Abstract
We report a novel self-referenced diffraction-based leaky waveguide (LW) comprising a thin (~2 µm) film of a photofunctionalisable hydrogel created by covalent attachment of a biotinylated photocleavable linker to chitosan. Streptavidin attached to the chitosan via the photocleavable linker was selectively removed by shining 365 nm light through a photomask to create an array of strips with high and low loading of the protein, which served as sensor and reference regions respectively. The differential measurements between sensor and reference regions were used for measuring analytes (i.e., biotin protein A and IgG) while reducing environmental and non-specific effects. These include changes in temperature and sample composition caused by non-adsorbing and adsorbing species, leading to reduction in effects by ~98%, ~99%, and ~97% respectively compared to the absolute measurements. The novelty of this work lies in combining photofunctionalisable hydrogels with diffraction-based LWs for referencing. This is needed to realise the full potential of label-free optical biosensors to measure analyte concentrations in real samples that are complex mixtures, and to allow for sample analysis outside of laboratories where drifts and fluctuations in temperature are observed.
Highlights
Leaky waveguides (LWs) are a type of label-free optical biosensor, comprising of a few microns thick film with refractive index (RI) lower than the substrate but higher than the sample applied to the sensor [1,2,3]
Glass microscope slides were purchased from VWR (UK), dialysis tubing cellulose membrane was purchased from Sigma Aldrich (UK), and syringe filters with cut-off size of 5 μm were purchased from Scientific Lab Suppliers (UK). 100 mM phosphate buffer (PB) solution at pH 8.5 was prepared by dissolving appropriate amounts of sodium phosphate monobasic and dibasic salts in de-ionised (DI) water. 100 mM HEPES buffer solution of pH 7.4 was prepared
A typical output of a diffraction-based LW with an unpatterned chitosan film is shown in Figure 2a where interference fringes were observed at the resonance angle
Summary
Leaky waveguides (LWs) are a type of label-free optical biosensor, comprising of a few microns thick film with refractive index (RI) lower than the substrate but higher than the sample applied to the sensor [1,2,3]. In comparison to pre-fabricated electrodes, the use of light combined with digital photomasks is beneficial because the shape and distribution of sensor and reference regions can be rapidly changed on-demand Towards this end, photocleavable linkers for patterning biomolecules on surfaces [23] and hydrogels [24] have been reported. The photolysis kinetics of these photocleavable linkers has been studied using label-free detection methods [23], but their application for the fabrication of sensor and reference regions of label-free optical biosensors has so far not been reported This is the first report of a diffraction-based LW with an array of alternate strips of different RI where the resonance angle corresponding to each strip was independently visualised as interference fringes. It can be seen that the diffraction-based LWs, when using TE polarised light, have the best DFOM, while the RM using TE polarised light provides the worst DFOM
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
