The architecture and working of a smartphone-based biosensor for the quantification of leukocytes at point of care is presented in this paper. The biosensor consists of a microscopic smartphone attachment with a resolution of 6.2 μm and a disposable microfluidic biochip for capturing leukocytes. Polymorphonuclear leukocytes (PMNL) were isolated from whole blood before being seeded into PBS solution to mimic the biological samples from patients suffering from various diseases. To capture all the leukocytes, antihuman CD45 antibody was immobilized in the capture chamber of microfluidic biochip for one hour for adsorption. Leukocyte spiked PBS sample was then flowed through the microfluidic biochip at 10 μl/min for capturing leukocytes. 50 μl of a green nuclear stain was then flowed through the biochip for fluorescent imaging. Leukocyte capture was verified by imaging the biochip in the smartphone setup. ImageJ was then used for detection and quantification of leukocytes from the captured images. The obtained results showcase the feasibility of this setup for detection of multiple biomarkers from different body fluids at point of care.