Fast, accurate detection and identification of viable bacterial pathogens remain challenging in the past decades. Nowadays, bacteriophages have become more popular for bacteria detection due to their low-cost, high stability and specificity. A phage could infect and lyse only viable host bacteria via the specific receptor binding proteins (RBPs) on its tail fibers. However, most of the published works focused on increasing the phage coverage for signal enhancement but ignored the effect of phage orientation. Optimized immobilization protocol had been studied to anchor more effective phages on the chemically functionalized surface under external electric field in terms of key factors like the normalized Debye length and phage concentration. With the optimized immobilization protocol, the...[ Read more ]

Fast, accurate detection and identification of viable bacterial pathogens remain challenging in the past decades. Nowadays, bacteriophages have become more popular for bacteria detection due to their low-cost, high stability and specificity. A phage could infect and lyse only viable host bacteria via the specific receptor binding proteins (RBPs) on its tail fibers. However, most of the published works focused on increasing the phage coverage for signal enhancement but ignored the effect of phage orientation. Optimized immobilization protocol had been studied to anchor more effective phages on the chemically functionalized surface under external electric field in terms of key factors like the normalized Debye length and phage concentration. With the optimized immobilization protocol, the phage-based micro electrochemical sensor showed a wide dynamic range of 1.9×10¹~1.9×10⁸ cfu/mL and low limit of detection (LOD) down to 14±5 cfu/mL via Differential Pulse Voltammetry (DPV), which also had been confirmed to be able to discriminate viable and dead bacteria with high specificity. Electrochemical Impedance Spectroscopy (EIS) had also been employed for the bacteria viability assessment. A specific equivalent circuit model (ECM) had been established representing not only the electric double layer (EDL) but also bacteria cells suspended in the medium. Usually, the membrane capacitance is the dominant factor in determining the cell’s dielectrophoretic response in the frequency range and suspension conductivity. The great difference in the dielectric property of cell membrane detected from experimental results is due to the change of cell permeability when heat-killed, based on which we can determine the cell viability status. If employing the viability detection from conventional fluorescence staining technique as a reference, more direct understanding of the electric property change due to the cell viability status can be achieved.

In addition, Extended-Gate Field-Effect Transistors (EGFETs) were employed for bacteria detection. Generalized transconductance efficiency (g_m/I_d) theory was employed for normalized electronic-electrochemical sensitivity analysis, identifying the optimized FET working regime as well. Due to the discrete structures of EGFET, this sensitivity could also be separated into the electrochemical part that characterizes the interactions occurring on the extended gate and the electronic part that will not be affected by analyte suspensions. The shift of threshold voltage was related to the chemical potential induced by the cell lysis, based on which the LOD can be determined as 16±3 cfu/mL for potentiometric output signals with a wide dynamic detection range as 10²~10⁸ cfu/mL. A portable and low-cost Arduino-based EGFET system for bacteria detection has been successfully demonstrated. With additional system integration with microfluidics and microelectronic circuits, this will be a promising solution for real-time global health monitoring of pathogenic bacteria using advanced nano CMOS technology and heterogeneous packaging technology.