Electronics-Based Bio-Sensing, Single Molecule Metrology, and Membrane Protein Structure-Function

Nearly 14 years ago, we demonstrated that a single nanopore could be used to electrically detect individual molecules of single-stranded RNA and DNA (PNAS, 1996). Each polynucleotide that is driven into the pore by an applied electric field reduces the ionic current that otherwise flows freely. Based on the results of that study, we suggested that nanopores might prove useful for rapid DNA sequencing. The method has spawned many other applications.     

More recently, we demonstrated experimental proof-of-concept, and a theory for the use of a single nanopore to separate molecules based on their size and charge (PNAS, 2007 & 2010). Specifically, we showed that the degree to which a polymer reduces the pore's ionic conductance is in proportion to the polymer mass. Importantly, this simple method easily resolves polymers that differ in size by a single monomer (better than 44 g/mol). The method also discriminates between molecules whose charge differs by that of a single electron. We are currently determining the potential for this method to detect and quantify a wide range of biomarkers.

We are also leading other basic and applied science projects, including understanding the molecular basis of bacterial toxins and determining the structure of membrane proteins.

Molecular Mechanism of Bacterial Toxins     

In collaboration with scientists at the US Army Medical Research Institute for Infectious Diseases (Fort Detrick), we have been studying the mechanism of late-stage anthrax infection using electrophysiology (J. Biol. Chem., 2005; Biophys. J., 2008). Based on this research, we are currently developing biochips that could be used to rapidly screen for potential therapeutic agents against bacterial pathogens.

Structure/Function of Membrane Proteins      

We recently developed a novel method to determine the structures of membrane proteins (Biophys. J., 2009), which are difficult to crystallize properly. Importantly, the technique also probes the function of the molecules and could be used to determine the stoichiometry and location of molecules (e.g., toxins, therapeutic agents) binding to membrane proteins.

• Developed a novel theory and experiment for discriminating molecules based on their size and charge using electrical measurements
• Estimated the diameter of the anthrax toxin that punches holes in cells
• Measured the strength of interaction between anthrax toxins, which offers an alternative model for late-stage anthrax infection
• Developed a method that combines electronic measurements and neutron reflectometry to determine the structure of fully-functional membrane proteins
• Extracted intact single mitochondria from cells for disease studies