A microfluidic impedance biosensor based on immunomagnetic separation and urease catalysis for continuous-flow detection of E. coli O157:H7

Electrochemical Immuno- and Aptamer-Based Assays for Bacteria: Pros and Cons over Traditional Detection Schemes

“…Requirements for a higher stability, simplicity and lower cost of e-immunoassays triggers application of low-cost redox inactive hydrolases as enzymatic labels in e-ELISA: lipase [ 138 ], urease [ 89 ] and cellulase [ 139 ] can also be effectively used in bacterial RNA and protein e-ELISA [ 9 , 140 , 141 ]. With hydrolase labels, products of hydrolysis of their substrates are electrochemically detected: bio-transformation of urea to ammonium carbonate increases the impedance of the system, while cellulase digestion of nitrocellulose films formed on graphite electrodes increases their electronic conductivity ( Figure 2 F).…”

“…Such assays by itself rely not on the reactivity of the electrode, but rather on the enzymatic label reactivity with their substrates. That allowed highly sensitive and specific detection of 12 CFU mL −1 of E. coli in the buffer solution and in milk, in 2 h [ 89 ], and down to 1 CFU mL −1 of E. coli in tap water (2 CFU mL −1 of E. coli in milk) within 3 h, by assembling a hybrid aptamer ( E. coli )Ab sandwich on MBs [ 90 ]. 100 CFU mL −1 of Salmonella enteretidis , Enterobacter agglomerans, Pseudomonas putida , Staphylococcus aureus and Bacillus subtilis did not interfere with the single E. coli detection when Ab was used as a capture element [ 90 ].…”

“…Both assays did not require any sample pre-treatment (e.g., cell pre-enrichment), are electrochemically label-free (no redox indicator/mediator was used), and are cost-effective due to the low cost of urease ($0.5 per mg) and cellulase (from $0.002 to $0.2 per mg) and their high storage stability. The urease assay could be well-integrated within the microfluidic format [ 89 ]. Both assays are general and can be adapted for specific detection of any other bacterial species once the corresponding Ab and aptamers are used.…”

“…Impedimetric, label-free 40 min e-immunoassaying of 7 CFU mL −1 [ 152 ] and 20 min e-ELISA of 50 CFU mL −1 of E. coli [ 98 ] in microfluidic devices are promising examples of the devices for real worlds sample analysis. The same refers to the urease-linked e-ELISA on MBs (12 CFU mL −1 2 h) [ 89 ] and cellulase-linked e-ELISA on MBs (1 CFU mL −1 in 3 h) [ 90 ]. Both can be adapted to microfludics and electrochemical LFI, whose electrochemical adaptations are still scarce.…”

Microfluidic based impedance biosensor for pathogens detection in food products

“…Electrospun detection technique combined magnetic separation technique, capillary immunoassay, and direct electrical measurement for rapid and accurate sensing of the E. coli O157:H7 cells, the electrospun biosensor device has a linear detection for E. coli O157:H7 concentration of 10 1 to 10 4 CFU/mL with a low concentration of 67 CFU/mL . The impedimetric biosensor approach was implemented and studied (See Table ) by measuring the change in the impedance of the electrodes which indicates the presence or absence of the pathogen cells. These pathogen cells bind to the receptors such as antibodies that are immobilized on the interdigitated electrode arrays (IDEAs).…”