The ability of DNA to self-assemble into one-, two- and three-dimensional nanostructures, combined with the precision that is now possible when positioning nanoparticles or proteins on DNA scaffolds, provide a promising approach for the self-organization of composite nanostructures. Predicting and controlling the functions that emerge in self-organized biomolecular nanostructures is a major challenge in systems biology, and although a number of innovative examples have been reported, the emergent properties of systems in which enzymes are coupled together have not been fully explored. Here, we report the self-assembly of a DNA scaffold made of DNA strips that include 'hinges' to which biomolecules can be tethered. We attach either two enzymes or a cofactor-enzyme pair to the scaffold, and show that enzyme cascades or cofactor-mediated biocatalysis can proceed effectively; similar processes are not observed in diffusion-controlled homogeneous mixtures of the same components. Furthermore, because the relative position of the two enzymes or the cofactor-enzyme pair is determined by the topology of the DNA scaffold, it is possible to control the reactivity of the system through the design of the individual DNA strips. This method could lead to the self-organization of complex multi-enzyme cascades.

Dedicated to Prof. Helmut Schwarz on the occasion of his 60th birthday.The combination of biological molecules and novel nanomaterial components is of great importance in the process of developing new nanoscale devices for future biological, medical, and electronic applications.[1] The electrical contacting of redox enzymes with electrodes is a subject of extensive research over the last decade, with important implications for developing biosensing enzyme electrodes, biofuel cells and bioelectronic systems. [2][3][4] Tethering of redox-relay units to enzymes associated with electrodes, [5][6][7] the immobilization of enzymes in redox-polymers, [8] and the reconstitution of apo enzymes on relay-cofactor units associated with electrodes [9] were reported as means to establish electrical communication between redox proteins and electrodes. Recently, the reconstitution of the apo-flavoenzyme glucose oxidase, GOx, with a single Au nanoparticle functionalized with the flavin adenine dinucleotide (FAD) cofactor was reported.[10]The assembly of the Au-nanoparticle/GOx biocatalyst on an electrode led to an effective electrically contacted enzyme electrode. Single-walled carbon nanotubes (SWCNTs) exhibit unique structural, mechanical, and electronic properties, [11][12][13][14] and recent studies have demonstrated the use of SWCNTs in nanodevices and sensors. [15][16][17][18][19] Several research activities have addressed the generation of biomaterial-SWCNT hybrid systems, protein-linked CNT [20] and nucleic acid-functionalized SWCNT. [21,22] The oriented assembly of short SWCNT normal to electrode surfaces was accomplished by the covalent attachment of the CNT to the electrode surfaces. [23][24][25][26] This structural alignment of the SWCNTs allows the secondary association of redox-active components to the CNT, and the examination of charge transport through the SWCNT. Herein we wish to report on the structural alignment of the enzyme glucose oxidase, GOx, on electrodes by using SWCNTs as electrical connectors between the enzyme redox centers and the electrode. We demonstrate that the surfaceassembled GOx is electrically contacted to the electrode by means of the SWCNTs, which acts as conductive nanoneedles that electrically wire the enzyme redox-active site to the transducer surface. The effect of the length of the SWCNT on controlling the electrical-communication properties between the enzyme redox center and the electrode is discussed.SWCNTs (Carbolex, Sigma) were first purified by heating the as-received nanotubes in refluxing 3 m nitric acid for 24 h and then washing the resulting nanotubes with water by using a 0.6 mm polycarbonate membrane filter (Millipore). The purified long SWCNTs were chemically shortened by oxidation in a mixture of concentrated sulfuric and nitric acids (3:1, 98 % and 70 %, respectively) that was subjected to sonication for 8 h in an ice/water bath. This procedure yields shortened SWCNTs with a broad length distribution and that have terminal carboxyl functionalities. The shortened SWCNTs ...

CdSe-ZnS core-shell quantum dots (QDs) act as photochemical centers for lighting-up the dynamics of telomerization or DNA replication.

The synthesis of conductive nanowires or patterned conductive nanoelements is a challenging goal for the future fabrication of nanoscale circuitry. Similarly, the realization of nanoscale mechanics might introduce a new facet to the area of nanobiotechnology. Here we report on the design of conductive and patterned actin-based gold nanowires, and on the ATP-driven motility of the nano-objects. The polymerization of G-actin labelled with Au nanoparticles, followed by the catalytic enlargement of the nanoparticles, yields gold wires (1-4 microm long and 80-200 nm high) exhibiting high electrical conductivity. The polymerization of the Au nanoparticle/G-actin monomer followed by the polymerization of free G-actin, or alternatively the polymerization of the Au-nanoparticle-labelled G-actin on polymerized F-actin followed by the catalytic enlargement of the particles, yields patterned actin-Au wire-actin or Au wire-actin-Au wire nanostructures, respectively. We demonstrate the ATP-fuelled motility of the actin-Au wire-actin filaments on a myosin interface. These actin-based metallic wires and their nanotransporting funcionality introduce new concepts for developing biological/inorganic hybrid devices.

No abstract