Paper test card for detection of adulterated milk

Abstract

In developing countries, milk is adulterated to meet demand and increase profit. Often the milk is diluted with water, and sugar, urea, and starch are added to mimic the color, consistency, and nitrogen content of the real thing. Since laboratory tests for detecting these adulterants are difficult to perform in a field setting, we developed an inexpensive, paper analytical device (MilkPAD) to detect these analytes in milk. All of the reagents, buffers, and enzymes needed to perform each test are stored in dry form in the paper. The user just needs to pipette several drops of the milk onto each reaction area, wait 40 minutes, and take a cell phone photo of the test card. The test card can colorimetrically detect a variety of starches (0.005% w/v), urea (in excess of 70 mg dL⁻¹), and the sugars glucose and sucrose (in excess of 0.1 mM). The sensitivity and specificity of the MilkPAD is greater than 90% for detection of any of these adulterants at concentrations that are typically found in adulterated milk.