Selective, controllable, and reversible aggregation of polystyrene latex microspheres via DNA hybridization

The directed three-dimensional self-assembly of microstructures and nanostructures through the selective hybridization of DNA is the focus of great interest toward the fabrication of new materials. Single-stranded DNA is covalently attached to polystyrene latex microspheres. Single-stranded DNA can function as a sequence-selective Velcro by only bonding to another strand of DNA that has a complementary sequence. The attachment of the DNA increases the charge stabilization of the microspheres and allows controllable aggregation of microspheres by hybridization of complementary DNA sequences. In a mixture of microspheres derivatized with different sequences of DNA, microspheres with complementary DNA form aggregates, while microspheres with noncomplementary sequences remain suspended. The process is reversible by heating, with a characteristic "aggregate dissociation temperature" that is predictably dependent on salt concentration, and the evolution of aggregate dissociation with temperature is observed with optical microscopy.     

Spectral intensities in the fundamental bands of HF and HCl

The transition intensities of the fundamental bands of natural isotopic HF and HCl vapors have been measured with Doppler-limited resolution using a tunable difference-frequency laser spectrometer. Precise values for the band intensities, vibrational moments and Herman-Wallis F factors have been obtained for H¹⁹F, H³⁵Cl and H³⁷Cl.     

Doppler-limited spectroscopy of the 3ν3 band of SF6

The strongest portion of the 3ν₃ band of SF₆ has been recorded at T = 160 and 295 K with Doppler-limited resolution using a tunable laser difference-frequency spectrometer. The structure in this band has been identified with the P, Q, and R branches of one F_1u sublevel (with essentially l = 1 character) within the 3ν₃ vibrational manifold. Preliminary effective rotational constants have been obtained for this band from which the anharmonic parameters X₃₃, G₃₃, and T₃₃ can be estimated. The role of hot bands and of the other anharmonic sublevels is discussed in relation to prior interpretations of low resolution spectra and of the initial isotope selective stages of CO₂ laser photo-dissociation of SF₆.