In the last 10 years the field of molecular diagnostics has witnessed an explosion of interest in the use of nanomaterials in assays for gases, metal ions, and DNA and protein markers for many diseases. Intense research has been fueled by the need for practical, robust, and highly sensitive and selective detection agents that can address the deficiencies of conventional technologies. Chemists are playing an important role in designing and fabricating new materials for application in diagnostic assays. In certain cases assays based upon nanomaterials have offered significant advantages over conventional diagnostic systems with regard to assay sensitivity, selectivity, and practicality. Some of these new methods have recently been reviewed elsewhere with a focus on the materials themselves or as subclassifications in more generalized overviews of biological applications of nanomaterials.1-7 We intend to review some of the major advances and milestones in the field of detection systems based upon nanomaterials and their roles in biodiagnostic screening for nucleic acids, * To whom correspondence should be addressed. Phone: 847-4913907. Fax: 847-467-5123. E-mail: chadnano@northwestern.edu. Nathaniel L. Rosi earned his B.A. degree at Grinnell College (1999) and his Ph.D. degree from the University of Michigan (2003), where he studied the design, synthesis, and gas storage applications of metal−organic frameworks under the guidance of Professor Omar M. Yaghi. In 2003 he began postdoctoral studies as a member of Professor Mirkin’s group at Northwestern University. His current research focuses on the rational assembly of DNA-modified nanostructures into larger-scale materials.

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Nanostructures in Biodiagnostics

We demonstrate the efficient chemical vapor deposition synthesis of single-walled carbon nanotubes where the activity and lifetime of the catalysts are enhanced by water. Water-stimulated enhanced catalytic activity results in massive growth of superdense and vertically aligned nanotube forests with heights up to 2.5 millimeters that can be easily separated from the catalysts, providing nanotube material with carbon purity above 99.98%. Moreover, patterned, highly organized intrinsic nanotube structures were successfully fabricated. The water-assisted synthesis method addresses many critical problems that currently plague carbon nanotube synthesis.

http://science.sciencemag.org/content/sci/306/5700/1362.full.pdf

Water-Assisted Highly Efficient Synthesis of Impurity-Free Single-Walled Carbon Nanotubes

http://absimage.aps.org/image/MAR05/MWS_MAR05-2004-000692.pdf

Water-Assisted Highly Efficient Synthesis of Impurity-Free Single-Walled Carbon Nanotubes-``Super-Growth''

Conductometric semiconducting metal oxide gas sensors have been widely used and investigated in the detection of gases. Investigations have indicated that the gas sensing process is strongly related to surface reactions, so one of the important parameters of gas sensors, the sensitivity of the metal oxide based materials, will change with the factors influencing the surface reactions, such as chemical components, surface-modification and microstructures of sensing layers, temperature and humidity. In this brief review, attention will be focused on changes of sensitivity of conductometric semiconducting metal oxide gas sensors due to the five factors mentioned above.

Metal oxide gas sensors: Sensitivity and influencing factors

A gas sensor, fabricated by the simple casting of single-walled carbon nanotubes (SWNTs) on an interdigitated electrode (IDE), is presented for gas and organic vapor detection at room temperature. The sensor responses are linear for concentrations of sub ppm to hundreds of ppm with detection limits of 44 ppb for NO2 and 262 ppb for nitrotoluene. The time is on the order of seconds for the detection response and minutes for the recovery. The variation of the sensitivity is less than 6% for all of the tested devices, comparable with commercial metal oxide or polymer microfilm sensors while retaining the room-temperature high sensitivity of the SWNT transistor sensors and manufacturability of the commercial sensors. The extended detection capability from gas to organic vapors is attributed to direct charge transfer on individual semiconducting SWNT conductivity with additional electron hopping effects on intertube conductivity through physically adsorbed molecules between SWNTs.

/pdf/carbon-nanotube-sensors-for-gas-and-organic-vapor-detection-ip2iitcwf8.pdf

Carbon Nanotube Sensors for Gas and Organic Vapor Detection

Room temperature methane detection using palladium loaded single-walled carbon nanotube sensors

CO2 adsorption in single-walled carbon nanotubes

A humidity sensor on cellulose paper is demonstrated using single-walled carbon nanotubes functionalized with carboxylic acid. The conductance shift of the nanotube network entangled on the microfibril cellulose is utilized for the humidity sensing. Compared to the control sensor made on a glass substrate, the cellulose-mediated charge transport on the paper substrate enhances the sensitivity. The sensor response exhibits linear behavior up to a relative humidity of 75% with good repeatability and low hysteresis. A simple circuit model is used to explain the sensor results. This approach is a step toward future paper electronics for low-cost disposable applications.

Jing Li

Papers

Carbon Nanotube Sensors for Gas and Organic Vapor Detection

Room temperature methane detection using palladium loaded single-walled carbon nanotube sensors

CO2 adsorption in single-walled carbon nanotubes

Carbon Nanotube Based Humidity Sensor on Cellulose Paper

Pore structure of raw and purified HiPco single-walled carbon nanotubes