Molecular-electromechanical system for unamplified detection of trace analytes in biofluids

Biological research and diagnostic applications normally require analysis of trace analytes in biofluids. Although considerable advancements have been made in developing precise molecular assays, the trade-off between sensitivity and ability to resist non-specific adsorption remains a challenge. Here, we describe the implementation of a testing platform based on a molecular-electromechanical system (MolEMS) immobilized on graphene field-effect transistors. A MolEMS is a self-assembled DNA nanostructure, containing a stiff tetrahedral base and a flexible single-stranded DNA cantilever. Electromechanical actuation of the cantilever modulates sensing events close to the transistor channel, improving signal-transduction efficiency, while the stiff base prevents non-specific adsorption of background molecules present in biofluids. A MolEMS realizes unamplified detection of proteins, ions, small molecules and nucleic acids within minutes and has a limit of detection of several copies in 100 μl of testing solution, offering an assay methodology with wide-ranging applications. In this protocol, we provide step-by-step procedures for MolEMS design and assemblage, sensor manufacture and operation of a MolEMS in several applications. We also describe adaptations to construct a portable detection platform. It takes ~18 h to construct the device and ~4 min to finish the testing from sample addition to result. We present the design, assembly and implementation of a molecular-electromechanical system composed of a tetrahedral DNA nanostructure immobilized on a graphene field-effect transistor for unamplified detection of trace amounts of analytes in biofluids.