Currently, one of the most important application of flow cytometry is the real-time analysis of aerosols, in particular, to ensure biosafety. In most cases, such analysis is aimed at detecting fluorescent signals from aerosol particles corresponding to the light emission of tryptophan and nicotinamide adenine dinucleotide (NADH). Further development of the method is largely related to the improvement of the light detecting systems for recording and processing of fluorescence and scattered light signals. In this work, a comparative analysis of flow cytometers for bioaerosols detection based on photo-multiplier tubes (PMT) and avalanche photodiodes (APD) operating in analog and photon-counting modes was carried out. The limit of detection (LOD) of bioaerosols, response time and ability to detect particles with low scattering and fluorescence cross section were calculated and examined. The calculations were carried out for the well-known optical scheme of fluorescence detection based on discrete photodetectors and dichroic mirrors combined with an air flow chamber equipped with elliptical and spherical mirrors. An ultraviolet light emission diode (LED) was used as a model source of exciting radiation. To estimate the optical properties of aerosol particles, experimental results obtained for a model bovine serum albumin bioaerosol and published data on various other bioaerosols were used. The calculation of the total number of fluorescent photons, emitted by particles of various sizes while passing the flow chamber was carried out. The obtained data were compared with parameters of photodetectors operating in analog and photon-counting modes. The critical particle size was determined for the effective registration in a photon-counting mode. Considering the size distribution of aerosol particles, it was concluded that application of the photon-counting mode will reduce the LOD of bioaerosols by more than an order of magnitude.
Testing the environment for bio-aerosols is an important feature of biosafety in the modern world. It is often necessary to collect aerosols from large areas in a short time, which requires outstanding collection efficiency, sufficiently high flow rate of incoming air and ability to maintain the viability of the collected samples. The paper presents the results of creating an effective sampling device capable of operating at airflow rates of 4000 liters per minute. The device consists of two functional parts - a virtual impactor and a cyclone collector with liquid phase of deposition. We present all the necessary calculations and algorithm to simulate parameters of the impactor. The sampling device was tested using dry and liquid dispersed particles with a diameter of 0.5 to 5 μm. We demonstrated that at a flow rate of about 4000 l / min, the efficiency of collecting of particles is more than 20% of the total aerosol mass, and at a flow rate of more than 300 l / min, this value exceeds 60 %. The proposed device supports the viability of the collected microorganisms. The paper also presents the results of testing the device at infrastructure objects. The device is portable, with easy settings for sampling and cleaning, and can be controlled remotely over a network
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