Abstract
Cryptosporidium is a protozoan parasite causing cryptosporidiosis; a diarrheal disease of varying severity. The infection is transmitted by tiny spores called oocysts resistant to harsh environmental conditions and various disinfectants. Cryptosporidium infection and recovery from the illness is dependent on the body’s immune system. It is important to be able to detect these parasites quickly to reduce the risk of infection. Multiple-angle light scattering systems have been developed for detecting Cryptosporidium oocysts suspended in water. The proposed systems were set up with a single wavelength (red AlGalnP laser: 658. 4 nm) and two wavelength (violet InGaN laser: 405. 7 nm and red AlGalnP laser: 658. 4 nm) sources. The single wavelength system was developed for measuring particle concentration and particle size and refractive index. It combined multiple-angle scattering detection, to collect angle-resolved scattered intensities from suspensions, and the partial least square regression method (PLS-R) to predict characterizing information of samples under investigation based on calibration models. The calibration models were composed from the calibration data generated from the experiments for particle concentration measurement and according to Mie theory with refraction and transmission corrections included for particles’ size and refractive index measurements. The dual wavelength system was set up for particle identification by using relative wavelength scattered intensity as the identifying means. Measurement of particle concentration, size and refractive index by the single multiple angle light scattering system was validated using polystyrene spheres in aqueous suspensions. Applying the systems to Cryptosporidium oocyst suspensions, the concentration measurement results had lowest errors from the references 9. 5 % at concentration of 2. 00x106 oocysts/ml in mono-dispersion and 3. 6 % at concentration of 7. 50x 105 oocysts/ml for Cryptosporidium and mixed suspensions with polystyrene sphere suspensions. The measured Cryptosporidium oocysts’ size and refractive index were 4. 37 ± 0. 16 μm and 1. 38 ± 0. 05 which also had good agreement to the reference value (size: 4. 38 ± 0. 23 μm, refractive index: 1. 37). The dual wavelength multiple-angle light scattering system collected the relative wavelength scattered intensities from suspensions of the Cryptosporidium oocysts comparing to polystyrene spheres and E. coli. The relative wavelength multiple-angle scattered intensity of Cryptosporidium oocysts suspension showed a characteristic scattering pattern and significantly different pattern from the polystyrene spheres and bacteria E. coli. The results presented in this research have demonstrated that the proposed multiple-angle light scattering systems have the capability to initially detect Cryptosporidium oocysts in suspension. These systems could be further developed for online Cryptosporidium detection by combination with pattern recognition techniques.