A nanoporous membrane-based impedimetric immunosensor for label-free detection of pathogenic bacteria in whole milk

We introduce a nanoporous membrane based impedimetric immunosensor for the label-free detection of bacterial pathogens in whole milk. A simple and rapid method to modify a commercially available alumina nanoporous membrane with hyaluronic acid (HA) effectively reduced the non-specific binding of biomolecules and other cells, and permitted successful immobilization of antibodies. Escherichia coli O157:H7, one of the most harmful food-borne pathogenic bacteria, was tested as a model pathogen in this study. The ionic impedance of electrolytes through nanopores, due to antibody-pathogen interactions, was monitored by impedance spectra and analyzed by normalized impedance change (NIC). The regression equation for the NIC at 1 kHz versus concentration of E. coli O157:H7 (10-10(5)cfu/ml) was obtained, and the detection limit found to be as low as 10 cfu/ml. In addition, the proposed immunosensor was successfully used for the detection of E. coli O157:H7 in whole milk samples with the detection limit as low as 83.7 cfu/ml with 95% probability. The specificity of the immunosensor was also demonstrated using non-target bacteria, including Staphylococcus aureus, Bacillus cereus, and non pathogenic E. coli DH5α. This study shows that a HA-functionalized nanoporous membrane-based impedimetric sensor is capable of detecting pathogenic bacteria in whole milk without any pretreatment. This is a significant step for evaluating the safety of food and environmental samples and other medical diagnostics.