Magnesium and sulfate are each known to affect calcite growth and dissolution, but little is known about their combined effects on calcite growth rates. We grew calcite using the constant composition approach at ambient conditions, monitoring inhibition in solutions of Mg 2+ and SO 4 2− individually and together. The growth rate for pure calcite averaged 4.35 × 10 −6 mol m −2 s −1 but decreased to 0.34, 0.16, and 0.08 × 10 −6 mol m −2 s −1 in solutions with 40 mM of SO 4 2− , 13.3 mM of Mg 2+ , and 12.7 mM of MgSO 4 . We characterized the crystal form with scanning electron microscopy and atomic force microscopy. The {101̅ 0} crystal surface developed as the foreign ion concentration increased in the order SO 4 2− < Mg 2+ < MgSO 4 . Powder X-ray diffraction and X-ray photoelectron spectroscopy showed Mg incorporation of as much as 9.2 mol %. Mg 2+ inhibits calcite growth more effectively when SO 4 2− is also present, which we interpret to be the result of MgSO 4 ion pair formation. Sulfate promotes Mg 2+ dehydration, thereby allowing calcite uptake at lower temperatures. These results improve general understanding about the controls on biomineralisation and imply a need for re-examining the validity of the Mg/Ca thermometer, which uses the Mg composition in foraminifer for interpreting ancient seawater temperatures.

Semiconductor nanowire arrays offer significant potential for biosensing applications with optical read-out due to their high surface area and due to the unique optical properties of one-dimensional materials. A challenge for optical read-out of analyte-binding to the nanowires is the need to efficiently collect and detect light from a three-dimensional volume. Here we show that light from fluorophores attached along several μm long vertical Al2O3 coated gallium phosphide nanowires couples into the wires, is guided along them and emitted at the tip. This enables effective collection of light emitted by fluorescent analytes located at different focal planes along the nanowire. We unequivocally demonstrate the light-guiding effect using a novel method whereby the changes in emitted fluorescence intensity are observed when fluorescent cytoskeletal filaments are propelled by molecular motors along the wires. The findings are discussed in relation to nanobiosensor developments, other nanotechnological applications, and fundamental studies of motor function.

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We present a study of x-ray synchrotron radiation and neutron reflectivity on solid-supported lipid membranes prepared by spin coating. This technique has the advantage of allowing the control of the number of lipid layers by varying the deposition parameters. The experiments were performed on the cationic lipid 1,2-dioleoyl-3-trimethylammonium-propane chloride salt (DOTAP), the neutral lipid 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), the lipid mixture (DOTAP-DOPC), and the complex (DOTAP-DOPC∕DNA) deposited on wafers. Only single neutral lipids or lipid-peptide mixtures were deposited on solid substrate using the spin coating technique and characterized. Results on the structure of the deposited lipid layers indicate that DNA contributes to the order in the lipoplexes.

Biomolecular motors offer self-propelled, directed transport in designed microscale networks and can potentially replace pump-driven nanofluidics. However, in existing systems, transportation is limited to the two-dimensional plane. Here we demonstrate fully one-dimensional (1D) myosin-driven motion of fluorescent probes (actin filaments) through 80 nm wide, Al2O3 hollow nanowires of micrometer length. The motor-driven transport is orders of magnitude faster than would be possible by passive diffusion. The system represents a necessary element for advanced devices based on gliding assays, for example, in lab-on-a-chip systems with channel crossings and in pumpless nanosyringes. It may also serve as a scaffold for bottom-up assembly of muscle proteins into ordered contractile units, mimicking the muscle sarcomere.