A Mobile Device‐based Platform for Point‐of‐care Quantification of sTfR for Assessment of Iron Deficiency

Iron deficiency anemia (IDA) is a global public health problem that has devastating effects on maternal and child health outcomes. However, our ability to diagnose or monitor it, particularly at the national level, often relies on hemoglobin measurements for a vast majority of the population due to poor access and affordability. Also, differentiating between IDA and anemia of chronic disease (ACD) is important, since unnecessary iron supplementation could have a detrimental effect on patients with ACD. Both ferritin and soluble transferrin receptor (sTfR) are indicators of iron deficiency (ID) and the World Health Organization (WHO) recommends testing for both, in addition to Hemoglobin and an acute phase protein such as CRP, for assessment of iron status. We report a lateral flow detection scheme coupled with a mobile device for quantitative detection of sTfR in finger‐prick blood samples within 15 min. The mobile device‐based platform consists of a lateral flow immunoassay test strip (consumable) with all the test reagents positioned inside an accessory (reusable) that can be attached to the backside of a smartphone. The user places a drop of blood (collected by finger‐prick) on the test strip and the sample begins to flow up the strip via capillary action. First, the sample interacts with gold nanoparticles coupled to specific antibodies, followed by interaction with two bands of immobilized antibodies, to undergo a sandwich immunoassay reaction, resulting in a relative color change in the bands. The mobile device camera captures an image of the colored bands and post‐processing is performed to provide quantitative results of the sTfR concentration. The calibration test results of our current test strip with standard solutions of sTfR indicates that the calibration curve is linear for sTfR concentrations up to 10 micrograms/mL, which meets the iron deficiency cut‐off level of 8 micrograms/mL for sTfR. This mobile device‐based platform will enable iron deficiency screening and diagnostic tests at a low cost in both home‐use and field settings, particularly for national surveys, bypassing the need for a cold‐chain, expensive laboratory equipment, and trained personnel. Support or Funding Information This work was supported in part by the Thrasher Research Fund, National Science Foundation, and Micronutrient Initiative. 1(a) Lateral flow immunoassay (LFIA) architecture and sandwich immunoassay scheme for sTfR detection (b) Mobile device‐based platform components (left) and assembled test system (right)2Developed test and control lines on sTfR strips after the completion of immunoassay. Test line intensity increases with concentration of sTfR.3Test and control line signals detected by the mobile device app as local intensity minima for 10 mg/ml of sTfR, to calculate T/C ratio4Calibration curve showing the T/C ratios of the colorimetric signals at various known sTfR concentrations