Nanotoxicology and the risk assessment of nanomaterials is now a priority strategic thrust for the NIOH. The Toxicology and Biochemistry Section of the NIOH under the leadership of the NIOH has is currently setting up a Nano-toxicology Unit that will contribute to NIOH efforts to support the responsible development of the nanotechnology in South Africa. Nano-toxicology is a sub-specialty of particle toxicology and is dedicated to the study of the toxicity of nanomaterials. This unit will focus on the risk assessment of engineered nano-particles in general and their toxicity assessment in particular.
Nanotechnology refers to the branch of science and engineering devoted to designing, producing, and using structures, devices, and systems by manipulating atoms and molecules at nano-scale. A major output of this activity is the development of new materials in the nanometer scale, including nanoparticles, i.e. particulate materials with at least one dimension of less than 100 nanometers (100 millionth of a millimeter) or less. One nanometer is 10-9 m or 10-3 μm, by comparison, by comparison, a human hair is approximately 70,000 nm in diameter, a red blood cell is approximately 5,000 nm wide and simple organic molecules have sizes ranging from 0.5 to 5 nm.
Length scale below (figure 1) illustrates the nano-meter in context. The length scale at the top ranges from 1m to 10-10m, and illustrates the size of a football compared to a carbon 60 (C60) molecule, also known as a buckyball. For comparison the world is approximately one hundred million times larger than a football, which is in turn one hundred million times larger than a buckyball.
Owing to their unique nano-scale, nanoparticles are provided with many special and unusual physicochemical properties that raise many concerns about the safety of these materials. Assessment of health risks arising from exposure to chemicals or other substances requires understanding of the intrinsic toxicity of the substance.
To this end the section, with contribution from the Mine Health and Safety Council (MHSC) has just acquired state of the art equipment to characterize the physical properties of fine and nanoparticles, namely the Scanning Mobility Particle Sizer (SMPS) and Aerodynamic Particle Sizer (APS) for particle characterization, e.g. number of particles and specific surface area of nanoparticles. The TSI APS is capable of analyzing particle aerodynamic diameter in the range 0.5 – 20 μm of solids and nonvolatile liquids. Aerodynamic diameter is a significant size parameter because it determines the behavior of airborne particles. It is defined as the physical diameter of a unit density sphere that settles through the air with a velocity equal to that of the particle in question. Knowledge of a particle's aerodynamic diameter allows you to determine: 1) If and where the particle will be deposited in the human respiratory tract. 2) How long the particle will remain airborne in the atmosphere or in an aerosol. 3) Whether the particle will penetrate a filter, cyclone, or other particle-removing device. 4) Whether the particle will enter a particle-sampling system.
On the other hand the SMPS is capable of classifying particle size and particle concentration of particulate matter and nonvolatile liquids from 10 to 1000nm.
Figure 2: Typical number based distribution of MnO2 powder (collected from an iron smelter in South Africa). The histogram shown is combined data from a TSI APS (Model 3321) and TSI SMPS (consisting of an Electrostatic Classifier, Model 3080 and Condensation Particle Counter, Model 3372) at the NIOH.
Figure 3: TSI SMPS (consisting of an Electrostatic Classifier, Model 3080 and Condensation Particle Counter, Model 3372) first two instrument, and TSI APS (Model 3321) sitting on top of a TSI Small Scale Powder Dispenser (Model 3433) for bulk powder sampling.
To further investigate the uptake and toxicity of nanoparticles, the Toxicology Department has also recently purchased a CytoViva Hyperspectral Imaging System, shown in figure 4.
Figure 4. The CytoViva Hyperspectral Imaging System
CytoViva, Inc. has developed the CytoViva high performance optical imaging system for nanoscale research. This optical system provides researchers in both life and materials sciences with the ability to image sub-100 nanometer particles and materials, live and in real time. CytoViva Imaging Technology provides real-time optical imaging of nanomaterials and biologicals, as well as spectral imaging analysis of nanomaterials and cellular features. CytoViva's patented illumination technology integrates onto a standard optical microscope, creating a high signal-to-noise, darkfield-based image. This specialized capability enables fast observation of a wide range of nanomaterials and pathogens along with unlabeled or fluorescently labeled cells and tissue.
The CytoViva Hyperspectral Imaging System (HSI) attaches to the CytoViva Microscope System. It serves to quantify the presence of a wide range of nanomaterials in cells and tissue or in composites. The system captures the VNIR (400-1000nm) spectrum within each pixel of the scanned field of view. Advanced analytical software then provides detailed spectral analysis of the scanned materials. When used with the CytoViva Dual Mode Fluorescence system, the interactions between fluorescently labelled nano-particles or bacteria and unlabelled live cells can be observed. This unique feature eliminates the need to overlay images using computer software. In addition, the CytoViva Environmental Chamber which enables long term, live cell imaging with the ability to control temperature and perfusion rate.
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