Droplet-Guiding Superhydrophobic Arrays of Plasmonic Microposts for Molecular Concentration and Detection.

Droplet-guiding superhydrophobic SERS substrates are created by a combinatorial lithographic technique. Photolithography defines the pattern of a micropillar array with a radial density gradient, whereas colloidal lithography features a nanotip array on the top surface of each micropillar. The nanotip array renders the surface superhydrophobic, and the pattern of micropillars endows the radial gradient of the contact angle, enabling the spontaneous droplet migration toward the center of the pattern. Water droplets containing target molecules are guided to the center, and the molecules dissolved in the droplets are concentrated at the surface of the central micropillar during droplet evaporation. Therefore, the molecules can be analyzed at the predefined position by Raman spectra without scanning the entire substrate. At the same time, the SERS-active nanotip array provides high sensitivity of Raman measurement.

Effects of ß-sheet crystals and a glycine-rich matrix on the thermal conductivity of spider dragline silk.

We measured the thermal conductivity of Araneus ventricosus' spider dragline silk using a suspended microdevice. The thermal conductivity of the silk fiber was approximately 0.4Wm-1K-1 at room temperature and gradually increased with an increasing temperature in a manner similar to that of other disordered crystals or proteins. In order to elucidate the effect of ß-sheet crystals in the silk, thermal denaturation was used to reduce the quantity of the ß-sheet crystals. A calculation with an effective medium approximation supported this measurement result showing that the thermal conductivity of ß-sheet crystals had an insignificant effect on the thermal conductivity of SDS. Additionally, the enhancement of bonding strength in a glycine-rich matrix by atomic layer deposition did not increase the thermal conductivity. Thus, this study suggests that the disordered part of the glycine-rich matrix prevented the peptide chains from being coaxially extended via the cross-linking covalent bonds.

Hierarchically structured ZnO/petal hybrid composites with tuned optoelectronic and mechanical properties.

Impressive biophotonic functions of flora in Mother Nature are often attributed to the optical diffraction occurring on hierarchically structured surfaces. The petals, displaying vivid colors, have diverse surface structures. The shapes of those structures alter significantly depending on the part of the petal, and they adjust the intensity of the reflected color and the light absorbance. Here, we added semiconducting properties to those intriguing optical functions arising from the unique surface structures. By means of atomic layer deposition (ALD), we conformally deposited a ZnO layer on the yellow rose petal, which has hierarchical surface structures and exhibits peculiar light absorbance behaviors. The resulting ZnO/petal composites revealed unique optoelectronic characteristics by synergetic effects between the biophotonic structures and inherent semiconducting properties. From several control experiments, we identified that the biophotonic hierarchical structures give rise to strong modulation of the light absorbance. We found that ZnO/petal exhibits superior mechanical stability to the raw petal likely due to the Zn infiltration into the petal. The design inspired by floral creatures with photonic structures and manufactured in the form of composite with mechanical stability and distinctive optoelectronic properties is believed to offer a new paradigm for the preparation of bioinspired photonic devices.

In-situ electrical conductivity measurement of oxidation of tin nanocluster film.

An in-situ electrical conductivity measurement of thin films of tin oxide nanoclusters for nano-devices was performed during metal cluster deposition and subsequent oxidation. From the current observation, the percolation threshold and the oxidation process are suggested. During baking at 200 degrees C, tin nanoclusters were transformed into low-conductivity stannous oxide and then into high-conductivity stannic oxide. From electron micrographs, it is suggested that the baking procedure is responsible for changing the oxide state and/or the crystallinity of the individual nanoclusters rather than changing the morphology of the film.

Vertically aligned carbon nanotube electrodes directly grown on a glassy carbon electrode.

Three-dimensional microelectrodes were fabricated using glassy carbon electrodes combined with vertically aligned carbon nanotubes (VACNTs). VACNTs were grown on various conducting electrode patterns including a carbon electrode fabricated by pyrolysis of a negative photoresist, with plasma-enhanced chemical vapor deposition using a bilayer Fe/Al catalyst. VACNT electrodes grown on the glassy carbon showed excellent electrochemical behavior, whereas VACNT electrodes grown on Pt showed poor electrochemical performance, presumably due to the poor contact between VACNTs and the Pt electrode. Electron microscopy showed that the VACNT layer was strongly bound to the carbon electrode, while that on Pt tended to peel away. The versatility of the all-carbon microelectrodes was also tested by using them for interfacing stem cells. Their superior mechanical properties and the electrical connectivity between the carbon electrode and the VACNTs, along with the simple fabrication process, suggest that glassy carbon may be a good conducting substrate for VACNT electrodes.

Carbon nanotube biosensors with aptamers as molecular recognition elements.

In this chapter, we discuss in detail the fabrication of carbon nanotube biosensors that use a single-walled carbon nanotube field-effect transistor (SWNT-FET) as a transducer, and aptamers as molecular recognition elements. We use a patterned growth technique to grow SWNTs on Si/SiO(2) substrates, and standard microfabrication procedures are then employed to fabricate sensing devices.

Oriented immobilization of antibody fragments on Ni-decorated single-walled carbon nanotube devices.

We herein demonstrate that Ni-decorated single-walled carbon nanotube field effect transistors (SWNT-FETs) combined with antibody fragments can be used as effective biosensing platforms. Nanoscales Ni particles 20 to 60 nm in diameter were formed on the sidewalls of SWNT-FETs using an electrochemical method. Carcinoembryonic antigen (CEA)-binding single chain variable fragments (scFvs) with a hexahistidine tag [(his)(6)] were synthesized using genetic engineering, and ordered immobilization of anti-CEA ScFvs on Ni nanoparticles was achieved by exploiting the specific interaction between hexahistidine and Ni. Whereas randomly oriented anti-CEA scFvs did not impart a noticeable change of conductance upon addition of CEA, a clear increase in conductance was observed using Ni-decorated SWNT-FETs functionalized with engineered scFvs.

Aptamers as molecular recognition elements for electrical nanobiosensors.

Recent advances in nanotechnology have enabled the development of nanoscale sensors that outperform conventional biosensors. This review summarizes the nanoscale biosensors that use aptamers as molecular recognition elements. The advantages of aptamers over antibodies as sensors are highlighted. These advantages are especially apparent with electrical sensors such as electrochemical sensors or those using field-effect transistors.

Detection of tumor markers using single-walled carbon nanotube field effect transistors.

We have developed a biosensor capable of detecting carcinoembryonic antigen (CEA) markers using single-walled carbon nanotube field effect transistors (SWNT-FETs). These SWNT-FETs were fabricated using nanotubes produced by a patterned catalyst growth technique, where the top contact electrodes were generated using conventional photolithography. For biosensor applications, SU-8 negative photoresist patterns were used as an insulation layer. CEA antibodies were employed as recognition elements to specific tumor markers, and were successfully immobilized on the sides of a single-walled carbon nanotube using CDI-Tween 20 linking molecules. The binding of tumor markers to these antibody-functionalized SWNT-FETs was then monitored continuously during exposure to dilute CEA solutions. The observed sharp decrease in conductance demonstrates the possibility of realizing highly sensitive, label-free SWNT-FET-based tumor sensors.

Single-walled carbon nanotube biosensors using aptamers as molecular recognition elements.

We report the real-time detection of protein using SWNT-FET-based biosensors comprising DNA aptamers as molecular recognition elements. Anti-thrombin aptamers that are highly specific to serine protein thrombin were immobilized on the sidewall of a SWNT-FET using CDI-Tween linking molecules. The binding of thrombin aptamers to SWNT-FETs causes a rightward shift of the threshold gate voltages, presumably due to the negatively charged backbone of the DNA aptamers. While the addition of thrombin solution causes an abrupt decrease in the conductance of the thrombin aptamer immobilized SWNT-FET, no noticeable change was observed with elastase.

Fano resonance in crossed carbon nanotubes.

We report the observation of the resonant transport in multiwall carbon nanotubes in a crossed geometry. The resonant transport is manifested by an asymmetric peak in the differential conductance curve. The observed asymmetric conductance peak is well explained by the Fano resonance originating from the scattering at the contact region of the two nanotubes. The conductance peak depends sensitively on the external magnetic field and exhibits Aharonov-Bohm-type oscillation.