Ultra-sensitive biosensor based on SU-8 planar interferometer

SU-8 resist was used as a core/cladding waveguide material to fabricate a Mach-Zehnder interferometer (MZI) for biochemical sensing. The refractive index and the UV lithography processes of the SU-8 resist were optimized to give a SU-8 MZI chip with single-mode and high-efficiency transmission. Optical measurements reveal that the SU-8 MZI chip can transmit the NIR laser (λ=1310 nm) with a total loss less than 6 dB. The bio-probes (rabbit IgG) were then immobilized on the surface of the SU-8 waveguide. When one branch of the MZI is in contact with the analyte (sheep anti-IgG), the interfered intensity changes accordingly and then stabilizes when the soaking time extended. The MZI chip is very sensitive and a dilute anti-IgG solution with a concentration as low as 10^-15 g/ml can be detected. The polymer MZI chip is fabricated by molding (or LIGA) process. The low-cost, label-free, real-time and high-sensitivity MZI chip benefit many applications related to biological, environmental and industrial detection.