Advanced hydrogel-based volume holographic gratings for label-free biosensing

Hydrogels have been investigated as materials for the fabrication of label-free (LF) holographic sensors, given their ability to undergo structural changes upon interaction with specific analytes [1]. Hydrogel-based holographic biosensors are emerging as a new technology for the development of portable or wearable analytical devices of clinical interest, leveraging their biocompatibility and capacity to mimic biological environments. Despite their potential, their use is still in its infancy as the materials developed so far have some drawbacks, such as brittleness or mechanical instability. Slide-ring (SR) gels, developed by Ito [2] informed the development of the new biosensitive hydrogels with advanced properties presented here. This work focuses on the optimization of the recording process of volume holographic gratings (VHGs) in hydrogel films based on SR aimed at LF detection. Hydrogels containing phosphorylcholine and methylated polyrotaxanes were synthesized and characterized by scanning electron microscopy (SEM) and swelling kinetics studies. The bioavailability of hydrogels for the specific recognition of C-reactive protein (CRP) was verified by fluorescence detection. Then, the formation of VHGs in the films was achieved initially by holographic recording using two-beam interference at 532nm [3] and further optimized for high Diffraction Efficiency by contact copying a master grating [4]. Diffraction efficiency measurements were then used for the direct LF detection of CRP. This research paves the way for future applications of VHGs in clinical analysis and provides a basis for a forward-Thinking approach to biomolecular detection.