A protamine-mediated heparin sensing device.

A convenient, protamine mediated strip assay for heparin was developed. The assay is established on the specific interaction between heparin and protamine, and the metachromatic color change of methylene blue dye from blue to purple in the presence of heparin. The device consists of a fibrin cup fabricated with a cellulose paper strip containing immobilized protamine. To analyze plasma heparin levels, a fixed volume of the test sample is placed in the fibrin cup and allowed to migrate through the strip in a descending manner until exhaustion. The region to which heparin binds is then visualized as purple in color by spraying methylene blue dye onto the strip. The heparin level in the sample is estimated from the length of the purple region using a preconstructed standard curve. This device proved to be capable of detecting and differentiating heparin in clinically relevant concentrations.