Going nano to beat crime

Forensic science has advanced rapidly in the last 20 years. Now, many think that to beat the growing crime rate technology has to go small and make the next leap – the leap to the nanoscale.

"A novel application of nanotechnology is the creation of high-performance anti-graffiti coatings"

So why is nanotechnology effective in crime prevention and detection? It is about applying highly advanced scientific techniques that may have been developed for a variety of applications, to many criminal situations. These include techniques for preventing crime, and techniques for detecting the traces left by a criminal that uniquely identifies them. Nanotechnology offers many benefits – it enables increased speed and accuracy of response, it enables accurate identification of materials from very small samples; it enables the incorporation of unique recognition features into products in order to prevent counterfeiting, and it can be used unobtrusively for product tracking and provenance identification.

So what is nanotechnology? A nanometre is a billionth of a metre (10-9m), which is about 1/80,000 of the diameter of a human hair; and nanotechnology can be defined in its simplest terms as “engineering at the nanometre scale”. At this scale materials behave in a radically different manner. For example, in bulk form, aluminium can be used to make a solid object. In a finely divided, nanoparticulate form, aluminium becomes a highly combustible fuel.

New properties come into play at the nanoscale, and they can be chosen or engineered to perform specific functions. At present the most successful commercial opportunities in nanotechnology are created mainly through advanced chemical techniques.

New technologies are slow to be applied to crime prevention and detection, and this is possibly due to a variety of reasons. Often crime prevention is not immediately recognised as a primary application by researchers (who may be working on other field such as medicine or materials) and there can be difficulties in technology transfer between scientists and product manufacturers due in part to a lack of communication between user and developer groups. Furthermore, there can be a lack of knowledge and understanding of the benefits of the new technology, there is often a need for training of personnel, including those administering the law, and often quite simply, and there is a justifiable conservatism about the adoption of unproven, new technology until it is accepted as fully reliable and able to be used to secure a conviction.
However, if courage prevails, using advanced technology can have great economic benefit. It can, paradoxically, be considerably cheaper to apply (for example, field analysis is cheaper and faster than analysis in a laboratory, and may be more reliable as it is less likely to be subject to contamination, denaturing etc). Nanotechnologies are particularly suited to be used in mass-produced products, they are difficult to copy, and the results should be easy to interpret, reducing the need for trained personnel.

So which nanotechnologies may be useful for crime prevention? These include, for example:
? Rapid, high throughput and accurate analytical and diagnostic techniques, that require low sample and reagent volumes (which are often costly).
? Advanced imaging techniques.
? Quantum dots for “invisible” security tagging applications (prevention of counterfeiting, simplifying traceability of goods etc). Quantum dots are semi-conductor nanoparticles which are invisible to the naked eye. They can be printed on to packaging or goods, without affecting them, to produce an invisible bar code. This fluoresces under ultraviolet light, and can consequently be easily read.
? Molecular “tagging” (for pharmaceutical drug provenance applications). These can be biological tags which also do not affect the product in any way. One example is the tagging of farmers red diesel in order to identify stolen property.
? Novel sensing techniques (such as electronic “noses” and “tongues” for fast detection and identification of explosives, impurities, poisons, toxic gases etc). These depend on sensors built on to semiconductor chips, that provide high sensitivity and fast results – on site.
? New nanomaterials. These can be used for cheap, highly durable, shatterproof, fire and bullet resistant applications. Polymer ceramics have particular applications for lighter, stronger, longer lasting bullet proof vets, and new kinds of aerogels based on nanotechnology that are lightweight and have fire resistant and important insulation properties.
? High technology thin films, including holograms, for credit card and banknote security etc. These films can be deposited in offset layers, offering a range of visual and strength attributes.
? Nanometrology (for tiny measurements) for the comparison of counterfeit with real products.
? Simple techniques using nanochemistry for tamper-indicating packaging, easily identified through colour change effects.

One example of the application of nanotechnology is in the relatively new area of portable nanobiosensors. Over the past decade, attention was given to the idea of developing an electronic biosensor that would operate at the molecular level, and combine the high selectivity of biological systems with the appropriate sensitivity of physical devices. The development of biosensors and especially their commercialisation, however, was hindered by several problems associated with the properties of biological material. For example low stability, poor performance in organic solvents, at low and high pHs and at high temperature, absence of enzymes or receptors that are able to recognise certain target analytes, problems with immobilisation of biomolecules, and poor compatibility with micromachining technology.

New nanotach could mean coatings that allow graffiti to simply be wiped away

The search for possible solutions to these problems led scientists to the development of stable synthetic analogues of natural receptors and antibodies. If nature can produce enzymes, receptors and antibodies by evolution, it was argued, molecular engineers should be able to develop materials with similar properties by design, and smart materials with biorecognition functions would posses enormous potential for the development of new generation, stable biomimetic sensors

This has indeed happened, and new bionanosensors can find application in a number of testing areas related to crime prevention and detection. These encompass in the main, the identification of the presence of toxins, the detection of biological warfare agents and screening for drugs of abuse and explosives.

The main areas of use are:
? In food safety and water - the identification of GM foods, chlorophenols, chloranisoles, nitrosamines, aflatoxins, endocrine disruptersand algal toxins.
? In environmental protection - pesticides, VOCs, formaldehyde, hydrocarbons.
? For defence - identification of biological and chemical Warfare agentsSecurity: identification of drugs of abuse, explosives, adulteration.
? In clinical medicine for disease detection and management, e.g. cancer, heart disease, diabetes management. The ability to undertake the onsite detection of toxins is highly desirable, as it allows for practically instant drug testing. This obviates the need for having to undergo the costly and time-consuming process of taking a sample then sending it to a lab for analysis.

Another novel application is the application of nanotechnology to the creation of high-performance anti-graffiti coatings. This has a much wider applications that might be immediately apparent. Graffiti is not just scribblings on a wall, but a signal that a particular neighbourhood is becoming susceptible to crime, and is possibly on the first step to a downward spiral of neglect and possible takeover by criminal elements.

From a technological viewpoint, tools utilised for graffiti have evolved from simple pens and markers, which limited the type of surfaces to be worked on, to spray paints, which can stain basically any material or texture. In the 21st century, graffiti represents a very important social and economical phenomenon. Although the precise cost of graffiti cleaning worldwide is unknown, estimates are around £5 million /year for London and $150 million dollars/year for Los Angeles. 
Graffiti offers a technological challenge that requires the use of state-of-the-art technology. The importance of the world’s paint and coating industries makes them attractive to the latest nanotechnology available, aiming to produce high-performance coatings. This has resulted in creating a unique paint with complete oil and water repellency, impressive scratch and UV resistance, with a maintenance-free character.  The technology can be used on stone, brick, mortar, glass, plastics and other materials, as well as the potential application in clean rooms, surgery facilities and a number of forensic needs. It was developed at Centro de Física Aplicada y Tecnología Avanzada, Universidad Nacional Autónoma de México in México.

The coating was created in the following way: Nanoparticles produced by standard synthesis methods such as the so-called sol-gel route, retain on their surfaces a number of either unreacted or still- active chemical groups that can be used as sites for chemical reactions at will. In this way, molecules can be attached to those sites, as to produce a true nanohybrid material. Technically, the fundamental idea is to take advantage of the fact that nanoparticles can be conveniently regarded as nano-chemical reactors.

This approach allowed researchers at the Universidad Nacional Autónoma de México to produce nanobiomaterials, nanoparticles for metal ion removal in polluted water and a whole family of nano-technology based coatings for many applications, ranging from anti-corrosion, anti-staining of pure silver objects, caries-resistance for human teeth, copper protection and anti-graffiti purposes among others.

The coating is a two-component system, consisting of a high-performance polymeric base, that includes the nanoparticles and oil and water-proof molecules, and a cross linking agent. The system is physicochemically-designed as to induce the segregation of the oil and water-repellent molecules to the surface upon drying, while keeping the nanoparticles evenly distributed throughout the whole film. The coating described is not simply a physical mixture of components since the chemical stabilization of all the components plays a key role to ensure transparency, wear resistance and, of course, full anti-graffiti effect.  This is achieved by the proper chemical fictionalisation of both the nanoparticles and the polymers involved, which enables the production of controlled suspensions that can last for months without changing their properties.

The unique composition of the coating makes it a highly efficient anti-graffiti agent, since the repellency capability to any water-based or oil-based paint, of the type used for graffiti, is extremely high, to the extent that most of the graffiti does not stick to the surface and the remaining can be easily removed by washing with water. The coating is able to stand repetitive graffiti attacks. Moreover, the coating is much more than a good anti-graffiti coating. It can be best described as a maintenance-free coating  as no dust, grease or dirt sticks to the surface and it has a very high resistance to scratching, to chemicals, including most commercial and industrial solvents and to UV degradation.

Acknowledgement
Biosensor information courtesy of Professor Anthony Turner; anti-graffiti coating information courtesy of Professor Victor Castano.

By Ottilia Saxl. Ottilia is Chief Executive and founder of the Institute of Nanotechnology. She has been involved in managing strategic contracts for government and industry, and has authored several publications on opportunities for industry in the application of nanotechnology.