Characterising single airborne particles by fluorescence emission and spatial analysis of elastic scattered light

Abstract

The use of intrinsic fluorescence to characterise airborne particles is often applied to the detection of biological materials, particularly micro-organisms. However, as a number of particles which are found in the atmosphere also fluoresce (whether natural or artificially generated), simple measures of particle fluorescence alone may not be sufficient to indicate the presence of biological agents in the atmosphere. An instrument has been developed for the real-time measurement of aerosols using UV induced fluorescence emission and elastic scattered light to characterise individual particles in terms of size, shape and fluorescence. Particles are detected as they scatter light from a CW red laser beam, which triggers a pulse of 266nm radiation to induce fluorescence. Elastic scatter from the red laser beam is used to measure particle size and shape parameters, and total fluorescence between ~300 to 500nm is collected. The performance of the instrument has been investigated in laboratory tests and field trials, using a range of biological agent simulants and interferents. An automated classification technique has been applied to assess the ability of the instrument to recognise potential threats against the natural background environment.

Direct‐reading Aerosol Sampling Instruments

“…The problem is summarised in Figure 20.22 where it is shown how a combination of measurement of particle size, particle shape and particle nature (biological versus nonbiological) can provide options for rapid detection and identification Figure 20.22 Diagram to indicate how a combination of measurement of particle size, particle shape and particle nature (biological versus nonbiological) can provide options for rapid detection and identification of bioaerosols of bioaerosols and narrow down the discrimination process (Foot et al, 2004). The 'fluorescent aerosol particle sizer' approach allows identification of the presence of biological material but not specific biological species.…”

Detection of fluorescence spectra of individual bioaerosol particles

“…These detectors can reach close to real-time warning. Multiple excitations (266 and 355 nm) for the detection of bioaerosols have been reported [5] as well as the spectral characteristics of fluorescence from particles excited at 266 nm [6][7][8]. In order to increase the specificity and lower the false positive alarms, we are developing an early-warning system measuring the fluorescence spectrum of individual BWA aerosol particles excited with dual wavelengths (about 290 nm and 340 nm) ultraviolet (UV) laser pulses.…”

A dual-wavelength single particle aerosol fluorescence monitor

“…In the earliest systems, continuous wave lasers were employed, for example 1,2 , though these were usually large and fragile and operated at wavelengths which were too long for efficient excitation of some of the important bio-fluorophores such as tryptophan, for which optimal excitation occurred at wavelengths of ~260-280 nm. Hence the use of various solid-state lasers employing harmonic generation, such as frequency quadrupled Nd-YAG lasers, has gained acceptance [3][4][5][6][7][8][9][10][11] , both for the output wavelength of 266nm and because they offered a generally smaller form-factor than continuous-wave gas lasers.…”