During the past 20 years, improvements in nanoscale materials synthesis and characterization have given scientists great control over the fabrication of materials with features between 1 and 100 nm, unlocking many unique size-dependent properties and, thus, promising many new and/or improved technologies. Recent years have found the integration of such materials into commercial goods; a current estimate suggests there are over 800 nanoparticle-containing consumer products (The Project on Emerging Nanotechnologies Consumer Products Inventory, , accessed Oct. 2008), accounting for 147 billion USD in products in 2007 (Nanomaterials state of the market Q3 2008: stealth success, broad impact, Lux Research Inc., New York, NY, 2008). Despite this increase in the prevalence of engineered nanomaterials, there is little known about their potential impacts on environmental health and safety. The field of nanotoxicology has formed in response to this lack of information and resulted in a flurry of research studies. Nanotoxicology relies on many analytical methods for the characterization of nanomaterials as well as their impacts on in vitro and in vivo function. This review provides a critical overview of these techniques from the perspective of an analytical chemist, and is intended to be used as a reference for scientists interested in conducting nanotoxicological research as well as those interested in nanotoxicological assay development.

A mast cell/fibroblast co-culture system is used as a model to assess the toxicity of Au nanoparticles over the course of 72 hours of exposure. Cellular uptake of nanoparticles was found to increase over the 72 hr exposure period and the nanoparticles localized within granular bodies of the primary culture mast cells. These granules were found to increase in volume with the addition of nanoparticles. There was no decrease in viability for 24 hr exposed cells but a slight viability decrease was found after 48 and 72 hr exposure. Carbon-fiber amperometry analysis of exocytosis of serotonin from mast cells revealed changing release profiles over the time course of exposure. In early exposure times, granular secretion of serotonin increased with exposure to Au nanoparticles whereas 72 hr exposure showed decreased secretion of serotonin with nanoparticle exposure. The kinetics of this release was also found to be affected by Au colloid exposure where the rate of serotonin expulsion decreased with increasing nanoparticle exposure. These results illustrate the dynamic nature of nanoparticle-cell interactions and the critical changes in cell behavior even when viability is unaffected.

In this work, carbon-fiber microelectrode amperometry is used to characterize serotonin exocytosis from murine peritoneal mast cells cocultured with fibroblasts in the presence of Au nanoparticles. In the case of mast cell exposure to 1 nM 28 nm diameter spherical Au nanoparticles, there is a decrease of greater than 30% in the number of successful granule transport and fusion events, greater than 30% increase in the rate of intragranular matrix expansion, and greater than 20% increase in the number of secreted serotonin molecules per granule. These results suggest that nanoparticles interrupt the dense-core biopolymer intragranular matrix and present the potential for systematic studies showing how exocytotic function is influenced by nanoparticle size, shape, and composition.

Motivation: Human assist devices such as hand tools and orthotics require high force, low speed, compact size, and light weight, which match hydraulics. Traditionally, hydraulic systems are used in applications that require large amounts of power so components are large and heavy. To apply hydraulic technologies to human assist devices, traditional hydraulic components must be scaled down to appropriate power levels, that is, from thousands of watts to about 100 W. To apply small-scale ͑10-100 W͒ hydraulics to human assist devices, three steps were taken. First, a hydraulic ankle foot orthosis ͑AFO͒ was built and tested to understand the feasibility of using small-scale hydraulics in human assist devices. Second, a small-scale electrohydraulic actuator ͑EHA͒ system was built to identify the gaps between the desired small-scale hydraulic components and the smallest off-the-shelf hydraulic components. Third, basic fluid mechanics and structural equations were used to model the efficiency of small-scale hydraulic components, which is the key to miniaturize traditional hydraulic systems. Results: The AFO platform showed that sufficient torque and range of motion can be realized with a hydraulic system but confirmed the need for small hydraulics to reduce the weight and bulk. The EHA system showed that the smallest offthe-shelf components are oversized for a small-scale hydraulic system and identified the need for custom small-scale hydraulic components. The efficiency models showed that reasonable efficiencies are achievable for small-scale hydraulic components, but different design rules are required.