The physical behavior of a particle is determined largely by its size. The settling velocity of the particle, light scattered from the particle, and adhesion of a particle to a surface are examples of particle-size-dependent physical properties important in contamination control. It follows that selection of the measuring instruments, cleaning techniques, and understanding detrimental effects from particles are critically dependent on the particle size. A particle size distribution is the concentration of particles as a function of particle size. The normal distribution results from the action of many random additive and subtractive effects on an initially homogeneous population. In particle statistics, normal distributions are only found in cases of a vary narrow size range. Examples are nearly monodisperse calibration aerosols. Distribution models allow to simplify the way we look at data and include normal, log-normal, and power law distributions.

Sampling for culturable (e.g., viable) aerosolized microbes (bioaerosols) is a useful means to provide information for public health monitoring and studies. However, it is challenging to maintain microbe culturability when sampling at high flow rates (>12L/min) and extended periods of time (4h). We developed a first-generation, viable bioaerosol collection system (VBCS) utilizing temperature (T) and relative humidity (RH)-conditioned filtration at a flow rate of 25L/min. A two-stage system of tube-in-shell Nafion exchange units provides cooling to 10 degrees C and RH conditioning to 80-95%. Aerosol particles are collected on a polyurethane nanofiber filter providing a physical collection efficiency of >95% for sizes 0.06-10 mu m. The T and RH conditions at the collection filter are maintained, despite changes to ambient conditions. The initial testing of the VBCS was done under indoor, laboratory conditions with aerosolized, vegetative E. coli. A scenario of a 30-min challenge of bioaerosol followed by continued sampling of clean air for various times was used to judge culturability maintenance under extended-term sampling. An initial loss of culturability upon collection onto the filter was observed; 23 13% relative to 4-mm all-glass impinger. However once collected, 98% of culturability was maintained for an additional 4.5h of sampling. An exponential decay in culturability was observed from 8h to 15h of sampling. Also, 24-h cold storage of the filters collected was studied. The VBCS is based on the use of dry filter cassettes, needs minimal maintenance, and preserves culturability of vegetative bacteria for >4h.(c) 2017 RTI International and Aerosol Dynamics Inc.

Airborne viruses represent a potentially significant health threat. However, only recently have researchers begun to characterize the size and infectivity of viral bioaerosols in the nanoscale size range. There are limitations in the generation of test viral aerosols and the ability to sample with acceptable efficiency. Reported here is use of a laminar-flow water condensation method to efficiently sample nanoscale bioaerosols to sizes well below 100 nm. We used MS2 bacteriophage in water to provide an aerosol with particles sizes from 300 nm down to 45 nm for sampling by both an all-glass impinger (4 mm; AGI-4) and the water condensation bioaerosol sampler. We demonstrated the existence of infectious viral particles below 100 nm and a higher collection efficiency by the water condensation sampler compared to the AGI-4 at nanoscale sizes. For example, the water condensation bioaerosol sampler that collected particles at 45 nm in diameter had 20 times more infective virions per collected particle compared to the AGI-4. However, when we corrected the AGI-4 data for particle size-dependent collection efficiency, the results were similar. We also used quantitative reverse transcription polymerase chain reaction, along with culturing for infectivity to determine the percent infectivity of the aerosol by particle size. Finally, we used a simple calculation to determine that a large fraction of sub-100 nm particles did not contain infectious virus because of the low titer concentration of virus in the Collison fluid.

The objective of this study was to characterize an assortment of as received, commercially available, non-functionalized multiwalled carbon nanotubes (MWCNT) samples (n = 24) using thermogravimetric analysis, energy dispersive X-ray fluorescence spectrometry, high-resolution transmission electron microscopy and scanning electron microscopy. Each sample was assigned to one of six types based on nominal length and diameter. Some of the samples from the product assortment exhibited significant differences in purity and morphology from their nominal values. Variability in the physicochemical properties of MWCNTs may be a significant factor in why many toxicological investigations have findings that are difficult to reproduce. Therefore, it is strongly recommended that investigators studying these materials present characterization information in addition to providing their source.

An integrated sensor system was developed using mats formed of electrospun polymer/single-walled carbon nanotube composite nanofibers combined with inter-digitated electrodes directly printed on the surface to detect volatile organic compounds. When the polymer in the fibers swells due to vapor adsorption, the carbon nanotubes separate from each other and increase electrical resistance of the material. The conductivity change of the composite-sensing material was monitored with a multi-meter when exposed to volatile organic compounds. The response to different vapors showed a linear relationship between resistance change and vapor concentration. We obtained both sensitivity and selectivity data on the sensor with several different vapor analytes – methanol is used as an example in this paper.

This paper reports an interlaboratory comparison that evaluated a protocol for measuring and analysing the particle size distribution of discrete, metallic, spheroidal nanoparticles using transmission electron microscopy (TEM). The study was focused on automated image capture and automated particle analysis. NIST RM8012 gold nanoparticles (30 nm nominal diameter) were measured for area-equivalent diameter distributions by eight laboratories. Statistical analysis was used to (1) assess the data quality without using size distribution reference models, (2) determine reference model parameters for different size distribution reference models and non-linear regression fitting methods and (3) assess the measurement uncertainty of a size distribution parameter by using its coefficient of variation. The interlaboratory area-equivalent diameter mean, 27.6 nm ± 2.4 nm (computed based on a normal distribution), was quite similar to the area-equivalent diameter, 27.6 nm, assigned to NIST RM8012. The lognormal reference model was the preferred choice for these particle size distributions as, for all laboratories, its parameters had lower relative standard errors (RSEs) than the other size distribution reference models tested (normal, Weibull and Rosin-Rammler-Bennett). The RSEs for the fitted standard deviations were two orders of magnitude higher than those for the fitted means, suggesting that most of the parameter estimate errors were associated with estimating the breadth of the distributions. The coefficients of variation for the interlaboratory statistics also confirmed the lognormal reference model as the preferred choice. From quasi-linear plots, the typical range for good fits between the model and cumulative number-based distributions was 1.9 fitted standard deviations less than the mean to 2.3 fitted standard deviations above the mean. Automated image capture, automated particle analysis and statistical evaluation of the data and fitting coefficients provide a framework for assessing nanoparticle size distributions using TEM for image acquisition.

This chapter contains sections titled: Introduction Cleanrooms Particle Detection Standards and Recommended Practices ISO Standards 14644-1 and -2 Measuring Particle Emissions Viable Aerosols Monitoring Summary Conclusions List of Symbols References

Nanotechnology as a concept is usually credited to Feynman [1] who presented the idea in a 1959 after-dinner speech entitled, “There’s plenty of room at the bottom.” Interest in nanotechnology at the national level grew to the point that the United States Government launched the National Nanotechnology Initiative (NNI) in 1999 [2]. From a programmatic standpoint, materials related disciplines were combined using the unifying principle that some feature of the material should fall within the nanoscale size range. Nanoscale is defined as the size from approximately 1–100 nm [3]. Also some well-known materials associated with nanotechnology, such as fullerene and single wall carbon nanotubes were discovered in only the last 25 years [4, 5]. Much of the supporting science is well established in fields such as electronics, polymers, powders, colloids, and aerosols. However, the nanotechnology field is currently expanding rapidly with the discovery of new techniques, insights, applications and materials. It is clear that unifying principles and appropriate standards need to be developed to allow a systematic approach to managing the applications and risks of nanotechnology. These challenges have been faced by ISO Technical Committee 229 “Nanotechnologies” in its program to develop documents consistent with the goals of international standardization. The purposes of international standardization are to facilitate international trade; improvement of quality, safety, security, environmental and consumer protection, as well as the rational use of natural resources; and global dissemination of technologies and good practices [6].

Endotoxin has established health impacts and may be a potential confounding factor in toxicity studies of engineered nanomaterials (ENM). We aimed to characterize endotoxin contamination for a representative set of carbon-based ENM. The established method for quantifying endotoxin relies on its activity in a complex biochemical assay system. Because of their physical and chemical properties, measurement of endotoxin associated with many ENM presents non-trivial technical challenges. We have made progress in identifying and implementing methods for ENM analysis with respect to endotoxin content, revealing varying levels of endotoxin contamination in the ENM examined here. The physical association of ENM and endotoxin and their shared physiological effects suggest the possibility that contaminating endotoxin may contribute to the toxicity that is ascribed to ENM. We found in this small number of samples that endotoxin levels were not related to type of ENM or surface area but may be introduced randomly during manufacture.

Electrospun polymer nanofiber materials have attracted tremendous interest in sensor applications as their effective sensing surface area dramatically increases with decreasing fiber diameter. The highly tunable polymer composite chemistry and surface functionality of the nanofiber material provides a wide platform for exploring different applications, such as filtration media, sound isolation materials, and sensor components. This paper presents a nanofiber sensor platform device composed of electrospun polymer/carbon composite nanofibers combined with electrodes directly printed onto the surface of the electrospun fiber mat. This structure forms an integrated sensor system for detecting various chemical vapors including volatile organic compounds (VOCs) and oxidative gases. In this sensor, the composite polymer nanofibers form a chemo-resistor sensing material, and the conductivity of these composite sensing materials varies with chemical vapor exposure. The sensor performance exhibits very stable baselines with dramatically reduced noise levels compared to conventional interdigitated electrodes. Furthermore, the sensor response to different vapors shows a linear relationship between conductivity change and vapor concentration in the range of ppb – ppm for some analytes, including methanol, chloroform and ozone. The sensitivity and selectivity of these sensors to different vapor analytes will also be discussed.