Synthesising Polymer Sensors for the Detection of Macronutrients in
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Synthesising Polymer Sensors for the Detection of Macronutrients in
Synthesising Polymer Sensors for the Detection of Macronutrients in Agriculture Introduction This PhD project investigates the development of polymer sensors for use in nutrient monitoring (N, P and K) in agriculture. By carefully monitoring and controlling nutrient levels throughout a plant’s growth cycle it is possible to produce the optimum crop yield. An industrial application for this is in hydroponics (figure 1), where an aqueous growth media must contain a careful balance of nutrients and minerals. The University of Manchester is working with an industrial partner, Saturn Bioponics, to develop this technology. Figure 1 a.) An indoor hydroponics unit at Saturn Bioponics. b.) A schematic of water and nutrient flow through a hydroponic stack. Materials and Methods A molecularly imprinted polymer (MIP) is used as the transduction material for the polymer sensors. As the polymer binds to target nutrient molecules, it’s electrical properties change proportionally; this allows for the nutrient concentration to be measured via impedance and capacitance. The polymer is synthesised using a spin coating method (figure 2) in order to produce very thin film coatings over silicon substrates. These contain gold electrodes on the surface, and the polymer acts as a dielectric layer. Figure 2 The spin coating of a silicon wafer, showing a.) The pipetting of the monomer solution, followed by b.) The simultaneous spinning of the substrate (at 3000 rpm), the spreading out and photopolymerisation of the solution, and finally c.) The completed polymer film. Results a.) A profilometer is then used to measure the thickness of the polymer film on the substrate. This may vary from 200 nm to 1 µm, depending on polymer viscosity, spin speed and surface hydrophobicity. b.) c.) Attenuated total reflectance infrared spectroscopy (ATR-IR) allows us to determine the structure of the polymer film. Specifically the allylthiourea binding site is the most significant structure on the surface, with the functional group absorbing at the 3000 1/cm region. Figure 3 IR Spectroscopy via a.) ATR through a germanium crystal pressed against a sample, and b.) The Bruker Vertex 70 model used to produce the spectra, and c.) the IR spectra for the spin coater polymer on a silicon wafer. Conclusions During the first year of the PhD project, it was possible to successfully produce a method for synthesising thin polymer films for applications as chemical sensors with nutrient detectors. This was carried out using a spin coater and rapid photopolymerisation to produce 200 nm polymer films on a silanised silicon substrate. Further work within the project will now focus on the development of electronics for taking capacitance and impedance measurements of the material, and the construction of a flow cell for integration within a hydroponics unit. eAgri – Sensing, Imaging & Signal Processing School of Electrical and Electronic Engineering The University of Manchester For details contact: Christopher Storer; Tel.: 0161 306 2815; E-Mail: christopher.storer@postgrad.manchester.ac.uk Supervisor: Dr Bruce Grieve; Tel.: 0161 306 8941 E-Mail: bruce.grieve@manchester.ac.uk Acknowledgements: Saturn Bioponics
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