A New Biorecognition-Element-Free IDμE Sensor for the Identification and Quantification of E. coli

Abstract

The label-free biosensor has emerged as an effective tool for the purpose of early detection of causative pathogens such as Escherichia coli as a preventive measure. In this study, a biorecognition-element-free interdigitated microelectrode (IDμE) sensor is designed and developed with this in mind, with good reliability and affordability. Results show that the designed sensor can identify E. coli with good selectivity using an impedance and capacitance of 7.69 MHz. At its optimum impedance of 1.3 kHz, the IDμE sensor can reliably quantify E. coli in a range of measurement (10^3.2~10⁶ cfu/mL), linearity (R² = 0.97), sensitivity (18.15 kΩ/log (cfu/mL)), and limit of detection (10^3.2 cfu/mL). In summary, the IDμE sensor developed possesses high potential for industrial and clinical applications.

Keywords: Escherichia coli; biorecognition element free; capacitance; impedance; interdigitated microelectrodes.

Figure 1

The configuration of the IDμE sensor.

Figure 2

SEM images of the IDμE sensor. (a) Top plane, (b) side tomography.

Figure 3

Experimental setup for impedance-capacitance spectrum measurements.

Figure 4

Impedance spectrum of (a) E. coli and (b) Salmonella samples.

Figure 5

Capacitance spectrum of (a) E. coli and (b) Salmonella samples.

Figure 6

Differences in the (a) impedance and (b) capacitance between E. coli and Salmonella samples with NC at the characteristic frequency of 7.69 MHz.

Figure 7

Mean value of the (a) impedance and (b) capacitance measurement data of E. coli, Salmonella, and their NC at the characteristic frequency of 7.69 MHz. Remarks: ** significant at p < 0.001.

Figure 8

The spectrum of the impedance response of the IDμE sensor to various concentrations (10³ to 10⁶ cfu/mL) of E. coli samples. The optimal measurement frequency (1.3 kHz) and a specific measurement frequency range (96.6 Hz–31.1 kHz).

Figure 9

Calibration curves of the impedance magnitude of E. coli samples at different concentrations tested at the optimum frequency of 1.3 kHz. The limit of detection was determined by means of NC − 3 x standard deviation of NC. R² is the coefficient of determination between the sensor’s impedance response and the logarithmic concentration of E. coli.

Figure 10

The “Cole–Cole plot” of the impedance and the fitted curve at 10⁶ cfu/mL of E. coli (a); equivalent Randle’s circuit representing the electrochemical system of the IDμE sensor (b).