A smartphone-integrated low-cost, reagent-free, non-destructive dried blood spot-based paper sensor for hematocrit measurement.

The blood hematocrit (Hct) level provides vital information about a person's health. Traditional Hct measurement equipment relies heavily on infrastructure and skilled manpower, limiting its broad implementation in resource-limited contexts. Therefore, we developed a simple, reagent-free, non-destructive, smartphone-integrated paper-based device for Hct measurement by analyzing blood-spreading area on a paper substrate. Blood spreading area was found to be dependent on the Hct value, paper properties, and assay duration. This device was calibrated using a custom-made Python algorithm with 10 μl of blood, which produced a sensitivity of -1.90 ± 0.03 mm