Aptamers at the Clinical Interface: Molecular Recognition, Device Architecture and the Evidence Required for Adoption

Aptamers, short single-stranded oligonucleotides selected to bind a chosen target, have for three decades been presented as programmable substitutes for antibodies. The past five years have changed the terms of that comparison. Selection can now be performed inside living cells, generative models propose binders that were never present in the starting library, and electrochemical aptamer switches report drug concentrations in human interstitial fluid with minute resolution over a day. In parallel, population-scale aptamer proteomics has made the aptamer a workhorse of biomarker discovery rather than a curiosity of the assay laboratory. Clinical adoption nevertheless remains uneven, and the reasons are mechanistic rather than merely engineering-related. An aptamer is a conformational ensemble whose binding equilibrium is re-weighted by ions, competing proteins and surface chemistry, so an affinity measured in selection buffer is a poor predictor of behaviour in blood. Here we examine the molecular principles that govern aptamer recognition, the device architectures that convert binding into a clinical readout, and the clinical evidence accumulated since 2021. We argue that the rate-limiting step has moved from molecular discovery to the construction of evidence that regulators, payers and clinicians can audit, and we propose a framework for generating it.