The quantification of analyte concentrations using lateral flow assays is a low-cost and user-friendly alternative to traditional lab-based assays. However, sandwich-type immunoassays are often limited by the high-dose hook effect, which causes falsely low results when analytes are present in very high concentrations. In this paper, we present a reaction kinetics-based technique that solves this problem, significantly increasing the dynamic range of these devices. With the use of a traditional sandwich lateral flow immunoassay, a portable imaging device, and a mobile interface, we demonstrate the technique by quantifying C-reactive protein concentrations in human serum over a large portion of the physiological range. The technique could be applied to any hook effect-limited sandwich lateral flow assay and has a high level of accuracy even in the hook effect range.

Interest in developing paper-based devices for point-of-care diagnostics in resource-limited settings has risen remarkably in recent decades. In this paper, we demonstrate what we refer to as “High Yield Passive Erythrocyte Removal” (HYPER) technology, which utilizes capillary forces in a unique cross-flow filtration for the separation of whole blood with performance comparable to centrifuges. As we will demonstrate, state-of-the-art passive blood separation methods implemented in paper-based systems exhibit rapid blood cell clogging on the filtration media or serum outlet and yield only about 10%−30% of the total serum present in the sample. Our innovation results from the inclusion of a differentiation pad, which exploits hydrodynamic effects to reduce the formation of a fouling layer on the blood filtration membrane resulting in more than 60% serum yield with undiluted whole blood as direct input. To demonstrate the effectiveness of the HYPER technology we implement it in a lateral flow system and demonstrate the accurate quantification of vitamin A and iron levels in whole blood samples in 15 minutes.

Micronutrient deficiencies such as those of vitamin A and iron affect a third of the world's population with consequences such as night blindness, higher child mortality, anemia, poor pregnancy outcomes, and reduced work capacity. Many efforts to prevent or treat these deficiencies are hampered by the lack of adequate, accessible, and affordable diagnostic methods that can enable better targeting of interventions. In this work, we demonstrate a rapid diagnostic test and mobile enabled platform for simultaneously quantifying iron (ferritin), vitamin A (retinol-binding protein), and inflammation (C-reactive protein) status. Our approach, enabled by combining multiple florescent markers and immunoassay approaches on a single test, allows us to provide accurate quantification in 15 min even though the physiological range of the markers of interest varies over five orders of magnitude. We report sensitivities of 88%, 100%, and 80% and specificities of 97%, 100%, and 97% for iron deficiency (ferritin <15 ng/mL or 32 pmol/L), vitamin A deficiency (retinol-binding protein <14.7 μg/mL or 0.70 μmol/L) and inflammation status (C-reactive protein >3.0 μg/mL or 120 nmol/L), respectively. This technology is suitable for point-of-care use in both resource-rich and resource-limited settings and can be read either by a standard laptop computer or through our previously developed NutriPhone technology. If implemented as either a population-level screening or clinical diagnostic tool, we believe this platform can transform nutritional status assessment and monitoring globally.