Mitigating the Hook Effect in Lateral Flow Sandwich Immunoassays Using Real-Time Reaction Kinetics.

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 at 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.

Fluorescence lateral flow competitive protein binding assay for the assessment of serum folate concentrations.

Folate is a micronutrient required for the production of new cells, making it a key factor in early fetal development and ensuring normal growth and maintenance of health. The increase in consumption of folate due to increased periconceptional supplementation and fortification of grains in many countries has led to a decrease in occurrence of folate deficiency and a class of birth defects called neural tube defects. However, an opportunity remains to further improve folate status of populations in areas with limited access to fortified foods and supplementation. Screening of women of reproductive age and other vulnerable populations for folate status would increase our understanding of the magnitude of the burden of folate deficiency and inform monitoring of public health programs. Current gold standard methods for folate assessment are time-intensive and require cold chain, sophisticated laboratory infrastructure, and highly-trained personnel. Our lateral flow assay is low-cost, easy to use, and allows a user to assess folate insufficiency at the point of care in less than 40 minutes. We evaluated the sensitivity and specificity of our assay in 24 human serum samples, including 8 samples with folate concentrations less than 10.0 nmol/L and 14 samples less than 13.4 nmol/L using the Immulite 2000 commercial assay as a reference standard. The sensitivity and specificity were found to be 93% (95% CI: 54.7-100.0) and 91% (95% CI: 80.0-100.0), respectively, when using our test to determine folate insufficiency based on a cutoff of 13.4 nmol/L. Our point-of-care diagnostic test for folate concentrations could inform screening and public health programs in at-risk populations.