Ionic current flow through ZnO nanotubes.

The control of ionic current (electrolyte) flow through zinc oxide (ZnO) nanotubes is investigated. We studied a structure operating like a field effect transistor with a tunable ionic flow. The main investigation tool used was molecular dynamics simulation. We complemented the molecular dynamics simulation with the site binding method in order to study the effect of the double layer on the ionic current flowing through the nanotube. We achieved this by considering the electrolyte solution as a virtual semiconductor wire. The double layer capacitance and surface charge of the inner walls of the ZnO nanotube have been calculated. The results indicate that ZnO nanotubes can be tuned to operate as ion selectors. ZnO nanotubes exhibit enhanced functionality with characteristics similar to those of the nanopore membrane.

ZnO nanorods as an intracellular sensor for pH measurements.

High-density ZnO nanorods of 60-80 nm in diameter and 500-700 nm in length grown on the silver-coated tip of a borosilicate glass capillary (0.7 mum in diameter) demonstrate a remarkable linear response to proton H(3)O(+) concentrations in solution. These nanorods were used to create a highly sensitive pH sensor for monitoring in vivo biological process within single cells. The ZnO nanorods exhibit a pH-dependent electrochemical potential difference versus an Ag/AgCl microelectrode. The potential difference was linear over a large dynamic range (pH, 4-11) and had a sensitivity equal to 51.88 mV/pH at 22 degrees C, which could be understood in terms of changes in surface charge during protonation and deprotonation. Vertically grown nanoelectrodes of this type can be smoothly and gently applied to penetrate a single living cell without causing cell apoptosis.

Analysis of biomolecules using surface plasmons.

Surface plasmon resonance (SPR) biosensors are optical sensors that use special electromagnetic waves (surface plasmon-polaritons) to probe interactions between an analyte in solution and a biomolecular recognition element immobilized on the SPR sensor surface. Major application areas include the detection of biological analytes and analysis of biomolecular interactions, where SPR biosensors provide benefits of label-free real-time analytical technology. The information obtained is both qualitative and quantitative and it is possible to obtain the kinetic parameters of the interaction. This new technology has been used to study a diverse set of interaction partners of biological interest, such as protein-protein, protein-lipids, protein-nucleic acids, or protein and low molecular weight molecules such as drugs, substrates, and cofactors. In addition to basic biomedical research, the SPR biosensor has recently been used in food analysis, proteomics, immunogenicity, and drug discovery. This chapter reviews the major developments in SPR technology. The main application areas are outlined and examples of applications of SPR sensor technology are presented. Future prospects of SPR sensor technology are discussed.

The pH Response and Sensing Mechanism of n-Type ZnO/Electrolyte Interfaces.

Ever since the discovery of the pH-sensing properties of ZnO crystals, researchers have been exploring their potential in electrochemical applications. The recent expansion and availability of chemical modification methods has made it possible to generate a new class of electrochemically active ZnO nanorods. This reduction in size of ZnO (to a nanocrystalline form) using new growth techniques is essentially an example of the nanotechnology fabrication principle. The availability of these ZnO nanorods opens up an entire new and exciting research direction in the field of electrochemical sensing. This review covers the latest advances and mechanism of pH-sensing using ZnO nanorods, with an emphasis on the nano-interface mechanism. We discuss methods for calculating the effect of surface states on pH-sensing at a ZnO/electrolyte interface. All of these current research topics aim to explain the mechanism of pH-sensing using a ZnO bulk- or nano-scale single crystal. An important goal of these investigations is the translation of these nanotechnology-modified nanorods into potential novel applications.