Pursuing excitonic energy transfer with programmable DNA-based optical breadboards.

DNA nanotechnology has now enabled the self-assembly of almost any prescribed 3-dimensional nanoscale structure in large numbers and with high fidelity. These structures are also amenable to site-specific modification with a variety of small molecules ranging from drugs to reporter dyes. Beyond obvious application in biotechnology, such DNA structures are being pursued as programmable nanoscale optical breadboards where multiple different/identical fluorophores can be positioned with sub-nanometer resolution in a manner designed to allow them to engage in multistep excitonic energy-transfer (ET) Förster resonance energy transfer (FRET) or other related processes.

Self assembling nanoparticle enzyme clusters provide access to substrate channeling in multienzymatic cascades.

Access to efficient enzymatic channeling is desired for improving all manner of designer biocatalysis. We demonstrate that enzymes constituting a multistep cascade can self-assemble with nanoparticle scaffolds into nanoclusters that access substrate channeling and improve catalytic flux by orders of magnitude. Utilizing saccharification and glycolytic enzymes with quantum dots (QDs) as a model system, nanoclustered-cascades incorporating from 4 to 10 enzymatic steps are prototyped.

Understanding Förster Resonance Energy Transfer in the Sheet Regime with DNA Brick-Based Dye Networks.

Controlling excitonic energy transfer at the molecular level is a key requirement for transitioning nanophotonics research to viable devices with the main inspiration coming from biological light-harvesting antennas that collect and direct light energy with near-unity efficiency using Förster resonance energy transfer (FRET). Among putative FRET processes, point-to-plane FRET between donors and acceptors arrayed in two-dimensional sheets is predicted to be particularly efficient with a theoretical 1/ energy transfer distance () dependency the 1/ dependency seen for a single donor-acceptor interaction. However, quantitative validation has been confounded by a lack of robust experimental approaches that can rigidly place dyes in the required nanoscale arrangements.

Enhanced Catalysis from Multienzyme Cascades Assembled on a DNA Origami Triangle.

Developing reliable methods of constructing cell-free multienzyme biocatalytic systems is a milestone goal of synthetic biology. It would enable overcoming the limitations of current cell-based systems, which suffer from the presence of competing pathways, toxicity, and inefficient access to extracellular reactants and removal of products. DNA nanostructures have been suggested as ideal scaffolds for assembling sequential enzymatic cascades in close enough proximity to potentially allow for exploiting of channeling effects; however, initial demonstrations have provided somewhat contradictory results toward confirming this phenomenon.

Nanoparticle Size Influences Localized Enzymatic Enhancement-A Case Study with Phosphotriesterase.

Enhancements in enzymatic catalytic activity are frequently observed when an enzyme is displayed on a nanoparticle (NP) surface. The exact mechanisms of how this unique interfacial environment gives rise to this phenomenon are still not understood, although evidence suggests that it can help alleviate some of the enzyme's rate-limiting mechanistic steps. The physicochemical limitations that govern when this process arises are also not known including, in particular, the range of NP size and curvature that are associated with it.

Transducing Protease Activity into DNA Output for Developing Smart Bionanosensors.

DNA can process information through sequence-based reorganization but cannot typically receive input information from most biological processes and translate that into DNA compatible language. Coupling DNA to a substrate responsive to biological events can address this limitation. A two-component sensor incorporating a chimeric peptide-DNA substrate is evaluated here as a protease-to-DNA signal convertor which transduces protease activity through DNA gates that discriminate between different input proteases.

Enhancing Coupled Enzymatic Activity by Colocalization on Nanoparticle Surfaces: Kinetic Evidence for Directed Channeling of Intermediates.

Multistep enzymatic cascades are becoming more prevalent in industrial settings as engineers strive to synthesize complex products and pharmaceuticals in economical, environmentally friendly ways. Previous work has shown that immobilizing enzymes on nanoparticles can enhance their activity significantly due to localized interfacial effects, and this enhancement remains in place even when that enzyme's activity is coupled to another enzyme that is still freely diffusing. Here, we investigate the effects of displaying two enzymes with coupled catalytic activity directly on the same nanoparticle surface.

Pursuing the Promise of Enzymatic Enhancement with Nanoparticle Assemblies.

The growing emphasis on green chemistry, renewable resources, synthetic biology, regio-/stereospecific chemical transformations, and nanotechnology for providing new biological products and therapeutics is reinvigorating research into enzymatic catalysis. Although the promise is profound, many complex issues remain to be addressed before this effort will have a significant impact. Prime among these is to combat the degradation of enzymes frequently seen in ex vivo formats following immobilization to stabilize the enzymes for long-term application and to find ways of enhancing their activity.

Time-Gated FRET and DNA-Based Photonic Molecular Logic Gates: AND, OR, NAND, and NOR.

Molecular logic devices (MLDs) constructed from DNA are promising for applications in bioanalysis, computing, and other applications requiring Boolean logic. These MLDs accept oligonucleotide inputs and generate fluorescence output through changes in structure. Although fluorescent dyes are most common in MLD designs, nontraditional luminescent materials with unique optical properties can potentially enhance MLD capabilities.

Evaluating Dye-Labeled DNA Dendrimers for Potential Applications in Molecular Biosensing.

DNA nanostructures provide a reliable and predictable scaffold for precisely positioning fluorescent dyes to form energy transfer cascades. Furthermore, these structures and their attendant dye networks can be dynamically manipulated by biochemical inputs, with the changes reflected in the spectral response. However, the complexity of DNA structures that have undergone such types of manipulation for direct biosensing applications is quite limited.

Enhancing coupled enzymatic activity by conjugating one enzyme to a nanoparticle.

Enzymes have long been a prime research target for the commercial production of commodity and specialty chemicals, design of sensing devices, and the development of therapeutics and new chemical processes. Industrial applications for enzymes can potentially be enhanced by enzyme immobilization which often allows for increased enzyme stability, facile product purification, and minimized substrate diffusion times in multienzymatic cascades, but this is usually at the cost of a significant decrease in catalytic rates. Recently, enzyme immobilization has been advanced by the discovery that nanoparticle surfaces are frequently able to enhance the activity of the bound enzyme.

Fluorescence and Energy Transfer in Dye-Labeled DNA Crystals.

DNA crystals make it possible to organize guest molecules into specific periodic 3D patterns at the nanoscale, and thereby to create novel macroscopic objects with potentially useful functionality. Here, we describe the fluorescence and energy transfer properties of DNA crystals that are self-assembled from DNA tensegrity triangles with covalently attached Cy3 and Cy5 dyes. When compared to reference DNA strands in solution, the fluorescence measurements indicate that the dyes in the crystal experience a more homogeneous environment, resulting in a 2-fold increase in Cy3 quantum yield and single-exponential Cy3 fluorescence decays.

Time-Resolved Nucleic Acid Hybridization Beacons Utilizing Unimolecular and Toehold-Mediated Strand Displacement Designs.

Nucleic acid hybridization probes are sought after for numerous assay and imaging applications. These probes are often limited by the properties of fluorescent dyes, prompting the development of new probes where dyes are paired with novel or nontraditional luminescent materials. Luminescent terbium complexes are an example of such a material, and these complexes offer several unique spectroscopic advantages.

Understanding How Nanoparticle Attachment Enhances Phosphotriesterase Kinetic Efficiency.

As a specific example of the enhancement of enzymatic activity that can be induced by nanoparticles, we investigate the hydrolysis of the organophosphate paraoxon by phosphotriesterase (PTE) when the latter is displayed on semiconductor quantum dots (QDs). PTE conjugation to QDs underwent extensive characterization including structural simulations, electrophoretic mobility shift assays, and dynamic light scattering to confirm orientational and ratiometric control over enzyme display which appears to be necessary for enhancement. PTE hydrolytic activity was then examined when attached to ca.

Assembling programmable FRET-based photonic networks using designer DNA scaffolds.

DNA demonstrates a remarkable capacity for creating designer nanostructures and devices. A growing number of these structures utilize Förster resonance energy transfer (FRET) as part of the device's functionality, readout or characterization, and, as device sophistication increases so do the concomitant FRET requirements. Here we create multi-dye FRET cascades and assess how well DNA can marshal organic dyes into nanoantennae that focus excitonic energy.

Extending FRET cascades on linear DNA photonic wires.

Photonic wires were constructed by sequentially arranging up to 7 fluorophores along a concatenated DNA scaffold. This yielded nanostructures displaying from one- to six-energy transfer steps where end-to-end efficiency reflected the multiple underlying photophysical processes and the ability of long-range interactions to compensate for localized non-ideal dye behaviour.

Complex logic functions implemented with quantum dot bionanophotonic circuits.

We combine quantum dots (QDs) with long-lifetime terbium complexes (Tb), a near-IR Alexa Fluor dye (A647), and self-assembling peptides to demonstrate combinatorial and sequential bionanophotonic logic devices that function by time-gated Förster resonance energy transfer (FRET). Upon excitation, the Tb-QD-A647 FRET-complex produces time-dependent photoluminescent signatures from multi-FRET pathways enabled by the capacitor-like behavior of the Tb. The unique photoluminescent signatures are manipulated by ratiometrically varying dye/Tb inputs and collection time.

Biophotonic logic devices based on quantum dots and temporally-staggered Förster energy transfer relays.

Integrating photonic inputs/outputs into unimolecular logic devices can provide significantly increased functional complexity and the ability to expand the repertoire of available operations. Here, we build upon a system previously utilized for biosensing to assemble and prototype several increasingly sophisticated biophotonic logic devices that function based upon multistep Förster resonance energy transfer (FRET) relays. The core system combines a central semiconductor quantum dot (QD) nanoplatform with a long-lifetime Tb complex FRET donor and a near-IR organic fluorophore acceptor; the latter acts as two unique inputs for the QD-based device.

Achieving effective terminal exciton delivery in quantum dot antenna-sensitized multistep DNA photonic wires.

Assembling DNA-based photonic wires around semiconductor quantum dots (QDs) creates optically active hybrid architectures that exploit the unique properties of both components. DNA hybridization allows positioning of multiple, carefully arranged fluorophores that can engage in sequential energy transfer steps while the QDs provide a superior energy harvesting antenna capacity that drives a Förster resonance energy transfer (FRET) cascade through the structures. Although the first generation of these composites demonstrated four-sequential energy transfer steps across a distance >150 Å, the exciton transfer efficiency reaching the final, terminal dye was estimated to be only ~0.

Assembly of a concentric Förster resonance energy transfer relay on a quantum dot scaffold: characterization and application to multiplexed protease sensing.

Semiconductor nanocrystals, or quantum dots (QDs), are one of the most widely utilized nanomaterials for biological applications. Their cumulative physicochemical and optical properties are both unique among nanomaterials and highly advantageous. In particular, Förster resonance energy transfer (FRET) has been widely utilized as a spectroscopic tool with QDs, whether for characterizing QD bioconjugates as a "molecular ruler" or for modulating QD luminescence "on" and "off" in biosensing configurations.

Nanodimensionally driven analyte response reversal in gold nanocluster chemiresistor sensing.

The modulation of electron transport through an ensemble of ligand-stabilized gold nanoclusters by the sorption of vapors is made exceptionally sensitive and selective by terminal carboxylic acid functionalization of the alkanethiol ligand. Of further importance, the directionality of the response (conductance increase or decrease) is strongly dependent on the nanoscale dimensions of the gold core and ligand shell thickness. Films of gold nanoclusters composed of a 2 nm metal core with a 0.

Fluorine-labeling as a diagnostic for thiol-ligand and gold nanocluster self-assembly.

An omega-fluorine-labeled oxyethylene thiol ligand, F(CH2CH2O)2CH2CH2SH, was synthesized, characterized and incorporated into mixed self-assembled monolayers with CH3(OCH2CH2)3SH onto a planar gold substrate and onto 2 nm gold nanoclusters. The fluorine-labeled nanocluster was self-assembled onto gold substrates using alkane dithiol (HS(CH2)nSH; n = 5, 8, 11) and oxyethylene dithiol (HS(CH2CH2O)nCH2CH2SH; n = 1, 2, 3) linking agents with equivalent chain lengths for comparative purposes. X-ray photoelectron spectroscopy (XPS) was used to track the fluorine-label in the self-assembly operations and to evaluate the effectiveness of the dithiols.

Self-assembly of trioxyethylene-encapsulated gold nanoclusters under aqueous conditions.

The aqueous self-assembly of methyl-terminated tri(oxyethylene)thiol-encapsulated gold nanoclusters of varying core size is demonstrated on micrometer scale Au/SiO2 interdigital electrodes. This self-assembly process consists of alternate exposures of the substrate to solutions of either an alpha,omega-dithiol or the gold nanoclusters, resulting in the deposition of these materials onto the electrode surface. A comparison of the procedure in both H2O and CHCl3 solvents shows that the assembly, as monitored by the electrical conductivity of the device, occurs more rapidly in the H2O system.

Ion-induced discrete charging of immobilized water-soluble gold nanoclusters.

Hydrophilic gold nanoclusters were immobilized onto monolayer-modified gold electrodes and PF6-(-)induced rectification and stepwise capacitance charging was studied in aqueous supporting electrolyte by cyclic voltammetry and ac voltammetry.