Development of a lateral flow dipstick immunoassay for evaluation of folate levels in maize

Folates (vitamin B9) are essential for all organisms as cofactors for one-carbon metabolism. However, measurement of folates is technically complicated and time-consuming. In this study, we developed a dipstick immunoassay using a folate-specific monoclonal antibody (mAb), allowing rapid and low-cost detection of folates. The indicator range of the dipstick for 5-formylterahydrofolate (5-CHO-THF), 5-methyltetrahydrofolate (5-CH3-THF) and their polyglutamyl forms was 100-200 ng mL(-1); moreover, no cross-reactivity was observed with tetrahydrofolate (THF) or 5,10-methenyltetrahydrofolate (5,10-CH=THF) at 500 ng mL(-1), or with the folate precursors pterin-6-COOH, p-aminobenzoate (pABA), and L-glutamate, or with the folate analogues methotrexate and 10-formyltetrahydrofolate (10-CHO-THF) at up to 1000 ng mL(-1). The dipstick immunoassay was tested in maize seeds; the results classified the seeds into those with low, moderate, and high levels of folates, and were in agreement with those of liquid chromatography-mass spectrometry. Thus, we conclude that the dipstick assay will provide a versatile tool to facilitate large-scale screening of maize rich in folates.