The development of paper-based microfluidic devices for environmental and food quality analysis

Abstract

Providing safe and nutritious food and water, both domestically and internationally, has long been a goal for improving global health. Recent legislations enacted within the United States have enabled government agencies to further regulate agricultural and industry standards, necessitating the need for more preventative approaches with regards to food and beverage quality and safety. Increasing detection speed and enabling field and production detection of point-source contamination are crucial to maintaining food and beverage safety as well as preventing detrimental disease outbreaks, such as those caused by bacterial contamination. The development of simple, inexpensive, and portable methods for detecting contamination indicators are key to reaching this goal. Moreover, recent developments into microfluidic approaches for analysis have shown great promise as platforms for providing faster simplified methods for detection. The work conducted within this dissertation focuses on the development of simple, inexpensive and disposable platforms for colorimetric and electrochemical analysis of food and beverage quality. Aside from more commonly studied polymer-based devices, recent advances in paper-based diagnostics have demonstrated use as an analytical platform capable of self-pumping, reagent storage, mixing, and implementation of various detection motifs. Herein, the development of microfluidic paper-based analytical devices (μPADs) is presented as a platform for the colorimetric detection of bacteria in food and water samples. Initial work was conducted for the paper-based, colorimetric detection of Listeria monocytogenes, Salmonella Typhimurium, and E. coli O157:H7 bacteria species, all of which have been associated with fatal, multistate food- and waterborne outbreaks. Detection was performed on ready-to-eat meats using a swabbing technique to collect and quickly culture surface contamination of bacteria using enzymatic assays within paper-based microwells. A scanner was used for imaging followed by use of image analysis software for semi-quantitative measurement determination. This method was further applied to the detection of bacteria in irrigation water, a known source of foodborne contamination, using a 3D-printed filter for collection and culture of bacteria present in low concentrations within water. Although colorimetric detection offers a simple, visual detection method, electrochemistry is an alternative, sensitive and portable method for detection. Use of common office materials such as transparency film and copy paper, as well as laboratory filter papers were studied and developed for optimal electrochemical platform performance. The use of microwires as a simple fabrication method for incorporating metallic or modified metallic electrodes into electrochemical paper-based devices (ePADs) was also developed. Electrochemical behavior in both well-based and flow-based ePADs was studied and implemented for the nonenzymatic detection of sugars in beverages using copper oxide modified microwires, and for the in-line flow detection of enzymatic assays using gold and platinum microwire electrodes respectively. Furthermore, the fast, inexpensive, and simple fabrication of carbon stencil-printed electrodes (CSPEs) on transparency film were demonstrated for the electrochemical detection of E. coli and Enterococci bacteria species, both indicators of fecal contamination, in food and water samples using enzymatic assays. These same assays could also be determined colorimetrically and a more portable cell phone was used to image and wirelessly send paper-based well-plate results. This method was developed for use in place of a more bulky and expensive plate reader, and results were used for comparison to electrochemical detection of bacteria from a single assay.