NULL-METHOD IN IMMERSION REFRACTOMETRY FOR BIOPHYSICAL MEASUREMENT OF CRYPTOSPORIDIUM AND GIARDIA LAMBLIA

This paper presents an on-chip null-method immersion refractometer for the measurement of size, shape and refractive index of protozoa in treated water. The key features of the on-chip immersion refractometer include (1) multiple single cyst trapping sites, which enable the measurement of multiple sample per test; and (2) zig-zag micromixer, which enables the refractive index variation of external medium as the key component of immersion refractometry. The results show that Cryptosporidium parvum oocysts have size of 3 to 7 μm, spherical with ovality lower than 0.3, and refractive index of 1.418. Giardia lamblia cysts have size of 8 to 12 μm, oval with ovality higher than 0.3, and refractive index of 1.433. The refractive indices of the samples are measured with high precision of < 10 -3 .