No abstract

We report here on the interaction of the fluorescent dye rhodamine B (RB) with single-walled carbon nanotubes (SWCNTs). We observe that SWCNTs statically quench the fluorescence of RB by forming a stable ground state complex. Careful spectroscopic analysis indicates that the complex formation is efficient mainly with certain chiral forms. We propose three different applications utilizing this quenching mechanism and the associated complexation. Firstly, the quenching efficiency can be utilized as a measure for the characterization and quantification of nanotube dispersions. Secondly, we demonstrate that the specific complexation of RB can be deployed to enrich certain chiral forms in suspension. Finally, we show that RB can be effectively used to visualize nanotubes deposited on substrates.

Large-scale fabrication of graphene-based devices is an aspect of great importance for various applications including chemical and biological sensing. Toward this goal, we present here a novel chemical route for the site-specific realization of devices based on reduced graphene oxide (RGO). Electrodes patterned by photolithography are modified with amino functional groups through electrodeposition. The amine groups function as hooks for the attachment of graphene oxide flakes selectively onto the electrodes. Graphene-like electrical behavior is attained by a subsequent thermal annealing step. We show that this anchoring strategy can be scaled-up to obtain RGO devices at a wafer scale in a facile manner. The scalability of our approach coupled with the use of photolithography is promising for the rapid realization of graphene-based devices. We demonstrate one possible application of the fabricated RGO devices as electrical biosensors through the immunodetection of amyloid beta peptide.

Monolayer graphene field-effect sensors operating in liquid have been widely deployed for detecting a range of analyte species often under equilibrium conditions. Here we report on the real-time detection of the binding kinetics of the essential human enzyme, topoisomerase I interacting with substrate molecules (DNA probes) that are immobilized electrochemically on to monolayer graphene strips. By monitoring the field-effect characteristics of the graphene biosensor in real-time during the enzyme-substrate interactions, we are able to decipher the surface binding constant for the cleavage reaction step of topoisomerase I activity in a label-free manner. Moreover, an appropriate design of the capture probes allows us to distinctly follow the cleavage step of topoisomerase I functioning in real-time down to picomolar concentrations. The presented results are promising for future rapid screening of drugs that are being evaluated for regulating enzyme activity.

We present a novel nonenzymatic carbon nanotube sensor integrated in a microfluidic channel for the detection of sugars. The sensor is assembled as a liquid-gated field-effect transistor, with the transistor channel composed of 1 to 10 nanotubes, which are controllably functionalized with boronic acid receptors. The devices show sensitivity to glucose in a concentration range of 5 to 30 mM. Furthermore, by controlling the type of nanotube-receptor coupling (as covalent or noncovalent) and by deploying a sensitive impedance-based detection technique, we corroborate in detail the transduction mechanism of our affinity-based sensor. In the case of covalent coupling, charge carrier scattering along the nanotubes is the dominant mechanism. While in the noncovalent case, surface charge effects dominate. The identification of the mechanism along with the tunability of the chemical coupling and the cost-effective integration in microchannels constitute a solid basis for the entry of nanotube-based sensors in lab-on-a-chip applications.

Die Haarnadel im Heuhaufen: Mithilfe eines markierungsfreien Chip‐basierten Nachweisverfahrens, das Kohlenstoffnanoröhren nutzt (siehe Bild), gelang es, eine Oligonucleotid‐Zielsequenz ohne den Einsatz von PCR zu detektieren, von der weniger als 2000 Exemplare in einem 30‐μL‐Probentropfen vorhanden waren. Empfindliche, rauscharme Impedanzmessungen zusammen mit Feldeffektdetektion ermöglichten den Nachweis attomolarer Mengen DNA in einer heterogenen Umgebung.

Abstract

Nanostructures appear to be promising for a number of applications in molecular diagnostics, mainly due to the increased surface-to-volume ratio they can offer, the very low limit of detection achievable, and the possibility to fabricate point-of-care diagnostic devices. In this paper, we review examples of the use of nanostructures as diagnostic tools that bring in marked improvements over prevalent classical assays. The focus is laid on the various sensing paradigms that possess the potential or have demonstrated the capability to replace or augment current analytical strategies. We start with a brief introduction of the various types of nanostructures and their physical properties that determine the transduction principle. This is followed by a concise collection of various functionalization protocols used to immobilize biomolecules on the nanostructure surface. The sensing paradigms are discussed in two contexts: the nanostructure acting as a label for detection, or the nanostructure acting as a support upon which the molecular recognition events take place. In order to be successful in the field of molecular diagnostics, it is important that the nanoanalytical tools be evaluated in the appropriate biological environment. The final section of the review compiles such examples, where the nanostructure-based diagnostic tools have been tested on realistic samples such as serum, demonstrating their analytical power even in the presence of complex matrix effects. The ability of nanodiagnostic tools to detect ultralow concentrations of one or more analytes coupled with portability and the use of low sample volumes is expected to have a broad impact in the field of molecular diagnostics.