Fig 6. Influence of samples spiked with serial dilutions of an inhibitor on quantification by the qPCR and ddPCR assays.

The ddPCR assay exhibits superior tolerance to citrus extracts and Cu²⁺ compared to the qPCR assay. A 100% inhibition represents a completely suppressed reaction with no positive signal and a 0% inhibition indicates no suppression with the same target concentration as the no-inhibition control. (a) Citrus extract, (b) CuSO₄ and (d) cupravit had an enhancing effect on both the ddPCR and qPCR assays at low levels of spiking. (d) A 1-D plot of ddPCR reactions spiked with different amounts of citrus extracts. Fluorescent signals of both positive and negative droplets were increased with increasing amounts of citrus extracts.