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.

/pdf/nanostructures-in-biodiagnostics-5553cs9yqw.pdf

Nanostructures in Biodiagnostics

Department of Materials Science, University of Patras, 26504 Rio Patras, Greece, Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, 48 Vass. Constantinou Avenue, 116 35 Athens, Greece, Institut de Biologie Moleculaire et Cellulaire, UPR9021 CNRS, Immunologie et Chimie Therapeutiques, 67084 Strasbourg, France, and Dipartimento di Scienze Farmaceutiche, Universita di Trieste, Piazzale Europa 1, 34127 Trieste, Italy

Chemistry of Carbon Nanotubes

The thermal properties of a suspended metallic single-wall carbon nanotube (SWNT) are extracted from its high-bias (I−V) electrical characteristics over the 300−800 K temperature range, achieved by Joule self-heating. The thermal conductance is approximately 2.4 nW/K, and the thermal conductivity is nearly 3500 Wm-1K-1 at room temperature for a SWNT of length 2.6 μm and diameter 1.7 nm. A subtle decrease in thermal conductivity steeper than 1/T is observed at the upper end of the temperature range, which is attributed to second-order three-phonon scattering between two acoustic modes and one optical mode. We discuss sources of uncertainty and propose a simple analytical model for the SWNT thermal conductivity including length and temperature dependence.

/pdf/thermal-conductance-of-an-individual-single-wall-carbon-38snsfspy6.pdf

Thermal Conductance of an Individual Single-Wall Carbon Nanotube above Room Temperature

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

The important life-supporting role of hydrogen sulfide (H2S) has evolved from bacteria to plants, invertebrates, vertebrates, and finally to mammals. Over the centuries, however, H2S had only been known for its toxicity and environmental hazard. Physiological importance of H2S has been appreciated for about a decade. It started by the discovery of endogenous H2S production in mammalian cells and gained momentum by typifying this gasotransmitter with a variety of physiological functions. The H2S-catalyzing enzymes are differentially expressed in cardiovascular, neuronal, immune, renal, respiratory, gastrointestinal, reproductive, liver, and endocrine systems and affect the functions of these systems through the production of H2S. The physiological functions of H2S are mediated by different molecular targets, such as different ion channels and signaling proteins. Alternations of H2S metabolism lead to an array of pathological disturbances in the form of hypertension, atherosclerosis, heart failure, diabetes...

/pdf/physiological-implications-of-hydrogen-sulfide-a-whiff-xqyg8lj2zr.pdf

Physiological Implications of Hydrogen Sulfide: A Whiff Exploration That Blossomed

Arrays of electrical devices with each comprising multiple single-walled carbon nanotubes (SWNT) bridging metal electrodes are obtained by chemical vapor deposition (CVD) of nanotubes across prefabricated electrode arrays. The ensemble of nanotubes in such a device collectively exhibits large electrical conductance changes under electrostatic gating, owing to the high percentage of semiconducting nanotubes. This leads to the fabrication of large arrays of low-noise electrical nanotube sensors with 100% yield for detecting gas molecules. Polymer functionalization is used to impart high sensitivity and selectivity to the sensors. Polyethyleneimine coating affords n-type nanotube devices capable of detecting NO2 at less than 1 ppb (parts-per-billion) concentrations while being insensitive to NH3. Coating Nafion (a polymeric perfluorinated sulfonic acid ionomer) on nanotubes blocks NO2 and allows for selective sensing of NH3. Multiplex functionalization of a nanotube sensor array is carried out by microspotti...

http://nano.eecs.berkeley.edu/publications/NanoLett_2003_NO2.pdf

Toward Large Arrays of Multiplex Functionalized Carbon Nanotube Sensors for Highly Sensitive and Selective Molecular Detection

Metallic and semiconducting carbon nanotubes generally coexist in as-grown materials We present a gas-phase plasma hydrocarbonation reaction to selectively etch and gasify metallic nanotubes, retaining the semiconducting nanotubes in near-pristine form With this process, 100% of purely semiconducting nanotubes were obtained and connected in parallel for high-current transistors The diameter- and metallicity-dependent "dry" chemical etching approach is scalable and compatible with existing semiconductor processing for future integrated circuits

https://science.sciencemag.org/content/sci/314/5801/974.full.pdf

Selective etching of metallic carbon nanotubes by gas-phase reaction.

Ab initio study of CNT NO2 gas sensor

As the dimensions of electronic devices approach those of molecules, the size, geometry, and chemical composition of the contact electrodes play increasingly dominant roles in device functions. It is shown here that single-walled carbon nanotubes (SWNT) can be used as quasi-one-dimensional (1D) electrodes to construct organic field effect transistors (FET) with molecular scale width (∼2 nm) and channel length (1−3 nm). An important feature owing to the quasi-1D electrode geometry is the favorable gate electrostatics that allows for efficient switching of ultra-short organic channels. This affords room temperature conductance modulation by orders of magnitude for organic transistors that are only several molecules in length, with switching characteristics superior to similar devices with lithographically patterned metal electrodes. With nanotubes, covalent carbon−carbon bonds could be utilized to form contacts to molecular materials. The unique geometrical, physical, and chemical properties of carbon nanot...

/pdf/miniature-organic-transistors-with-carbon-nanotubes-as-quasi-304z3oyvrm.pdf

Miniature Organic Transistors with Carbon Nanotubes as Quasi-One-Dimensional Electrodes

We present a systematic experimental investigation of the reactions between hydrogen plasma and single-walled carbon nanotubes (SWNTs) at various temperatures. Microscopy, infrared (IR) and Raman spectroscopy, and electrical transport measurements are carried out to investigate the properties of SWNTs after hydrogenation. Structural deformations, drastically reduced electrical conductance, and an increased semiconducting nature of SWNTs upon sidewall hydrogenation are observed. These changes are reversible upon thermal annealing at 500 °C via dehydrogenation. Harsh plasma or high temperature reactions lead to etching of nanotubes likely via hydrocarbonation. Smaller SWNTs are markedly less stable against hydrocarbonation than larger tubes. The results are fundamental and may have implications to basic and practical applications including hydrogen storage, sensing, band gap engineering for novel electronics, and new methods of manipulation, functionalization, and etching of nanotubes.

Pengfei Qi

Papers

Toward Large Arrays of Multiplex Functionalized Carbon Nanotube Sensors for Highly Sensitive and Selective Molecular Detection

Selective etching of metallic carbon nanotubes by gas-phase reaction.

Ab initio study of CNT NO2 gas sensor

Miniature Organic Transistors with Carbon Nanotubes as Quasi-One-Dimensional Electrodes

Hydrogenation and Hydrocarbonation and Etching of Single-Walled Carbon Nanotubes