(a) Cell phone image of fluorescently labeled HCMV at a concentration of 107 PFU/mL. (b) Photon-counting map for dashed area in (a) using a confocal laser microscope. Note that absolute photon counts are different. (c) Distribution of intensity of HCMV in cell phone images. (d) Cell-phone-based virus density vs. virus incubation concentrations [taken from Wei et al. ACS Nano (2013)].