Direct light written holographic volume grating as a novel optical platform for sensing characterization of solution

We proposed a novel photosensitive hydrogel based holographic sensor for the detection of hydrogel swelling and hence the chemical concentrations, which formed by thermally polymerizing 2-hydroxyethyl methacrylate. Holographic volume grating recorded in the hydrogel as an optical sensing platform was employed in response to the hydrogel deformation induced by target molecules. Co-monomer methacrylic acid with carboxyl groups functionalized the polymer matrix for improving the selectivity. Peak wavelength shift of the diffraction spectrum was a significant parameter in sensing the pH value of the buffer. The extracted time constant of the wavelength shift curve evaluated the sensitivity of the novel holographic sensor. There were good exponential relations between peak wavelength and pH value with various thicknesses. The novel sensor could be considered as an effective platform for sensing the analytes concentration of solution. The reversible measurement experimentally demonstrated the repeatability of the holographic sensor. The novel photosensitive hydrogel and its sensor provided a probability for sensing the performance of solution and accelerating the development of water resistant holographic sensor based on polymer hydrogel.