On the temporal stability of analyte recognition with an e-nose based on a metal oxide sensor array in practical applications

The paper deals with a functional instability of electronic nose (e-nose) units which significantly limits their real-life applications. Here we demonstrate how to approach this issue with example of an e-nose based on a metal oxide sensor array developed at the Karlsruhe Institute of Technology (Germany). We consider the instability of e-nose operation at different time scales ranging from minutes to many years. To test the e-nose we employ open-air and headspace sampling of analyte odors. The multivariate recognition algorithm to process the multisensor array signals is based on the linear discriminant analysis method. Accounting for the received results, we argue that the stability of device operation is mostly affected by accidental changes in the ambient air composition. To overcome instabilities, we introduce the add-training procedure which is found to successfully manage both the temporal changes of ambient and the drift of multisensor array properties, even long-term. The method can be easily implemented in practical applications of e-noses and improve prospects for device marketing

Untersuchungen zur Signalstabilisierung miniaturisierter optochemischer Sensoren durch spektrale Referenzierung oder phasensensitive Lumineszenzdetektion

Miniaturised optochemical sensors with a sensitive area of 50 nm diameter were developed to determine potassium and chloride concentrations as well as pH. The signal was transmitted by luminescent dyes the intensity of decay time of which was detected, respectively. As an example for intensity based measurement a potassium sensor was developed based on the principle of ion-exchange optodes, combining the specific molecular recognition of potassium by a ligand with the optical transduction by a luminescent pH indicator. Additionally to the measuring dye with its changing intensity a reference dye with constant intensity was added, thus providing a highly reproducible ratio signal. The dynamic range of the sensors covered extracellular potassium concentration, a distinction of extra- and intracellular concentrations was possible. The measuring accuracy was 0.2 units of pK. Photostability of both the measuring and reference dye was excellent. Even with the nanosensor (50 nm) 23000 measurements can be carried out before an error of 1% occurs. An error of 1% due to dye leaching occurred only after 17 hours of continuous rinsing of the sensor. The sensor showed no cross-sensitivity to oxygen. (orig.)Available from TIB Hannover: ZA 5141(6456) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman