Jaclyn A. Adkins

Development of a paper-based analytical device for colorimetric detection of select foodborne pathogens.

Foodborne pathogens are a major public health threat and financial burden for the food industry, individuals, and society, with an estimated 76 million cases of food-related illness occurring in the United States alone each year. Three of the most important causative bacterial agents of foodborne diseases are pathogenic strains of Escherichia coli , Salmonella spp., and Listeria monocytogenes , due to the severity and frequency of illness and disproportionally high number of fatalities. Their continued persistence in food has dictated the ongoing need for faster, simpler, and less expensive analytical systems capable of live pathogen detection in complex samples. Culture techniques for detection and identification of foodborne pathogens require 5-7 days to complete. Major improvements to molecular detection techniques have been introduced recently, including polymerase chain reaction (PCR). These methods can be tedious; require complex, expensive instrumentation; necessitate highly trained personnel; and are not easily amenable to routine screening. Here, a paper-based analytical device (μPAD) has been developed for the detection of E. coli O157:H7, Salmonella Typhimurium, and L. monocytogenes in food samples as a screening system. In this work, a paper-based microspot assay was created by use of wax printing on filter paper. Detection is achieved by measuring the color change when an enzyme associated with the pathogen of interest reacts with a chromogenic substrate. When combined with enrichment procedures, the method allows for an enrichment time of 12 h or less and is capable of detecting bacteria in concentrations in inoculated ready-to-eat (RTE) meat as low as 10(1) colony-forming units/cm(2).

Electrochemical paper-based microfluidic devices.

Self‐pumping porous microfluidic devices have attracted significant interest because of their low cost and broad applicability in point‐of‐care and low resource settings. One limitation of many of the devices is sensitivity and selectivity for detection. Electrochemistry can provide a sensitive, selective detection method while still using low cost, portable instrumentation as typified by handheld glucometers. Here, the development of electrochemical paper‐based analytical devices (ePADs) is reviewed. Given the importance of electrode geometry and composition, fabrication methods are reviewed first. This is followed by a review of example applications demonstrated for ePADs. Finally, major accomplishments and future directions are summarized.

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

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 (101 CFU/mL) of pathogenic and nonpathogenic E. coli isolates and (100 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 × 102 and 3.1 × 101 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.