Spin proximity effect in ultrathin superconducting Be-Au bilayers.

We present a detailed study of the effects of interface spin-orbit coupling on the critical field behavior of ultrathin superconducting Be/Au bilayers. Parallel field measurements were made in bilayers with Be thicknesses in the range of d=2-30 nm and Au coverages of 0.5 nm. Though the Au had little effect on the superconducting gap, it produced profound changes in the spin states of the system. In particular, the parallel critical field exceeded the Clogston limit by an order of magnitude in the thinnest films studied. In addition, the parallel critical field unexpectedly scaled as [FORMULA: SEE TEXT], suggesting that the spin-orbit coupling energy was proportional to Delta0/d2. Tilted field measurements showed that, contrary to recent theory, the interface spin-orbit coupling induces a large in-plane superconducting susceptibility but only a very small transverse susceptibility.

Cu(0) nanoclusters derived from poly(propylene imine) dendrimer complexes of Cu(II).

A family of diaminobutane core, poly(propylene imine) dendrimers coordinated to Cu(II), DAB-Am(n)-Cu(II)x (n = 4, 8, 16, 32, 64, x = n/2), was studied by means of extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) spectroscopies. The geometry of the dipropylene triamine (dpt)-Cu(II) end-group complexes for all dendrimer generations is reported for the first time and is found to be that of a square-based pyramid with each Cu ion bound to three nitrogen atoms (Cu-N distance approximately 2.03 A) of the dpt end group of the dendrimer. An oxygen atom residing 1.96 A from the Cu ion also occupies the equatorial plane, and the pyramid is completed by an axial oxygen at approximately 2.65 A. In addition, we report for the first time that reduction of the Cu(II)-dendrimer complexes with NaBH4 yields DAB-Am(n)-Cu(0)(cluster) species. Transmission electron microscopy (TEM) studies of the reduced species demonstrate that there is a systematic decrease in the size of the generated Cu clusters with increasing dendrimer generation. Additionally, it was found that the size of the nanoclusters is a function of the n/x ratio of the DAB-Am(n)-Cu(II)x precursor, with highly monodisperse, extremely small nanoclusters (r(cluster) = 8.0 +/- 1.6 A) obtained with n = 64 and x = 16. EXAFS and XANES measurements on the reduced DAB-Am(n)-Cu(0)(cluster) corroborate the TEM data, and provide additional information on the possible encapsulation of the Cu nanoclusters by the dendrimers.

Surface modification of poly(methyl methacrylate) used in the fabrication of microanalytical devices.

We report here the chemical modification of poly(methyl methacrylate) (PMMA) surfaces by their reaction with the monoanion of alpha,omega-diaminoalkanes (aminolysis reaction) to yield amine-terminated PMMA surfaces. It is found that the amine functionalities are tethered to the PMMA backbone through an alkane bridge to amide bonds formed during the aminolysis of the surface ester functionalities. The distribution of the amine termini is quite uniform as judged by fluorescence micrographs. It is found that the electroosmotic flow in aminated PMMA microchannels is reversed when compared to that in unmodified channels. In addition, it is demonstrated that enzymes can be immobilized onto the amine-terminated PMMA surfaces and are effective in the restriction digestion of dsDNAs. Finally, the availability of the surface amine groups is further demonstrated by their reaction with n-octadecane-1-isocyanate to form PMMA surfaces terminated with well-ordered and highly crystalline octadecane chains.

High-resolution near-infrared imaging of DNA microarrays with time-resolved acquisition of fluorescence lifetimes.

Ultrasensitive, near-infrared (NIR), time-resolved fluorescence is evaluated as a detection method for reading DNA hybridization events on solid surfaces for microarray applications. In addition, the potential of mulitiplexed analyses using time-resolved identification protocols is described. To carry out this work, a NIR time-resolved confocal imager was constructed to read fluorescence signatures from the arrays. The device utilized a 780-nm pulsed diode laser, a single-photon avalanche diode (SPAD), and a high-numerical-aperture microscope objective mounted in an epi-illumination format. Due to the small size of the components that are required to construct this imager, the entire detector could easily be mounted on high-resolution translational stages and scanned over the stationary arrays. The instrument response function of the device was determined to be 275 ps (fwhm), which is adequate for measuring fluorophores with subnanosecond lifetimes. To characterize the system, NIR dyes were deposited directly on different substrate materials typically used for DNA microarrays, and the fluorescence lifetimes of two representative dyes were measured. The fluorescence lifetime for aluminum tetrasulfonated naphthalocyanine was found to be 1.92 ns, and a value of 1.21 ns was determined for the tricarbocyanine dye, IRD800, when it was deposited onto poly(methyl methacrylate) (PMMA) and measured in the dry state. Finally, the imager was used to monitor hybridization events using probe oligonucleotides chemically tethered to a PMMA substrate via a glutardialdehyde linkage to an aminated-PMMA surface. The limit of detection for oligonucleotides containing a NIR fluorescent reporter was determined to be 0.38 molecules/microm2, with this detection limit improving by a factor of 10 when a time-gate was implemented. Fluorescence lifetime analysis of the hybridization events on PMMA indicated a lifetime value of 1.23 ns for the NIR-labeled oligonucleotides when using maximum-likelihood estimators.