The metal-clad leaky waveguide (MCLW) is an optical biosensor consisting of a metal layer and a low index waveguide layer on a glass substrate. This label-free sensor measures refractive index (RI) changes within the waveguide layer. This work shows the development and optimization of acrylate based-hydrogel as the waveguide layer formed from PEG diacrylate (PEGDA, M n700), PEG methyl ether acrylate (PEGMEA, M n480), and acrylate-PEG 2000-NHS fabricated on a substrate coated with 9.5 nm of titanium. The acrylate-based hydrogel is a synthetic polymer, so properties such as optical transparency, porosity, and hydrogel functionalization by a well-controlled reactive group can be tailored for immobilization of the bioreceptor within the hydrogel matrix. The waveguide sensor demonstrated an equal response to solutions of identical RI containing small (glycerol) and large (bovine serum albumin; BSA) analyte molecules, indicating that the hydrogel waveguide film is highly porous to both sizes of molecule, thus potentially allowing penetration of a range of analytes within the porous matrix. The final optimized MCLW chip was formed from a total hydrogel concentration of 40% v/v of PEGMEA-PEGDA (M n700), functionalized with 2.5% v/v of acrylate-PEG 2000-NHS. The sensor generated a single-moded waveguide signal with a RI sensitivity of 128.61 ± 0.15° RIU -1and limit of detection obtained at 2.2 × 10 -6RIU with excellent signal-to-noise ratio for the glycerol detection. The sensor demonstrated RI detection by monitoring changes in the out-coupled angle resulting from successful binding of d-biotin to streptavidin immobilized on functionalized acrylate hydrogel, generating a binding signal of (12.379 ± 0.452) × 10 -3°.
Bibliographical noteFunding Information:
The authors greatly appreciate the technical support from Dr. Bernard Treves Brown, Dr. Behnam Bestani, and Mr. Alan Kniveton from The University of Manchester. The first author has been awarded a SLAI scholarship, 600-IRMI/FRGS-RACER5/3 (011/2019) from the Ministry of Higher Education Malaysia and a travel grant from Armourers & Brasiers’ Company, UK.
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ASJC Scopus subject areas
- Analytical Chemistry