Conditional-sampling spectrograph detection system for fluorescence measurements of individual airborne biological particles

Abstract

We report the design and operation of a prototype conditional-sampling spectrograph detection system that can record the fluorescence spectra of individual, micrometer-sized aerosols as they traverse an intense 488-nm intracavity laser beam. The instrument's image-intensified CCD detector is gated by elastic scattering or by undispersed fluorescence from particles that enter the spectrograph's field of view. It records spectra only from particles with preselected scattering-fluorescence levels (a fiber-optic-photomultiplier subsystem provides the gating signal). This conditional-sampling procedure reduces data-handling rates and increases the signal-to-noise ratio by restricting the system's exposures to brief periods when aerosols traverse the beam. We demonstrate these advantages by reliably capturing spectra from individual fluorescent microspheres dispersed in an airstream. The conditional-sampling procedure also permits some discrimination among different types of particles, so that spectra may be recorded from the few interesting particles present in a cloud of background aerosol. We demonstrate such discrimination by measuring spectra from selected fluorescent microspheres in a mixture of two types of microspheres, and from bacterial spores in a mixture of spores and nonfluorescent kaolin particles.

Aerosol Characteristics in a Subway Environment

“…Due to the fact that certain amino acids (principally tryptophan and tyrosine) fluoresce when excited near their absorption peaks in the ultraviolet (UV) region of the spectrum, a strong particle fluorescence signal indicates the presence of biological material since these amino acids occur in nearly all proteins. Therefore this spectroscopic characteristic was used to indicate the presence of biological aerosols (Seaver et al 1998;Faris et al 1997;Nachman et al 1996), and the SPFA provides both a total aerosol particle count rate and a biological particle count rate. For sizing, both the SPFA and the Met One instruments utilize the particles' optical scattering cross section to indicate size.…”

Performance assessment of UVAPS: Influence of fungal spore age and air exposure

“…These can be divided into three groups. The first group includes trials and studies to design and test an instrument capable of differentiating between biological and non biological aerosols such as a Fluorescence Spectrum Analyser and an Ultraviolet Aerodynamic Particle Sizer (UVAPS) (Brosseau et al, 2000;Chen et al, 1996;Hariston et al, 1997;Hill et al, 1995;Ho et al, 1999;Kaye et al, 2000;Nachman et al, 1996;Pan et al, 2003;Pinnick et al, 1998;Pinnick et al, 1995). The second group of studies aimed at designing and testing an instrument with the capability to characterise particle composition in order to discriminate between the bioaerosols themselves (Cheng et al, 1999;Pan et al, 1999;Seaver et al, 1999;Sivaprakasam et al, 2004;Weichert et al, 2002).…”

Development of Rapid Assessment Method to Determine Bacterial Viability Based on Ultraviolet and Visible (UV-Vis) Spectroscopy Analysis Including Application to Bioaerosols

“…With the increasing concern on biological contamination of indoor environments, the importance of rapid monitoring of bioaerosols increases. Previous studies reported the feasibility for rapid detection of bioaerosols using modified Raman facility (Sengupta et al, 2005) or laser light source and fluorescence measurement system (Nachman et al, 1996;Hairston et al, 1997). The system developed by Hairston et al (1997) was improved into UV-APS (ultraviolet aerodynamic particle sizer spectrometer) which is a commercial instrument for realtime, continuous monitoring of airborne particles and viable airborne microorganisms.…”