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EPSRC Reference: EP/D501563/1
Title: The Synthesis & Characterisation of Rare-Earth Phosphide Nanomaterials; Towards Environmentally Benign Nanoparticulate Biolabels
Principal Investigator: Green, Professor M
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Kings College London University of Oxford
Department: Physics
Organisation: Kings College London
Scheme: First Grant Scheme Pre-FEC
Starts: 01 October 2005 Ends: 30 September 2008 Value (£): 126,286
EPSRC Research Topic Classifications:
Cells Chemical Synthetic Methodology
Materials Characterisation
EPSRC Industrial Sector Classifications:
Healthcare Pharmaceuticals and Biotechnology
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Panel History:  
Summary on Grant Application Form
Nanoparticles are materials with dimensions in the region of a billionth of a meter (a nanometer). In comparison, a smoke particle is approximately 1000 nm in diameter, whilst a human hair is approximately 50,000 nm in diameter. Particles prepared in this size regime behave differently to micro scale particles used in everyday applications, as physical laws that govern macroscale phenomena do not apply at this size range. Nanometer sized particles of a semiconductor (materials that conduct and can emit light once given a push of energy, termed 'excitation') such as cadmium selenide glow strongly when prepared between sizes of 2 to 8 nm, a consequence of the particles behaving quantum mechanically. If these particles are synthesised correctly they can be made to emit different colours, and when linked to biological tissues, can be used to detect cancer cells, image blood flow, and in other medical applications. These are better than conventional dyes that are currently used, which often fade when exposed to air and do not give clear definite colours.The problem with current nanoparticle biotags is the constituent elements; semiconductors are often made of heavy metals such as cadmium. Recent research has shown that the cadmium leaches from the particle and can kill biological cells (cytotoxicity). In our research group, we have shown parts of the biotag such as selenium or sulphur, oxidises, leaves the particle surface, and can damage DNA.We propose a novel type of nano-scale biological tag that doesn't affect DNA or cells and is composed of biologically inert materials. The nanoparticle will not be a semiconductor, but composed of ions that are known to emit clear coloured emission when excited. The material will consist of a luminescent rare-earth cation, and a phosphide anion (rare-earth phosphide). The material is based on previous work that shows that metal phosphide particles form stable surface oxides that do not leach into solution upon exposure to the environment.To prepare nano-scale rare-earth phosphides requires complex air sensitive chemistry, and two methods are to be used to synthesis the materials. The first involves the reaction of two precursors containing the required ions in a solvent that stops the particles growing too large. The method is efficient and simple, however, the phosphorous precursor is hard to handle, air sensitive and toxic. A simpler way is to thermolyse (heat) a single chemical, which then breaks down into the required product. This single source approach requires novel precursors to be designed. Whilst also requiring air sensitive chemicals, this route is generally less toxic and easily controlled.Once the particles are prepared at the correct size (small enough to enter a cell, for example) we need to add a molecule that allows the particles to be both water soluble, and in most cases, allow attachment to a specific biological entity, for example, certain peptides bind preferentially to certain tumour cells. Once the nanoparticle is linked, colleagues will attach the particles to the required biological tissue (such as a tumour cell), where the emission from the particle can be seen under a microscope highlighting the cancer. This has obvious advantages in diagnosing disease and helping in surgery.
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