Limits...
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.

Show MeSH

Related in: MedlinePlus

Average impedance change (a) between a control sample and nanobeads captured E. coli O157:H7 with a magnet underneath; (b) pure E. coli O157:H7; (c) between a control sample and nanobeads captured E. coli O157:H7 with no magnet underneath. E. coli O157:H7 concentration was 107 cfu·mL−1. Error bars were based on standard deviation of triplicate tests. LDL line was determined by signal/noise ratio of 3, where noise was defined as the standard deviation of the pure redox probe measurements.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4697145&req=5

biosensors-05-00791-f005: Average impedance change (a) between a control sample and nanobeads captured E. coli O157:H7 with a magnet underneath; (b) pure E. coli O157:H7; (c) between a control sample and nanobeads captured E. coli O157:H7 with no magnet underneath. E. coli O157:H7 concentration was 107 cfu·mL−1. Error bars were based on standard deviation of triplicate tests. LDL line was determined by signal/noise ratio of 3, where noise was defined as the standard deviation of the pure redox probe measurements.

Mentions: The magnetic nanobeads were determined to be necessary for detection by both experimental analysis and computer simulation. Escherichia coli cells without magnetic nanobeads were suspended in a redox probe solution and a drop of the sample was placed on a screen-printed electrode and the impedance was measured after 10 min. No detectable signal could be seen for E. coli cells only in a redox probe. Also E. coli samples were prepared as described in Section 2.5 but no magnetic field was applied after placing the samples on the electrode. Again, no detectable signal was seen. This data is included in Figure 5. Without a magnet underneath the electrode, the bacteria/nanobead complexes were loosely suspended in the drop solution without tight attachment onto the electrode surface, which might have negligible effect on the electrode surface. Based on the equivalent circuit shown in Figure 3 used for data analysis, the Rsur element (electrode surface roughness) contributed the majority of the impedance change. When the magnet was applied underneath the electrode, the bacteria/nanobead complexes were tightly attached onto the electrode surface, which could increase the electrode surface roughness, resulting in a change in impedance. A simulation using Comsol Multiphysics (Figure 7) also showed that the impedance change decreases as the distance between the E. coli cells and electrode increases.


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)

Average impedance change (a) between a control sample and nanobeads captured E. coli O157:H7 with a magnet underneath; (b) pure E. coli O157:H7; (c) between a control sample and nanobeads captured E. coli O157:H7 with no magnet underneath. E. coli O157:H7 concentration was 107 cfu·mL−1. Error bars were based on standard deviation of triplicate tests. LDL line was determined by signal/noise ratio of 3, where noise was defined as the standard deviation of the pure redox probe measurements.
© Copyright Policy
Related In: Results  -  Collection

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

biosensors-05-00791-f005: Average impedance change (a) between a control sample and nanobeads captured E. coli O157:H7 with a magnet underneath; (b) pure E. coli O157:H7; (c) between a control sample and nanobeads captured E. coli O157:H7 with no magnet underneath. E. coli O157:H7 concentration was 107 cfu·mL−1. Error bars were based on standard deviation of triplicate tests. LDL line was determined by signal/noise ratio of 3, where noise was defined as the standard deviation of the pure redox probe measurements.
Mentions: The magnetic nanobeads were determined to be necessary for detection by both experimental analysis and computer simulation. Escherichia coli cells without magnetic nanobeads were suspended in a redox probe solution and a drop of the sample was placed on a screen-printed electrode and the impedance was measured after 10 min. No detectable signal could be seen for E. coli cells only in a redox probe. Also E. coli samples were prepared as described in Section 2.5 but no magnetic field was applied after placing the samples on the electrode. Again, no detectable signal was seen. This data is included in Figure 5. Without a magnet underneath the electrode, the bacteria/nanobead complexes were loosely suspended in the drop solution without tight attachment onto the electrode surface, which might have negligible effect on the electrode surface. Based on the equivalent circuit shown in Figure 3 used for data analysis, the Rsur element (electrode surface roughness) contributed the majority of the impedance change. When the magnet was applied underneath the electrode, the bacteria/nanobead complexes were tightly attached onto the electrode surface, which could increase the electrode surface roughness, resulting in a change in impedance. A simulation using Comsol Multiphysics (Figure 7) also showed that the impedance change decreases as the distance between the E. coli cells and electrode increases.

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