Extracting an Optical Finger-Print – a New Approach toSingle Particle Analysis

摘要

A fully automated system has been developed for microscope-based single particle analysisby extracting optical finger prints from individual particles in ambient air samples. For thispurpose, light microscopy was utilized to facilitate an objective measuring technique byemploying a novel pattern recognition technique. This automated particle classification isbased on so-called grey scale invariants, extracted from microscopic images of translucent,fluorescent and dark field microscopy. This information was bundled to a feature vectorproviding a kind of finger print for every particle. In a first step this approach was used for anautomated recognition of allergen carriers such as pollen and fungal spores. A leave-one-outtest gave a recognition rate of about 95% for 26 of the most frequent pollen species in centralEurope. Because no pollen-specific code was used, the recognition software was alsoemployed, without changes, for an automated recognition of fungal spores. Six of the mostfrequent airborne fungal spore genera in Central Europe were classified with a meanrecognition rate of 93%. These results provided the basis for a research project aiming at thedevelopment of a fully automated system. The instrument should combine (1) high-volume sampling of coarse particles >2.5 μm, (2) electrostatic precipitation of this fraction onto asurface suitable for optical analysis, (3) automatic preparation for microscopic single particleanalysis, (4) imaging by various microscopic techniques, e.g. transmitted, fluorescence anddark field microscopy, (5) feature extraction by grey scale invariants, (6) classification byself-learning Support Vector Machines and (7) hourly output of number concentration ofairborne pollen, fungal spores and other particles of interest. A prototype was demonstrated inearly 2005. First field tests are planned for the first half of 2005. A commercialised deviceshould be available as of 2007. The project is funded by the German Ministry of Educationand Research.