Quantitative Measurement of Fibrinogen Concentration by a Spotting Test on a Paper Microfluidic Device

Fibrinogen is an important protein involved in coagulation and haemostasis and is closely related to human health. In this work, we develop a low-cost paper based microfluidic analytical device ($\mu \text{PAD}$) based on a filtration membrane and adhesive tapes for the quantitative measurement of fibrinogen. The filtration membrane with asymmetric microstructure is sandwiched by two layers of hydrophilic adhesive tapes. There is a circular pore with a diameter of 0.7 mm on the top tape layer, which can aspirate the liquid sample under capillary action after contacting the mixture of serum sample and thrombin solution. When the mixture diffuses into the filtration membrane, a circular spot will form on it. The area of this circular spot is affected by the concentration of fibrinogen, therefore we can use the area of the circular spot to infer the concentration of fibrinogen. We build an exponential calibration curve between the area of the circular spot and the fibrinogen concentration, which has a correlation coefficient $\left(\mathbf{R}^{\mathbf{2}}\right)>0.98$ for serum samples with fibrinogen concentrations ranging from 0 to $5.0 \text{mg} / \text{mL}$. This chip can complete the measurement of fibrinogen concentration within 5 minutes, and only $30 \mu \mathrm{L}$ of sample is consumed in a single measurement, making it very suitable for point-of-care diagnostics in resource limited areas.