Nanomaterial Enabled Biosensors for Pathogen Monitoring - A Review PETER J. VIKESLAND* AND KRISTA R. WIGGINTON Department of Civil and Environmental Engineering and Institute of Critical Technology and Applied Science (ICTAS), Virginia Polytechnic Institute and State University, 418 Durham Hall, Blacksburg, Virginia 24060-0246 Received December 7, 2009. Revised manuscript received March 27, 2010. Accepted March 30, 2010. One promising, but currently underexplored, area for the future of drinking water pathogen monitoring stems from the development of nanomaterial-enabled detection strategies. The nanoscience literature contains numerous reports of nanoe- nabled biosensors; however, to date only a small percentage have focused on the detection of whole cells, in general, and waterborne pathogens, in particular. There are significant opportunities for the use of nanoenabled biosensors for environmental monitoring, and this review is intended to both illustrate the state of this field and to spur additional research in this area. Introduction Despite advanced water treatment processes and stringent regulations, outbreaks of waterborne disease regularly occur in the U.S. and other highly developed countries. In the U.S. alone, it is estimated that $20 billion per year of economic productivity is lost due to illnesses caused by waterborne pathogens (1). A recent comprehensive study (2) showed that the agents responsible for outbreaks across the world ranged from protozoa (Cryptosporidium, Giardia, Toxo- plasma) to bacteria (pathogenic Escherichia coli, Salmonella, Shigella) and viruses (norovirus, rotavirus, hepatitis). Given the biological diversity of these and other disease agents it is a continual challenge to prevent waterborne disease outbreaks. Nonetheless, to adequately protect public health this challenge must be met. Existing methods for detection of waterborne pathogens are highly diverse with the range of techniques having a breadth comparable to that of the organisms they are designed to detect. Faster, simpler, and more reliable pathogen detection methods would greatly assist drinking water treatment utilities and policy makers and would help protect consumers. Bioterrorist threats, global population growth, and increased stresses on our freshwater resources due to global climate change only exacerbate the need for improved drinking water pathogen monitoring. To address these concerns, there have been a number of recent reports of improved methods for detection of bacterial, protozoan, and viral pathogens that have included immunological (3-5), molecular (6-10), and culture-based protocols (11). The expectation is that future methods should be capable of detecting numerous species/classes of organisms simulta- neously, will discern viable from nonviable organisms, and will be capable of incorporation into a real-time, in-line monitoring system. One promising, but currently underdeveloped, area for the future of drinking water pathogen monitoring stems from the recent development of nanomaterial-enabled detection strategies. The nanoscience literature is rife with reports of nanoenabled biosensors; however, the historical emphasis of work in this area has been on the detection of biomolecules for biomedical purposes and not on whole cell detection. As documented herein, however, considerable gains have also been made in the development of whole cell nanoenabled biosensors. We believe that there are significant opportunities to use nanoenabled biosensors for environmental monitor- ing, and this review is intended to both illustrate the state of this field and to spur additional research in this area. We note that because the biosensor field is broad, we have limited our discussion to whole cell and virus biosensors and only refer to biomolecule sensors that have applicability to whole cell monitoring. Numerous review articles discuss nanoma- terial based biosensors for the detection of soluble toxins and other biomolecules (12, 13). Nanomaterial Enabled Biosensors To detect the low concentrations of pathogens typically found in treated and untreated drinking water, a biosensor must have both sufficient specificity and sensitivity to pick the proverbial needle out of a haystack. For a biosensor to achieve these goals, samples are concentrated and cleaned of extraneous debris via filtration or other separation processes. We note that an entire review article focusing explicitly on methodologies for sample concentration and clean up could be written; however, our focus here is solely on nanomaterial- enabled detection strategies. Following clean up and con- centration, biosensor specificity is incorporated through the use of recognition elements that recognize antigens or other epitopes on the exterior of a pathogen. Sensitivity is achieved via signal transduction modalities that explicitly detect the interaction between the pathogen and the recognition element. In a nanomaterial-enabled biosensor, the recogni- tion element is typically bound to the surface of the nanomaterial, and the interaction of this conjugate with a pathogen is monitored via a signal transduction mechanism (Figure 1). A variety of nanomaterials are currently used in biosensor applications, and the nanomaterial used has ramifications for both the type of recognition element employed as well as the signal transduction method utilized. Regardless of what combination recognition element/ nanomaterial/signal transduction mechanism is employed, an ideal biosensor should be able to 1) discriminate between closely related pathogenic and nonpathogenic organisms; 2) detect small quantities of a target within a complicated * Corresponding author e-mail address: pvikes@vt.edu. Environ. Sci. Technol. 2010, 44, 3656–3669 3656 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 44, NO. 10, 2010 10.1021/es903704z  2010 American Chemical Society Published on Web 04/20/2010