Rapid Determination of Uric Acid in Whole Blood by Colorimetric Method Based on Microfluidic Paper Chip

A method for the rapid determination of uric acid in whole blood by colorimetric method based on microfluidic paper chip was proposed. The designed microchannel grid was printed on chromatographic paper by wax jet printer, and the microfluidic paper chip was obtained after heat treatment. To prepare the microfluidic paper chip detection platform, 3.2 μL of 0.10 g·mL^-1 ethylenediamine tetraacetic acid (EDTA) solution and 4.8 μL of 0.015 g·mL^-1 chitosan solution were added onto zone I (sample pretreatment zone), and the chip was dried. The whole blood sample and phosphate buffer solution (pH 7.4) were mixed at volume ratio of 1∶4, and an aliquot of the mixture (13 μL) was added onto zone I. Red blood cells and plasma were separated by the agglutination of chitosan and EDTA, and plasma flowed to zone II (coloration zone). After plasma completely covered zone II, 3 μL of the mixed solution of ferric trichloride and o-diazophene was added for settling reaction for 2 min. Photo was taken by a mobile phone, and Photoshop CS2 software was employed to analyze the color intensity of the coloration zone, and then RGB value (representing the superposition value of red, green and blue) was obtained to calculate the uric acid content based on the standard curve. It was shown that common reducing substances in whole blood, such as glucose, did not interfere with the determination of uric acid. Linear relationship between the concentration of uric acid and RGB value was kept in the range of 0.05-0.85 mmol·L^-1, with detection limit (3.3s/k) of 0.03 mmol·L^-1. The method was used to analyze actual whole blood samples and compared the determined results from a clinical laboratory of hospital. It was shown that there was no significant difference between the determined results of the method and the hospital. Test for recovery by standard addition method on the actual sample, giving results in the range of 103%-110%.