Label-free and Culture-Free Quantification of Lactic Acid Bacteria Using Ring-Shaped Interdigitated Electrodes

Quantification of lactic acid bacteria has great significance in the probiotic industry. However, conventional bacteria quantification methods usually take more than 24 hrs to perform, which is not ideal for manufacturing since production proceeds to different stages at a fast pace. To address this problem, a rapid bacteria quantification platform was developed, which utilized ring-shaped interdigitated electrodes to concentrate bacteria particles via electrokinetic forces. The application of an AC signal with 500 Hz and 12 VPP resulted in the collection of bacteria cells suspended in a medium of low conductivity (<15 µS/cm), which was then analyzed with an image analysis software. This was used for samples with bacteria concentrations ranging from 1 × 104 to 1 × 106 CFU/mL. The analysis is inexpensive (<5 USD per test), requires only a small sample volume (160 µL/test), and had a fast total analysis time (within 10 min per sample), which is much faster compared with plate culture methods. The accuracy was verified with blind tests using 61 production line samples and obtained a 100 % predictive accuracy. It is suitable for situations that require rapid bacteria detection and has a high potential for commercial use.