Lab-on-a-chip pathogen sensors for food safety

Abstract

There have been a number of cases of foodborne illness among humans that are caused by pathogens such as Escherichia coli O157:H7, Salmonella typhimurium, etc. The current practices to detect such pathogenic agents are cell culturing, immunoassays, or polymerase chain reactions (PCRs). These methods are essentially laboratory-based methods that are not at all real-time and thus unavailable for early-monitoring of such pathogens. They are also very difficult to implement in the field. Lab-on-a-chip biosensors, however, have a strong potential to be used in the field since they can be miniaturized and automated; they are also potentially fast and very sensitive. These lab-on-a-chip biosensors can detect pathogens in farms, packaging/processing facilities, delivery/distribution systems, and at the consumer level. There are still several issues to be resolved before applying these lab-on-a-chip sensors to field applications, including the pre-treatment of a sample, proper storage of reagents, full integration into a battery-powered system, and demonstration of very high sensitivity, which are addressed in this review article. Several different types of lab-on-a-chip biosensors, including immunoassay- and PCR-based, have been developed and tested for detecting foodborne pathogens. Their assay performance, including detection limit and assay time, are also summarized. Finally, the use of optical fibers or optical waveguide is discussed as a means to improve the portability and sensitivity of lab-on-a-chip pathogen sensors.

Keywords: E. coli; Salmonella; bioMEMS; food safety; microfluidics; water safety.

Figure 1.

A lab-on-a-chip contains a network of channels and wells. Reprinted from [12] with permission © Am erican Chemical Society.

Figure 2.

Microfluidic mixers [13]. Pure passive mixer: molecules diffuse to the other side purely by perpendicular diffusion. Pulse mixer: the fluid is supplied with pulse flow, allowing axial (i.e., parallel to the flow) diffusion. Serpentine mixer: allows both perpendicular and axial diffusions.

Figure 3.

Sample/reagent injection and suction in immunoassay lab-on-a-chip devices.

Figure 4.

Lab-on-a-CD.

Figure 5.

Schematic of LFA.

Figure 6.

ELISA lab-on-a-chip.

Figure 7.

SPR lab-on-a-chip.

Figure 8.

Latex immunoagglutination assay—formation of a doublet or bigger clumps through multiple epitope binding. Reprinted from [47] with permission © American Society of Agricultural and Biological Engineers.

Figure 9.

IME (interdigitated microelectrode) immunoassay lab-on-a-chip.

Figure 10.

Left: A short sequence of DNA captures a target, complementary sequence, and a subsequent signal is detected in a manner similar to ELISA. Right: The same is demonstrated in a microfluidic channel in a manner similar to ELISA lab-on-a-chip.

Figure 11.

Continuous-flow PCR on a chip. Reprinted from [80] with permission © American Association for the Advancement of Science.

Figure 12.

PCR demonstrations in digital microfluidics: EWOD (top), SAW (middle), and magnetofluidics (bottom). Reprinted from [89] and [91] with permission © Springer. Reprinted [90] with permission © Royal Society of Chemistry.

Figure 13.

Wire-guided droplet PCR.

Figure 14.

Loop-mediated isothermal amplification (LAMP). Reprinted from [94] with permission © American Society for Microbiology.

Figure 15.

Embedded and proximity optical fibers for lab-on-a-chip. Reprinted from [47] with permission © American Society for Agricultural and Biological Engineers.

Figure 16.

The lab-on-a-chip with optical waveguide channels to irradiate the main microfluidic channel and detect light scattering from it. Silicone oil within the optical waveguide channel acts as a core and the surrounding polydimethyl siloxane (PDMS) lab-on-a-chip acts as a cladding of an optical fiber. Reprinted from [107] with permission © SPIE.