Simon Clavaguera

Review of nanomaterial aging and transformations through the life cycle of nano-enhanced products.

In the context of assessing potential risks of engineered nanoparticles (ENPs), life cycle thinking can represent a holistic view on the impacts of ENPs through the entire value chain of nano-enhanced products from production, through use, and finally to disposal. Exposure to ENPs in consumer or environmental settings may either be to the original, pristine ENPs, or more likely, to ENPs that have been incorporated into products, released, aged and transformed. Here, key product-use related aging and transformation processes affecting ENPs are reviewed. The focus is on processes resulting in ENP release and on the transformation(s) the released particles undergo in the use and disposal phases of its product life cycle for several nanomaterials (Ag, ZnO, TiO2, carbon nanotubes, CeO2, SiO2 etc.). These include photochemical transformations, oxidation and reduction, dissolution, precipitation, adsorption and desorption, combustion, abrasion and biotransformation, among other biogeochemical processes. To date, few studies have tried to establish what changes the ENPs undergo when they are incorporated into, and released from, products. As a result there is major uncertainty as to the state of many ENPs following their release because much of current testing on pristine ENPs may not be fully relevant for risk assessment purposes. The goal of this present review is therefore to use knowledge on the life cycle of nano-products to derive possible transformations common ENPs in nano-products may undergo based on how these products will be used by the consumer and eventually discarded. By determining specific gaps in knowledge of the ENP transformation process, this approach should prove useful in narrowing the number of physical experiments that need to be conducted and illuminate where more focused effort can be placed.

Airborne engineered nanomaterials in the workplace—a review of release and worker exposure during nanomaterial production and handling processes

For exposure and risk assessment in occupational settings involving engineered nanomaterials (ENMs), it is important to understand the mechanisms of release and how they are influenced by the ENM, the matrix material, and process characteristics. This review summarizes studies providing ENM release information in occupational settings, during different industrial activities and using various nanomaterials. It also assesses the contextual information - such as the amounts of materials handled, protective measures, and measurement strategies - to understand which release scenarios can result in exposure. High-energy processes such as synthesis, spraying, and machining were associated with the release of large numbers of predominantly small-sized particles. Low-energy processes, including laboratory handling, cleaning, and industrial bagging activities, usually resulted in slight or moderate releases of relatively large agglomerates. The present analysis suggests that process-based release potential can be ranked, thus helping to prioritize release assessments, which is useful for tiered exposure assessment approaches and for guiding the implementation of workplace safety strategies. The contextual information provided in the literature was often insufficient to directly link release to exposure. The studies that did allow an analysis suggested that significant worker exposure might mainly occur when engineering safeguards and personal protection strategies were not carried out as recommended.

Sub-ppm Detection of Nerve Agents Using Chemically Functionalized Silicon Nanoribbon Field-Effect Transistors†

Organophosphorus compounds (OPs) represent one of the most important and lethal classes of chemical warfare agents (e.g. sarin, tabun, soman). Highly active volatile OPs are powerful inhibitors of acetylcholinesterase, which is a critical enzyme of the nervous system. The ease of manufacturing OPs based on inexpensive starting materials makes these agents a weapon of choice for terrorist attacks. Thus, the rapid sensing of these nerve agents has recently become an increasingly important research goal. Various approaches have been reported for the detection of these chemical warfare agents including colorimetric and fluorimetric spectroscopies, enzymatic assays, piezoelectric devices, single-walled carbon nanotube resistors and capacitors. However, these systems are plagued by limitations such as slow response time, moderate selectivity, operational complexity, or limited portability. Field-effect transistors (FET) based on nanomaterials such as semiconducting nanowires, nanoribbons, or carbon nanotubes have been recently explored for chemical and biological detection. Their high effectiveness is mainly ascribed to an extreme sensitivity to electrostatic changes at the surface of the semiconductor and/or modifications of the Schottky barrier at the semiconductor/metal interface. A charge generation in the vicinity of the semiconductor of a FET is known to alter the electrical properties of the device. Several research groups have independently developed a series of small-molecule fluorescent sensors for OPs detection. They investigated organic moieties reactive towards OPs by formation of a phosphate ester intermediate and subsequent intramolecular nucleophilic substitution, which led to an ammonium salt and thus charge formation. We thought monitoring this charge generation with a functionalized FET could be a particularly promising approach. Herein, we report the development of an OPs chemical sensor based on highly sensitive silicon nanoribbon field-effect transistors (SiNR-FETs) functionalized with compound 1 (Scheme 1).

Review of measurement techniques and methods for assessing personal exposure to airborne nanomaterials in workplaces

Exposure to airborne agents needs to be assessed in the personal breathing zone by the use of personal measurement equipment. Specific measurement devices for assessing personal exposure to airborne nanomaterials have only become available in the recent years. They can be differentiated into direct-reading personal monitors and personal samplers that collect the airborne nanomaterials for subsequent analyses. This article presents a review of the available personal monitors and samplers and summarizes the available literature regarding their accuracy, comparability and field applicability. Due to the novelty of the instruments, the number of published studies is still relatively low. Where applicable, literature data is therefore complemented with published and unpublished results from the recently finished nanoIndEx project. The presented data show that the samplers and monitors are robust and ready for field use with sufficient accuracy and comparability. However, several limitations apply, e.g. regarding the particle size range of the personal monitors and their in general lower accuracy and comparability compared with their stationary counterparts. The decision whether a personal monitor or a personal sampler shall be preferred depends strongly on the question to tackle. In many cases, a combination of a personal monitor and a personal sampler may be the best choice to obtain conclusive results.

High Gain and Fast Detection of Warfare Agents Using Back-Gated Silicon-Nanowired MOSFETs

The top-down fabrication of doped p-type silicon-nanowired (NW) arrays and their application as gas detectors is presented. After surface functionalization with 3-(4-ethynylbenzyl)-1, 5, 7-trimethyl-3-azabicyclo [3.3.1] nonane-7-methanol molecules, the wires were subjected to an organophosphorous simulant, and both static and dynamic measurements were performed. A current gain of 4 × 106 is obtained upon the detection of the subpart-per-million concentration of a nerve-agent simulant. This represents a four-decade improvement over previous demonstration based on nanoribbons, proving better sensing capabilities of NWs. Technology-computer-aided-design simulations before and after gas detection have been performed to gain insight into the physical mechanisms involved in the gas detection and to investigate the impact of the surface-to-volume ratio on sensor sensitivity.

Development of an autonomous detector for sensing of nerve agents based on functionalized silicon nanowire field-effect transistors.

The ability to detect minute traces of chemical warfare agents is mandatory both for military forces and homeland security. Various detectors based on different technologies are available but still suffer from serious drawbacks such as false positives. There is still a need for the development of innovative reliable sensors, in particular for organophosphorus nerve agents like Sarin. We report herein on the fabrication of a portable, battery-operated, microprocessor-based prototype sensor system relying on silicon nanowire field-effect transistors for the detection of nerve agents. A fast, supersensitive and highly selective detection of organophosphorus molecules is reported. The results show also high selectivity in complex mixtures and on contaminated materials.

Inter-comparison of personal monitors for nanoparticles exposure at workplaces and in the environment

Personal monitors based on unipolar diffusion charging (miniDiSC/DiSCmini, NanoTracer, Partector) can be used to assess the individual exposure to nanoparticles in different environments. The charge acquired by the aerosol particles is nearly proportional to the particle diameter and, by coincidence, also nearly proportional to the alveolar lung-deposited surface area (LDSA), the metric reported by all three instruments. In addition, the miniDiSC/DiSCmini and the NanoTracer report particle number concentration and mean particle size. In view of their use for personal exposure studies, the comparability of these personal monitors was assessed in two measurement campaigns. Altogether 29 different polydisperse test aerosols were generated during the two campaigns, covering a large range of particle sizes, morphologies and concentrations. The data provided by the personal monitors were compared with those obtained from reference instruments: a scanning mobility particle sizer (SMPS) for LDSA and mean particle size and a ultrafine particle counter (UCPC) for number concentration. The results indicated that the LDSA concentrations and the mean particle sizes provided by all investigated instruments in this study were in the order of ±30% of the reference value obtained from the SMPS when the particle sizes of the test aerosols generated were within 20-400nm and the instruments were properly calibrated. Particle size, morphology and concentration did not have a major effect within the aforementioned limits. The comparability of the number concentrations was found to be slightly worse and in the range of ±50% of the reference value obtained from the UCPC. In addition, a minor effect of the particle morphology on the number concentration measurements was observed. The presence of particles >400nm can drastically bias the measurement results of all instruments and all metrics determined.

Measurement Methods for Nanoparticles in Indoor and Outdoor Air

A large variety of measurement methods for the characterization of airborne nanoparticles in indoor or outdoor air exist. The choice of an appropriate method depends strongly on the questions to be tackled. If the aerosol is to be characterized only for a single location, one may use stationary equipment that is rather bulky but provides the most details and is most accurate. Spatially resolved measurements can only be conducted with portable or personal measurement equipment which provide a limited dataset with lower accuracy. Furthermore, the metrics to be measured (e.g., number, surface area of mass concentration, chemical composition, etc.) determine the choice of measurement methods as no single method can do it all. Another determining factor is the time resolution of the instruments. While direct-reading monitors deliver the information with high time resolution (often 1 s) and hence allow for linking the measured concentration to certain activities, samplers collect the particles for subsequent analyses and therefore provide an average over the sampling time. Consequently, the choice of a measurement instrument for the characterization of airborne nanoparticles remains a compromise. In many practical applications, the combination of different techniques may be required.

Functionalization of Silicon Nanowires for Specific Sensing

Thanks to their large surface-to-volume ratio, silicon nanowires (Si NWs) are extremely sensitive to all phenomena which could alter their surface potential and charge distribution. Those surface variations lead to a change of the Si NWs equivalent conductance. The use of the output conductance of a silicon nanowire as a compact transducer for direct detection of (bio)chemical molecules or gases has gained immense attention these last years. In this paper, fabrication of silicon nanowires using top-down approach is shown, with simple calculations to determine hole mobility, hole concentration and resistivity. Transfer characteristics and sampling measurements were performed on the nanowires with and without surface functionalization under various ambient conditions indicating the importance of functionalization in order to avoid any environment effect on the transport properties of the nanowires.

New Chemically Functionalized Nanomaterials for Electrical Nerve Agents Sensors

A chemical receptor specific to traces of organophosphorus nerve agents (OPs) has been synthesized and grafted to carbon nanotubes and silicon nanowires in order to make electrical sensors. Our results show that it is possible to detect efficiently sub-ppm traces of OPs with excellent selectivity notably with the use of silicon nanowires by monitoring the Drain-Source current of the SiNW-FET at an optimum back Gate voltage as a function of time. First developments of a prototype have also been realized.