高田 忠雄

Abstract Fluorescence imaging uses changes in the fluorescence intensity and emission wavelength to analyze multiple targets simultaneously. To increase the number of targets that can be identified simultaneously, fluorescence blinking can be used as an additional parameter. To understand and eventually control blinking, we used DNA as a platform to elucidate the processes of electron transfer (ET) leading to blinking, down to the rate constants. With a fixed ET distance, various blinking patterns were observed depending on the DNA sequence between the donor and acceptor units of the DNA platform. The blinking pattern was successfully described with a combination of ET rate constants. Therefore, molecules with various blinking patterns can be developed by tuning ET. It is expected that the number of targets that can be analyzed simultaneously will increase by the power of the number of blinking patterns.

B- to Z-DNA transitions play a crucial role in biological systems and have attracted the interest of researchers for their applications in DNA nanotechnology. DNA and DNA analogues have also been used as templates to construct helical chromophore associations with π interactions. In this work, the B- to Z-DNA transition-induced switching of pyrene in an association manner was evaluated using DNA duplexes with non-nucleosidic pyrene residues in the middle of d(CG) repeat sequences. One of the pyrene-labeled DNAs was shown to exhibit inverted exciton coupled circular dichroism signals upon pyrene association through a B- to Z-DNA transition. This observation indicates that pyrene association switches the DNA conformation from right- to left-handed. Interestingly, the fluorescence of the pyrene-labeled DNA duplex also dynamically changed upon switching of the pyrene in an association-based manner. Taken together, these studies demonstrate that pyrene-labeled DNA shows promise as a chiroptical molecular switch.

The construction of zipper-like chromophore-arrays in the major groove of duplex DNA remains a challenge because only a few chromophores for this application have been discovered. To address the challenge, dual-chromophore labeled DNAs having a self-complementary sequence were prepared using a solid-phase, post-synthetic, copper-catalyzed, alkyne-azide cycloaddition. The resulting chromophore-arrays on the labeled DNA duplexes were characterized. The dual-tetraphenylethene (TPE) or dual-pyrene (Py) labeled DNA formed self-complementary B-form duplexes and resulted in the construction of chromophore-arrays in the major groove. The TPE-arrays, in which TPEs were arranged in a zipper-like fashion, slightly destabilized the duplex because of their bulkiness and exhibited aggregation-induced-emission. The Py-arrays, in which Pys were not arranged in a zipper-like fashion, had no effect on duplex stability and exhibited weak excimer emission because Py was sufficiently small for free rotation in the major groove.

The construction of one-dimensional chromophore aggregates of naphthalenediimide (NDI) and bis(2-thienyl)diketopyrrolopyrrole (TDPP) using 40-mer oligodeoxythymidines (dT40) as a scaffold was previously reported. Furthermore, the chromophore-aggregate (NDI-dT40/TDPP-dT40) co-immobilized heterojunction gold electrode exhibited a more efficient photocurrent than the TDPP?dT40-immobilized electrode with selective photoexcitation of TDPP-dT40. In this work, a system comprising three components (in which the chromophore aggregates of diphenyl-diketopyrrolopyrrole (PDPP-dT40) are employed as a third component) was examined in order to enhance photocurrent efficiency. Selective photoexcitation of TDPP-dT40 on the NDI-dT40/TDPP-dT40/PDPP-dT40 electrode shows photocurrent responses with greater quantum yield than those of the TDPP-dT40, NDI-dT40/TDPP-dT40 and TDPP-dT40/PDPP-dT40 electrodes. The results suggest the addition of PDPP-dT40 can control charge separation and charge recombination between the electron and the hole (generated by an electron transfer from the photoexcited TDPP-dT40 to NDI-dT40).The construction of one-dimensional chromophore aggregates of naphthalenediimide (NDI) and bis(2-thienyl)diketopyrrolopyrrole (TDPP) using 40-mer oligodeoxythymidines (dT40) as a scaffold was previously reported. Furthermore, the chromophore-aggregate (NDI-dT40/TDPP-dT40) co-immobilized heterojunction gold electrode exhibited a more efficient photocurrent than the TDPP?dT40-immobilized electrode with selective photoexcitation of TDPP-dT40. In this work, a system comprising three components (in which the chromophore aggregates of diphenyl-diketopyrrolopyrrole (PDPP-dT40) are employed as a third component) was examined in order to enhance photocurrent efficiency. Selective photoexcitation of TDPP-dT40 on the NDI-dT40/TDPP-dT40/PDPP-dT40 electrode shows photocurrent responses with greater quantum yield than those of the TDPP-dT40, NDI-dT40/TDPP-dT40 and TDPP-dT40/PDPP-dT40 electrodes. The results suggest the addition of PDPP-dT40 can control charge separation and charge recombination between the electron and the hole (generated by an electron transfer from the photoexcited TDPP-dT40 to NDI-dT40).

We describe an approach to the development of a new electronic aptamer-based biosensor for multiprotein targets on a single platform. The multiple protein biosensing involves the co-adsorption of several thiol-terminated capture DNA sequences on a gold surface, along with the hybridization of redox-tagged aptamer to each corresponding capture sequences on the electrode, addition of target proteins, and monitoring aptamer-strand release through electrochemical measurement.