Intracellular recording of action potentials is important to understand electrically-excitable cells. Recently, vertical nanoelectrodes have been developed to achieve highly sensitive, minimally invasive, and large scale intracellular recording. It has been demonstrated that the vertical geometry is crucial for the enhanced signal detection. Here we develop nanoelectrodes made up of nanotubes of iridium oxide. When cardiomyocytes are cultured upon those nanotubes, the cell membrane not only wraps around the vertical tubes but also protrudes deep into the hollow center. We show that this geometry enhances cell-electrode coupling and results in measuring much larger intracellular action potentials. The nanotube electrodes afford much longer intracellular access and are minimally invasive, making it possible to achieve stable recording up to an hour in a single session and more than 8 days of consecutive daily recording. This study suggests that the electrode performance can be significantly improved by optimizing the electrode geometry.

Interest in using DNA as a building block for nanoelectronic sensors and devices stems from its efficient hole-conducting properties and the relative ease with which it can be organized into predictable nanometre-sized two- and three-dimensional structures. However, because a hole migrates along DNA through the highest occupied molecular orbital of the guanine bases, its conductivity decreases as the adenine-thymine base-pair content increases. This means that there are limitations on what sequences can be used to construct functional nanoelectronic circuits, particularly those rich in adenine-thymine pairs. Here we show that the charge-transfer efficiency can be dramatically increased in a manner independent of guanine-cytosine content by adjusting the highest occupied molecular orbital level of the adenine-thymine base pair to be closer to that of the guanine-cytosine pair. This is achieved by substituting the N7 nitrogen atom of adenine with a C-H group to give 7-deazaadenine, which does not disturb the complementary base pairing observed in DNA.

Retrograde trophic signaling of the nerve growth factor (NGF) supports neuronal survival and differentiation. Dysregulated trophic signaling could lead to various neurological disorders. Charcot-Marie-Tooth type 2B (CMT2B) is one of the most common inherited peripheral neuropathies characterized by severe terminal axonal loss. Genetic analysis of human CMT2B patients has revealed four missense point mutations in Rab7, a small GTPase that regulates late endosomal/lysosomal pathways, but the exact pathological mechanism remains poorly understood. Here, we show that these Rab7 mutants dysregulated axonal transport and diminished the retrograde signaling of nerve growth factor (NGF) and its TrkA receptor. We found that all CMT2B Rab7 mutants were transported significantly faster than Rab7wt in the anterograde direction, accompanied with an increased percentile of anterograde Rab7-vesicles. In PC12M cells, the CMT2B Rab7 mutants drastically reduced the level of surface TrkA and NGF binding, presumably by premature degradation of TrkA. On the other hand, siRNA knock-down of endogenous Rab7 led to the appearance of large TrkA puncta in enlarged Rab5-early endosomes within the cytoplasm, suggesting delayed TrkA degradation. We also show that CMT2B Rab7 mutants markedly impaired NGF-induced Erk1/2 activation and differentiation in PC12M cells. Further analysis revealed that CMT2B Rab7 mutants caused axonal degeneration in rat E15.5 DRG neurons. We propose that Rab7 mutants induce premature degradation of retrograde NGF-TrkA trophic signaling, which may potentially contribute to the CMT2B disease.

DNA nanostructures based on programmable DNA molecular recognition have been developed, but the nanoelectronics of using DNA is still challenging. A more rapid charge-transfer (CT) process through the DNA nanoassembly is required for further development of programmable DNA nanoelectronics. In this article, we present direct absorption measurements of the long-range CT over a 140-Å DNA assembly based on a GC repetitive sequence constructed by simply mixing DNA building blocks. We show that a CT through DNA nanoscale assembly is possible and programmable with the designed DNA sequence.transient absorption measurement ͉ nanostructure hole transfer ͉ DNA oxidation ͉ nanotechnology D NA has been used extensively to form nanoscale structures that may be used as nanotechnology devices in the future (1-3). Although many DNA nanostructures have been constructed (4, 5), the realization of DNA-based molecular nanoelectronics is still challenging because its physical and chemical properties continue to remain unclear (6).There are many reports on the construction of desired structures using DNA. Structurally controlled DNA motifs, called DNA tiles, have been used as building blocks for creating DNA nanostructures. Such DNA tiles are linked together with a branched junction, called sticky-end DNAs, which are used for self-assembling nanostructures, such as two-or threedimensional DNA nanostructures (1, 4, 7). These selfassembling nanostructures are produced simply by mixing the short single strands of the DNA. In addition, a DNA automated synthetic method has made it possible to synthesize site-specific functionalized DNAs, such as a photosensitizer-modified DNA (7). By using these functionalized DNAs as building blocks, the creation of functionalized DNA nanostructures could be accomplished, leading to DNA frontier nanotechnologies and nanoelectronics (8).Charge transfer (CT) in a duplex B-DNA has been studied intensively (9)(10)(11)(12)(13)(14). Particularly, the CT mechanism has been investigated by various experimental methods and theoretical calculations (15). Giese and coworkers (16,17) demonstrated that the CT between guanine (G) sites occurs via a multihopping mechanism. Furthermore, they revealed that the CT between Gs separated by (A:T) n (n Ն 4) sequences can take place because the adenines (As) also act as the charge carriers (18). An alternative mechanism in which the delocalized charge is transported by polarons has been proposed by Schuster and coworkers (19). More recently, Barton and O'Neill (20,21) proved that CT through a DNA is described as a conformational gated hopping among stacked domains. Although somewhat controversial, DNA sequences as well as conformational dynamics and local flexibility seem to contribute to the CT through DNA. Previously, we reported the direct observation of CT between Gs through a DNA in which the long-range CT between Gs across A͞T base pairs occurs in a slow time scale, microsecond-tomillisecond range (22). A more rapid CT is required for further development of programmable ...

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A series of naphthalimide (NI)- and 5-bromocytosine ((br)C)-modified oligodeoxynucleotides (ODNs) were prepared, and their lifetimes of the charge-separated states during the photosensitized one-electron oxidation of DNA were measured. Various lifetimes of the charge-separated states were observed depending on the sequence and the incorporation sites of (br)C, and the oxidation potential of G in the (br)C:G base-pair relative to that of G in the C:G base-pair and in the GGG sequence was determined by comparing the lifetimes of the charge-separated states. The change in the cytosine C5 hydrogen to bromine resulted in a 24 mV increase in the oxidation potential of G in the (br)C:G base-pair as compared to that of G in the C:G base-pair, the value of which is comparable to a 58 mV decrease in the oxidation potential of G in the GGG sequence. These results clearly demonstrate that hole transfer in DNA can be controlled through hydrogen bonding by introducing a substituent on the cytosine.

The photochromic molecule diarylethene works as a "toggle switch" for biocompatible fluorescence polymer dots and enables fluorescence switching in biological samples.

Based on direct spectroscopic measurements of hole transfer in DNA and quantification of the yield of DNA oxidative damage, consecutive adenine sequences were found to be a good launching site for photosensitizers to inject a hole in DNA, where the following rapid hole transfer between adenines causes a long-lived charge-separated state leading to DNA oxidative damage. According to the results, the essential requisites for an efficient and/or harmful photosensitizer are determined as follows: to be able to oxidize adenine to trigger hole transfer between adenines, and react rapidly with molecular oxygen following its reduction, avoiding charge recombination and making the reaction irreversible. These results will greatly help us to classify photosensitizers harmful to human health, and to design an improved photosensitizer for biochemical applications.