Prof. Siwy and her group at the University of California, Irvine will study single nanopores therefore 'holes' whose diameter is 100,000 smaller than the thickness of a human hair. With the support of the Analytical and Surface Chemistry Program in the Chemistry Division of the National Science Foundation, Prof. Siwy and coworkers are addressing questions to understand the transport of ions and charged molecules through nanopores whose geometry and surface characteristics will be fully controlled. Transport properties of nanopores differ greatly from those of micrometer-sized pores. It is because the increased surface to volume ratio causes ions and molecules passing through the nanopore to be strongly influenced by the properties of the pore walls. The researchers will examine interactions of transported ions with the pore walls and study the relation between structure of nanopores and their transport properties. New methods will be developed to pattern surface charge of nanopores so that a maximum control of ionic transport is achieved.
Success of this project will lead to the development of new and improved devices that would be applicable in biosensing, lab-on-a-chip, and nanofluidic systems. The project will help us to understand interactions of ions and charged molecules with surfaces in nanopores. These nanopores have a volume domain that is below femto-liters. The research of Prof. Siwy will provide interdisciplinary training opportunities for graduate and undergraduate students in surface chemistry, nanofabrication, biophysics and biotechnology. The education program of this Career Award is focused on organizing visits of middle and high school students to UC Irvine combined with research experience in nanotechnology. The outreach activities for high schools will be done in collaboration with the UCI School Partnership in Research and Information Technology (SPIRIT) program.
Research performed within the award focused on understanding ionic and molecular transport at the nanoscale. The research program was inspired by transport properties of biological channels, which are embedded in a cell membrane. We created single polymer nanopores, which similar to properties of some biological channels passed ions only in one direction, and blocked the current in the opposite direction. Such ionic diodes were obtained by patterning walls of polymer nanopores and formation of two zones with opposite surface charges. We optimized the pore geometry as well as chemical modification to obtain diodes with the highest degree of asymmetry in the current-voltage curves. Modeling of physical mechanisms underlying functioning of the devices was performed as well. The concept of ionic diode was also used in the preparation of a sensor of anthrax. The sensor consisted of a single nanopore whose pore walls were decorated with a monoclonal antibody towards components of a capsule of the bacterium Bacillus anthracis. Being inspired by the properties of biological voltage-gated channels, which play a key role e.g. in nerve signaling, we designed artificial voltage-gated channels which opened and closed in the response of an external electric signal. The artificial channels contained attached single-stranded DNA molecules which when deflecting in external electric field would change the effective opening of the pores. Research was also performed on how hydrophobic interactions in addition to electrostatics could be used in controlling transport of water and all dissolved in it species. Reported hydrophobic nanopores could become the basis for on-demand drug-delivery systems. Research was also focused on the development of new and versatile membranes in SiN. The reported track-etched SiN membranes have a tunable porosity between 1 and 1010 pores per cm2, and controllable shape. These membranes will find application in processes of separation, purification, sensing and many others. The Siwy group actively participated in the formation of the outreach program LEAPS - Laboratory Experience and Activities in Physical Sciences. Visits from local middle schools in the Siwy lab were focused on understanding importance of nanotechnology in every day life.
