Following Glucose Oxidase Activity by Chemiluminescence and Chemiluminescence Resonance Energy Transfer (CRET) Processes Involving Enzyme-DNAzyme Conjugates

A hybrid consisting of glucose oxidase-functionalized with hemin/G-quadruplex units is used for the chemiluminescence detection of glucose. The glucose oxidase-mediated oxidation of glucose yields gluconic acid and H2O2. The latter in the presence of luminol acts as substrate for the hemin/G-quadruplex-catalyzed generation of chemiluminescence. The glucose oxidase/hemin G-quadruplex hybrid was immobilized on CdSe/ZnS quantum dots (QDs). The light generated by the hybrid, in the presence of glucose, activated a chemiluminescence resonance energy transfer process to the QDs, resulting in the luminescence of the QDs. The intensities of the luminescence of the QDs at different concentrations of glucose provided an optical means to detect glucose

Switching Photonic and Electrochemical Functions of a DNAzyme by DNA Machines

DNA nanostructures acting as DNA machines are described. Specifically, DNA “walkers” assembled on nucleic acid scaffolds and triggered by fuel/antifuel strands are activated in solution or on surfaces, for example, electrodes or semiconductor CdSe/ZnS quantum dots (QDs). The DNA machines led to the switchable formation or dissociation of the hemin/G-quadruplex DNAzyme on the DNA scaffolds. This enabled the chemiluminescence, chemiluminescence resonance energy transfer (CRET), electrochemical, or photoelectrochemical transduction of the switchable states of the different DNA machines

Photoelectrochemical Biosensors Without External Irradiation: Probing Enzyme Activities and DNA Sensing Using Hemin/G-Quadruplex-Stimulated Chemiluminescence Resonance Energy Transfer (CRET) Generation of Photocurrents

A hemin/G-quadruplex nanostructure that is immobilized on CdS quantum dots (QDs) associated with an electrode leads, in the presence of luminol, H₂O₂, and triethanolamine as an electron donor, to the generation of photocurrents with no external irradiation of the QDs. The hemin/G-quadruplex-catalyzed generation of chemiluminescence leads to the chemiluminescence resonance energy transfer (CRET) to the QDs, resulting in the photoexcitation of the QDs and the generation of electron–hole pairs. The transfer of the conduction-band electrons to the electrode, and the concomitant scavenging of the valence-band holes by the triethanolamine electron donor result in the generation of photocurrents. The CRET-stimulated generation of photocurrents is applied to sense DNA by the labeling of the probe–analyte complex with a hemin/G-quadruple, and is also implemented to follow the activity of glucose oxidase and to sense glucose, by the labeling of the enzyme with the hemin/G-quadruplex catalyst

Probing Biocatalytic Transformations with Luminescent DNA/Silver Nanoclusters

DNA-stabilized Ag nanoclusters, AgNCs, act as fluorescent labels for probing enzyme activities and their substrates. The effective quenching of AgNCs by H₂O₂ enables the probing of H₂O₂-generating oxidases. This is demonstrated by following the glucose oxidase-stimulated oxidation of glucose through the enzyme-catalyzed formation of H₂O₂. Similarly, the effective quenching of the AgNCs by quinones enabled the detection of tyrosinase through the biocatalyzed oxidation of tyrosine, dopamine, or tyramine to the respective quinone products. The sensitive probing of biocatalytic processes by the AgNCs was further implemented to follow bienzyme catalytic cascades involving alkaline phosphatase/tyrosinase and acetylcholine esterase/choline oxidase. The characterization of the alkaline phosphatase/tyrosinase cascade enabled the ultrasensitive detection of alkaline phosphatase (5 × 10^–5 units/mL) and the detection of <i>o</i>-phospho-l-tyrosine that is an important intracellular promoter and control growth factor

Free-Standing Nanocrystalline Materials Assembled from Small Molecules

We demonstrate a solution-based fabrication of centimeter-size free-standing films assembled from organic nanocrystals based on common organic dyes (perylene diimides, PDIs). These nanostructured films exhibit good mechanical stability, and thermal robustness superior to most plastics, retaining the crystalline microstructure and macroscopic shape upon heating up to 250–300 °C. The films show nonlinear optical response and can be used as ultrafiltration membranes. The macroscopic functional materials based on small molecules can be alternative or complementary to materials based on macromolecules