Nanowire Electron Scattering Spectroscopy
- Thursday, 02 July 2009
Multiple chemical compounds could be sensed, without the need to chemically functionalize nanowires.
Nanowire electron scattering spectroscopy (NESS) has been proposed as the basis of a class of ultra-small, ultra-low-power sensors that could be used to detect and identify chemical compounds present in extremely small quantities. State-of-the-art nanowire chemical sensors have already been demonstrated to be capable of detecting a variety of compounds in femtomolar quantities. However, to date, chemically specific sensing of molecules using these sensors has required the use of chemically functionalized nanowires with receptors tailored to individual molecules of interest. While potentially effective, this functionalization requires labor-intensive treatment of many nanowires to sense a broad spectrum of molecules. In contrast, NESS would eliminate the need for chemical functionalization of nanowires and would enable the use of the same sensor to detect and identify multiple compounds.
NESS is analogous to Raman spectroscopy, the main difference being that in NESS, one would utilize inelastic scattering of electrons instead of photons to determine molecular vibrational energy levels. More specifically, in NESS, one would exploit inelastic scattering of electrons by low-lying vibrational quantum states of molecules attached to a nanowire or nanotube (see figure). The energy of the electrons is set by the voltage bias applied across the nanowire. When the electron energies correspond to particular molecular vibrational levels, enhanced electronic scattering will lead to a change in the differential conductance (dI/dV, where I is current and V is voltage) at that voltage. Thus changes in the conductance provide a direct readout of molecular vibrational energies, to enable spectroscopic identification of the attached molecules.