UV-LIGA interferometer biosensor based on the SU-8 optical waveguide

Abstract: SU-8 resist was used as a core/cladding waveguide material to fabricate a Mach¿Zehnder interferometer (MZI) for biochemical sensing. The refractive index of the SU-8 resist was fine-tuned with a ¿n of 0.004 for single-mode transmission. The UV lithography processes of the SU-8 resist were also optimized to pattern the high resolution (1µm) and high aspect ratio (AR=6) Y-branch structure of the optical interferometer. Optical measurements reveal that the SU-8 MZI chip can efficiently transmit the NIR laser (¿=1310nm) with a total loss less than 6dB. When one branch of the MZI is in contact with the analyte, the interfered intensity stabilizes after the soaking time exceeds 5min. NaCl solution with a concentration of 10-9g/l can be detected using the SU-8 MZI chip. In the future, the polymer MZI chip can be mass-produced by molding process (or the LIGA process). The low-cost, label-free, real-time and high-sensitivity MZI chip will benefit many applications related to biological, environmental and industrial detection. [Copyright &y& Elsevier]