Phenylboronic Acid-Based Photonic Hydrogel Nanocomposite Fiber Probe for Real-Time and Continuous Glucose Monitoring

Diabetes mellitus (DM) is a significant global health issue characterized by elevated blood glucose levels, highlighting the urgent need for an affordable, rapid, and reliable continuous glucose monitoring (CGM) solution. In this study, we developed phenylboronic acid (PBA)-based hydrogel sensors using a straightforward one-step polymerization technique. The glucose-sensitive hydrogel was directly polymerized onto the tip of a commercial optical fiber (OF). Gold nanoparticles (AuNPs) were synthesized via the Turkevich method, a simple chemical reduction process, and subsequently integrated into the polymerized fiber tip using a dipping technique. Fourier-transform infrared (FTIR) spectroscopy was conducted to characterize the sensing gel and confirm successful polymerization. The FTIR spectra validated the functionalization of the hydrogel with PBA and confirmed the complete polymerization of the sensing gel on the fiber tip. The synthesized AuNPs were characterized using transmission electron microscopy (TEM) and UV-vis spectroscopy. TEM analysis confirmed the spherical shape of the nanoparticles, with an average size of 10 nm, while UV-vis spectroscopy revealed a surface plasmon resonance (SPR) peak at 518 nm. The sensing mechanism relies on the binding interaction between PBA and the cis-diol groups in glucose, which increases osmotic pressure within the hydrogel matrix. This leads to swelling of the sensing matrix and a change in the optical signal output. The performance of the fabricated sensor was evaluated across a glucose concentration range of 0–20 mM using both transmission and reflection modes. The sensor exhibited a 25% overall increase in transmission percentage (1.25%/mM) and a 4 nm SPR blueshift (0.2 nm/mM) as glucose concentrations increased from 0 to 20 mM. In reflection mode, the sensor demonstrated a sensitivity of 0.5%/mM glucose concentration, indicating potential for remote sensing applications. Given that the SPR wavelength aligns with the green laser wavelength, a 532 nm green laser was used to validate these results by measuring the transmitted and reflected power. The sensor displayed a sensitivity of 3.75 µW/mM for transmitted power and 8.25 nW/mM for reflected power. The sensor also exhibited a rapid response time of 30 seconds and a saturation time of 3 minutes. Additionally, the sensor was tested over multiple cycles to demonstrate its reusability and repeatability. Finally, the sensor's readout methodology was simplified by integrating it with a smartphone.