Impedance spectroscopy measurements of volatile organic compounds adsorbed on nanoporous anodized aluminum oxide sensors

Chemometric sensing encompasses a diverse spectrum of applications employing significant numbers of substrate materials that serve as binding sites for analytes. Porous aluminum oxide has served as one such substrate, being relegated solely to water vapor and moisture-sensing applications. Recent work has shown that nanoporous anodized aluminum oxide adsorbs alcohol vapors and cyclic volatile organic compounds and the electrical response of these adsorbates may be measured using impedance spectroscopy. From this work it is demonstrated that the impedance spectrum of pore-adsorbed analytes provides a unique electronic signature. The method developed from this work allows identification of simple compounds including structural isomers that are not readily resolved using conventional analytical methods.;Template-assisted growth of nanowires has been of interest during the last decade using a multi-step anodization and etching process. The resultant self-supporting nanowires have been studied as chemometric sensors. These devices have proven mechanically unreliable and costly to manufacture. Additional work by our laboratory has shown that nanowires grown and permanently contained within a nanoporous aluminum oxide matrix function as sensing devices when coupled to a metallic backplane. Permanent containment of the nanowires in the matrix serves to maintain a robust device that does not suffer from the failures and shortcomings of self-supporting nanowires.;The significance of impedance spectroscopy coupled with nanoporous aluminum oxide sensors manifests itself in the simplicity of the method. Microcomputer and microcontroller-based designs are inexpensive, portable and employ efficient software algorithms capable of generating the required frequency spectrum and analyzing the sensor response. Unreliable and bulky analytical instrumentation containing large numbers of electronic components may be eliminated. It is expected that further work with nanoporous aluminum oxide will move the sensor technology forward for other applications, specifically, environmental monitoring, hydrogen fuel cell controls, solar energy conversion and possibly carbon sequestration.