Modulating Optoelectronic Properties of Two-Dimensional Transition Metal Dichalcogenide Semiconductors by Photoinduced Charge Transfer

Atomically thin transition metal dichalcogenides (TMDCs) have attracted great interest as a new class of two-dimensional (2D) direct band gap semiconducting materials. The controllable modulation of optical and electrical properties of TMDCs is of fundamental importance to enable a wide range of future optoelectronic devices. Here we demonstrate a modulation of the optoelectronic properties of 2D TMDCs, including MoS₂, MoSe₂, and WSe₂, by interfacing them with two metal-centered phthalocyanine (MPc) molecules: nickel Pc (NiPc) and magnesium Pc (MgPc). We show that the photoluminescence (PL) emission can be selectively and reversibly engineered through energetically favorable electron transfer from photoexcited TMDCs to MPcs. NiPc molecules, whose reduction potential is positioned below the conduction band minima (CBM) of monolayer MoSe₂ and WSe₂, but is higher than that of MoS₂, quench the PL signatures of MoSe₂ and WSe₂, but not MoS₂. Similarly, MgPc quenches only WSe₂, as its reduction potential is situated below the CBM of WSe₂, but above those of MoS₂ and MoSe₂. The quenched PL emission can be fully recovered when MPc molecules are removed from the TMDC surfaces, which may be refunctionalized and recycled multiple times. We also find that photocurrents from TMDCs, probed by photoconductive atomic force microscopy, increase over 2-fold only when the PL is quenched by MPcs, further supporting the photoinduced charge transfer mechanism. Our results should benefit design strategies for 2D inorganic–organic optoelectronic devices and systems with tunable properties and improved performances

Multiplexed Optical Detection of Plasma Porphyrins Using DNA Aptamer-Functionalized Carbon Nanotubes

A novel optical platform based on DNA aptamer-functionalized SWCNTs (a-SWCNTs) is developed for multiplexed detection of plasma porphyrins. We have investigated the interactions of a-SWCNTs with heme (FePP), protoporphyrin (PP), coproporphyrin (CP), and uroporphyrin (UP). Two interaction mechanisms, specific binding, and nonspecific adsorption between porphyrins and a-SWCNTs are proposed based on observed optical signal modulations. The optical transduction signals are used to formulate a multiplexed detection strategy for the four porphyrin species without a laborious separation process. The detection scheme is sensitive, selective, and can readily be used for porphyrin detection in plasma samples when combined with a solvent extraction method. Our optical platform offers novel analytical tools for probing the surface chemistry at the porphyrin/a-SWCNTs interface, showing great promise for both research and clinical applications

Understanding Photophysical Interactions of Semiconducting Carbon Nanotubes with Porphyrin Chromophores

Donor–acceptor complexes of porphyrins and semiconducting single-walled carbon nanotubes (SWCNTs) are noncovalently assembled using oligonucleotide DNA, and their photophysical interactions are studied for light-harvesting. Five cationic 5,10,15,20-tetrakis­(<i>N</i>-methyl­pyridynium-4-yl)­porphyrins with a free-base (H₂T4) or metal ions at the core (MT4, M = Zn²⁺, Pt²⁺, Pd²⁺, and Cu²⁺) are explored as donor chromophores as they exhibit species-unique optical signatures, such as fluorescence, phosphorescence, or both. These porphyrins are examined for their abilities to interact with semiconducting carbon nanotubes after photoexcitation. We find that carbon nanotubes efficiently quench the emission properties of porphyrins via charge transfer, which is confirmed by the quenching of singlet oxygen emission generated by porphyrins. Phosphorescence lifetime measurements reveal that the lifetime in the triplet states is largely constant in porphyrins interacting with both DNA alone and DNA-coated SWCNTs, suggesting that photoexcited electrons are transferred to carbon nanotubes from the low-lying singlet state before an intersystem crossing to the triplet state. We demonstrate that the DNA-assembled porphyrin–SWCNT complexes in a photoelectrochemical cell produce stable anodic photocurrents with a conversion efficiency of approximately 1.5%

Understanding the Mechanical Properties of DNA Origami Tiles and Controlling the Kinetics of Their Folding and Unfolding Reconfiguration

DNA origami represents a class of highly programmable macromolecules that can go through conformational changes in response to external signals. Here we show that a two-dimensional origami rectangle can be effectively folded into a short, cylindrical tube by connecting the two opposite edges through the hybridization of linker strands and that this process can be efficiently reversed via toehold-mediated strand displacement. The reconfiguration kinetics was experimentally studied as a function of incubation temperature, initial origami concentration, missing staples, and origami geometry. A kinetic model was developed by introducing the <i>j</i> factor to describe the reaction rates in the cyclization process. We found that the cyclization efficiency (<i>j</i> factor) increases sharply with temperature and depends strongly on the structural flexibility and geometry. A simple mechanical model was used to correlate the observed cyclization efficiency with origami structure details. The mechanical analysis suggests two sources of the energy barrier for DNA origami folding: overcoming global twisting and bending the structure into a circular conformation. It also provides the first semiquantitative estimation of the rigidity of DNA interhelix crossovers, an essential element in structural DNA nanotechnology. This work demonstrates efficient DNA origami reconfiguration, advances our understanding of the dynamics and mechanical properties of self-assembled DNA structures, and should be valuable to the field of DNA nanotechnology

Design Principles of DNA Enzyme-Based Walkers: Translocation Kinetics and Photoregulation

Dynamic DNA enzyme-based walkers complete their stepwise movements along the prescribed track through a series of reactions, including hybridization, enzymatic cleavage, and strand displacement; however, their overall translocation kinetics is not well understood. Here, we perform mechanistic studies to elucidate several key parameters that govern the kinetics and processivity of DNA enzyme-based walkers. These parameters include DNA enzyme core type and structure, upper and lower recognition arm lengths, and divalent metal cation species and concentration. A theoretical model is developed within the framework of single-molecule kinetics to describe overall translocation kinetics as well as each reaction step. A better understanding of kinetics and design parameters enables us to demonstrate a walker movement near 5 μm at an average speed of ∼1 nm s^–1. We also show that the translocation kinetics of DNA walkers can be effectively controlled by external light stimuli using photoisomerizable azobenzene moieties. A 2-fold increase in the cleavage reaction is observed when the hairpin stems of enzyme catalytic cores are open under UV irradiation. This study provides general design guidelines to construct highly processive, autonomous DNA walker systems and to regulate their translocation kinetics, which would facilitate the development of functional DNA walkers

Dynamic and Progressive Control of DNA Origami Conformation by Modulating DNA Helicity with Chemical Adducts

DNA origami has received enormous attention for its ability to program complex nanostructures with a few nanometer precision. Dynamic origami structures that change conformation in response to environmental cues or external signals hold great promises in sensing and actuation at the nanoscale. The reconfiguration mechanism of existing dynamic origami structures is mostly limited to single-stranded hinges and relies almost exclusively on DNA hybridization or strand displacement. Here, we show an alternative approach by demonstrating on-demand conformation changes with DNA-binding molecules, which intercalate between base pairs and unwind DNA double helices. The unwinding effect modulates the helicity mismatch in DNA origami, which significantly influences the internal stress and the global conformation of the origami structure. We demonstrate the switching of a polymerized origami nanoribbon between different twisting states and a well-constrained torsional deformation in a monomeric origami shaft. The structural transformation is shown to be reversible, and binding isotherms confirm the reconfiguration mechanism. This approach provides a rapid and reversible means to change DNA origami conformation, which can be used for dynamic and progressive control at the nanoscale

Accessibility and External versus Intercalative Binding to DNA As Assessed by Oxygen-Induced Quenching of the Palladium(II)-Containing Cationic Porphyrins Pd(T4) and Pd(<i>t</i>D4)

Studies reveal that it is possible to design a palladium­(II)-containing porphyrin to bind exclusively by intercalation to double-stranded DNA while simultaneously enhancing the ability to sensitize the formation of singlet oxygen. The comparisons revolve around the cations [5,10,15,20-tetra­(<i>N</i>-methylpyridinium-4-yl)­porphyrin]­palladium­(II), or Pd­(T4), and [5,15-di­(<i>N</i>-methylpyridinium-4-yl)­porphyrin]­palladium­(II), or Pd­(<i>t</i>D4), in conjunction with AT and GC rich DNA binding sequences. Methods employed include X-ray crystallography of the ligands as well as absorbance, circular dichroism, and emission spectroscopies of the adducts and the emission from singlet oxygen in solution. In the case of the bulky Pd­(T4) system, external binding is almost as effective as intercalation in slowing the rate of oxygen-induced quenching of the porphyrin’s triplet excited state. The fractional efficiency of quenching by oxygen nevertheless approaches 1 for intercalated forms of Pd­(<i>t</i>D4), because of intrinsically long triplet lifetimes. The intensity of the sensitized, steady-state emission signal varies with the system and depends on many factors, but the Pd­(<i>t</i>D4) system is impressive. Intercalated forms of Pd­(<i>t</i>D4) produce higher sensitized emission yields than Pd­(T4) is capable of in the absence of DNA

Regeneration of Light-Harvesting Complexes via Dynamic Replacement of Photodegraded Chromophores

All-synthetic molecular donor–acceptor complexes are designed, which are capable of counteracting the effect of photoinduced degradation of donor chromophores. Anionic gallium protoporphyrin IX (GaPP) and semiconducting carbon nanotube (CNT) are used as a model donor–acceptor complex, which is assembled using DNA oligonucleotides. The GaPP-DNA-CNT complex produces an anodic photocurrent in a photoelectrochemical cell, which steadily decays due to photo-oxidation. By modulating the chemical environment, we showed that the photodegraded chromophores may be dissociated from the complex, whereas the DNA-coated carbon nanotube acceptors are kept intact. Reassociation with fresh porphyrins leads to the full recovery of GaPP absorption and photocurrents. This strategy could form a basis for improving the light-harvesting performance of molecular donor–acceptor complexes and extending their operation lifetime

Fixed effects from mixed effects models estimating the longitudinal course of post FEV1 during 10 years between SHAPTB group and normal group.

<p>Fixed effects from mixed effects models estimating the longitudinal course of post FEV1 during 10 years between SHAPTB group and normal group.</p

Longitudinal course of post FEV1 from mixed effects model for 10 years in the normal and SHPTB groups.

<p>Nl = normal group; SHPTB = spontaneous healed pulmonary tuberculosis group.</p