An ultrasensitive impedance biosensor using circular fully symmetrical electrode for rapid detection of Salmonella

Foodborne bacteria screening is essential for food safety. An impedance biosensor was innovatively developed in this study using a circular fully symmetrical (CFS) electrode for ultrasensitive Salmonella detection. The target Salmonella cells were first captured by immune magnetic nanoparticles (MNPs) and subsequently labeled with immune glucose oxidase@zeolitic imidazolate framework-8 (GOD@ZIF-8), forming MNP-Salmonella-GOD@ZIF-8 complexes. The GODs on these complexes were employed to catalyze non-conductive glucose into conductive gluconic acid. The resulting impedance change of the catalysate was monitored in real time at a characteristic frequency of 10 kHz using the CFS electrode to quantify bacterial concentration. The CFS electrode was verified with 100 times higher sensitivity than some traditional interdigitated electrodes. The biosensor achieved detection within 1 h, with a linear range of 1.0 × 10¹-1.0 × 10⁵ CFU/mL and a detection limit of 3 CFU/mL. Average recoveries of Salmonella in spiked chicken, lettuce, and milk samples were 98.3 %, 103.7 %, and 97.5 %, respectively, demonstrating its good practicality. This biosensor was featured with high sensitivity, rapid response and good specificity, making it a valuable tool for the effective surveillance of foodborne bacteria.