The specific detection in clinical samples of analytes with dimensions in the tens to hundreds of nanometers, such as viruses and large proteins, would improve disease diagnosis. Detection of these "mesoscale" analytes (as opposed to their nanoscale components), however, is challenging as it requires the simultaneous binding of multiple recognition sites often spaced over tens of nanometers. In response, we have adapted DNA origami, with its unparalleled customizability to precisely display multiple target-binding sites over the relevant length scale, to an electrochemical biosensor platform. Our proof-of-concept employs triangular origami covalently attached to a gold electrode and functionalized with redox reporters. Electrochemical interrogation of this platform successfully monitors mesoscale, target-binding-induced changes in electron transfer in a manner consistent with coarse-grained molecular dynamics simulations. Our approach enables the specific detection of analytes displaying recognition sites that are separated by ∼40 nm, a spacing significantly greater than that achieved in similar sensor architectures employing either antibodies or aptamers.