This work examines the possibility of real-time detecting of single nitro compounds microcrystals [cyclotrimethylenetrinitramine (RDX) and pentaerythritol tetranitrate (PETN)] with sizes of similar to 130 to 600 mu m by the terahertz (THz) imaging. A THz video camera based on a microbolometer matrix was used to record images in transmission and reflection optical schemes. A photoconductive antenna was used as a THz source. It was experimentally demonstrated that the spectral selectivity of identifying of nitro compounds microcrystals in the THz range strongly depends on their size, and the results of mathematical modeling based on the Mie scattering theory showed that this effect is due to the complex dependence of the extinction cross section of the microcrystals on their size. The results of the work can be used in the development of real-time THz visualization systems.

The THz reflection spectra of optically thin hexogen (RDX) samples were studied by terahertz imaging with spectral resolution. A photoconductive antenna excited by femtosecond laser radiation was used as a source of broadband THz radiation. The presence of a Fourier spectrometer (as well as band-pass THz filters) and a microbolometric THz video camera in the experimental setup made it possible to use the terahertz imaging method to study reflection spectra taking into account scattering in the range of 0.6 to 1 THz. The influence of the optical characteristics of the substrate on the THz reflection spectra was studied. In particular, the conditions for observing the effect of anomalous dispersion for RDX samples with different dispersion in the frequency region of the RDX absorption band 0.8 THz were studied. The obtained results demonstrate the application of the method of terahertz imaging with spectral resolution based on THz video camera for the identification of explosives with concentrations 0.75 to 50mg/cm(2) on various surfaces. (c) 2023 Society of Photo-Optical Instrumentation Engineers (SPIE)

Ion mobility spectrometry (IMS) today figures prominently among analytical methods for detection of explosives and is widely used for transport security. This method is highly appreciated for capability to distinguish low quantity of different types of explosives at atmospheric pressure. The main obstacle for sensing some kinds of explosives is their very low vapor pressure so that the limit of detection of state-of-the-art IMS instrumentation 10-13 –10-14 g/cm3 lacks at least an order of magnitude. In this paper we combine promising UV laser radiation along with application of organic compounds (dopants) to improve ionization efficiency and vapor detection capabilities of IMS. Dopants with low ionization energy (toluene and 1-methylnaphtalene) were used for negative ion formation of nitro group-based explosives: trinitrotoluene (TNT), cyclotrimethylenetrinitramine (RDX) and pentaerythritol tetranitrate (PETN). Presence of dopants in the sample results in multiple growth of ion yield at laser intensities lower than 2 × 107 W/cm2. Limits of detection with dopant-assisted laser ionization (4.7 × 10-16 g/cm3 for RDX and 9.8 × 10-15 g/cm3 for PETN) show up to 2-fold improvement compared with no dopant case. Results propose a way to further improve sensitivity of detectors and reduce manufacturing costs by lowering requirements to laser pulse energy and using cheaper lasers.

Detection of low-volatile explosives in concentrations below 10-14 g/cm3 is a great challenge for portable ion mobility spectrometers (IMS) and field asymmetric IMS (FAIMS). We study the capabilities of FAIMS detector with ultraviolet laser ionization combined with organic additives (dopants) toluene and 1-methylnaphtalene to sense nitro-explosives: trinitrotoluene (TNT) and low-volatile cyclonite (RDX) and nitropentaerythritol (PETN). Differential mobility coefficients were measured for target ion peaks of TNT, RDX and PETN. Presence of dopants in the sample results in multiple growth of ion yield at laser intensities lower than 2 x 107 W/cm2. Limits of detection with dopant-assisted laser ionization were determined: 4.7 x 10-16 g/cm3 for RDX and 9.8 x 10-15 g/ cm3 for PETN. Obtained results propose a way to further improve sensitivity of detectors along with improvement of portability of current laser-based FAIMS prototypes by using less powerful and smaller lasers.

We exploit micro-nano structuration to achieve multifunctional windows offering outstanding optical and fluidic properties to enhance the operation of surveillance or detection devices under rainy conditions. These windows are based on synthesis of an artificial index gradient for antireflection properties and improvement of their water repellency property thanks to their structuration at a subwavelength scale with controlled conical geometries. We demonstrate the realization of multifunctional germanium windows for LWIR camera, using two approaches: nanoimprint lithography, well-known for its very high resolution enabling applications from visible to thermal infrared domain, followed by etching techniques, and 3D direct laser writing based on Two-Photon Polymerization (TPP), which is of interest thanks to its ability to manufacture complex 3D structuration directly. Optical characterization shows the ability of such windows to improve optical transmission within 8-14μm spectral range, as compared to non-structured window. In terms of water repellency, the structured windows enable an increase of the contact angle up to 160° with a very low hysteresis. To evaluate the advantage of the multifunctional windows for imaging devices, the windows are integrated in front of a thermal infrared camera and images analysis shows that the camera sensitivity is increased for the nanoimprint window thanks to the multifunctional window and high water repellency in presence of water.

The presence of peculiarities in terahertz spectra of many organic compounds allows the use of THz imaging and spectroscopy for the detection of various hazardous and explosive substances. This work is devoted to the study of the detection of trace amounts of 1,3,5-Trinitro-1,3,5-triazinane (RDX) in the form of particles localized in millimeter and submillimeter sizes using THz imaging with spectral resolution. As a result of the work, images of trace amounts of RDX in reflected THz radiation were obtained. The contrast in these images made it possible to detect single particles of the powdery substance. The difference in contrast for RDX and polyethylene (PE) in the obtained terahertz images makes it possible to use THz imaging with spectral resolution not only for detection, but also for the identification of chemical compounds.

Aerosol samplers with a recirculating liquid film are promising devices for remote biological monitoring. The presence of the liquid film provides a high survival rate for biological objects. The relatively simpler design allows portability to the sampler, which will make it possible to conduct tests outside the laboratory. In this study an analytical expression, describing the capturing efficiency of aerosol particles in the water film, taking into account the friction forces arising from interaction of water and air in a cyclone-based aerosol collector, was obtained. A new element, took over from the theory of centrifugal sprayers - a vortex chamber, was added to the theory and design of the collector. It allows increasing the initial angular moment of the elements of air volume entering the collector, which leads in appropriately an increase of maximal height of rising liquid film and particle capturing efficiency. To analyze the obtained expressions, graphs of particle capturing efficiency on basic parameters of modified cyclone collector and volumetric air flow were calculated. The graphs made it possible to determine the optimal geometric parameters for the portable cyclone-based collector. The introduced dependence on viscosity made it possible to estimate more accurately the efficiency of the device at various temperatures (including negative temperatures). For the selected parameters, graphs particle capturing efficiency were plotted. Water-alcohol solution and Novec 1230 fluid were used as fluids capable of operating at subzero temperatures. To check the operability of the sampler, tests were carried out to collect samples of sprayed inactivated adenovirus in a microbiological safety box at the Gamaleya Institute. The results of tests are discussed.

In this paper we study the influence of the carrier and drift gas composition on ionization processes taking place inside drift chamber of field asymmetric ion mobility spectrometer with laser ionization. Solid state nanosecond laser of YAG:Nd 3+ type with fourth harmonic unit (λ = 266 nm, τpulse = 6 ns, E pulse = 700 – 2500 μJ, ν = 10 – 20 Hz) was used for negative ion generation. In this study we experimentally discover the features of laser ionization of four nitro-compounds: cyclotrimethylenetrinitramine (RDX), cyclotetramethylenetetranitramine (HMX), pentaerythritol tetranitrate (PETN), trinitrotoluene (TNT) explosives. Drift and sample carrier gas were prepared by mixing purified air with different amounts of water vapor and organic dopants. Ion mobility increments were calculated after calibration of field asymmetric ion mobility spectrometer (FAIMS) based on published data for TNT and Iodine and measured alternating separation field waveform. The experimental setup also included drift time ion mobility spectrometer (IMS) which was used to verify linear ion mobility spectra to supplement ion mobility increment values, obtained by FAIMS. Previous studies of laser ionization with optimization of intensity and pulse repetition rates gave LOD values well below 10−15 g/cm3: 3 × 10−15 g/cm3 for RDX, 8 × 10−15 g/cm3 for PETN and less than 3 × 10−15 g/cm3 for HMX. Common ideas about ionization mechanisms of nitro-based explosives propose that indirect processes with ion-molecular reactions substantially contribute to negative ion formation as well as resonant enhanced multi photon ionization (REMPI) direct processes. Ionization process starts with electron generation by organic impurities in atmospheric air. These organic compounds have low ionization energy and require less than two photons to ionize. Current research involves doping air sample with such substances as: toluene acetone, naphthalene and chloroform at different UV irradiation modes. Such compounds can act as electron source for rising TNT and RDX ion signal levels above background. Such selectivity enhancement can be a step on the way to achieving even lower detection limits to sense trace explosive vapor concentrations in real conditions.

The issue of civil security and prevention of terrorist attacks in public places is becoming more and more actual every year. In this regard, increased attention is paid to detection of explosives. Of particular interest are methods to detect trinitrotoluene (TNT), hexogen (RDX), penthrite (PETN), octogen (HMX). Recently, gas-analytical, nuclear-physical, electromagnetic, terahertz, and biological detection methods have been developed. The lowest detection limit was achieved using gas-analytical methods, namely the non-linear ion mobility spectrometry method, with a limit of detection of 5.10-15 g/cm3. However, the question of feasibility of using these methods in real conditions is increasingly raised. There is an opinion that it is much more effective to detect explosives by traces than by vapor. In this work we investigated the possibility of detecting vapors of pure explosives with low saturated pressure of vapors. By the example of pure and faсtory hexogen, using the method of thermal-programmed desorption and mass spectrometry, it was shown that it is hexogen vapor, and not technological impurities or additives with saturated vapor pressure exceeding the saturated vapor pressure of hexogen, that are registered in the gas phase by ion mobility spectrometry. A technique was developed and proposed to concentrate RDX vapors. Using temperature-programmed desorption, the minimal time of concentration and surface fill factor were determined.

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.

Cyclotrhylmethylentrinitramine (RDX) is one of the most dangerous explosive substances. The presence of impurities in this explosive may be important for its determination as residual traces at the scene of incidents, as well as in the quick analysis of passengers and luggage by ion mobility spectrometers. In the work industrially manufactured RDX samples, that were not undergone any purification, were investigated by gas chromatography-mass spectrometry method. The attention was paid to search precursors and possible technological admixtures. On the basis of received chromatograms and mass spectra it was established the presence in the analyzed RDX samples of urotropin, acetic anhydride, acetic acid, triazine and octogen. The mass content of the substances was estimated. Special attention was paid to the products of RDX biodegradation, which can occur both in aerobic and anaerobic environments during its storage. The quantitative content of RDX biodegradation products in samples under study was estimated. Sorption of chemically pure and industrially manufactured RDX vapors on a concentrator from metal meshes were carried out. By the method of thermodesorption mass spectrometry the composition and differences of the concentrated samples were analyzed. Recommendations for taking into account the results obtained when working with vapors and traces of RDX by ion mobility spectrometers were given.

Early detection of pathogens is crucial for ensuring safe living conditions. Conventional sampling methods do not ensure the sustainability of captured microorganisms. Cyclone-based liquid absorptive samplers are the most promising devices in this regard. Most samplers have limited application scope as they are intended for laboratories. In the study we developed a special liquid-based sampler for mounting on a drone. A structure and base values of a cyclone collector were determined. The chosen design provides maximum particle capturing efficiency in terms of low air flow rate and small size of the collector. Projected capturing efficiency for particles of the size of 1mcm is approximately 20%, for particles of the size bigger than 2,5mcm is 100%. Mathematical modeling proved the correctness of theoretical considerations. This made it possible to design and fabricate a prototype of a sampler device which also includes a fan, a peristaltic pump, valves, a sensor for liquid levels monitoring, a display for operation mode controlling. Outdoor sampling on a drone has successfully proved performance efficiency at close to zero temperatures. A study on capturing efficiency was carried out by sampling sucrose aerosol with a fluorescein dye in a microbiological safety box. Specific efficiency of our sampler is 1,18 [relative units/(litre/min)], which is over twice s.e. of 0,43 [r.u./(l/min)] of existing laboratory devices. The device provides for the issuance of collected samples on standard immunochemical test strips for the analysis of adenovirus, rotavirus, influenza and other respiratory diseases with a full analysis time of 10 minutes.

Ion mobility spectrometry instrumentation today is widespread in the area of transport security and counterterrorism. This method of detection of explosive substances is highly appreciated for the existence of portable detectors capable of detecting concentrations of 10−13–10−14 g/cm3 at atmospheric pressure using traditional ionization methods including corona discharge and beta radiation. However, low vapor pressure of some explosives imposes requirements on limit of detection (LOD) down to 10–15‒10−16 g/cm3. In this paper we compare a radioactive 63Ni ionization source with a laser ionization source and reveal the parameters of laser ionization of a group of explosives, namely trinitrotoluene (TNT), cyclotrimethylene-trinitramine (RDX), cyclotetramethylene-tetranitramine (HMX) and pentaerythritol tetranitrate (PETN), which can reduce the limit of detection of portable devices. A laser ionization source can provide a higher signal to noise ratio than radioactive 63Ni at optimal intensity of laser radiation for PETN and HMX of 3 × 107 W/cm2 and 2.5 × 107 W/cm2, respectively. Limits of detection were estimated: 3 × 10−15 g/cm3 for RDX, 8 × 10−15 g/cm3 for PETN and less than 3 × 10−15 g/cm3 for HMX. These results are promising to further improve the capabilities of detectors of low volatility explosives without sacrificing portability, light weight and reasonable cost of the laser source.

The distinctive features of laser ionization source in field asymmetric ion mobility spectrometry method are studied in this paper. A YAG:Nd 3+ nanosecond laser (λ = 266 nm, τpulse = 6 ns) with variable pulse energy E pulse = 700 – 2500 μJ and frequency ν = 10 – 20 Hz was used as a source of laser radiation. Pentaerythritol tetranitrate (PETN), trinitrotoluene (TNT) cyclotrimethylenetrinitramine (RDX), 1,3,5,7-tetranitro-1,3,5,7-tetrazoctane (HMX), explosives were investigated with use of field asymmetric ion mobility spectrometry (FAIMS) method. Ion spectra were recorded by with separating fields 8 – 12 kV/cm. Nickel radioactive isotope 63Ni was used as reference ionization source for explosive molecules. Non-linear ion mobility spectra of each substance ionized with UV laser radiation and radioactive 63Ni were compared and reasons for similarities and distinctive features are discussed. For peaks of explosives and reactant-ion peaks the dependences of their positions along compensating voltage axis on the magnitude of separating voltage (separating electric field) were measured for all the ion sources and substances. All the experiments were carried out under controlled ambient temperature and relative humidity (t=25℃, RH 30%). Humidity was supported the same inside and outside the gas system to minimize the influence of water cluster formation on the results obtained. Explosives vapors generators were made with 10mg samples of chemically pure explosives. RDX, HMX and PETN were heated (RDX 50℃, HMX 50℃, PETN 45℃) to increase the concentration of ions. It was shown that the behavior of the peaks of the explosives at laser excitation is different from the behavior at radioactive source for each of the substances. This indicates the presence of an additional ionization mechanism under laser radiation along with the traditional one. Spectra of reactant ion peaks under radioactive ionization also show difference in ion formation for each substance. Behavior of reactant-ion peaks of each of the substances with laser ion source shows nearly perfect coincidence. This fact can demonstrate well controlled experimental conditions and further confirms the difference in ionization mechanisms for laser and nickel radioactive ion source.

The presence of characteristic peaks in the terahertz (THz) absorption spectra of many organic substances and the active development of the technology for manufacturing video cameras based on microbolometric matrices create an increased interest in methods for identifying explosive compounds using THz imaging with simultaneous recording of spectral information. The results of relevant studies can be used in the development of security systems. THz images (taking into account the spectral information in each pixel) were obtained in this work by passing radiation through a sample based on hexogen (RDX) microcrystals deposited on a polyethylene (PE) film. A photoconductive antenna was used as a source of broadband radiation in the range from 0.5 THz to 2.5 THz. Spectral resolution was provided using a Fourier spectrometer based on a Michelson interferometer. The images were recorded using a THz video camera based on a microbolometric matrix. The possibility of identifying RDX microcrystals using color visualization of spectral information in the frequency range of one of the characteristic RDX peaks (~0.8 THz) has been demonstrated.

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

The study of using a cyclone collector with a liquid recirculation phase for collecting microparticles of TNT (trinitrotoluene) explosive, located in the form of traces on solid and fibrous surfaces was conducted in this work. Fragments of fibrous nonwoven material, as well as flax fabric fragments were used as a basis on which TNT powder was randomly distributed. The TNT sample area was about 900 cm2 . The cyclone collector with recirculating liquid phase originally designed for aerosol particles collection was used as a device for pre-concentration of explosives particles. Inlet air velocity was equal to 500 cm3 /min. Quantitative measurements of collected TNT amount were provided by gas chromatography – mass-spectrometry method. Experiments to compare the efficiency of cyclone collector sampling to the currently used methods of explosives microparticles collection - by wiping of surfaces and by dry filtration - were carried out. Cyclone collector showed high collection efficiency, amounting to 91% by weight of originally TNT spread on the surface that is more than 3 times higher than efficiencies of the wiping method (24% of the total mass of the trace) and the dry filtration method (23% of the total mass of the trace).

The work is devoted to the influence of scattering of terahertz (THz) radiation by hexogen particles (RDX) in powdery samples on their transmission and reflection spectra. A terahertz radio-vision installation with spectral resolution was used to determine experimentally THz spectra of RDX. For samples with small RDX particles (the typical particle size is 100 μm), characteristic peaks at 0.8 THz and 1.06 THz are observed in absorption spectra despite scattering, that can be used to identify this substance. For large hexogen particles (a typical particle size is 450 μm), experiments and numerical simulation showed that even the most intense peak at 0.8 THz is not observed in absorption spectra, and the spectra are mainly due to the scattering effect and its depending on the wavelength of radiation. The reflection spectra of RDX layers (particle size is about 100 μm) qualitatively differ from the reflection spectra of RDX crystals and are formed as a result of absorption during propagation of THz radiation in the particle layer. Thus, the substance can be identified by absorption spectra in a reflection scheme.

Testing the surrounding environment for the presence of biogenic aerosols is crucial in ensuring its safety for the population. It is often necessary to collect aerosol samples from large areas in short time, which demands excellent particle collection efficiency, a sufficient incoming air flow rate and a capacity to maintain the viability of the collected samples. Below we present the aerosol sampler with a high volumetric flow rate based on a two-stage particle concentration algorithm and consisting of a virtual impactor and a cyclone concentrator with a recirculating liquid phase. We provide all necessary calculations and an algorithm for modeling impactor parameters. The sampler was tested using dry and liquid formulations dispersed into the particles of 0.5 to 5 μm in diameter. We demonstrate that at volumetric flow rates over 4,000 l/min efficiency of particle collection into the liquid phase at a volume of 10 ml makes over 20% of the total aerosol mass and at volumetric flow rates over 300 l/min this value is over 60%. The proposed device maintains viability of the collected microorganisms. The sampler is portable, with flexible settings for sampling and cleaning, and can be controlled remotely over the network.