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A Label-free, Microfluidics and Interdigitated Array Microelectrode Based Impedance Biosensor in Combination with Nanoparticles Immunoseparation for Detection of Escherichia coli O157:H7 in Food Samples

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  2007 ASAE Annual Meeting  077111.(doi:10.13031/2013.23470)
Authors:   Madhukar (or initial) Varshney, Yanbin (or initial) Li, Balaji (or initial) Srinivasan, Steve (or initial) Tung
Keywords:   Interdigitated array microelectrode, Microfluidic flow cell, E coli O157-H7, Magnetic nanoparticles, Impedance biosensor, Label-free detection

A microfluidic flow cell with embedded gold interdigitated array microelectrode (IDAM) was developed and integrated with nanoparticle-antibody conjugates into an impedance biosensor to rapidly detect pathogenic bacteria. The flow cell consisting of a detection microchamber and inlet and outlet microchannels was fabricated by bonding an IDAM chip to a Poly(dimethylsiloxane) (PDMS) microchannel. The detection microchamber with a dimension of 7 x 0.5 x 0.02 mm and a volume of 60 nl was used to collect bacterial cells in the active layer above the electrode. Magnetic nanoparticle antibody conjugates (MNAC) were prepared by conjugating streptavidin-coated magnetic nanoparticles with biotin-labeled polyclonal goat anti-E. coli antibodies and were used in the separation and concentration of target bacteria. The cells of E. coli O157:H7 inoculated in a food sample were first captured by the MNAC, separated and concentrated by applying a magnetic field, washed, and then suspended in mannitol solution and finally injected through the microfluidic flow cell for impedance measurement. The lowest detection limit of this biosensor for detection of E. coli O157:H7 in pure culture and ground beef samples was 8.4 x 105 and 7.9 x 106 cfu ml-1, respectively, and the total detection time from sampling to measurement was 35 min. Equivalent circuit analysis indicated that the bulk medium resistance, double layer capacitance, and dielectric capacitance were responsible for causing the impedance change due to the presence of E. coli O157:H7 cells on the surface of IDAM. Sample pre-enrichment, electrode surface immobilization, and redox probes were not needed in this impedance biosensor.

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