title: A new drug-sensing paradigm based on ion-current rectification in a conically shaped nanopore.
abstract: OBJECTIVE
  To utilize the ion-current rectification phenomenon observed for conically shaped nanopores as the basis for designing sensors for drug molecules that adsorb to the walls of the nanopore.
  
  
  METHODS
  The conically shaped nanopore was prepared by the well-known track-etch method in a polyimide (Kapton) membrane. The ion current flowing through the nanopore was measured as a function of applied transmembrane potential in the presence of the analyte drug molecule, Hoechst 33258.
  
  
  RESULTS
  The pore walls in the Kapton membrane are hydrophobic yet have fixed carboxylate groups that give the walls a net negative charge. This fixed anionic surface charge causes the nanopore to rectify the ion current flowing through it. The analyte drug molecule, Hoechst 33258, is cationic yet also hydrophobic. When the membrane is exposed to this molecule, it adsorbs to the pore walls and neutralizes the anionic surface charge, thus lowering the extent of ion-current rectification. The change in rectification is proportional to the concentration of the drug.
  
  
  CONCLUSIONS
  This nanopore sensor is selective for hydrophobic cations relative to anions, neutral molecules and less hydrophobic cations. Future work will explore ways of augmenting this hydrophobic effect-based selectivity so that more highly selective sensors can be obtained.
authors.affiliation: University of Florida, Department of Chemistry & Center for Research at the Bio/Nano Interface, Gainesville, FL 32605, USA.
authors.forename: Jiahai
authors.initials: J
authors.lastname: Wang
authors.forename: Charles R
authors.initials: CR
authors.lastname: Martin
mesh_terms: D002412:Cations; D004563:Electrochemistry / Q000379:methods*; D004574:Electromagnetic Fields; D007477:Ions; D008422:Materials Testing; D008567:Membranes, Artificial; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure; D010316:Particle Size; D004364:Pharmaceutical Preparations / Q000032:analysis* / Q000737:chemistry*; D016062:Porosity; D012117:Resins, Synthetic / Q000737:chemistry*; D014159:Transducers
chemical_list: D002412:Cations; D007477:Ions; D008567:Membranes, Artificial; D004364:Pharmaceutical Preparations; D012117:Resins, Synthetic; C029945:polyimide resin