Photofunctionalizable Hydrogel for Fabricating Volume Optical Diffractive Sensors

Abstract

Volume amplitude gratings made of mesoporous hydrogels are beneficial for sensing, but are difficult to fabricate because they involve creating high aspect ratio features in soft materials. A novel photofunctionalizable hydrogel is reported and its suitability for fabricating grating sensors is demonstrated comprising of features with an aspect ratio of ≈3.2. To make a photofunctionalizable hydrogel with high optical quality that can be patterned using widely available light sources, a water‐soluble photoactive monomer and sensitizer are synthesized. A transmission amplitude grating is subsequently fabricated in a ≈100 µm thick photofunctionalizable hydrogel film by reaction of the free amines generated in the photoexposed regions with pH‐responsive fluorescein isothiocyanate. The volume hydrogel grating described herein is shown to be suitable for real‐time sensing of pH as an exemplar analyte. This work will have a significant impact on the fabrication of diffractive optical structures in thick films of hydrogels that are highly promising for biomolecular sensing in disease diagnosis and healthcare monitoring.

A feasibility study of a leaky waveguide aptasensor for thrombin

“…LW is a completely dielectric structure and hence its integration with electrokinetic sample processing is much easier than other label-free biosensors with continuous metal layers such as surface plasmon resonance (SPR) and metal-clad leaky waveguide (MCLW). Additionally, we have developed a photofunctionalisable hydrogel 43 where amine groups can be selectively freed using widely available 405 nm light sources. These freed amines groups can then be reacted with aptamers with selectivity towards different analytes and LW biosensor can be operated in imaging mode for multiplexed sensing.…”

Reflective leaky waveguide gratings (LWGs) with internal referencing for sensing

“…Hydrogel gratings have been used to sense a wide variety of analytes including microorganisms, 1 proteins, 2–5 glucose, 6 pH, 7,8 metal ions, 9,10 and volatiles. 11,12 In comparison to other label-free optical sensors, 13–15 hydrogel gratings can provide more effective referencing because sensor and reference regions are closely spaced.…”

Hydrogel-based holographic sensors and biosensors: past, present, and future

“…In most cases, the swelling or shrinking of hydrogels because of the presence of the analyte alters lattice spacing and provokes a change in the refractive index modulation, which modifies diffracted light characteristics. Other changes, just in the refractive index (RI) or in the absorption coefficient [39], can bring about the modification of the diffraction pattern, but have yet to be reported using holographic hydrogels. Multilayered Bragg diffraction gratings sensors were first proposed by Lowe's group [40].…”