IEEE SENSORS JOURNAL, VOL. 8, NO. 6, JUNE 2008 693 Miniaturized Sensor for Microbial Pathogens DNA and Chemical Toxins Gopala Krishna Darbha, Eumin Lee, Yolanda R Anderson, Preston Fowler, Kanieshia Mitchell, and Paresh Chandra Ray Abstract—A miniaturized, inexpensive and battery operated ultra-sensitive nanomaterial-based fluorescence resonance energy transfer (NSET) probe has been developed and evaluated for screening microbial pathogens DNA and chemical toxins at high sensitivity and selectivity. This paper illustrates application of the NSET portable device to detect microbial pathogens, e.g., Campylobacter, C. perfringens, and S. aureus DNA based on quenching of the NSET signal by gold nanoparticles to detect single base-mismatch DNA with high sensitivity (600 fM). Pres- ence of the fluorescence signal indicates that the target DNA has been detected. We also report that the NSET probe is capable of screening chemical toxins like mercury from contaminated water with excellent sensitivity (2 parts-per-trillion) and selectivity for Hg over competing analytes. Index Terms—DNA, fluorescence resonance energy transfer, gold nanoparticles, mercury. I. INTRODUCTION I NDUSTRIAL CHEMICAL TOXINS and biological toxins like warfare agents pose a major threat to the life of people who work in such environments, as well as soldiers in the bat- tlefield [1]–[5]. Detection of biological toxins is an extremely challenging technical problem of great societal importance. Very small concentrations of a biological toxin introduced into a city’s water supply could be a serious health threat because of the toxin’s potency. Biological toxin could kill more people than a nuclear or chemical attack. For example, 10 grams of weaponized anthrax spores could result in the deaths of as many people as an attack using a ton of the nerve agent sarin. Many local and state authorities are inadequately prepared to deal with biological-based incidents, and first responders to such incidents will face considerable risk. In addition, since public Manuscript received August 14, 2007; revised January 8, 2008; accepted Jan- uary 15, 2008. This work was supported in part by the U.S. NSF-PREM under Grant DMR-0611539, in part by NSF-CRIFMU under Grant 0443547, and and in part by ARO under Grant W911NF-06-1-0512. We thank for their generous funding. The associate editor coordinating the review of this paper and ap- proving it for publication was Dr. Janet Jensen. G. K. Darbha is with Jackson State University, Jackson, MS 39218 USA (e-mail: gkdarbha80@yahoo.com). E. Lee is with Clinton High School, Clinton, MS 39056 USA. Y. R. Anderson is with the Department of Chemistry, Jackson Public School, Jackson, MS 39213 USA (e-mail: yanderson@jackson.k12.ms.us). P. Fowler is with Jim Hill High School, Jackson, MS 39204 USA (e-mail: perry2018@aol.com). K. Mitchell is with Tougloo College, Tougloo, MS 39174 USA (e-mail: kanieshia@netscape.com). P. C. Ray is with the Department of Chemistry, Jackson State University, Jackson, MS 39217 USA (e-mail: paresh.c.ray@jsums.edu). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JSEN.2008.922727 health personnel rarely encounter any of the 30 or so pathogens on various agency threat lists, the ability to rapidly identify their infection is waning. Mercury is a known neurotoxin and for this reason it has been targeted by the Environmental Pro- tection Agency (EPA) [6] as a primary toxic exposure threat. The National Research Council cites prenatal exposure effects ranging from mental retardation and cerebral palsy to deafness and blindness. In the past, mercury has been used as a chemical toxin in several incidents [7], e.g., Europeans in at least three countries became ill from eating Israeli citrus products—or- anges, lemons, and grapefruit, that had been contaminated with mercury, which presumably had been injected under the skins of the citrus products with a syringe. A group identifying itself as the Arab Revolutionary Army Palestinian Commandos, in a letter to the Dutch government, announced that its goal was “to sabotage the Israeli economy.” Concerns over biological and chemical toxins and security of environmental system have accelerated the implementation of sensor technology as a major part of toxin identification. Possibility of miniaturization and ability to work with the complex samples (food and environ- mental matrices) are the major requirements for sensors. In this paper, we report a highly sensitive nanomaterial-based fluores- cence resonance energy transfer (NSET) [8]–[22] probe which is capable of detecting both microbial pathogens DNA and chemical toxins in the environment. The material for such an application needs to be robust, highly selective, and reactive to the agent of concern so as to detect its presence and neutralize its effect, thereby demanding high specificity. Conventional analytical methods [23]–[25] used to detect biological and chemical toxins, such as high-performance liquid chromatography, gas chromatography, and mass spec- troscopy, require expensive equipments that may be difficult to field-deploy. Although still in its infancy, the application of surface-functionalized nanomaterials such as nanoparticles in sequence recognition schemes has shown [8]–[22], [26]–[36] great promise in achieving high sensitivity and specificity, which are difficult to achieve by conventional methods. Nanotech- nology is an emerging field that has great potential for use in commercial, defense, and security applications. The novel prop- erties of nanostructured materials make nanostructures excellent components for sensing. Interfaces between nanostructures and biomaterials are also critical to chemical and biological defense. There have been many recent efforts for the development of fluorescence assays for toxin detection [38]–[40]. These assays are based on FRET [42] or non-FRET quenching mechanisms. FRET [42] is a spectroscopic technique for measuring distances in the 30–80 range. Excitation energy of the donor is trans- ferred to the acceptor via an induced-dipole, induced-dipole 1530-437X/$25.00 © 2008 IEEE