DETERMINATION OF E. COLI O157: H7 BACTERIA WITH QCM BIOSENSOR FUNCTIONALIZED WITH ZNO NANOSTARS.

Objective: Escherichia coli O157:H7 (E. coli O157:H7) is a highly pathogenic bacteria threatening human life. This bacterium causes serious effects to human health such as bloody diarrhea, bloody feces, anemia and kidney failure. Hence, establishment of a rapid and sensitive method to detect E. coli is required to control this pathogenic bacterium especially in water supplies and foods. Recent advances in the biocompatible nanomaterials and biotechnology open a new era in the biosensor field. MOX nanostructure based materials have their unique advantages such as biocompatibility, high isoelectric point and high surface-to-volume ratio, which make them a good candidate for biosensing. In this work, we used the QCM sensors modified with ZnO NRs to detect E. coli O157:H7 bacteria. ZnO NRs were directly grown on a gold electrode of QCM by electrochemical deposition route. The sensor showed sensitive behavior against E. coli O157:H7 bacteria. Materials-Method: ZnO NRs were directly grown on QCM device by two step electrochemical deposition method. Firstly, a ZnO thin film was coated on QCM as a seed layer. Then, ZnO NRs were grown on this seed layer. After fabrication of ZnO NRs on QCM electrode, the anti-E. coli O157:H7 was immobilized on the ZnO NRs. Fabricated QCM based sensors were mounted into a home-made QCM cell. One of the crystal surfaces was exposed to reaction solution. Analyte flow was provided by a peristaltic pump and frequency of the oscillator was monitored by a computer controlled electronic circuit. Results: The ZnO NRs were vertically well-aligned and uniformly distributed on the Au electrode of the QCM. These highly ordered vertical nanostructures confirm the increased surface area and thus increased sensitivity for the sensor. XRD results showed that fabricated ZnO NRs have wurtzite crystal structure. We prepared QCM sensors which were modified by ZnO NRs immobilized with anti-E. coli to test E. coli O157:H7 bacteria. Fabricated biosensors were exposed to 4x106 CFU E. coli O157:H7. When the sensor was exposed to E. coli, frequency shift was observed. Moreover, the sensor was recovered when exposed to PBS solution (without E. coli). Conclusion: A QCM biosensor modified with ZnO NRs for E. coli O157:H7 detection was developed. ZnO NRs were successfully grown on QCM electrodes. The sensor revealed sensitive and clear sensor response against E. coli O157:H7 bacteria. This study showed that ZnO nanostructures have great potential for biosensing applications. [ABSTRACT FROM AUTHOR]