Why do we have so many definitions for nanoscience and nanotechnology?

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Nanoscience and nanotechnology have an enormous scientific and practical future in the emerging field of nanomedicine. However, most experts seem to disagree on how to define and use nano-related terms. As a consequence, a surprising number of different definitions can be found both in the popular and the scientific literature for nanoscience and nanotechnology, not to mention nanomedicine. What’s more, these definitions keep changing all the time.

Clearly, we have three types of definitions: scientific, public, and decision-enabling ones. Scientists responding to new research observations are continuously creating new definitions that fit their research field. Whenever there is a breakthrough, journalists translate these narrow scientific definitions to public ones using laymen’s terms and usually attach examples from the macro-world. Meanwhile, there is a public policy need to having a more standardized terminology and nomenclature to enable decision-making, so funding agencies and policy makers also generate their own more stringent (but still different) definitions of nanoscale, nanotechnology, and reiterate the origin of nanoscale properties.

For example, the National Nanotechnology Initiative states: “Nanotechnology is the understanding and control of matter at dimensions between approximately 1 and 100 nanometers, where unique phenomena enables novel applications… Encompassing nanoscale science, engineering and technology, nanotechnology involves imaging, measuring, modeling and manipulating matter at this length scale.” (The National Nanotechnology Initiative – Strategic Plan, 2007).

“Working at the atomic, molecular and supramolecular levels, in the length scale of approximately 1 – 100 nm range, in order to understand and create materials, devices and systems with fundamentally new properties and functions because of their small structure”, says http://nano.gov. “Dimensions between approximately 1 and 100 nanometers are known as the nanoscale. Unusual physical, chemical, and biological properties can emerge in materials at the nanoscale. These properties may differ in important ways from the properties of bulk materials and single atoms or molecules. (http://www.nano.gov/html/facts/whatIsNano.html)”.

However, in 2009 for cancer nanotechnology the field was defined as: “Individual research and development projects to address major barriers and/or questions in cancer biology, diagnosis, prevention, and/or treatment of the disease using innovative nanotechnology solutions. Devices or base materials must be smaller than 1000 nm in size although the assembly, synthesis, and/or fabrication of components of these final structures at dimensions less than 300 nm should be demonstrated. Devices/materials used and/or proposed to be developed must be either (a) synthetic materials or (b) biomaterials engineered to provide novel properties or modified functions based on nanoscale size, i.e., nanomaterials.” (NCI RFA-CA-09-013).

The British Standard Institute Publicly Available Specification (BSI PAS 136:2007, 2.8) devalues the significance of the lower limit, and laconically says:

The ASTM E 2456-06, Terminology for Nanotechnology document acknowledges the multiple use of the term “nano”: “nano, n—(1) The SI definition, a prefix used to form decimal submultiples of the SI unit “meter”, designating a factor of 10^-9 denoted by the symbol “n”. (2) Pertaining to things on a scale of approximately 1 to 100 nanometers (nm). (3) A prefix referring to an activity, material, process or device that pertains to a field of knowledge defined by nanotechnology and nanoscience. Unfortunately, (1) contradicts with (2) and (3) is simply tautology, reasoning that nano is there, wherever nanotechnology exists, and nanoscience is the science of nanoscale.

Now, how can we choose? Are the meanings really different? Is it possible to come up with one universal definition? First of all, we have to be aware that definitions are changing, because all decision-enabling definitions are products of consensus between interested parties participating in the process and the content reflects their actual views. Confusion originates from three major sources: (1) the original meaning of “nano”, (2) defining “nano” as a “characteristic property” and/or a unique phenomena within a length-scale (usually interpreted as a size-range), and (3) the way “nano”-related terms are created.

(1) The original meaning of ‘nano’ is 10⁻⁹ (or 0.000000001) without a dimension. Consequently, ‘nano-scale` could be assigned to any dimension. For length, which is measured in meters in SI, nanoscale regime is naturally between 1-1000 nanometers.

(2) For materials, the “nano” world lies in between the atomic/molecular and the “macro-scale” of a specific material. (This length-scale is different for different materials, e.g., for gold, Bi, Fe₃O₄, or CdSe, because the sizes of the primary objects are different.) Properties of nanoscale materials differ from both the macro-scale (bulk) properties and from the characteristics of an isolated molecule because they transition from a strictly quantum-laws defined atomic and molecular state towards the bulk, which is dominated by interatomic or intermolecular interactions. This change in observable intensive properties together with particle surface interactions is what we observe as “nanoscale” property.

For sizes, shapes, and forms in this regime (often referred to as nano-scale “architecture”) one has to measure length, surface and volume, and may describe how the parts are connected. When length is interpreted as size, this leads to the assumption that all “nano-“ PROPERTIES ARE ONLY SIZE-RELATED, which is incorrect. Although length is the simplest to measure, surface, volume, mass, density, etc. are also needed to describe Intensive properties. In other words, INTENSIVE PROPERTIES ARE NOT EXCLUSIVELY DETERMINED BY SIZE, and can be defined only as a system that contains the nanosized object and includes its environment it directly interacts with.

(3) In the common practice of coining “nano” language, terms usually contain the word ‘NANO” either separately as an adjective or as a prefix fused with a noun, which is usually taken from existing “macro” descriptors of materials, shapes, forms, devices, processes, and activities, such as nanosilver, nanoparticle, nanotube, nanowhisker, nanopillar, nanobeacon, nanorobot, nanodevice, and so on. However, the human brain works through associations. “Macro”-words associated with well-known shapes and materials recall associations, which usually work well, when the “nano” prefix is added (nanotubes, nanoparticles, nanorods, nanodiamond, nanogold, nanosilver etc.). Other “macro” descriptors, especially those that are associated with some kind of action, device or activity (e.g., robot, device, machine, etc.) usually bring up wrong associations when “nano” is added (see: “nanorobots”, “nanodevices”, “nano-actuators”, etc.), suggesting that a nano-robot or a nano-device is like its macroscopic version, but much smaller. This is wrong: the world at the “nanoscale” operates differently from the “macro-scale.” Use of these terms may lead to different thought associations for different people, therefore creating alternate meanings, which ultimately might result in unintentional misunderstanding of concepts.

In addition to all this, we have to be aware that all definitions are products of consensus between interested parties (scientists, journalists, stakeholders, etc.) participating in the process, therefore the content reflects their actual views. For a general definition, we simply don’t know enough yet.

Our view at Nanomedicine NBM is that for now, instead of considering any definition to be exclusively descriptive, the realm, in which the given definition is valid, has to be defined. Meanwhile, we just have to keep learning more and more about this exciting world.