An ultrasensitive universal detector based on neutralizer displacement

Diagnostic technologies that can provide the simultaneous detection of nucleic acids for gene expression, proteins for host response and small molecules for profiling the human metabolome will have a significant advantage in providing comprehensive patient monitoring. Molecular sensors that report changes in the electrostatics of a sensor's surface on analyte binding have shown unprecedented sensitivity in the detection of charged biomolecules, but do not lend themselves to the detection of small molecules, which do not carry significant charge. Here, we introduce the neutralizer displacement assay that allows charge-based sensing to be applied to any class of molecule irrespective of the analyte charge. The neutralizer displacement assay starts with an aptamer probe bound to a neutralizer. When analyte binding occurs the neutralizer is displaced, which results in a dramatic change in the surface charge for all types of analytes. We have tested the sensitivity, speed and specificity of this system in the detection of a panel of molecules: (deoxy)ribonucleic acid, ribonucleic acid, cocaine, adenosine triphosphate and thrombin. A universal detector of small molecules, proteins and nucleic acids is described that relies on the displacement of a neutralizer molecule from a sensor surface. When the neutralizer is displaced by an analyte, an electrochemical signal is generated. Ultrasensitive limits of detection are achieved, and a new record for the electrochemical detection of bacteria (0.15 colony-forming units per microlitre) is reported.