Development of synthetic conical nanopores for protein sensing applications

The goal of this research is to develop protein sensing devices from artificial conical nanopores. In the first part of this work, single conical nanotubes are used as resistive-pulse sensing devices. A key challenge for this sensing paradigm is building selectivity into the protocol so that the current pulses for the target analyte can be distinguished from current pulses for other species that might be present in the sample. It is demonstrated here that this can be accomplished with a protein analyte by adding to the solution an antibody that selectively binds the protein. Because the complex formed upon binding of the antibody to the protein is larger than the free protein molecule, the current-pulse signature for the complex can be easily distinguished from the free protein.;The second part of the research also involves resistive-pulse sensing of protein analytes. Proteins of various sizes were detected with a conical nanotube sensor. The effect of protein size on translocation through a narrow nanotube tip was examined. The size of the protein was found to have a dramatic effect on current-pulse duration. The current-pulse frequency was also affected by the protein size and nanotube tip opening diameter. These studies are important towards the optimization of protein resistive-pulse sensors.;In the third part, a new method for optimizing protein resistive-pulse sensing is investigated. Previously, all resistive-pulse sensing work has been done at potentials ≤ +/-1 V. In this work, proteins were sensed at much higher potentials (i.e., up to 4 V). High potential sensing results in a significant decrease in the standard deviation of current-pulse duration for protein analytes. Decreasing the standard deviation in duration allows for better discrimination of analytes, and allowed for two proteins in a mixture to be distinguished.;In the last part of this work, a new type of sensor is developed from single conical nanopores. Protein molecules are immobilized on the surface of the nanopore walls and the isoelectric point of the immobilized proteins are determined from current-voltage curves. Isoelectric point determination is made based on the ion current rectification phenomenon exhibited by conical nanopores. At pHs above and below the isoelectric point of the immobilized proteins, the nanopore surface will carry a charge, and therefore current-voltage curves will show ion current rectification. However, at the pH corresponding to the isoelectric point of the immobilized proteins, there will be no surface charge and the current-voltage curves will show no ion current rectification.