Current Physical Chemistry - Volume 1, Issue 4, 2011

I take great pleasure in offering to the readers of Current Physical Chemistry this special issue on Advanced Materials and Nanotechnology in DNA detection. DNA detection is of considerable importance in view of various applications in, e.g., biomedical and forensic contexts. In current post polymerase chain reaction (PCR) [please specify what this acronym stands for] era, the main focus is on highly selective and sensitive methods for DNA detection. The ideal devices should be portable, easy to use, and disposable. To achieve such goals, new smart materials and procedures must be developed. The papers of this special issue bear state-of-the art accounts of DNA detection, and they were contributed by expert scientists active in laboratories located in Europe, Japan and the US. I wish to thank all the authors for their excellent contributions, as well as the referees for their tremendous effort and for helping the present Guest Editor to select these papers and to improve their final quality.

This article focuses on recent advances and developments of field effect transistor (FET) devices for detecting DNA recognition events such as hybridization, SNP genotyping and primer extension. The unique features of FET biosensors highlight the potential advantages for high-throughput detection of DNA molecules in a label-free manner. In particular, FET devices represent a potential platform for the development of the next-generation DNA sequence instruments based on semiconductor technology. We also review an emerging class of FET devices that use nanomaterials such as silicon nanowires and single-walled carbon nanotubes as a gate channel for the ultrasensitive detection of biological analytes.

This paper reviews reports that have considered temperature as an important parameter in electrochemical DNA detection. Only a couple of years after the electrochemical activity of DNA had been discovered in 1958, oscillopolarography in a thermostated cell was applied to study thermal behavior of DNA double strands. DNA premelting was discovered and denaturation curve analysis established. Later it was found that heated electrodes allow simple and easy control over temperature during accumulation, hybridization, dehybridization, and detection. Electrochemical melting curve analysis has been reported recently as an alternative to the classic UV-spectrophotometric counterpart. Most recent developments include electrochemical real time PCR.

The electroactivity of DNA was discovered in 1958 by Emil Palecek. Since then a great progress and development have been done in electrochemistry of nucleic acids at various electrodes. In this review, after brief overview of milestones in research in electrochemistry, a history of electroanalysis of DNA follows. Then, the attention is paid to various electrochemical methods using a mercury electrode as a working one including linear sweep and cyclic polarography/voltammetry (elimination polarography/voltammetry), differential pulse polarography/voltammetry, square wave polarography/voltammetry, AC polarography/voltammetry and chronopotentiometry for analysis of DNA. Coupling of adsorptive transfer stripping technique to the above-mentioned methods is very promising for nucleic acid studying and is discussed. Further, advantages of mercury and amalgam electrodes are mentioned. The advantages of coupling of DNA electroanalysis at mercury electrodes with paramagnetic particles based isolation of target molecules are shown.

The use of nanomaterials in many life sciences for biological, pharmaceutical, clinical and environmental applications has attracted great attention. Among these nanomaterials, carbon nanotubes (CNTs) are widely used due to their good chemical, mechanical, electrical, optical and thermal properties. CNTs are also superior to other carbon-based materials mainly in special structure features. These advantages make CNTs very popular in electrochemistry for many applications including nanoelectronic devices, composites, chemical sensors and biosensors. Electrochemistry allows rapid, low cost and easy preparation of new electrodes for different purposes. The detection of DNA using electrochemical techniques is in increasing demand for obtaining high sensitivity, selectivity and stability. In this sense, the combination of electrochemistry and CNTs provides great opportunities by promoting electron transfer reactions, increasing surface area, enhancing signals and maintaining biocompatibility. This work summarizes the methodologies used in electrochemical DNA detection based on CNTs. Electrochemical DNA detection using CNT modified electrodes, CNT-polymer modified electrodes, CNT-nanoparticle modified electrodes and their applications are discussed in details. The combination of these technologies for electrochemical DNA detection is also summarized in the work.

Kinetic theory is used to predict the pressure within a sessile droplet containing a suspension of nanometer sized particles. The effect of an applied electric field upon the contact angle is examined. The applied electric field decreases the contact angle of the droplet by lowering the pressure within the droplet. The phenomenon of contact angle saturation is not predicted. It is seen that the pressure reductions required to decrease the contact angle below approximately 30deg grow rapidly. This requires a rapidly increasing electric field. The model assumes that the electric field induces electric dipoles on the nanoparticles. By doing so it decreases their kinetic contribution to the fluid pressure within the droplet. A simple analytical expression for the contact angle as a function of fluid pressure and the applied electric field is derived.

Dimethyl sulfoxide (DMSO) represents a dipolar aprotic solvent which incorporates a strongly polar sulfoxide group and two hydrophobic methyl moieties. Owing to its beneficial properties including low toxicity and environmental compatibility, DMSO has been and still is widely used as a solvent in industry as well as research. Applications can be found in many different areas ranging from medicine and biotechnology to electrochemistry and laser physics. In practical systems, DMSO is usually accompanied by other substances with whom it interacts at molecular scale. These interactions include, for instance, hydrogen bonds and van der Waals forces and determine the microscopic dissolution properties as well as the macroscopic solution behavior. Moreover, such interactions exert influence on the molecular structures of the involved molecules. In turn, this means that analyzing the molecular structure by means of theoretical and experimental approaches can shed light on the nature of interactions and help to achieve better understanding of the phenomena observed. In this article we review the literature reporting DMSO hydrogen bonding interactions with cosolvent molecules. In this context, theoretical as well as experimental studies are considered and compared in order to get a clear picture of this important solvent. Special attention is paid to the DMSO/water system which is well known for exhibiting a strongly nonideal mixing behavior. In addition, mixtures of DMSO with alcohols and other organic solvents are discussed.

Micellization of several monomeric surfactants in water-polar organic solvent mixtures has been investigated by different authors. The gradual replacement of water with other polar solvents allows one to explore the effects of solvent addition on the self-aggregation process in a wide bulk phase composition. For those polar organic solvents which are localized mainly in the bulk phase of the micellar solutions (they do not incorporate into the micellar aggregates), the variations in the cohesive energy density of the binary mixture, upon increasing the organic solvent content, seems to play a key role in the observed Gibbs energy of micellization, ΔG°M, changes. The cohesive energy density can be measured through the Gordon parameter. For a given surfactant, ΔG°M values obtained in several binary water-organic solvent mixtures can be fitted together. This ΔG°M vs. cohesive energy density correlation will permit the prediction of the variations in the Gibbs energy of micellization of monomeric surfactants upon addition of known quantities of a given polar organic solvent.