Salmonella enteritidis outbreaks continue to occur, and S. enteritidis-related outbreaks from various food sources have increased public awareness of this pathogen.
Even though some immunological rapid assays are available, these assays still require enrichment steps and give results in 18-48 h. Biosensors have shown great potential for rapid detection of foodborne pathogens. They are capable of direct monitoring the antigen-antibody reactions in real time. Among the biosensors, impedimetric biosensors have been widely adapted as an analysis tool for the study of various biological binding reactions because of their high sensitivity and reagentless operation.
In this study impedimetric biosensors, which have different specifications of interdigitated electrode, were developed. The sensor was fabricated from a glass wafer with a layer of Cr as an adhesive layer. An interdigitated gold electrode was deposited over the Cr layer using photolithographic processing methods to form an active sensing area. Three different electrode gap sizes (2µm, 5µm, 10µm) were tested to increase the sensitivity of the sensor.
Salmonella enteritidis was detected by reading impedance changes caused by the attachment of the cells to the anti-Salmonella antibodies immobilized on interdigitated gold electrodes. The antibodies were immobilized on the electrode surface by using avidin-biotin binding. The impedance across the interdigitated electrodes was measured after the series of sample introduction. Captured bacteria cells by the antibody changed the impedance between the electrodes.
Optimum input frequency was determined by analyzing frequency characteristics of the biosensor over ranges of applied frequencies from 10 Hz to 1 MHz. Lower than 100 kHz of input frequency, the biosensor was sensitive to the attachment of the bacteria on the sensor surface. The sensor, which has 2µm electrode gap, was most sensitive to the changes of the cell numbers in the sample. The 2µm gap biosensor was able to detect 104 CFU/mL in phosphate buffered saline (PBS) with a incubation time of 5 minutes. Also, the biosensor could detect 105 CFU/mL of Salmonella in pork meat extract.
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