Lensfree holographic microscope of Fig. 1 is used to image 4 different batches of diluted water samples containing Giardia Lamblia cysts at concentration levels of 1510/mL, 755/mL, 378/mL and 189/mL. For each dilution level, 13 different lensfree holograms corresponding to different samples of the same batch were acquired and digitally processed to reconstruct microscopic images of the samples. These reconstructed images were then automatically counted yielding the number of cysts per frame (over an imaging FOV of ~24 mm^{2}). The above figure illustrates the mean and the standard deviation of these count results, which accordingly measured the average parasite concentration in each dilution level as 1372/mL, 671/mL, 398/mL, and 270/mL respectively. The mean errors in these parasite concentration measurements are 9.1%, 11.1%, 5.3%, and 42.9% respectively. In these results, no data points among 52 measurements were eliminated regardless of their value with respect to the mean. By simply eliminating the maximum and the minimum of the measured values in each measurement batch (which reduces the number of data points to 11 from 13 for each dilution level), our mean error in concentration measurements then reduces to 7.4%, 7.3%, 3.5% and 37.2%, respectively. These results validate the performance of our lensfree holographic microscope to quantify Giardia Lamblia cyst concentration of a solution down to a level of ~380 parasites/mL with a mean error of <10%. This also implies that using well established pre-concentration steps such as centrifugation and filteration,28–30 we can potentially improve our detection limits by a factor of *e.g.*, ~100X to claim a detection sensitivity of <5 parasites/mL.

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