which is between these reported values. The sensor using Mach–Zehnder interferometer (MZI) with SiN slot waveguide is also reported but they measured only NaCl solution not the biological solutions. Concerning the Si ring biosensors there are many reports for measuring the biological solutions such biotin–streptavidin, PSA and bovine serum albumin (BSA. From Table 1 it is drawn that our work is the first demonstration of detection of biological solution using SiN ring biosensor