Selective Deflection and Localization of Flowing Aerosols onto a Substrate

Abstract

Pulsed airflow cued by the fluorescence spectrum of a particular aerosol can be used to distinguish and deflect particles of biological origin out of an aerosol stream, permitting concentration of these particles for subsequent analysis ). However, these high velocity pulses of air have an inherent tendency to scatter particles, confounding efforts to concentrate these deflected particles for analysis. The ability to concentrate large numbers of biological particles into a small area on a collection substrate is particularly important for more species-specific techniques such as Raman and FTIR (Fourier Transform Infra-Red) spectroscopy, which require long integration times due to their weak signal strength. In the present work, a simple method is developed for deflecting and localizing particles after classification by a pulsed airflow. The concept is both modeled and experimentally tested. A specially designed funnel is used to localize the scattered particles onto an area of substrate as small as 1 mm in diameter. Computational fluid dynamics simulations were performed to investigate the interaction of the pulsed airflow with the deflected particles and the localizing funnel, in order to gain insight into design parameters and operating conditions that affect the efficiency of this technique. The results show that the combination of pulsed airflow with a localizing funnel effectively deflects and localizes the concentrated bioaerosol onto a small area of substrate or an opening of a microfluidic cell.

Optics of Biological Particles

“…The Yale/ARL team developed such an algorithm by matching the fluorescence spectra through the relative intensity comparison between different wavelengths (divided into multiple bands) associated with its fluorescence quantum efficiency. As mentioned previously (Frain et al, 2006;Pan et al, 2003b;Pan et al, 2001b), this real-time, in-situ bio-aerosol detection and discrimination system based on single-shot UV-LIF dispersed spectra from single individual aerosol particles on-the-fly consists of the following key elements (see schematic diagram in Figure 49): (1) A concentrator that draws air at about 300 liters/min and is based on the virtual impact principle. The concentrator directs most of the particles in the 1 to 10 µm size range toward a slower speed pump end that exit about 1 liter/min.…”

“…Because the ambient aerosol particles have different dielectric constant, size, shape, and velocity, they enter the electrostatic sorting area with different time delay, charge/mass ratio, and momentum, and these factors increase the difficulty in sorting out the wanted particles with high efficiency and purity. The Yale/ARL team developed a rapid classification scheme based on fluorescence spectrum of the aerosol that provides the cue as to whether to deflect that particular aerosol particle by a puff of air (hence the name Puffer) emerging from a pulsed valve to sort and regroup by a particle aerodynamic localizer (PAL), and collect the potential bio-threat particles on different substrates or inside a small volume of liquid for further analysis or identification (Frain et al, 2006;Pan et al, 2004).…”

“…The concept of the rapid aerodynamic sorting system cued on single particle UV LIF fluorescence spectrum is shown in Figure 54 (Frain et al, 2006;Pan et al, 2004). The Puffer, an electromagnetic actuated pulsed valve, can generate a very short (60 µs) supersonic air-packet (18 psi) within 20 µs.…”

“…Unfortunately, the inertia of the gas-packet emitted by the Puffer is so strong (300 m/s from the exit of the puffer nozzle) that, although the pressure driving the puff ends abruptly, the gas-packet entrains surrounding gas and particles for milliseconds after the puff is triggered. The particles are launched on different trajectories depending on exactly when the particle interacted with the puffed air (Frain et al, 2006). Experiments have demonstrated that shorter gas pulses (60 µs) and lower gas pressure in the puffer nozzle (15 psi) help reduce the dispersion of the deflected particles.…”

Separating hazardous aerosols from ambient aerosols: role of fluorescence-spectral determination, aerodynamic deflector and pulse aerodynamic localizer (PAL)

“…Then the deflected particles are localized by a funnel into a small area around 1 mm in diameter. The details of the funnel along with computational fluid dynamic results will be discussed in a forthcoming publication [2].…”