Matti Putkiranta

Instrumentation for measuring fluorescence cross sections from airborne microsized particles

An experimental instrument for measuring a laser-induced fluorescence spectrum from a single aerosol particle is described. As a demonstration of instrument capabilities, the results of monodisperse 4.7 microm sodium chloride particles doped with fluorescent riboflavin, produced with an inkjet aerosol generator, are presented. The fluorescence of the aerosol particles is excited in the wide range from 210 to 419 nm using a pulsed, tunable optical parametric oscillator laser. The maximum of the fluorescence emission of separately measured particles is detected at 560 nm. The dependence of the fluorescence on the excitation wavelength is studied and fluorescence cross sections are estimated. Agreement between the measured fluorescence data and the literature data for riboflavin is observed.

Fluorescence cross sections of bioaerosols and suspended biological agents

Laser-induced fluorescence is used to investigate fluorescence properties of unwashed Bacillus thuringiensis and Bacillus subtilis spores, ovalbumin, and washed bacteriophage MS2. A fluorescence detector is calibrated to obtain absolute fluorescence cross sections. Fluorescence maps of biological aerosols and suspensions are measured at a wide excitation range from 210 to 419 nm and a wide detection range from 315 to 650 nm. The dominant features of the measured spectra are the amino acid peaks, having excitation maxima at 220 and 280 nm. The peaks are similar for the bacterial spores, both for aerosols and suspensions, whereas the peaks are shifted toward the shorter emission wavelengths for the suspended ovalbumin and MS2. Moreover, the fluorescence emission, excited above 320 nm is more intensive for the aerosols than the suspensions.

Improved laser-induced fluorescence method for bio-attack early warning detection system

Laser Induced Fluorescence (LIF) could permit fast early warning systems either for point or stand-off detection if a reliable classification of warfare biological agents versus biological or non-biological fluorescing background can be achieved. In order to improve LIF discrimination capability, a new system is described in which the fluorescence pattern is enriched by the use of multiple wavelength delayed excitation while usual spectral fluorescence analysis is extended to time domain to use both aspects as criteria for classification. General considerations and guidelines for the system design are given as well as results showing good discrimination between background and simulants.

Optical chamber design for aerosol particle fluorescent measurement

Optical chamber for aerosol particle fluorescence measurements is designed. With the designed chamber, UV-induced fluorescent spectrum of single particles can be measured. The design includes two-nozzle flow system, with sheath air flow and virtual impactor concentrator integrated into the chamber. The operation of the flow system was verified with computational fluid dynamics (CFD). The chamber is intended to be used with pulsed UV-laser source, and it includes triggering of the laser pulse to hit individual particles.