Interdigitated electrode DNA biosensor for detection of food-borne pathogens by impedance spectroscopy

The commercial application of biosensors has had a significant impact in a number of areas, particularly in the field of medical diagnostics. But in spite of the great number of publications, only a few systems are commercially available in food analysis. We propose an innovative approach to achieve safer food products by creating a user-oriented device for the detection of food-borne pathogens. Our aim is to perform quality control along the food-chain distribution to protect the consumer's health against contaminations; the measurement is based on the detection by impedance spectroscopy of DNA extracted from bacteria. Our work focuses on the conception of a DNA biosensor able to detect the presence of specific DNA sequences from Salmonella bacteria. Within the European project GoodFood, the choice was made to use dairy products and seafood as starting materials, from which cell growth and DNA amplification were performed by our partners, to finally be measured by impedance spectroscopy with the DNA biosensor. The major advantages of this approach are the portability, ease-of-use and rapidity of the system. The sensor fabrication was performed in several steps: At first, the design and the clean-room fabrication was optimized for platinum interdigitated structures with 5 µm spacing. Once the production of the metal electrodes was standardized, the immobilization of the probe DNA (capturing the target DNA) on the sensor surface was performed by silanization. The selectivity of the sensor towards the target DNA was evaluated by fluorescence microscopy using fluorescently-labelled DNA target sequences. The biochip, consisting of 4 interdigitated electrodes, was connected to an impedance analyzer and a first series of measurements was done without DNA, to characterize the sensor in high ionic strength solutions. A next series was performed with probe DNA on the sensor surface, with decreasing concentrations of synthetic target DNA to reach the nanomolar detection limit of the system. Finally, a series of measurements was carried out with DNA target sequences extracted from food samples spiked with salmonella, to apply the biosensor within a "real" biological DNA sample.