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Optical fibre biomimetic sensors based on Lossy Mode Resonances with Molecularly Imprinted Polymers

Periodic Reporting for period 1 - OFBioSens-MIP (Optical fibre biomimetic sensors based on Lossy Mode Resonances with Molecularly Imprinted Polymers)

Reporting period: 2016-09-05 to 2018-09-04

Testosterone is a steroid hormone of the androgen group. It affects some physiological functions, especially those related to fertility. In addition, its known benefits to training and muscle building have put it on the International Olympic Committee's list of banned substances. It also migrates through the environment, reducing water quality and threatening environmental and human health along with other endocrine disruptors. Therefore, the detection and quantification of testosterone in organisms (urine) or in the environment (water) is a matter of great interest . Due to its size and chemical structure, it is a suitable molecule to be used as a target in molecularly imprinted polymers (MIPs) fabrication. The development of optical fibre testosterone sensors based on MIPs would potentially provide faster, more accurate and selective (in-situ) measurements using cheap sensors that can be easily processed and manufactured, hence it could be of great benefit in a number of fields.

We aim to design, develop and fabricate highly sensitive and selective nanostructured optical fibre testosterone sensors based on lossy mode resonances (LMRs) and MIPs. The achievement of this goal would allow the use of these devices in fields like environmental and veterinary sciences or sports, in real applications such as detection of contaminants in water, anti-doping tests or illegal hormones in animals, but more importantly, would also demonstrate the generic concept and allow development of sensors for other analytes.

The following specific objectives have been established:

1. To design and develop suitable MIP formulations for the detection of T whilst simultaneously supporting generation of LMRs.
2. To characterise and evaluate the properties of the MIPs with respect to their structure, orientation and physical and chemical stability.
3. To study and optimise different deposition methods to coat the OF device with the selected MIP in order to obtain a T sensor displaying strong LMRs.
4. To establish a collaboration to model the OF sensor to predict its features and the optimum configuration (as an aid to future design optimisation).
5. To study the sensors’ response to different concentrations of T in samples, evaluating its sensitivity, stability and selectivity.
6. To develop a small, light and low-cost system for the sensor in order to explore its commercial potential.
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, “Fabrica
This work has pioneered the fabrication of LMR-based sensors with GO coatings. It was proven the suitability of GO to be not only exceptional sensitive coatings but also generator of lossy mode resonances. The very high sensitivities achieved offer exciting opportunities to add new analyte-selective functionality to the devices surface for monitoring a range of target analytes. The carboxylate functional groups at the edges of the GO sheets should provide excellent attachment sites for the required coupling chemistry to realize such devices, which will in turn generate a positive impact to citizens and environment.
Fig. 2. Schematic representation of single-layer and double-layer LMR-based optical fibre sensing co
Fig. 4. Responses of different sensors to variations in the concentration of aqueous solutions of et
Fig. 3. Shift of the LMR absorption peak after 10 minutes of UV polymerisation (black: initial posit
Fig. 9. Generation and shift of 3 LMR absorption peaks during the deposition of 20 bilayers of PEI/G
Fig. 1. Experimental setup used for the characterisation of optical fibre devices