Screen-printed Electrochemical Biosensor for the Detection of Bacteriophage of Lactococcus Lactis for Dairy Production

In the dairy industry, the spreading of phages of Lactococcus lactis (LL) prevents the proper lactic fermentation, causing waste of contaminated products and economic losses. This work presents a cheap biosensing method for rapidly detecting the LL phages. The detection is based on live LL bacteria covering the sensor electrodes, whose electrical response is measured by electrochemical impedance spectroscopy (EIS). Solutions contaminated by phages induce bacteria lysis, clearly reducing the bacteria coverage over the electrodes and leading to evident parametrical shifts in the charge transfer resistance and in the impedance phase at 400 Hz. Experimental tests with laboratory contaminated samples confirm the better detection capability of screen-printed gold sensors compared to the interdigitated gold electrodes. Two measurement protocols, called spill-out and drop-in methods, are evaluated to optimize the sensor detection capability and time. The EIS results are compared with optical absorbance measurements at 600 nm, in order to validate the proposed detection method with 107-PFU/mL phages and with a detection time of about 5 h. Finally, the proposed method is tested successfully with milk-based solutions. Evident shifts between phage-contaminated and non-contaminated sensors are measured in the charge transfer resistance of more than one order of magnitude with impedance phase differences of 43°.