Colloidal gold-based immunochromatographic strip for the detection of digitoxin in human plasma

Digitoxin is a cardiac glycoside used in the therapy of heart failure and arrhythmias, and has potential as an anti-cancer and anti-influenza treatment. However, digitoxin has the disadvantage of a narrow therapeutic window meaning that it is easy to cause toxicity. Consequently, there is an urgent need to accurately monitor the plasma concentration of patients. In this study, an anti-digitoxin monoclonal antibody (mAb) 5D2 was developed and purified, and found to have outstanding specificity, sensitivity, and affinity. The half inhibitory concentrations (IC50) and the limit of detection (LOD) values of mAb 5D2 in human plasma determined by ic-ELISA were 0.205 ng/mL and 0.010 ng/mL, while the cross-reactivity with other analogs was negligible. Based on mAb 5D2, a colloidal gold-based immunochromatographic assay was developed for the purpose of quickly monitoring the concentration of digitoxin in human plasma. The detection results could be obtained within 10 min, and were in agreement with those of liquid chromatography-tandem mass spectrometry (LC-MS/MS). The strip could be evaluated semi-quantitatively by the naked eye, with a visual LOD (vLOD) of 0.5 ng/mL and a cut-off value of 10 ng/mL. Meanwhile, the linear range was between 0.319 ng/mL and 2.406 ng/mL, which was obtained quantitatively by the strip reader. Therefore, the immunochromatographic strip could offer a new tool for rapid, accurate, and portable detection of digitoxin.