Microfluidic diffraction phase microscopy for high-throughput, artifact-free quantitative phase imaging and identification of waterborne parasites

Abstract An artifact-free microfluidic diffraction phase microscopy (MFDPM) system to measure quantitative phase maps of individual Giardia lamblia (G. lamblia) cysts and Cryptosporidium parvum (C. parvum) oocysts is developed. The system includes a diffraction phase imaging unit aligned with a polydimethylsiloxane (PDMS) microfluidic chip. The microfluidic chip consists of arrays of U-shaped hydrodynamic trapping structures used to trap single cysts/oocysts, and a micromixer to precisely adjust the refractive index of immersion medium in the microfluidic chamber. When the refractive index of immersion medium is tuned to be equal to that of PDMS, the pronounced artifacts in quantitative phase imaging (QPI) originating from diffraction and scattering at the edges of trapping structures can be eliminated. The artifact-free quantitative phase maps of single microparticles are retrieved using Goldstein’s algorithm. Principal component analysis (PCA) is implemented to extract the distinctive features of the quantitative phase maps of G. lamblia cysts and C. parvum oocysts, and they can be identified with 100% accuracy using linear discriminant analysis (LDA) algorithm. The MFDPM is demonstrated to be a simple, accurate and high-throughput technique for artifact-free quantitative phase imaging of waterborne protozoa, and has great potential for label-free and rapid detection and identification of waterborne microorganisms.