Determination of E. coli by a Graphene Oxide-Modified Quartz Crystal Microbalance

ABSTRACT

A biosensor for the determination of Escherichia coli using graphene oxide on the crystal (gold) surface was fabricated by the drop cast method. The E. coli sensing characteristics of the biosensor, such as a change in frequency, were examined by exposing the graphene oxide-coated crystal to various functionalization steps at room temperature. Graphene oxide was functionalized by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride–N-hydroxysuccinimide to covalently conjugate β-galactosidase antibodies to recognize microorganisms that produce this material. Frequency changes in the quartz crystal microbalance are dependent on the absorbed/desorbed masses of the analytes on the functional surface of the crystal. In addition, various characterization techniques were optimized for the morphological elemental analysis of the nanocoating that included field emission scanning electron microscopy, scanning electron microscopy, and electron diffraction spectroscopy. This surface was used in a quartz crystal microbalance nanoplatform for the rapid, sensitive, and label-free detection of E. coli. Under optimal conditions, the frequency of quartz crystal microbalance biosensor was directly proportional to the concentration of antigen with a dynamic range from 0.5 mg mL⁻¹ to 5 ng mL⁻¹ and a minimum detection limit of 5 ng mL⁻¹, and a sensitivity of 0.037 Hz g ml⁻¹ cm⁻¹. These results show that the graphene oxide-coated crystal had excellent performance for E. coli. This research reports a simple, inexpensive, and effective highly stable biosensor using graphene oxide as the sensing medium.

KEYWORDS:

• Escherichia coli
• graphene oxide nanofilm
• quartz crystal microbalance
• scanning electron microscopy

Acknowledgments

The authors acknowledge the grants provided by Department of Science and Technology (DST) under the Water Technology Initiative (WTI) program (DST/TN/WTI/2k10/258(G), dated: 17.11.2011).