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A Label-Free Impedance Immunosensor Using Screen-Printed Interdigitated Electrodes and Magnetic Nanobeads for the Detection of E. coli O157:H7.

Wang R, Lum J, Callaway Z, Lin J, Bottje W, Li Y - Biosensors (Basel) (2015)

Bottom Line: The impedance immunosensor could detect E. coli O157:H7 at a concentration of 10(4.45) cfu·mL(-1) (~1400 bacterial cells in the applied volume of 25 μL) in less than 1 h without pre-enrichment.A linear relationship between bacteria concentration and impedance value was obtained between 10(4.45) cfu·mL(-1) and 10(7) cfu·mL(-1).The magnetic field and impedance were simulated using COMSOL Multiphysics software.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological and Agricultural Engineering, University of Arkansas, Fayetteville, AR 72701, USA. rwang@uark.edu.

ABSTRACT
Escherichia coli O157:H7 is one of the leading bacterial pathogens causing foodborne illness. In this study, an impedance immunosensor based on the use of magnetic nanobeads and screen-printed interdigitated electrodes was developed for the rapid detection of E. coli O157:H7. Magnetic nanobeads coated with anti-E. coli antibody were mixed with an E. coli sample and used to isolate and concentrate the bacterial cells. The sample was suspended in redox probe solution and placed onto a screen-printed interdigitated electrode. A magnetic field was applied to concentrate the cells on the surface of the electrode and the impedance was measured. The impedance immunosensor could detect E. coli O157:H7 at a concentration of 10(4.45) cfu·mL(-1) (~1400 bacterial cells in the applied volume of 25 μL) in less than 1 h without pre-enrichment. A linear relationship between bacteria concentration and impedance value was obtained between 10(4.45) cfu·mL(-1) and 10(7) cfu·mL(-1). Though impedance measurement was carried out in the presence of a redox probe, analysis of the equivalent circuit model showed that the impedance change was primarily due to two elements: Double layer capacitance and resistance due to electrode surface roughness. The magnetic field and impedance were simulated using COMSOL Multiphysics software.

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(a) Average impedance change between the control and bacteria measurements at 100 Hz for E. coli O157:H7. Error bars were based on standard deviation of triplicate tests; (b) ESEM photograph of the antibody-coated nanobeads; and (c) ESEM photograph of an E. coli O157:H7 cell attached with antibody-coated nanobeads.
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biosensors-05-00791-f004: (a) Average impedance change between the control and bacteria measurements at 100 Hz for E. coli O157:H7. Error bars were based on standard deviation of triplicate tests; (b) ESEM photograph of the antibody-coated nanobeads; and (c) ESEM photograph of an E. coli O157:H7 cell attached with antibody-coated nanobeads.

Mentions: The impedance magnitude at 100 Hz was determined to be the best indicator of bacterial presence. Figure 4a shows the average impedance decrease for each E. coli O157:H7 concentration. Based on the t-tests results, the P-value of impedance change (ΔZ) between 104 and 105 cfu·mL−1, 105 and 106 cfu·mL−1, and 106 and 107 cfu·mL−1 was 0.04, 0.002 and 0.05, respectively, indicating a significant difference. A linear relationship (R2 = 0.94) was found to exist between log value of E. coli concentration (Cbact) in cfu·mL−1 and impedance change (ΔZ) in ohms between control and bacteria samples that corresponded to ΔZ = 13.6Cbact – 50.8. The lower detection limit was calculated to be 104.45 cfu·mL−1. This corresponded to a final bacteria count of ~1400 cells in the applied volume of 25 µL. The reproducibility of the biosensor was shown to be high, with small standard deviations (SD = 2 ± 1) at all bacteria concentrations. The capture of the bacteria by the antibody-coated nanobeads was confirmed by ESEM, shown in the Figure 4c. To improve the specificity of the immunosensor, the combination of monoclonal antibodies against unique epitopes on the O157 and H7 antigens is a logical approach for specific detection of E. coli O157:H7, minimizing interferences from other bacteria including non-O157 and non-H7 serotypes of E. coli.


A Label-Free Impedance Immunosensor Using Screen-Printed Interdigitated Electrodes and Magnetic Nanobeads for the Detection of E. coli O157:H7.

Wang R, Lum J, Callaway Z, Lin J, Bottje W, Li Y - Biosensors (Basel) (2015)

(a) Average impedance change between the control and bacteria measurements at 100 Hz for E. coli O157:H7. Error bars were based on standard deviation of triplicate tests; (b) ESEM photograph of the antibody-coated nanobeads; and (c) ESEM photograph of an E. coli O157:H7 cell attached with antibody-coated nanobeads.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4697145&req=5

biosensors-05-00791-f004: (a) Average impedance change between the control and bacteria measurements at 100 Hz for E. coli O157:H7. Error bars were based on standard deviation of triplicate tests; (b) ESEM photograph of the antibody-coated nanobeads; and (c) ESEM photograph of an E. coli O157:H7 cell attached with antibody-coated nanobeads.
Mentions: The impedance magnitude at 100 Hz was determined to be the best indicator of bacterial presence. Figure 4a shows the average impedance decrease for each E. coli O157:H7 concentration. Based on the t-tests results, the P-value of impedance change (ΔZ) between 104 and 105 cfu·mL−1, 105 and 106 cfu·mL−1, and 106 and 107 cfu·mL−1 was 0.04, 0.002 and 0.05, respectively, indicating a significant difference. A linear relationship (R2 = 0.94) was found to exist between log value of E. coli concentration (Cbact) in cfu·mL−1 and impedance change (ΔZ) in ohms between control and bacteria samples that corresponded to ΔZ = 13.6Cbact – 50.8. The lower detection limit was calculated to be 104.45 cfu·mL−1. This corresponded to a final bacteria count of ~1400 cells in the applied volume of 25 µL. The reproducibility of the biosensor was shown to be high, with small standard deviations (SD = 2 ± 1) at all bacteria concentrations. The capture of the bacteria by the antibody-coated nanobeads was confirmed by ESEM, shown in the Figure 4c. To improve the specificity of the immunosensor, the combination of monoclonal antibodies against unique epitopes on the O157 and H7 antigens is a logical approach for specific detection of E. coli O157:H7, minimizing interferences from other bacteria including non-O157 and non-H7 serotypes of E. coli.

Bottom Line: The impedance immunosensor could detect E. coli O157:H7 at a concentration of 10(4.45) cfu·mL(-1) (~1400 bacterial cells in the applied volume of 25 μL) in less than 1 h without pre-enrichment.A linear relationship between bacteria concentration and impedance value was obtained between 10(4.45) cfu·mL(-1) and 10(7) cfu·mL(-1).The magnetic field and impedance were simulated using COMSOL Multiphysics software.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological and Agricultural Engineering, University of Arkansas, Fayetteville, AR 72701, USA. rwang@uark.edu.

ABSTRACT
Escherichia coli O157:H7 is one of the leading bacterial pathogens causing foodborne illness. In this study, an impedance immunosensor based on the use of magnetic nanobeads and screen-printed interdigitated electrodes was developed for the rapid detection of E. coli O157:H7. Magnetic nanobeads coated with anti-E. coli antibody were mixed with an E. coli sample and used to isolate and concentrate the bacterial cells. The sample was suspended in redox probe solution and placed onto a screen-printed interdigitated electrode. A magnetic field was applied to concentrate the cells on the surface of the electrode and the impedance was measured. The impedance immunosensor could detect E. coli O157:H7 at a concentration of 10(4.45) cfu·mL(-1) (~1400 bacterial cells in the applied volume of 25 μL) in less than 1 h without pre-enrichment. A linear relationship between bacteria concentration and impedance value was obtained between 10(4.45) cfu·mL(-1) and 10(7) cfu·mL(-1). Though impedance measurement was carried out in the presence of a redox probe, analysis of the equivalent circuit model showed that the impedance change was primarily due to two elements: Double layer capacitance and resistance due to electrode surface roughness. The magnetic field and impedance were simulated using COMSOL Multiphysics software.

Show MeSH
Related in: MedlinePlus