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Makhsin, Siti R. and Goddard, Nicholas J. and Gupta, Ruchi and Gardner, Peter and Scully, Patricia
Optimisation synthesis and biosensing performance of an acrylate-based hydrogel as an optical waveguiding sensing film
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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 optimisation of acrylate based-hydrogel as the waveguide layer formed from PEG diacrylate (PEGDA, Mn 700), PEG methyl ether acrylate (PEGMEA, Mn 480), and acrylate-PEG2000-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 functionalisation by a well-controlled reactive group, can be tailored for immobilisation 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 optimised MCLW chip was formed from a total hydrogel concentration of 40\% v/v of PEGMEA - PEGDA (Mn 700), functionalised with 2.5\% v/v of acrylate-PEG2000-NHS. The sensor generated a single-moded waveguide signal with a RI sensitivity of 128.61  0.15° RIU1 and limit of detection obtained at 2.2x106 RIU 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 immobilised on functionalised acrylate hydrogel, generating a binding signal of (12.379  0.452)x103.
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