Hydrogel based Optical Fiber Probes for Sensing Applications

Abstract

Optical fiber technology has proven itself as one of the most promising and reliable technologies for optical sensing applications. This technology has advantages such as low power consumption, small size, large bandwidth, better spatial resolution, and ease in operation. Optical fibers combined with soft and biocompatible polymer materials (hydrogels) have opened a new sensing pathway. Hydrogels are known for their molecular permeability, making them the best candidate for sensing platforms. Which means they can be functionalized with stimuli-sensitive materials for various sensing applications. In this work, optical fiber sensors were fabricated using functionalized hydrogel for different sensing applications, including temperature, alcohol, and glucose. The hydrogels functionalized with various stimuli-sensitive materials can undergo a reversible volumetric change upon encountering sensing materials. This change in the physical dimensions of the hydrogel matrix alters the output optical response. This way, the change in the photonic signal is translated into the desired sensing measurement. The introduction of nanostructures and nanoparticles to the above-mentioned optical fiber sensors can play their role in enhancing effectiveness, readout, sensitivity, and response time. Aztec nanostructures, gold nanoparticles, and thermochromic powders were used to achieve different sensing capabilities. A simple polymerization process was used to fabricate optical fiber sensors where sensing gel was drop-casted on a commercial fiber tip and polymerized. Also, a novel UV polymerization method was developed where a signal droplet of sensing gel was used for the fabrication of long (up to 5 mm) sensors on the tip of commercial optical fiber. The fabrication followed the extraction of optical fiber with certain time intervals to enable layer-by-layer polymerization. The morphological and optical properties of materials and optical fiber sensors were evaluated using different characterization techniques, including SEM, TEM, optical microscopy, FTIR, and UVvis spectroscopy. The sensing capabilities of optical fiber sensors were tested using both transmission (the most practical mode for testing optical sensors) and reflection modes (remote sensing mode). All sensors were tested for multiple cycles to demonstrate the reusability, reproducibility, and reliability of sensing data. The integration of nanostructures and nanoparticles played a vital role in improving sensitivity, detection limit, and response time. These optical fiber sensors showed superior sensitivity and a rapid response time. In the end, a smartphone readout methodology was presented to eliminate convoluted readouts and demonstrate the practicality of sensors. The proposed optical fiber sensors showed higher sensitivity, rapid response time, improved detection limit, a simple readout methodology, and straightforward, low-cost fabrication. All these characteristics make them a perfect candidate for real-time and continuous biomarker monitoring in point-of-care settings.

Date of Award	16 Dec 2023
Original language	American English
Supervisor	Haider Butt (Supervisor)