WP1: DESIGN OF SUITABLE MIPs
Different formulations, polymerisation methods and deposition techniques have been tested and optimised in order to obtain consistent and satisfactory testosterone MIPs.
WP2: DEPOSITION OF THE MIPs ONTO THE OPTICAL FIBRE STRUCTURE
Among the different deposition methods tested, UV evanescent field polymerisation was found to be the most appropriate technique to deposit MIPs onto the optical fibres. The characterisation setup shown in Figure 1 was used to follow the generation and the shift of the LMR absorption peak during the construction of the sensitive coating.
WP3: CHARACTERISATION OF THE SENSORS RESPONSE
A metal-oxide thin-film was used to generate LMRs and the MIPs were deposited over it to act just as testosterone-sensitive materials in a double-layer configuration (Figure 2).
The different MIPs were deposited onto the coated optical fibres by using the UV evanescent field polymerisation. The satisfactory polymerisation of the MIPs was confirmed by the shift of the LMR absorption peak during the process as shown in Figure 3.
The devices were then tested as testosterone sensors by monitoring the shift of the LMR absorption peak when they were introduced in testosterone aqueous solutions with different concentrations. Unfortunately, these sensors were not sensitive enough to develop an interrogation system based on this technology.
To enhance their performance, we explored the possibility of using graphene oxide (GO).
The first approach was to use an LMR-based optical fibre sensing scheme consisting of an optical fibre with a metal-oxide layer sputtered onto the core, which performs as LMR-supporting coating, and a GO-based thin film deposited on top, acting as sensitive coating. The sensors with GO showed a maximum sensitivity enhancement of 176% with respect to the sensor without GO (Figure 4). To our knowledge, this was the first time that GO was used to make an optical fibre sensor based on LMR.
We also demonstrated the properties of GO as generator of LMRs, avoiding the sputtering of a metal oxide onto the fibre (Figure 5). This research opens very promising and exciting possibilities in the field of optical fibre sensors based on LMR, strategically including specific recognition groups to the device surface to exploit this high sensitivity for monitoring a range of target analytes.
WP4: DESIGN OF AN INTERROGATION SYSTEM BASED ON THE NEW SENSORS.
Due to the lack of measurable responses from the MIP-coated sensors, this work-package was not explored in the context of the MIP sensors, but some aspects of it were developed in relation to various uses of GO sensors explored during our evaluations of these materials.
DISSEMINATION OF RESULTS
Seminars to present this research work to other researchers and students of the Faculty of Science (UEA) and abroad:
• M. Hernaez, ”OFS based on micro and nanostructured coatings,” UNED, Madrid, 2017.
• M. Hernaez, “OFS based on LMR,” U Complutense de Madrid, 2017.
International conferences presenting the following communications:
• V. Kandjou et al, “The use of p-phenylenediamine to control graphene oxide membrane pore-gap and stability for water purification,” Carbon 2018, Madrid (Spain), 2018.
• V. Kandjou et al, “The fabrication of controlled thickness graphene oxide films by means of dip-assisted layer by layer assembly,” Carbon 2018, Madrid (Spain), 2018.
• M. Hernaez et al, “Sensitivity enhancement of lossy mode resonance-based ethanol sensors by graphene oxide coatings,” IEEE Sensors Conference, Glasgow (UK), 2017.
• P. Sanchez et al, “Optical fibre exhaled breath sensor based on lossy mode resonance using a graphene oxide sensitive coating,” 5th International Symposium on Sensor Science (I3S 2017), Barcelona (Spain), 2017.
• P. Sanchez et al, “Optical fibre sensors based on lossy mode resonance using graphene materials,” Carbon 2017, Melbourne (Australia), 2017.
• P. Sanchez et al, “Fabrication and characterisation of graphene oxide films with controlled thickness on silicon based substrates,” Carbon 2017, Melbourne (Australia), 2017.
Published papers:
• M. Hernaez et al, “Graphene oxide in lossy mode resonance-based optical fibre sensors for ethanol detection,” Sensors (Switzerland), vol. 18, article number 58, 2018.
• M. Hernaez et al, “Optical fibre sensors using graphene-based materials: a review,” Sensors (Switzerland), vol. 17 (1), article number 155, 2017.
