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Nanotechnology has been serendipitously employed by humanity for hundreds of years. Artistically, gold-ruby glass (cranberry glass), present in the Roman Lycurgus cup and later in many church stained glass windows, owes its striking red color and optical properties to gold nanoparticles created when a gold precursor is added to molten silicate glass.122 Cosmetically, to blacken hair, the Greco-Roman practice of mixing of lead oxide and slaked lime with water created lead sulfite nanocrystals (5 nm), which accumulated in the hair cuticle and cortex.371 Martially, seventeenth century Damascus steel sword blades owed their high-quality mechanical properties to carbon nanotubes (CNTs) and cementite (Fe3C) nanowires found within their structure.289 Medicinally, specially prepared, “Swarna bhasma,” nanosized colloidal gold, has been employed as an antirheumatic, anti-asthmatic, and anti-diabetic in Indian Ayurvedic practice for centuries.37
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Langmuir’s detailed experimental work establishing the existence of monatomic films garnered him the Nobel Prize in 1932.172 In 1959, the physicist Richard Feynman proposed the theoretical framework for “manipulating and controlling things” all the way down to the atomic level.89 Norio Taniguchi is generally credited with coining the term “nano-technology”—“the processing of separation, consolidation and deformation of materials by one atom or one molecule”—in 1974.340 The invention of the scanning tunneling microscope in 1981 enabled the visualization of individual atoms and allowed the direct physical manipulation of atomic surfaces.152 In 1985, Kroto and colleagues reported on a novel, minute crystalline allotropic form of carbon, conceptualized some 15 years previously.57,166,258 These soccer ball-shaped carbon-60 structures were named “buckminsterfullerenes” after Buckminster Fuller. The discovery of CNTs followed in 1991.134
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Health and safety of nanotoxicology came to fore during the first consumer recall of a purported nano-based invention.384 In 2006, the bathroom cleaning product “Magic-Nano” was released in Germany. Within days, more than 110 cases of illness were reported, and several patients were hospitalized with severe respiratory complaints, including acute lung injury. No further episodes of illness occurred after product recall only 3 days after introduction.147 Although it was ultimately determined that “Magic-Nano” contained no nanoparticles, the incident raised many questions about nanotechnology development, regulation, and health risks.21,22 More than 1600 consumer products now incorporate nanotechnology, with multiple products reaching the market weekly.346
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PHYSIOCHEMICAL PRINCIPLES
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Nanotechnology is defined as the “control and restructuring of matter at the nanoscale, in the size range of approximately 1 to 100 nanometers, in order to create materials, devices, and systems with fundamentally new properties and functions due to their small structure.”281 The American Society for Testing and Materials (ASTM) International defines an ultrafine particle as a particle ranging in size from approximately 0.001 (1 nm; 10 Å) to 0.1 μm (100 nm; 1000 Å) and a nanoparticle as an ultrafine particle with lengths in two or three dimensions greater than 0.001 ...