No abstract

A new fluorescent sensor, M201-DPA, based on [5]helicene derivative was utilized as dual-analyte sensor for determination of Cu or Zn in different media and different emission wavelengths. The sensor could provide selective and bifunctional determination of Cu in HEPES buffer containing Triton-X100 and Zn in Tris buffer/methanol without interference from each other and other ions. In HEPES buffer, M201-DPA demonstrated the selective ON-OFF fluorescence quenching at 524 nm toward Cu. On the other hand, in Tris buffer/methanol, M201-DPA showed the selective OFF-ON fluorescence enhancement upon the addition of Zn, which was specified by the hypsochromic shift at 448 nm. Additionally, M201-DPA showed extremely large Stokes shifts up to ∼150 nm. By controlling the concentration of Zn and Cu in a living cell, the imaging of a HepG2 cellular system was performed, in which the fluorescence of M201-DPA in the blue channel was decreased upon addition of Cu and was enhanced in UV channel upon addition of Zn. The detection limits of M201-DPA for Cu and Zn in buffer solutions were 5.6 and 3.8 ppb, respectively. Importantly, the Cu and Zn detection limits of the developed sensors were significantly lower than permitted Cu and Zn concentrations in drinking water as established by the U.S. EPA and WHO.

The direction and magnitude of surface dipoles directly affect the interfacial properties and can be tuned through molecular design. This article examines the effect of a hydrocarbon−fluorocarbon, "HC−FC", dipole on the structural and interfacial properties of self-assembled monolayers (SAMs) as the dipole is buried into the film. A series of selectively fluorinated alkanethiols with a progressively extended alkyl chain atop six fluorocarbons and an alkyl spacer of 11 hydrocarbons, H(CH 2 ) n (CF 2 ) 6 (CH 2 ) 11 SH, where n = 1−7 (HnF6H11SH) were prepared and used to generate SAMs on evaporated gold, allowing for the systematic burying of the HC−FC dipole into the film. Structural analyses of the films revealed well-ordered films with slight disorder/loose packing in the top alkyl chains. In addition, odd−even effects were observed in the orientation and wettability of the SAMs corresponding to the number of carbon atoms in the top alkyl chain, leading to the conclusion that the fluorinated segment behaves as a surrogate surface. As for the effect of the dipole on the wetting behavior of the films, the effect appears to be minimized after three methylene units; however, the structural features of the monolayers were also found to influence the wettability of the films.

This article examines the interfacial properties of phase-incompatible self-assembled monolayer (SAM) films derived from the adsorption of mixtures of bidentate alkanedithiols terminated with oligo(ethylene glycol) and perfluorocarbon tailgroups. Precise control of the composition of the surface was achieved by adjusting the mole fraction of the adsorbates in the developing solution, leading to the ability to tune the interfacial composition and properties. The key driving force for the mixing of the phase-incompatible adsorbates is the strong "chelate" binding of the bidentate headgroup to the surface of gold. To elucidate this phenomenon, SAMs generated from the analogous monodentate adsorbates were studied alongside those generated from the bidentate adsorbates. Characterization of the SAMs generated from the bidentate adsorbates revealed a 1:3 volume ratio of THF:EtOH solution as the optimal solvent for the generation of SAMs in which both sulfur atoms of the bidentate oligo(ethylene glycol) and perfluorocarbon adsorbates were predominantly bound to the surface of gold. All SAMs were characterized by ellipsometry, contact angle goniometry, X-ray photoelectron spectroscopy, and polarization modulation infrared reflection−absorption spectroscopy. These characterizations revealed the ability to generate films with mixed phase-incompatible groups in which the mole fraction of the adsorbates on the surface mirror those present in the developing solutions, opening up an avenue toward the creation of interfaces not found in nature, with potential use as nanoscale anti-adhesive coatings.