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

Sensitive optical biosensors for unlabeled targets: a review.

From diagnosis of life-threatening diseases to detection of biological agents in warfare or terrorist attacks, biosensors are becoming a critical part of modern life. Many recent biosensors have incorporated carbon nanotubes as sensing elements, while a growing body of work has begun to do the same with the emergent nanomaterial graphene, which is effectively an unrolled nanotube. With this widespread use of carbon nanomaterials in biosensors, it is timely to assess how this trend is contributing to the science and applications of biosensors. This Review explores these issues by presenting the latest advances in electrochemical, electrical, and optical biosensors that use carbon nanotubes and graphene, and critically compares the performance of the two carbon allotropes in this application. Ultimately, carbon nanomaterials, although still to meet key challenges in fabrication and handling, have a bright future as biosensors.

Carbon Nanomaterials in Biosensors: Should You Use Nanotubes or Graphene?

Nanostructuring electrodes with carbon nanotubes: A review on electrochemistry and applications for sensing

Creating functional electrical circuits using individual or ensemble molecules, often termed as “molecular-scale electronics”, not only meets the increasing technical demands of the miniaturization of traditional Si-based electronic devices, but also provides an ideal window of exploring the intrinsic properties of materials at the molecular level. This Review covers the major advances with the most general applicability and emphasizes new insights into the development of efficient platform methodologies for building reliable molecular electronic devices with desired functionalities through the combination of programmed bottom-up self-assembly and sophisticated top-down device fabrication. First, we summarize a number of different approaches of forming molecular-scale junctions and discuss various experimental techniques for examining these nanoscale circuits in details. We then give a full introduction of characterization techniques and theoretical simulations for molecular electronics. Third, we highlig...

Molecular-Scale Electronics: From Concept to Function

To date, surface plasmon resonance (SPR) spectroscopy identifies molecules via specific bindings with their ligands immobilized on a surface. We demonstrate here that a high-resolution multiwavelength SPR technique can measure the electronic states of the molecules and thus allow direct identification of the molecules. Using this new capability, we have studied the electronic and conformational differences between the oxidized and reduced states of cytochrome c immobilized on a modified gold electrode. When the wavelength of the incident light is far away from the optical absorption bands of the protein, a ∼0.008° decrease in the resonance angle, due to a conformational change, occurs as the protein is switched from the oxidized to reduced states. When the wavelength is tuned to the absorption bands, the resonance angle oscillates at the wavelengths of the absorption peaks, which provides electronic signatures of the protein.

High-resolution multiwavelength surface plasmon resonance spectroscopy for probing conformational and electronic changes in redox proteins.

In situ detection of cytochrome c adsorption with single walled carbon nanotube device

A method for detecting surface plasmon resonance with high resolution (∼10−5 degrees or ∼10−8 refractive index units) and fast response time (1 μs) is described. In the method, light is focused through a prism onto a metal film on which molecules to be detected are adsorbed. The total internal reflection of the incident light is collected with a bicell photodetector instead of a single cell or an array of photodetectors that are widely used in previous works. The ratio of the differential signal to the sum signal of the bicell photodetector provides an accurate measurement of shift in surface plasmon resonance angle caused by the adsorption of molecules onto the metal films or by conformational changes in the adsorbed molecules. Using the method, we have studied subtle conformational changes in redox protein, cytochrome c, due to an electron transfer reaction.

High resolution surface plasmon resonance spectroscopy

We describe a method to fabricate atomic-scale gaps and contacts between two metal electrodes. The method uses a directional electrodeposition process and has a built-in self-termination mechanism. The final gap width and contact size are preset by an external resistor (Rext) that is connected in series to one of the electrodes. If 1/Rext is chosen to be much smaller than the conductance quantum (G0=2e2/h), a small gap with conductance determined by electron tunneling is formed. If 1/Rext is comparable or greater than G0, a contact with conductance near a multiple of G0 is fabricated.

Atom-size gaps and contacts between electrodes fabricated with a self-terminated electrochemical method

We have studied myoglobin (Mb) on graphite basal plane and on self-assembled didodecyldi- methylammonium bromide (DDAB) mono- and multilayers with in situ tapping-mode AFM, cyclic voltammetry, and differential capacitance measurements. On graphite, Mb molecules adsorb and aggregate into chainlike features. The aggregation indicates an attractive interaction between the adsorbed molecules. In contrast, the molecules are randomly distributed on the DDAB layers. The adsorption on DDAB changes drastically the domains and defects in the DDAB layers due to a strong Mb-DDAB interaction. On both the bare and the DDAB-coated electrodes, the protein undergoes a fast electron-transfer reaction involving Fe 3+ + 1e - T Fe 2+ in the heme group. The structure of the DDAB film is potential dependent. At low potentials, the film is in a solidlike phase. When the potential is raised to 0 V, the film transforms into a liquidlike phase via a first- order phase transition. The liquidlike phase may be responsible for the fast diffusion of Mb through the DDAB layers.

Salah Boussaad

Papers

High-resolution multiwavelength surface plasmon resonance spectroscopy for probing conformational and electronic changes in redox proteins.

In situ detection of cytochrome c adsorption with single walled carbon nanotube device

High resolution surface plasmon resonance spectroscopy

Atom-size gaps and contacts between electrodes fabricated with a self-terminated electrochemical method

Electron Transfer and Adsorption of Myoglobin on Self-Assembled Surfactant Films: An Electrochemical Tapping-Mode AFM Study