PhD Research Project: CENTA NERC - On-a-chip arrays to assess nanomaterial reactivity
The physicochemical characterization of nanomaterials (NMs) is essential in order to fully understand and/or predict their behaviour in applications and their likely environmental and biological interactions after release. Physicochemical properties are commonly described as: (i) intrinsic (those of the pristine NMs), e.g. size, size distribution, chemical composition, shape, surface area, surface chemistry and coating stability; and (ii) extrinsic (acquired by the NMs through interactions with their surrounding media), such as hydrodynamic size, surface charge, aggregation/agglomeration and reactivity (e.g., redox potential, solubility). Extrinsic properties may vary significantly as they are dependent on the environment or matrix where the NM is found. They are thus particularly cumbersome to assess and difficult to measure reproducibly; they commonly require numerous replications.
On-a-chip technologies, based on microfluidic devices, may provide a solution to this challenge, by enabling automated, miniaturised, multichannel experimental arrays, which can feed into common laboratory instruments, thus enabling multiple spatially and temporally separated measurements, with a minimum consumption of materials and reagents. Increasingly such devises can have complex designs, integrating operations, such as mixing, separation, extraction, temperature modification, and parallel or serial measurements.
The proposed project aims to innovate on the measurement of NM reactivity, by developing novel, fast, easy to use nano-reactivity assays. The work will focus on two properties: solubility and hydrophobicity. Solubility is a measure of how easily a NM may release its component chemical species when released in an aqueous medium (whether in the environment or within an organism), whereas hydrophobicity is a measure of a NM’s affinity for water, with hydrophilic NMs being highly water-friendly, and hydrophobic being the opposite.
For the assessment of solubility, a two-step approach will be used allowing for an initial sweep followed by a more in-depth analysis. This first step will monitor a reduction in size of the NM while the second step will look at amount and composition of material lost and, if any, the material remaining. Firstly a fluidic cell will be manufactured, and work will then focus on developing an interface between the cell and a size-measuring device (such as an NTA, or a UV-vis instrument). Measurements will be carried out in a variety of media and on several NM types, to ensure method reproducibility and will be compared against traditional solubility assays and a multi-method characterisation array. A sub-set of assays will be studied in depth, including a full characterisation of individual components of spent chips to ensure a thorough system understanding, and that, for example, no secondary reactions occur within the fluidic channels.
For the assessment of the hydrophobicity/-philicity of NMs, a tiered investigation approach will be used employing existing detection systems with innovative multidimensional and semi-orthogonal separation systems in order to determine the hydrophobic nature of the NM surface. The array will be based on the concept of exposing NM-bearing suspensions to a panel of dyes which will adhere to them depending on hydrophobic/-philic interactions. Subsequently, the reacted mixtures will be separated and characterised. The analysis with a UV-DAD will allow a precise assessment of the dye concentrations in the nanomaterial fractions and in the carrier liquid. The hydrophobicity/-philicity will be derived from the concentration ratio of bound dye to unbound dye. Based on the first stage, a on-chip HIC assay for second dimension assessment of hydrophobicity will be developed. Here a chip with several separation channels filled with the neutral to hydrophobic stationary phases will be designed, fabricated, tested using standards and then evaluated for reproducibility of NM analysis. Finally aspects of both the separations will be evaluated to aid determination of the best solution or conditions for use or for online/offline interfacing. The method will be standardised and an interfacing chip will be generated for an integrated approach. Integrated separations will be demonstrated for 3 key NM as part of this project.
In addition to completing an online application form, you will also need to complete and submit the CENTA studentship application form available from www.centa.org.uk.
CENTA studentships are for 3.5 years and are funded by the Natural Environment Research Council (NERC). In addition to the full payment of their tuition fees, successful candidates will receive the following financial support.
Annual stipend, set at £14,296 for 2016/17
Research training support grant (RTSG) of £8,000
CENTA students are required to undertake from 45 days training throughout their PhD including a 10 day placement.
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2. Nel, A. E. et al., Where Are We Heading in Nanotechnology Environmental Health and Safety and Materials Characterization? ACS Nano 2015, 9, 5627-5630.
3. Lynch, I., Weiss, C., Valsami-Jones, E. A strategy for grouping of nanomaterials based on key physico-chemical descriptors as a basis for safer-by-design NMs. Nano Today 2015, 9(3), 266-270.
4. Nightingale, A. M.; Krishnadasan, S. H.; Berhanu, D.; Niu, X.; Drury, C.; McIntyre, R.; Valsami-Jones, E.; deMello, J. C., A stable droplet reactor for high temperature nanocrystal synthesis. Lab on a Chip 2011, 11 (7), 1221-1227.
5. Niu, X. Z.; Pereira, F.; Edel, J. B.; de Mello, A. J., Droplet-Interfaced Microchip and Capillary Electrophoretic Separations. Anal. Chem. 2013, 85 (18), 8654-8660.
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