass ratio, and high reactivity, making them different from bulk materials and overcoming some of the limitations found in traditional therapeutic and diagnostic agents. By combining both technologies, aptamer-conjugated nanoparticles offer new opportunities for applications in biomedicine, including early diagnosis and drug delivery. This review summarizes the recent developments in aptamer-mediated drug delivery for therapeutics based on aptamer conjugation with a variety of nanoparticles.