Relationship between Charge Transfer and Charge Recombination Determines Photocurrent Efficiency through DNA Films

Photoresponsive Electrodes Modified with DNA Duplexes Possessing a Porphyrin Dimer

This work describes the formation of a porphyrin (Por) dimer using a DNA duplex as a scaffold and photocurrent generation from electrodes modified with a monolayer of Por-DNA conjugates. The solid-phase click reaction between an azide-porphyrin and oligonucleotide labeled with an ethynyl group on CPG support was utilized to conjugate the Por to the DNA. UV/Vis absorption and circular dichroism (CD) spectral studies revealed that the Por dimer can be formed through DNA hybridization and that through-space electronic interactions, characterized from the exciton-coupled absorption and the bisignate CD, can occur between the two Por molecules. Photoelectrochemical experiments were performed for the electrodes functionalized with a monolayer composed of the Por-DNA conjugates. It was found that the Por dimer on the electrode, which was designed to resemble the special pair in natural photosynthesis, shows efficient photocurrent generation in the presence of electron-acceptor reagents compared with the Por monomer. These findings strongly support the idea that the DNA structures could be useful to construct Por arrays, which is essential for the design of photo- and bio-electronic devices.

Structure and Self-Assembly of Multicolored Naphthalene Diimides Semiconductor

The one-dimensional (1D) self-assembly of [Formula: see text]-electron molecules offers efficient strategies to enhance energy and charge transfer via highly ordered and conductive [Formula: see text] stacking of the chromophores. The chromophore rich nanostructures have great potential to serve as promising candidate materials for optoelectronic devices. However, the design and control of highly ordered nanostructures with multicolored chromophore redox gradients require finely chosen synthetic strategies and a delicate balance of supramolecular interactions. In this paper, we will introduce new strategies focused on self-assembly of nanofibers based on lysine derivatives functionalized with multi colored chromophores.

Sequence-Dependent Photocurrent Generation through Long-Distance Excess-Electron Transfer in DNA

Given its well-ordered continuous π stacking of nucleobases, DNA has been considered as a biomaterial for charge transfer in biosensors. For cathodic photocurrent generation resulting from hole transfer in DNA, sensitivity to DNA structure and base-pair stacking has been confirmed. However, such information has not been provided for anodic photocurrent generation resulting from excess-electron transfer in DNA. In the present study, we measured the anodic photocurrent of a DNA-modified Au electrode. Our results demonstrate long-distance excess-electron transfer in DNA, which is dominated by a hopping mechanism, and the photocurrent generation is sequence dependent.

Photoresponsive DNA monolayer prepared by primer extension reaction on the electrode

We describe a simple and convenient method for the preparation of photoresponsive DNA-modified electrodes using primer extension (PEX) reactions. A naphthalimide derivative was used as the photosensitizer that was attached to the C5-position of 2'-deoxyuridine-5'-triphosphate (dUTP(NI)). It has been found that dUTP(NI) is a good substrate for the PEX reactions using KOD Dash and Vent (exo-) enzymes in solutions to incorporate naphthalimide (NI) moieties into the DNA sequences. On the electrode surface immobilized with the primer/template DNA, the PEX reactions to incorporate dUTP(NI) molecules into the DNA sequence were found to efficiently proceed. With this solid-phase method, the DNA monolayers capable of generating photocurrent due to the photoresponsive NI molecule can be constructed. It was shown that the photocurrent generation was significantly suppressed by a single-nucleotide mismatch included in the primer/template DNA, which is applicable for the design of photoelectrochemical sensors to discriminate single-nucleotide sequences.

Photoelectrochemical bioanalysis: the state of the art

This review provides a panoramic snapshot of the state of the art in the dynamically developing field of photoelectrochemical bioanalysis.

Electron transport in DNA initiated by diaminonaphthalene donors alternatively bound by non-covalent and covalent association

Non-covalent association can identify active donors for study of charge transfer in DNA but may not establish detailed correlations between donor structure and transfer efficiency.

Detection of single-nucleotide variations by monitoring the blinking of fluorescence induced by charge transfer in DNA

Charge transfer dynamics in DNA: Photo-induced charge separation and charge-recombination dynamics in DNA was assessed by monitoring the blinking of fluorescence. Single nucleotide variations, mismatch and one base deletion, were differentiated based on the length of the off-time of the blinking, which corresponds to the lifetime of the charge-separated state.

Solution, surface, and single molecule platforms for the study of DNA-mediated charge transport

The structural core of DNA, a continuous stack of aromatic heterocycles, the base pairs, which extends down the helical axis, gives rise to the fascinating electronic properties of this molecule that is so critical for life. Our laboratory and others have developed diverse experimental platforms to investigate the capacity of DNA to conduct charge, termed DNA-mediated charge transport (DNA CT). Here, we present an overview of DNA CT experiments in solution, on surfaces, and with single molecules that collectively provide a broad and consistent perspective on the essential characteristics of this chemistry. DNA CT can proceed over long molecular distances but is remarkably sensitive to perturbations in base pair stacking. We discuss how this foundation, built with data from diverse platforms, can be used both to inform a mechanistic description of DNA CT and to inspire the next platforms for its study: living organisms and molecular electronics.

Potassium-doped graphene enhanced electrochemiluminescence of SiO(2)@CdS nanocomposites for sensitive detection of TATA-binding protein

Based on the amplified signal from SiO(2)@CdS nanocomposites integrated with K-doped graphene, a new electrochemiluminescence biosensor was developed for the successful detection of transcription factor TATA-binding protein (TBP).

Zipper and layer-by-layer assemblies of artificial photosystems analyzed by combining optical and piezoelectric surface techniques

Quartz crystal microbalance (QCM) and surface plasmon resonance (SPR) were used to study zipper and layer-by-layer multilayer assemblies of artificial photosystems based on naphthalenediimides (NDIs) attached to an oligophenylethynyl (OPE-NDI) or p-oligophenyl (POP-NDI) backbone in dry and wet state. For the most interesting OPE-NDI zipper, one obtains for the dry film a monolayer thickness of 1.85 nm and a density of 1.58 g/cm(3), while the wet film has a larger monolayer thickness of 3.6 nm with a water content of 36%. The dry thickness of a monolayer in OPE-NDI zippers corresponds to about one-half of the length of the OPE scaffold in agreement with the proposed structure of the zipper. The low water content of the OPE-NDI films confirms their compact structure. The dry monolayer thickness of the POP-NDI films of 1.45 nm is smaller than that for the OPE-NDI films, which is probably related to a tilt of the POP scaffolds within the adsorbed layer. The POP-NDI films swell in water much more substantially, suggesting a much more open structure. These features are in excellent agreement with the better photophysical performance of the OPE-NDI assemblies when compared to the POP-NDI films.

Enzymatic synthesis of organic-polymer-grafted DNA

To create bioorganic hybrid materials, interdisciplinary work in the fields of chemistry, biology and materials science is conducted. DNA block copolymers are promising hybrid materials due to the combination of properties intrinsic to both the polymer and the nucleic acid blocks. Until now, the coupling of DNA and organic polymers has been exercised post-synthetically in solution or on solid support. Herein, we report the first enzyme-catalysed synthesis of DNA-organic polymer chimeras. For this purpose, four novel 2'-deoxyuridine triphosphates carrying polymer-like moieties linked to the nucleobase were synthesised. Linear polyethylene glycol monomethyl ethers of different sizes (1) and branched polyamido dendrons with varying terminal groups (2) were chosen as building blocks. We investigated the ability of DNA polymerases to accept the copolymers in comparison to the natural substrate and showed, through primer extensions, polymerase chain reactions and rolling circle amplification, that these building blocks could serve as a surrogate for the natural thymidine. By this method, DNA hybrid materials with high molecular weight, modification density, and defined structure are accessible.

DNA hairpins containing a diaminostilbene derivative as a photoinduced electron donor for probing the effects of single-base mismatches on excess electron transfer in DNA

To investigate the effects of local structural disorder induced by a single-base mismatch on excess electron transfer (EET) in DNA, a novel hairpin DNA containing diaminostilbene (DAS) as a photoinducible electron donor has been developed. It was clearly demonstrated that EET efficiency depends on the electron injection modes from the electron donors and redox properties of the mismatched bases.

Back-electron transfer suppresses the periodic length dependence of DNA-mediated charge transport across adenine tracts

DNA-mediated charge transport (CT) is exquisitely sensitive to the integrity of the bridging pi-stack and is characterized by a shallow distance dependence. These properties are obscured by poor coupling between the donor/acceptor pair and the DNA bridge, or by convolution with other processes. Previously, we found a surprising periodic length dependence for the rate of DNA-mediated CT across adenine tracts monitored by 2-aminopurine fluorescence. Here we report a similar periodicity by monitoring N 2-cyclopropylguanosine decomposition by rhodium and anthraquinone photooxidants. Furthermore, we find that this periodicity is attenuated by consequent back-electron transfer (BET), as observed by direct comparison between sequences that allow and suppress BET. Thus, the periodicity can be controlled by engineering the extent of BET across the bridge. The periodic length dependence is not consistent with a periodicity predicted by molecular wire theory but is consistent with a model where multiples of four to five base pairs form an ideal CT-active length of a bridging adenine domain.

Photocurrent response after enzymatic treatment of DNA duplexes immobilized on gold electrodes: electrochemical discrimination of 5-methylcytosine modification in DNA

We demonstrate a photoelectrochemical approach to the detection of the methylation status of cytosine bases in DNA. We prepared anthraquinone (AQ) photosensitizer-tethered oligodeoxynucleotide (ODN) duplexes bearing 5-methylcytosine (mC) or the corresponding cytosine (C) at a restriction site of the ODN strand immobilized on gold electrodes, and measured their photocurrent responses arising from hole transport after enzymatic digestion. Treatment with HapII or HhaI of the duplexes bearing normal C led to strand cleavage, and the photosensitizer unit was eliminated from the ODN strand immobilized on the gold electrode, exclusively reducing the photocurrent density. With a similar treatment, the duplexes bearing mC showed higher photocurrent responses arising from hole transport through the duplex. This significant difference in the photocurrent response between mC and normal C residues in DNA on the gold electrodes is potentially applicable to the detection of mC modification in DNA.