Detection of small molecules by fluorescence intensity using single dye labeled aptamers and quencher transition metal ions.

We describe herein an aptamer-based sensing approach that signal the presence of small-molecule targets when fluorescent DNA probes are challenged with the Ni2+ or Co2+ quencher metal ions. Functional oligonucleotides targeting L-tyrosinamide (L-Tym), adenosine (Ade) or cocaine (Coc) were end-labeled by the Texas-Red fluorophore. A fluorescence quenching occurred upon association of these transition metal ions with the free conjugates. The formation of the target-probe complex, by the way of variations in the overall binding of quencher metal ions along the DNA strands, led to a partial restoration (for the Ade and Coc systems) or a further attenuation (for the L-Tym system) of the fluorescence intensity. The absolute signal gain varied from 40 to 180% depending on the target-probe pair investigated. The approach was also used to detect the compound Ade in a spiked biological matrix in 1 min or less. The transition metal ion-based quenching strategy is characterized by its very simple implementation, low cost, and rapid signaling.

Aptamer Switches Regulated by Post-Transition/Transition Metal Ions.

We introduced an aptamer switch design that relies on the ability of post-transition/transition metal ions to trigger, through their coordination to nucleobases, substantial DNA destabilization. In the absence of molecular target, the addition of one such metal ion to usual aptamer working solutions promotes the formation of an alternative, inert DNA state. Upon exposure to the cognate compound, the equilibrium is shifted towards the competent DNA form. The switching process was preferentially activated by metal ions of intermediate base over phosphate complexation preference (i.e. Pb2+ , Cd2+ ) and operated with diversely structured DNA molecules. This very simple aptamer switch scheme was applied to the detection of small organics using the fluorescence anisotropy readout mode. We envision that the approach could be adapted to a variety of signalling methods that report on changes in the surface charge density of DNA receptors.

Imine and metal-ligand dynamic bonds in soft polymers for autonomous self-healing capacitive-based pressure sensors.

In this work, a facile and simple yet effective method to generate intrinsic autonomous self-healing polymers was developed, leading to new materials that can be easily fine-tuned both mechanically and chemically. The new materials were designed to incorporate two dynamic and reversible types of chemical bonds, namely dynamic imine and metal-coordinating bonds, to enable autonomous self-healing, controlled degradability and ultra-high tunable stretchability (up to 800% strain) based on the ratio of metal to ligand incorporated. Through an easy condensation reaction, imine bonds are generated at the end-termini of a short siloxane chain. The new dynamic system was characterized by a variety of techniques, including tensile-pull strain testing, atomic force microscopy and UV-Vis spectroscopy, which showed that the highly dynamic imine bonds, combined with coordination with Fe2+ ions, allow for the material to regenerate 88% of its mechanical strength after physical damage. The materials were also controlled to be degraded in mild acidic conditions. Lastly, application in self-healable electronics was demonstrated through the fabrication of a capacitive-based pressure sensor, which shows good sensitivity and dynamic response (∼0.33 kPa-1) before and after healing.

Morphology and Electronic Properties of Semiconducting Polymer and Branched Polyethylene Blends.

A new strategy for influencing the solid-state morphology of conjugated polymers was developed through physical blending with a low-molecular-weight branched polyethylene. This nontoxic and low-boiling-point additive was blended with a high-charge-mobility diketopyrrolopyrrole-based conjugated polymer, and a detailed investigation of the new blended materials was performed by various characterization tools, including X-ray diffraction, UV-vis spectroscopy, and atomic force microscopy. Interestingly, the branched additive was shown to reduce the crystallinity of the conjugated polymer while promoting aggregation and phase separation in the solid state. Upon thermal removal of the olefinic additive, the thin films maintained a lower crystallinity and aggregated morphology in comparison to a nonblended polymer. The semiconducting performance of the new branched polyethylene/conjugated polymer blends was also investigated in organic field-effect transistors, which showed a stable charge mobility of around 0.3 cm2 V-1 s-1 without thermal annealing, independent of the blending ratio. Furthermore, using the new polyethylene-based additive, the concentration of a conjugated polymer required for the fabrication of organic field-effect transistor devices was reduced down to 0.05 wt %, without affecting charge transport, which represents a significant improvement compared to usual concentrations used for solution deposition. Our results demonstrate that the physical blending of a conjugated polymer with nontoxic, low-molecular-weight branched polyethylene is a promising strategy for the modification and fine-tuning of the solid-state morphology of conjugated polymers without sacrificing their charge-transport properties, thus creating new opportunities for the large-scale processing of organic semiconductors.