Fluorescent Particle Tracers Research Articles

A comparative analysis of potential aerosol exposure in a wide-body aircraft cabin using tracer gas and fluorescent particles

We compare two aerosol surrogate tracers in aircraft cabins for breathing and coughing sources: tracer gas collected in the ACER Boeing 767 mock-up and fluorescent particles collected in an actual Boeing 767 aircraft by the US Transportation Command (TRANSCOM). Each source was located individually in window and middle seats. Exposure generally decreased with source distance. A window seat breathing source resulted in good agreement between datasets for exposure (as percent of release) for the TRANSCOM hangar-AFT testing mode, which corresponds to the 11-row cabin ACER laboratory space. Average tracer gas exposure for a middle seat breathing source was higher in the ACER study than the fluorescent particle tracer exposure in the TRANSCOM study. Using a coughing source in a window seat, the exposure for the TRANSCOM data was higher within the first two rows from the source before decreasing to and tracking with the ACER levels, until increasing after about 5 m away. A similar trend was recorded for a middle seat coughing source with higher overall exposure for the TRANSCOM data. Sources of exposure variation between the studies include particle deposition. This work helps optimize aerosol dispersion research in aircraft cabins and provides some validation to the existing studies.

Stable Encapsulation of Methylene Blue in Polysulfide Organosilica Colloids for Fluorescent Tracking of Nanoparticle Uptake in Cells.

Methylene blue (MB), a century-old drug and a fluorescent dye, has a long history of diverse applications, both in drug therapy and as a tissue-staining agent. However, MB is inherently unstable when exposed to light and reducing agents. In this study, we aim to prepare and characterize polysulfide-based organosilica colloidal particles for efficient, stable, and protective encapsulation of MB. Disulfide- and tetrasulfide-containing organosilane congeners were used as organosilica precursors for direct synthesis of organosilica colloids based on the silica ouzo effect. MB was spontaneously entrapped into the colloidal particles during the particle formation process. The following properties of the colloidal MB were evaluated: particle size, surface charge, atomic distribution, encapsulation efficiency, MB release, photodynamic activity, thiol and ascorbate reactivity, and cytotoxicity. The DLS measurements show that the size of colloidal MB is tunable in a range of 100 nm to 1 μm. SEM images reveal spherical particles with composition-dependent particle sizes of 70–120 nm (coefficient of variation: 15–18%). MB was encapsulated in the colloidal particles with a maximal efficiency of 95%. The release of MB from the colloids was <1% at 4 h and <3.5% at 48 h. The colloidal particles show much reduced photodynamic activity, low reactivity toward reducing agents, and low cytotoxicity. Accordingly, the colloidal MB was proposed and further investigated as a fluorescent particle tracer for the study of cell–nanoparticle interactions. In conclusion, MB can be efficiently and stably loaded into polysulfide organosilica colloidal particles using a simple and convenient physical route.

Effective removal of fluorescent microparticles as Cryptosporidium parvum surrogates in drinking water treatment by metallic membrane

The diarrhoea-causing parasitic protozoan Cryptosporidium parvum (C. parvum) cannot be efficiently removed by conventional drinking water treatment and poses a biological threat to public health. To ensure the biological safety, three kinds of metallic membranes, laminating metal mesh filter, non-woven metal filter and sintered metal fiber filter were employed to compare their properties. The results showed that the sintered membrane possessed the best filtration performance and lowest membrane resistance among three metallic membranes. Therefore, the sintered membrane was selected for subsequent experiments. Due to the low infectious dose of C. parvum and sophisticated detection methods, fluorescent particle tracers, Crypto-tracer-1, were chosen as a feasible surrogate was proposed to investigate the removal efficiency of sintered membrane for C. parvum. The results indicated that the tracer log removal value (LRV) ranged between 5.1 and 5.4 log10 under different filtration flux, which equivalently means that C. parvum could be completely removed and further tests are needed to confirm the results obtained using C. parvum. Furthermore, a pilot-scale study was performed for 10 weeks in full-scale drinking water treatment systems. The turbidity could be efficiently removed (outlet water of membrane was 0.08 ± 0.04 NTU) and the average transmembrane pressure recovery rate was 84.6% after physical backwash. Fouling mechanism analysis indicated that the interaction energy between foulants and membrane material became stronger over time. The practical operation results showed that sintered membrane performed well in continuous operation for a long time and also had a good anti-pollution ability. These findings could facilitate application of metallic membrane in drinking water treatment.

Characterization of eco-friendly fluorescent nanoparticle-doped tracers for environmental sensing

Particle tracers are extensively used in quantitative flow visualization and environmental sensing. In this paper, we provide a thorough characterization of the novel eco-friendly fluorescent particle tracers formulated in Tauro et al. (AIP Adv 3(3): 032108, 2013). The tracers are synthesized from natural beeswax and are functionalized by encapsulating nontoxic fluorophore nanoparticles in the beads’ matrix through an inexpensive thermal procedure. Visibility and durability studies are conducted through a wide array of techniques to investigate the tracers’ surface morphological microfeatures, crystal nature and size, chemical composition, fluorophore incorporation into the beeswax matrix, and fluorescence response under severe settings resembling exposure to natural environments. Our findings demonstrate that fluorescent nanoparticles ranging from 1.51 to 3.73 nm are homogeneously distributed in the superficial layer (12 nm) of the tracers. In addition, fluorescence emissions are observed up to 26 days of continuous exposure of the tracers to high energy radiation. To demonstrate the particles’ use in environmental flow sensing, a set of proof of concept outdoor tests are conducted, in which image analysis tools are utilized for detecting the fluorescent tracers. Experimental results suggest that fluorescent microparticles deployed in high flow-rate flows (2 m/s) and under direct sunlight can be sensed through commercially available cameras (frame rate set to 30 Hz).

Fluorescent particle tracers in surface hydrology: a proof of concept in a semi-natural hillslope

Abstract. In this paper, a proof of concept experiment is conducted to assess the feasibility of tracing overland flow on an experimental hillslope plot via a novel fluorescent particle tracer. Experiments are performed by using beads of diameters ranging from 75 to 1180 μm. Particles are sensed through an experimental apparatus comprising a light source and a video acquisition unit. Runoff on the experimental plot is artificially simulated by using a custom-built rainfall system. Particle transits are detected through supervised methodologies requiring the presence of operators and unsupervised procedures based on image analysis techniques. Average flow velocity estimations are executed based on travel time measurements of the particles as they are dragged by the overland flow on the hillslope. Velocities are compared to flow measurements obtained using rhodamine dye. Experimental findings demonstrate the potential of the methodology for understanding overland flow dynamics in complex natural settings. In addition, insights on the optimization of particle size are presented based on the visibility of the beads and their accuracy in flow tracing.

Fluorescent particle tracers for surface flow measurements: A proof of concept in a natural stream

In this paper, a new particle tracer for surface hydrology is proposed. The approach leverages the complementary advantages offered by particle‐tracking velocimetry and traditional tracing technologies, such as dyes and chemicals, toward a practically feasible and low‐cost measurement system. Specifically, the proposed methodology is based on the detection and tracking of buoyant fluorescent microspheres through an experimental system that incorporates ultraviolet lamps to elicit the fluorescence response and a digital camera to record the particle transit. This low‐cost measurement system can be used in a variety of natural settings ranging from small‐scale streams to rills with scales on the order of a few centimeters in hillslopes. The use of insoluble buoyant particles reduces the amount of tracing material for experimental measurements. Further, particles' enhanced fluorescence allows for noninvasive flow characterization, that is, for nonintrusively detecting the tracer without deploying probes and samplers in the water. A proof of concept experiment for the proposed methodology is conducted on the Rio Cordon, a natural mountainous stream in the Italian Alps. Flow measurements at selected stream cross sections and travel time experiments on varying stream reaches are performed to ascertain the feasibility of fluorescent particle tracers. Such experimental findings demonstrate that the particles are visible in complex natural streams and are effective in estimating flow velocities and travel times.

The flow in an oil/water plate heat exchanger for the automotive industry

This paper presents an experimental and numerical work to analyze the flow in an oil/water plate heat exchanger for the automotive industry. The plate heat exchanger is designed as 21 equal plates assembled in a stack. Each plate has a series of grooves in the surface, and is mounted upside down with respect to the preceding one, so that channels are formed that should direct the fluid motion and increase the heat transfer area. The flow has been experimentally studied by means of planar laser-induced fluorescence (PLIF) to visualize its structure, and particle image velocimetry (PIV) with fluorescent particle tracers to measure its velocity. It has also been numerically simulated. In both cases, it has been observed that, for the analyzed design and either for oil or water, the flow is not uniform, and preferentially moves along the lateral extremes of the plates that conform the heat exchanger.

The use of tracers to evaluate the importance of bioturbation in remobilising contaminants in Baltic sediments

Large areas of the bottom sediments of the Baltic Sea are temporarily or permanently anoxic. These sediments are also an important sink for a variety of contaminants. Reoxygenation of bottom waters allows recolonisation by benthic infauna, which may have important implications for the fate of buried contaminants. This study used tracers to experimentally examine the role of bioturbation by benthic infauna in transporting sediment-associated contaminants in the Baltic Sea. Three different tracer methods were used in two experiments, using three key Baltic macrofaunal species: the amphipod crustacean Monoporeia affinis; the Baltic clam Macoma baltica; and the priapulid worm Halicryptus spinulosus. In the first experiment, a reoxygenation–recolonisation scenario was recreated in the laboratory, using hypoxic sediment cores collected in the field, to determine if there was remobilisation of buried 137Cs from the Chernobyl nuclear accident in 1986. The potential for the infauna to bury newly settled surface contamination was also investigated, using a fluorescent particle tracer. In the second experiment, artificially-created radiolabelled tracer layers ( 14C and 51Cr) were used to quantify both upward and downward movements of organic matter and sediment-associated contaminants by bioturbation. In both experiments there were clear visual differences between the sediment effects of the three species. Halicryptus spinulosus buried deepest into the sediment, creating a network of burrows, Monoporeia affinis burrowed actively in the upper few centimeters of the sediment, and Macoma baltica was quite stationary, but appeared to filter- and deposit feed at the sediment surface. Mixing depths in the hypoxic sediment varied from 4.0 ± 3.5 cm for M. baltica to 7.8 ± 2.1 cm for H. spinulosus. Biodiffusion rates ( D b) were similar for all treatments but biotransport rates ( r) were significantly different between treatments, mainly due to a high r value for H. spinulosus. In the experiment with radiolabelled tracer layers, 51Cr was transported more than 14C, and tracer originally at the surface transported more than tracer buried 4 cm below the surface. There was also transport of all tracers in treatments without added macrofauna. The most likely explanation is bioturbation by the meiofauna that were undoubtedly present in both experiments. Bioturbation by macrofauna both buries surface contaminants and remobilises those that are buried, but the effects are small and on a similar scale to transport caused by meiofauna. In addition, 137Cs profiles at the hypoxic site indicated that resuspension and redeposition of sediment by physical processes had occurred, and also showed that contaminants from the last 40 years were still present in the top 5–10 cm of the sediment, well within active mixing depths. At this site, as at many others in the Baltic, physical processes are likely to be far more important than biological processes in the redistribution of contaminants on a decadal timescale.

Validation of a fish farm waste resuspension model by use of a particulate tracer discharged from a point source in a coastal environment

To validate a resuspension model of particulate material (salmonid farm wastes), a UV fluorescent particle tracer was selected with similar settling characteristics. Tracer was introduced to the seabed (water depth ≈30 m) and sediment samples taken on days 0, 3, 10, 17 and 30 to measure the horizontal and vertical distribution of tracer in sediments. A concentric sampling grid was established at radii of 25, 50, 100, 150, 200, 400, 700 and 1, 000 m from the source on transects 30° apart. The bulk of the deployed tracer was initially concentrated in an area 25 m radius from the release point; tracer was observed to steadily decrease to zero over a period of 30 days. In a 200 m region measured from the release point in the direction of the residual current, the redeposition of tracer was low. A Lagrangian particle tracking model was validated using these observed data by varying resuspension model parameters within limits to obtain the best agreement between spatial and temporal distributions. The validated model generally gave good predictions of total mass budgets (±7% of total tracer released), particulary where tracer concentrations were high near the release point. Best fit model parameters (critical erosion shear stress=0.018 N m−2, erodibility constan=60 g m−2 d−1) are at the low end of reported parameters for coastal resuspension models. Such a low critical erosion shear stress indicates that the frequency of resuspension and deposition events for freshly deposited material is high.

Lidar discrimination of multiple fluorescent tracers of atmospheric motions

An analytical study demonstrates the feasibility of simultaneous lidar measurement and discrimination of multiple fluorescent particle tracers of air motions. Equations are presented for evaluating signal-to-noise ratio and interfering signals. Matrix methods can solve for the concentrations of several tracers from simultaneous measurements in at least as many spectral receiver channels, even when fluorescence spectra overlap. Two example systems, one with crosstalk and another without, are evaluated for accuracy in the presence of shot noise and calibration errors. Potential applications include observing the structure of complex flows and measuring the effect of release location on atmospheric transport and dispersion.

Changes in feeding and crawling rates of Hydrobia truncata (Prosobranchia: Hydrobiidae) in response to sedimentary chlorophyll-a and recently egested sediment

Experiments combining fluorescent particle tracer techniques with time-lapse video recording demonstrated that the gastropod Hydrobia truncata decreases crawling rate on patches rich in chlorophyll-a, while maintaining a constant feedng rate as sedimentary chlorophyll-a content varies. In contrast, H. truncata decreases feeding rate but does not change crawling rate upon encounter with patches of recently egested sediment. Depression of feeding rate is less pronounced if the egested material is enriched in chlorophyll-a. For deposit feeders inhabiting highly reworked sediments, the majority of available material may consist of sediment that has been recently egested. For an animal that responds negatively to recently egested sediment, the pool of material available for ingestion may be much reduced. The ability to independently control rates of energy input and expenditure in response to rapidly changing environmental conditions may enable an organism to control net energy gain over short time periods.