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Analysis of Bacterial Food Contamination Using Disposable Electrochemical Genosensor

September 1, 2006 By: Peter Adrian

This content is excerpted from Sensor Technology Alert and Newsletter, a sensor intelligence service published by the Technical Insights unit of Frost & Sullivan.

Sensor Technology Alert

Detection of food contamination by pathogenic, toxin producing bacteria such as Staphylococcus aureus, salmonella, E.Coli and many others has been an important issue for researchers across the globe. Based on specific microbiological and biochemical identifications, conventional methods for the detection and identification of bacteria take a very long time to yield results. However, it is now well known that genetic characterization methods are more rapid than the classical microbiological methods with explicit species identification. Of the genetic characterization methods, polymerase chain reaction (PCR) followed by hybridization of the PCR amplified target with a labeled single-stranded oligonucleotide probe is an effective method of sequence-specific DNA detection.

In these applications, electrochemical detection of DNA hybridization events offers novel routes due to its ability to meet demands for a reliable, faster, cheaper, miniaturized and multi-analyte analysis methodology. Led by Marco Mascini, a team of researchers at Dipartimento di Chimica, Universit`a Degli Studi di Firenze, Fiorentino, Italy, has developed an electrochemical genosensor array for the rapid and simultaneous detection of different food-contaminating pathogenic bacteria.

Mascini tells Sensor Technology "Detection of these pathogens has always been possible but with obvious disadvantages such as large analysis time and unreliable operation, which has led us to develop the sensing technique. The sensing principle is based on DNA hybridization and detection through electrochemical interrogation of the surface. We have modified the sensors with specific captures probes, and then identified specific bacteria after PCR amplification."

The team has demonstrated simultaneous detection of different food pathogenic bacteria by means of a disposable electrochemical low density genosensor array that relies on the use of screen-printed arrays of gold electrodes, modified using thiol-tethered oligonucleotide probes. Using corresponding genomic DNA through PCR amplification, the samples identifying the bacteria of interest were obtained. These unmodified PCR products were captured at the electrode interface via sandwich hybridization with surface-tethered probes and biotinylated signaling probes. Then, the resulting biotinylated hybrids were coupled with a streptavidin-alkaline phosphatase conjugate and exposed to an a-naphthyl phosphate solution. Differential pulse voltammetry was finally used to detect the a-naphthol signal. As a resultant, the researchers detected mixtures of DNA samples from different bacteria at the nanomolar level without any cross-interference quantifying reliable pathogen detection. The selectivity of the assay was also confirmed by the analysis of PCR products unrelated to the immobilized probes.

With food safety and quality as the primary focus of application, what differentiates this approach from peer sensing techniques is reduced system analysis time for pathogen identification and electrochemical detection, which can be obtained with small portable inexpensive equipment. Interestingly, the complete procedure can be carried out in a time frame of a few hours. Therefore, in comparison to conventional detection techniques that take about a week's time, the developed disposable electrochemical genosensing platform takes considerably less time and can immensely assist in timely action for events such as food-borne outbreaks where rapid resolution is required.

Mascini adds, "In the future, we're looking to extend this sensing principle to other specific applications [such as] detection of food allergens or detection of clinical specific problems. This is very well exemplified by the involvement of our group in a number of European and international projects where this work will be expanded and applied to other specific applications. Collaborations that can take this research to the next level are welcomed and we're looking forward to such partnerships."

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