FARAHI ET AL. VOL. 6 ’ NO. 6 ’ 4548–4556 ’ 2012 www.acsnano.org 4548 May 07, 2012 C 2012 American Chemical Society Critical Issues in Sensor Science To Aid Food and Water Safety R. H. Farahi, † A. Passian, †,‡, * L. Tetard, † and T. Thundat § † Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6123, United States, ‡ Department of Physics, The University of Tennessee, Knoxville, Tennessee 37996-1200, United States, and § Department of Chemical & Materials Engineering, University of Alberta, T6G 2 V4 Edmonton, Canada T he safety of our food and water may arguably hold the greatest socio- economic impact 1 compared to other threats to national and international secur- ity, while at the same time being the most vulnerable. 2 While the complex strategy to manage food and water safety is being debated and defined, it is universally agreed that one critical ingredient is information. Real-time, comprehensive data on the state of our food and water supply will allow shortened times for assessment of damage, comprehension of causal relationships and traceability, determination of actions for remediation, and notification of the affected populations. 3 In order to obtain the infor- mation needed to achieve these objectives, an extensive monitoring system integrated throughout the food chain would be ideal. Yet, how close we are to achieving such a system is unclear. In recent years, the num- bers of papers related to food and water sensors (FWSs) have exploded, covering a vast amalgamation of multidisciplinary tech- nologies. However, shared trends among current FWS development appear to be the capitalization of nanotechnology and emerging nanomaterials. By considering key issues such as the delivery of complex food samples to the sensor with minimal prepara- tion, operation in adverse field conditions, overcoming nonspecific responses, under- standing recognitionÀtransducer communi- cation, and understanding the ramifications of incorporating nanotechnology (Figure 1), we aim to focus on the critical issues com- mon to all types of FWS. Therefore, no effort is made in reviewing the vast numbers of current sensor technologies per se. The Role of Nanotechnology. Nanotechnol- ogy is a common thread in a majority of the new developments in FWS. Predominant nano- materials used in biosensors are nanoparticles (gold, silicon, magnetic composite, polymer), 4 nanowires (gold, polymer, composite), nanoporous surfaces, 5À7 carbon allotropes (notably nanotubes), and quantum dots. 4 Naturally small or downscaled systems with various geometries offer several unique ad- vantages in FWS: (1) high surface-to-volume ratios, which allow greater effective function- alized sensing surface area in a compact form; 6,8À11 (2) high sensitivity due to their small size; 12À14 (3) unique optical and elec- trical properties; 15 (4) fast response due to high elastic (spring) constants; and (5) highly localized detection of entities of comparable size. However, each of these advantages is intertwined with a set of challenges. For example, high sensitivity due to a small transducer surface produces challenges such as significantly reduced probability of interacting with the analyte. * Address correspondence to passianan@ornl.gov. Published online 10.1021/nn204999j ABSTRACT The stability of food and water supplies is widely recognized as a global issue of fundamental importance. Sensor development for food and water safety by nonconventional assays continues to overcome technological challenges. The delicate balance between attaining adequate limits of detection, chemical fingerprinting of the target species, dealing with the complex food matrix, and operating in difficult environments are still the focus of current efforts. While the traditional pursuit of robust recognition methods remains important, emerging engineered nanomaterials and nanotechnology promise better sensor performance but also bring about new challenges. Both advanced receptor-based sensors and emerging non-receptor-based physical sensors are evaluated for their critical challenges toward out-of- laboratory applications. PERSPECTIVE