Purpose: In order to evaluate the ME biosensor method, the ME biosensor method was compared with a TaqMan-based quantitative real-time PCR (qPCR) method.
Methods: Topological characteristics of adaxial and abaxial surfaces of spinach leaves were observed using scanning electron microscopy (SEM). Standard curves, correlations, and limits of detection (LOD) for the ME biosensor and qPCR methods were determined by inoculating S. Typhimurium suspensions (ranging from 1 to 8 log CFU/spinach) on the surface of spinach leaves. For the comparison of the detection methods, the S. Typhimurium suspension (3 log CFU) was directly inoculated and grown on 25 adaxial surfaces of spinach leaves. After 24 h, both methods were performed to detect S. Typhimurium on the spinach leaves.
Results: Although SEM microscopic images showed the topological difference of adaxial and abaxial surfaces, the distribution of S. Typhimurium was nearly similar on both sides. The LOD for the ME biosensor and qPCR were 3 ± 0.19 and 2 ± 0.11 log CFU/spinach, respectively. After 24 h, S. Typhimurium was positively detected by both methods and the quantified concentrations were 5.78 ± 0.79 and 5.89 ± 0.26 log CFU/spinach for the ME biosensor and the qPCR method, respectively. SEM was used to confirm the growth of S. Typhimurium on the spinach surfaces and the binding of S. Typhimurium on the measurement sensors.
Significance: This study demonstrates that the ME biosensor method was robust and competitive with qPCR and has great potential to serve as an on-site and in-field detection method, in order to improve the safety of fresh produce.