Single-walled carbon nanotubes-polymer modified graphite electrodes for DNA hybridization

Label-free rapid electrochemical detection of DNA hybridization using ultrasensitive standalone CNT aerogel biosensor

We report the development of an ultrasensitive label-free DNA biosensor device with fully integrated standalone carbon nanotube (CNT) aerogel electrode. The multi-directional tenuous network of clustered CNT embedding into the CNT aerogel electrode demonstrates linear ohmic and near isotropic electrical properties, thereby providing high sensitivity for nucleic acid detection. Using this device, the target DNA hybridization is detected by a quantifiable change in the electrochemical impedance, with a distinct response to the single-stranded probe alone or double-stranded target-probe complex. The target DNA is specifically detected with limit of detection (LoD) of 1 pM with a turnaround time of less than 20 min, which is unprecedented for a miniaturized CNT aerogel sensor and impedance spectroscopy without an intermediate DNA amplification step. Moreover, this system is able to differentiate between the closely related target sequences by the distinct impedance response rendering it highly specific. To the best of our knowledge, this is the first report showing the use of standalone bare CNT aerogel electrode without any substrate support, coupled with electrochemical impedance spectroscopy, for the detection of DNA hybridization. Altogether, the results show that our system is fast, sensitive and specific for label-free rapid direct DNA detection, promising a novel avenue for bio-sensing.

Poly-L-lysine Coated Surfaces for Ultrasensitive Nucleic Acid Detection

Poly-L-lysine is one of the biocompatible polymers having amino and carboxyl groups in its structure. This attractive feature of poly-L-lysine makes it very convenient for bioactive molecule attachment. This study details the preparation of poly-L-lysine-based pencil graphite electrodes (PLL/PGEs) and use of the coated electrodes for direct ultrasensitive DNA hybridization detection. In the first part of this study, poly-L-lysine coated electrodes were prepared using L-lysine as the monomer by cyclic voltammetry (CV) with different cyclic scans. The effect of these cyclic scans during the electropolymerization was investigated. Coated electrodes were characterized by cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). Then, one-pot preparation of poly-L-lysine composites with graphene (GN) and multi-walled carbon nanotubes (MWCNTs) onto the pencil graphite electrodes were achieved. Electrochemical responses of these 3 electrodes were compared. After all, electrochemical DNA hybridization was performed using the poly-L-lysine-based electrodes prepared at optimum polymerization condition. The PLL/PGE coated electrode presented a good linear response in the target concentration range of 1.0×10-13 to 1.0×10-6 with a detection limit of 2.25×10-14 using differential pulse voltammetry as the detection method. We believe that poly-L-lysine-based surfaces will be useful for further clinical applications.

Scanning Techniques for Nanobioconjugates of Carbon Nanotubes

Nanobioconjugates using carbon nanotubes (CNTs) are attractive and promising hybrid materials. Various biological applications using the CNT nanobioconjugates, for example, drug delivery systems and nanobiosensors, have been proposed by many authors. Scanning techniques such as scanning electron microscopy (SEM) and scanning probe microscopy (SPM) have advantages to characterize the CNT nanobioconjugates under various conditions, for example, isolated conjugates, conjugates in thin films, and conjugates in living cells. In this review article, almost 300 papers are categorized based on types of CNT applications, and various scanning data are introduced to illuminate merits of scanning techniques.

Pharmacogenomic study using bio- and nanobioelectrochemistry: Drug-DNA interaction

Small molecules that bind genomic DNA have proven that they can be effective anticancer, antibiotic and antiviral therapeutic agents that affect the well-being of millions of people worldwide. Drug-DNA interaction affects DNA replication and division; causes strand breaks, and mutations. Therefore, the investigation of drug-DNA interaction is needed to understand the mechanism of drug action as well as in designing DNA-targeted drugs. On the other hand, the interaction between DNA and drugs can cause chemical and conformational modifications and, thus, variation of the electrochemical properties of nucleobases. For this purpose, electrochemical methods/biosensors can be used toward detection of drug-DNA interactions. The present paper reviews the drug-DNA interactions, their types and applications of electrochemical techniques used to study interactions between DNA and drugs or small ligand molecules that are potentially of pharmaceutical interest. The results are used to determine drug binding sites and sequence preference, as well as conformational changes due to drug-DNA interactions. Also, the intention of this review is to give an overview of the present state of the drug-DNA interaction cognition. The applications of electrochemical techniques for investigation of drug-DNA interaction were reviewed and we have discussed the type of qualitative or quantitative information that can be obtained from the use of each technique.

Selective binding of single-stranded DNA-binding proteins onto DNA molecules adsorbed on single-walled carbon nanotubes

Single-stranded DNA-binding (SSB) proteins were treated with hybrids of DNA and single-walled carbon nanotubes (SWNTs) to examine the biological function of the DNA molecules adsorbed on the SWNT surface. When single-stranded DNA (ssDNA) was used for the hybridization, significant binding of the SSB molecules to the ssDNA-SWNT hybrids was observed by using atomic force microscopy (AFM) and agarose gel electrophoresis. When double-stranded DNA (dsDNA) was used, the SSB molecules did not bind to the dsDNA-SWNT hybrids in most of the conditions that we evaluated. A specifically modified electrophoresis procedure was used to monitor the locations of the DNA, SSB, and SWNT molecules. Our results clearly showed that ssDNA/dsDNA molecules on the SWNT surfaces retained their single-stranded/double-stranded structures.

Surface morphology of hybrids of double-stranded DNA and single-walled carbon nanotubes studied by atomic force microscopy

We examined the formation of hybrids of double-stranded DNA (dsDNA) and single-walled carbon nanotubes (SWNTs), which has not been well investigated yet. In particular, the adsorption of dsDNA onto SWNT produced by chemical vapor deposition (CVD) was examined for the first time. When small amount of dsDNA was mixed with CVD SWNT, well dispersed hybrids with smooth surfaces were observed by atomic force microscopy (AFM). Through a comparison of dsDNA, single-stranded DNA (ssDNA), CVD SWNT, and high-pressure carbon monoxide process (HiPco) SWNT, we found that the surface morphology of the hybrids was independent of the DNA type. Even when sonicated salmon testes DNA, which has a random sequence and length, was employed, smooth surfaces were obtained on the dsDNA-CVD hybrids as well as on the ssDNA-CVD hybrids. The ratio of monodispersed SWNT and bundled SWNT in a dispersion solution was also not affected by the DNA type. In contrast, the quantity of the fabricated hybrids was affected by the types of DNA especially when HiPco SWNT was used. Our results indicated that characteristic features of the dsDNA-CVD hybrids and provide an enhanced understanding of the adsorption mechanism of dsDNA onto SWNTs.