Colorimetric and Electrochemical Bacteria Detection Using Printed Paper- and Transparency-Based Analytic Devices

Abstract

The development of transparency-based electrochemical and paper-based colorimetric analytic detection platforms is presented as complementary methods for food and waterborne bacteria detection from a single assay. Escherichia coli and Enterococcus species, both indicators of fecal contamination, were detected using substrates specific to enzymes produced by each species. β-galactosidase (β-gal) and β-glucuronidase (β-glucur) are both produced by E. coli, while β-glucosidase (β-gluco) is produced by Enterococcus spp. Substrates used produced either p-nitrophenol (PNP), o-nitrophenol (ONP), or p-aminophenol (PAP) as products. Electrochemical detection using stencil-printed carbon electrodes (SPCEs) was found to provide optimal performance on inexpensive and disposable transparency film platforms. Using SPCEs, detection limits for electrochemically active substrates, PNP, ONP, and PAP were determined to be 1.1, 2.8, and 0.5 μM, respectively. A colorimetric paper-based well plate system was developed from a simple cardboard box and smart phone for the detection of PNP and ONP. Colorimetric detection limits were determined to be 81 μM and 119 μM for ONP and PNP respectively. While colorimetric detection methods gave higher detection limits than electrochemical detection, both methods provided similar times to positive bacteria detection. Low concentrations (10 CFU/mL) of pathogenic and nonpathogenic E. coli isolates and (10 CFU/mL) E. faecalis and E. faecium strains were detected within 4 and 8 h of pre-enrichment. Alfalfa sprout and lagoon water samples served as model food and water samples, and while water samples did not test positive, sprout samples did test positive within 4 h of pre-enrichment. Positive detection of inoculated (2.3 × 10 and 3.1 × 10 CFU/mL or g of E. coli and E. faecium, respectively) sprout and water samples tested positive within 4 and 12 h of pre-enrichment, respectively.

Electrochemical Detection of Pathogenic Bacteria—Recent Strategies, Advances and Challenges

“…One of the key advantages of electrochemical sensing technology is its sensitivity and hence detection limits as low as one or very few culture forming units (CFU) have been achieved . However, it has to be questioned if detecting infections at such low bacterial counts will truly be beneficial.…”

“…Paper‐based sensors have several advantages such as biocompatibility, easiness to pattern, flexibility, lightness and low in costs . In recent years, paper‐based electrochemical biosensors have attracted increasing attention for the detection of bacteria . In general, patterning of papers can be achieved by different methods: wax printing, inkjet printing, screen printing, photolithography, stamping and cutting …”

“…successfully detected enzyme activity in inoculated food and water samples containing E. coli and Enterococcus ssp . using stencil‐printed carbon electodes (SPCEs), shown in Figure . The β‐galactosidase and β‐glucuronidase production by E. coli , as well as β‐glucosidase expression by Enterococcus ssp .…”

“…(D) Final device image with 30 μL of solution contained within the central well and connected to potentiostat leads. Reprinted with permission from . Copyright 2017 American Chemical Society.…”

Paper‐Based Resistive Networks for Scalable Skin‐Like Sensing

“…[1][2][3][4][5][6][7][8] For these wired grids, the number of discrete sensing locations scales with the square of the number of wired leads connecting to the edges of the sensing surface. [39][40][41][42] The skin-like sensors in this work demonstrate the use of paper-based substrates for the potential scaling of humanmachine interfaces and liquid-leak detectors to large areas. This electronic layout with only two wired leads-excitation and ground-was capable of detecting human touch and dispensed water at defined spatial locations.…”