Paper-based microfluidic device for serum zinc assay by colorimetry†

Abstract

Zinc is an essential micronutrient playing several crucial roles in human pathophysiology and its deficiency leads to micronutrient malnutrition. Therefore, a rapid, inexpensive, and accurate protocol for serum zinc concentration measurement becomes essential in community healthcare. This study demonstrates the design, fabrication, and characterization of a low-cost, paper-based microfluidic device (μPAD) to detect serum zinc concentration by colorimetric techniques. The μPAD comprises circular spotting zones doped with diphenylthiocarbazone, commonly known as dithizone, that produces pink-colored chelates upon reacting with zinc and the color intensity monotonically changes with concentration even across the physiological range (i.e., 5–25 μM). The design and the doping protocol were optimized to generate a linear correlation (in water, R² = 0.94; in artificial plasma, R² = 0.98) between a suitable optical measure (i.e., the normalized Euclidean shift) evaluated by image analysis of photographs captured by the camera of a standard smartphone and zinc concentration. The calibration curve for artificial plasma was further used to evaluate the zinc concentrations in real blood serum samples, resulting in a high parity with the respective gold standard method. The device is expected to significantly contribute in diagnosis of micronutrient malnutrition with a particular emphasis on community healthcare and to reach resource-limited settings.