An impedance based microfluidic biosensor for simultaneous and rapid detection of Salmonella serotypes B and D in ready-to-eat (RTE) Turkey matrix has been presented. Detection of Salmonella at a concentration as low as 300 cells/ml with a total detection time of 1 hour has been achieved. The sensor has two sensing regions, with each formed from one interdigitated electrode array (IDE array) consisting of 50 finger pairs. First, Salmonella antibody type B and D were prepared and delivered to the sensor to functionalize each sensing region without causing any cross contamination. Then the RTE Turkey samples spiked with Salmonella types B and D were introduced into the biosensor via the antigen inlet. The response signal resulted from the binding between Salmonella and its specific antibody demonstrated the sensor’s ability to detect a single type of pathogen, and multiple pathogens simultaneously. In addition, the biosensor’s selectivity was tested using non-specific binding of E. coli O157 and E. coli DH5 Alpha while the IDE array was coated with the Salmonella antibody. The results also showed the sensor is capable to differentiate low concentration of live Salmonella cells from high concentration of dead Salmonella cells, and high concentration of E. coli cells. A detailed study on antibody immobilization that includes antibody concentration, antibody coating time (0.5–3 hours) and use of cross-linker has been performed. The study showed that Salmonella antibody to Salmonella antigen is not a factor of antibody concentration after electrodes were saturated with antibody, while the optimal coating time was found to be 1.5 hours, and the use of cross-linker has improved the signal response by 45–60%.

An impedance biosensor based on interdigitated electrode (IDE) arrays was designed, fabricated and tested for detection of Escherichia coli O157:H7. The device consists of two sets of gold IDE arrays embedded in a SU8-PDMS microchannel. The first set of electrodes uses positive dielectrophoresis (p-DEP) force to focus and concentrate the E. coli into the centre of the microchannel, and direct it towards the detection zone microchannel which has dimensions of a third of the first channel. The bulk fluid keeps flowing toward the outer channel into the waste outlets. The second sets of electrodes are located in the centre channel and are used for impedimetric detection of the E. coli. A combination of standard photolithography, wet etching and plasma treatment techniques were used to fabricate the biosensor. The E. coli cells in the test solution were focused into the centre of the channel when an excitation signal of 5 V_p–p at 5.6 MHz was applied across the electrode arrays. Before injecting the E. coli cells, polyclonal anti-E. coli antibodies were non-specifically immobilized on the sensing electrode array. This ensures specific detection of E. coli O157:H7 bacterial cells. As the concentrated E. coli cells (antigen) reach the sensing electrode array, they bind to the immobilized antibody sites. This antigen–antibody binding causes a change in the impedance, which is measured using an impedance analyzer. The device performance was tested by measuring the impedance, between 100 Hz and 1 MHz frequency, before and after applying p-DEP on the focusing electrode array, and after applying p-DEP on both the focusing and sensing electrodes. The result shows clearly that the use of p-DEP on the focusing IDE array significantly increased the measurement sensitivity with the lower detection limit being 3 × 10² CFU mL⁻¹. In addition, the use of p-DEP on both electrode arrays increased the measurement sensitivity by a factor of 2.9 to 4.5 times depending on the concentration.

We present a low cost, easy to fabricate biosensor, which can quickly and accurately detectSalmonella typhimurium. This study also compares the advantages of the microfluidic biosensor over a nonmicrofluidic biosensor. High density interdigitated electrode array was used to detectSalmonellacells inside a microfluidic chip. Monoclonal anti-Salmonellaantibodies were allowed to be immobilized on the surface of the electrode array for selective detection ofSalmonella typhimurium. An impedance analyzer was used to measure and record the response signal from the biosensor. The biosensor provides qualitative and quantitative results in 3 hours without any enrichment steps. The microfluidic biosensor’s lower detection limit was found to be3×103 CFU/mL compared to the3×104 CFU/mL of the nonmicrofluidic biosensor, which shows that the microfluidic biosensor has 10-fold increased sensitivity. The impedance response of microfluidic biosensor was also significantly higher (2 to 2.9 times) compared to the nonmicrofluidic biosensor.