Biosilicated CdSe/ZnS quantum dots as photoluminescent transducers for acetylcholinesterase-based biosensors.

CdSe/ZnS core/shell quantum dots (QDs) are functionalized with mercaptoundecanoic acid (MUA) and subsequently covered with poly-L-lysine (PLL) as the template for the formation of the silica outer shell. This nanocomposite is used as a transduction and stabilization system for optical biosensor development. The covalent immobilization of the enzyme acetylcholinesterase from Drosophila melanogaster (AChE) during the formation of the biomimetically synthesized silica is used here as a model, relatively unstable enzyme, as a proof of principle. The enzyme is successfully immobilized onto the QDs and then stabilized by the PLL capping and the subsequent formation of the outer nanoporous silica thin shell, giving rise to the QD/AChE/PLL/silica biosensor. It is shown that the poly-L-lysine templated silica outer shell does not modify the optical properties of the quantum dots, while it protects the enzyme from unfolding and denaturation. The small pores of the silica shell allow for the free diffusion of the analyte to the active center of the enzyme, while it does not allow for the proteases to reach the enzyme. The response of the QD/AChE/PLL/silica nano-biosensor to its substrate, acetylcholine chloride, is evaluated by monitoring the changes in the QDs' photoluminescence which are related to the changes in pH. These pH changes of the surrounding environment of the QDs are induced by the enzymatic reaction, and are associated with the analyte concentration in the solution. The biodetection system proposed is shown to be stable with a storage lifetime of more than 2 months. The data presented provides the grounds for the application of this nanostructured biosensor for the detection of AChE inhibitors.

Biomimetically synthesized silica-carbon nanofiber architectures for the development of highly stable electrochemical biosensor systems.

Biomimetically synthesized silica and conductive activated carbon nanofibers (CNFs) are used in a synergistic manner for the development of a novel electrochemical biosensor system. Poly(L-lysine) templated silica grows and encapsulates the CNF-immobilized enzyme generating a highly stabilizing nanostructured environment for the underlying protein. Concurrently, CNFs provide both the required surface area for the high-capacity enzyme immobilization required in biosensors as well as direct electron transfer to the inner platinum transducer. As a result, this silica/nanofiber superstructure is an ideal architecture for the development of electrochemical biosensor systems that can withstand exposure to extreme operational conditions, such as high temperatures or the presence of proteases. Acetylcholine esterase is used as the model catalyst and with the aid of spectroscopic data it is shown that the observed high operational stability of the biosensor is due to the direct interaction of the protein with the silica backbone, as well as due to the nanostructured enzyme confinement.

Novel methodology for the preparation of five-, seven-, and nine-membered fused rings on C60.

[reaction: see text] The photocycloaddition of dienyl cyclopropanes to C(60) gives a new synthetic approach to yield stereospecifically five-, seven-, and nine-membered [60]fullerene adducts. Our results suggest the formation of a biradical intermediate between the dienyl substrate and C(60). An electron transfer between the triplet excited state of C(60) and the dienyl substrate precedes the formation of the intermediate.

Reaction of an Aza[60]fullerene radical with diphenylmethanes and fluorenes: a mechanistic approach.

[reaction: see text] The mechanism of the reaction of azafullerene radical C(59)N(*) with diphenylmethane and 9-methyl-9H-fluorene has been investigated. The primary and secondary kinetic isotope effects provide strong evidence for a stepwise mechanism in which the hydrogen-atom abstraction is the rate-determining step.

Biradical intermediate in the [2 + 2] photocycloaddition of dienes and alkenes to [60]fullerene.

The photocycloaddition of vinylcyclopropanes to C60 yields stereospecifically a five-membered [60]fullerene adduct. These results suggest a biradical intermediate of the [2 + 2] photocycloaddition between dienes or arylalkenes and C60. An electron transfer between the triplet excited state of C60 and the unsaturated substrates precedes the formation of the intermediate.

Multicomponent redox gradients on photoactive electrode surfaces.

Redox gradients have been used to tailor the arrangement of photoactive ITO-electrodes at the molecular level.

Electrostatically arranged cytochrome c-fullerene photoelectrodes.

We have developed a molecular-level switch-a C(60)/cytochrome c modified ITO electrode-that reversibly transmits and processes solar energy.

Electrostatic complexation and photoinduced electron transfer between Zn-cytochrome c and [olyanionic fullerene dendrimers.

Two dendritic fullerene (DF) monoadducts, 2 and 3, which can carry up to 9 and 18 negative charges, respectively, were examined with respect to electrostatic complexation with Cytochrome c (Cytc). To facilitate comprehensive photophysical investigations, the zinc analogue of Cytc (ZnCytc) was prepared according to a novel, modified procedure. The association of ZnCytc and DF, and consequential photoinduced electron transfer within ZnCytc-DF from the photoexcited protein to the fullerene, was proven by fluorescence spectroscopy and transient absorption spectroscopy. These findings were also supported by circular dichroism as well as by extensive molecular dynamics (MD) simulations.