Immobilization of DNA for Single Molecule Detection

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Double-helical DNA is a supramolecular architecture composed of complementary base-pairings of adenine-thymine and cytosine-guanine based on specific hydrogen bonding, and carries genetic information. Due to the stacking interaction of p-electrons at the ground states of the base-pairs, DNA can act as a p-electron medium for the photoinduced electron transfer. Toward the single molecule detection of DNA by using a novel optical technique based on the combination of near field optics and photoinduced electron transfer, polynucleic acids have been immobilized as two-dimensional molecular assemblies or single molecule by means of the specific intermolecular interaction at the air-water interface. DNA, having phosphate groups in its backbone, was assembled with counter charged amphiphiles and fixed as a polyion complex monolayer at the air-water interface. We have investigated the effect of DNA on the fluorescence lifetime of a binary component monolayer of an acridine amphiphile and a cat … More ionic double chain amphiphile. Strong fluorescence quenching was found when polyG polyC was dissolved in a water subphase. Static quenching of acridine fluorescence, probably due to the electron transfer from guanine base, is occurred because the fluorescence life-time is not so reduced as fluorescence intensity. The photoinduced electron transfer to an ITO electrode was measured by an electrochemical method. Anodic photosensitized current of the amphiphilic acridine dye is enhanced by the complex formation with polynucleic acids. PolyG polyC, whose guanine base is assumed to be *idized by the excited state of the acridine moiety, is most effective for photocurrent generation. By using the simple casting method we have prepared mesoscopic stripe pattern of DNA on a mica substrate. An aqueous DNA solution mixed with/without an aqueous alginic acid solution was dropped onto a fleshly cleaved mica surface and dried by heating up to ca. 80ﾟC.The mesoscopic lines parallel to the receding direction of the solvent were observed in the cast film. When alginic acid were added in the aqueous DNA solution, more regularly aligned stripe patterns were obtained. Height of those lines was below 10 nm. Less