C-shaped embedded polymer waveguide for evanescent field absorption based lab on a chip biosensor

In this report a microfluidic chip with embedded C-shaped waveguides was fabricated and study was performed to determine its biosensing capabilities. The general fabrication procedure to couple the microchannel network with C-bend waveguides was a single step process in which the photo resist SU-8 layer was patterned into optical structures (C-bend waveguides), fiber-to-waveguide coupler and microchannel network structures (Fig. 2) using single mask (Fig. 1). The device was tested for sensitivity to refractive index variation in the analyte (by passing sucrose solutions of varying concentrations) as well as evanescent wave absorption (by passing various concentrations of Methylene Blue dye solutions) as explained in Fig 3 and Fig 4. These embedded C-shaped waveguide probes demonstrated biosensing with the help of Human IgG (HIgG) - FITC tagged goat anti IgG(GaHIgG) biomolecules as bioreceptor-analyte pair. For HIgG immobilization on C-shaped SU-8 waveguide the glycine was used as crosslinkers, before applying the carbodiimide/succinimide chemistry over the waveguide surface. The analyte (FITC tagged GaHIgG) was passed through the micro-channel embedded with the C-shaped waveguide. The antigen- antibody interaction and binding results in to the absorption of evanescent field by FITC tagged GaHIgG bio-molecule, causing a drop in light intensity output of the waveguide which was detected and calibrated. The results indicated that C-shaped waveguides can be used easily for more sensitive bio sensing of biomolecules either by evanescent wave absorption or by changes associated with refractive index in the microenvironment around a waveguide.