We report a nanofluidic transistor based on a metal-oxide-solution (MOSol) system that is similar to a metal-oxide-semiconductor field-effect transistor (MOSFET). Using a combination of fluorescence and electrical measurements, we demonstrate that gate voltage modulates the concentration of ions and molecules in the channel and controls the ionic conductance. Our results illustrate the efficacy of field-effect control in nanofluidics, which could have broad implications on integrated nanofluidic circuits for manipulation of ions and biomolecules in sub-femtoliter volumes.

Inorganic nanotubes were successfully integrated with microfluidic systems to create nanofluidic devices for single DNA molecule sensing. Inorganic nanotubes are unique in their high aspect ratio and exhibit translocation characteristics in which the DNA is fully stretched. Transient changes of ionic current indicate DNA translocation events. A transition from current decrease to current enhancement during translocation was observed on changing the buffer concentration, suggesting interplay between electrostatic charge and geometric blockage effects. These inorganic nanotube nanofluidic devices represent a new platform for the study of single biomolecule translocation with the potential for integration into nanofluidic circuits.

Hollow inorganic nanotubes are attracting a great deal of attention due to their fundamental significance and potential applications in bioanalysis and catalysis. 1 Among them, silica nanotubes are of special interest because of their hydrophilic nature, easy colloidal suspension formation, and surface functionalization accessibility for both inner and outer walls. These modified silica nanotubes and nanotube membrane have shown potential applications for bioseparation and biocatalysis. 2 Recently, bright visible photoluminescence from sol-gel template synthesized silica nanotubes was observed by Zhang et al. 3 In addition, the study of the physical and chemical nature of molecules or ions confined within the inorganic nanotubes is of great current interest.Silica nanotubes have been synthesized typically within the pores of porous alumina membrane templates using the sol-gel coating technique. 4 Alumina templates can be dissolved to liberate single silica nanotubes. These nanotubes prepared at low temperature [5][6][7] have porous walls and are relatively fragile. Once the templates are removed, the silica nanotubes will generally bundle up and become less oriented. The same applied to the silica nanotubes prepared at low temperature using other templates. [5][6][7] The fabrication of oriented, robust silica nanotube arrays is of interest for their potential use in nanoscale fluidic bioseparation, sensing, and catalysis. Here, we developed a well-controlled process to translate vertical silicon nanowire arrays into silica nanotube arrays through a thermal oxidation-etching approach. The obtained nanotubes perfectly retain the orientation of original silicon nanowire arrays. High-temperature oxidation (800-1000°C) produces relative thick and rigid walls that are made of condensed silica. This method could be useful for fabrication of single nanotube sensors and nanofluidic systems.Silicon nanowire arrays were prepared using chemical vapor deposition (CVD) epitaxial growth employing silicon tetrachloride (SiCl 4 , Aldrich, 99.99%) as the silicon source. Hydrogen (10% balanced by argon) is used to reduce SiCl 4 at high temperature (900-950°C). Gold thin film was coated on Si (111) substrates to initiate the growth of silicon nanowires via the vapor-liquid-solid growth mechanism. This approach was developed recently and has been used for the synthesis of vertical Si/SiGe superlattice nanowire arrays in our lab. 8,9 The silicon nanowire array samples are loaded into a tube furnace and heated at 800-1000°C for 1 h under the continuous flow of pure O 2 . These nanowires are uniformly oxidized to give SiO 2 sheaths with continuous silicon wire cores inside. We then leave the SiO 2 sheath intact and try to remove the thin silicon cores to create SiO 2 nanotubes. The processing details are presented in Figure 1. During the oxidation, the nanowire tips are also oxidized to give an oxide cap on each vertical wire, which could prevent the selective etching of silicon cores. Therefore, the first step after thermal oxidation...

We report the integration of inorganic nanotubes into metal-oxide-solution field effect transistors (FETs) which exhibit rapid field effect modulation of ionic conductance. Surface functionalization, analogous to doping in semiconductors, can switch the nanofluidic transistors from p-type to ambipolar and n-type field effect transistors. Transient study reveals the kinetics of field effect modulation is controlled by ion-exchange step. Nanofluidic FETs have potential implications in subfemtoliter analytical technology and large-scale nanofluidic integration.

When biomolecular reactions occur on one surface of a microcantilever beam, changes in intermolecular forces create surface stresses that bend the cantilever. While this phenomenon has been exploited to create label-free biosensors and biomolecular actuators, the mechanisms through which chemical free energy is transduced to mechanical work in such hybrid systems are not fully understood. To gain insight into these mechanisms, we use DNA hybridization as a model reaction system. We first show that the surface grafting density of single-stranded probe DNA (sspDNA) on a surface is strongly correlated to its radius of gyration in solution, which in turn depends on its persistence length and the DNA chain length. Since the persistence length depends on ionic strength, the grafting density of sspDNA can be controlled by changing a solution's ionic strength. The surface stresses produced by the reaction of complementary single-stranded target DNA (sstDNA) to sspDNA depend on the length of DNA, the grafting density, and the hybridization efficiency. We, however, observe a remarkable trend: regardless of the length and grafting density of sspDNA, the surface stress follows an exponential scaling relation with the density of hybridized sspDNA.

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We demonstrate two-dimensional multiplexed real-time, label-free antibody-antigen binding assays by optically detecting nanoscale motions of two-dimensional arrays of microcantilever beams. Prostate specific antigen (PSA) was assayed using antibodies covalently bound to one surface of the cantilevers by two different surface chemistries, while the nonreaction surfaces were passivated by poly(ethylene glycol)-silane. PSA as low as 1 ng/mL was detected while 2 mg/microl of bovine serum albumin induced only negligible deflection on the cantilevers.

A new multidentate ligand 1-(9-(1H-1,2,4-triazol-1-yl)anthracen-10-yl)-1H-1,2,4-triazole (tatrz) was designed and synthesized. Using tatrz as a building block, three novel coordination frameworks, namely, {[Cu(tatrz)2(NO3)2]·(CH3OH)·4H2O}n (1), {[Cu(tatrz)2(H2O)2](BF4)2}n (2), and [Mn(tatrz)2(SCN)2(CH3OH)]·2H2O (3) can be isolated. Anion-exchange experiment indicates that NO3(-) anions in the two-dimensional (2D) copper framework of 1 can be completely exchanged by ClO4(-) in an irreversible single crystal-to-single crystal (SC-SC) transformation fashion, as evidenced by the anion-exchange products of {[Cu(tatrz)2(H2O)2](ClO4)2·4CH3OH} (1a). Further, if 1a was employed as a precursor in N,N-dimethylformamide (DMF), an isomorphic solvate of {[Cu(tatrz)2(DMF)2](ClO4)2·2H2O}n (1b) can be generated during the reversible dynamic transformation process. When 1 was immersed in CH3OH, a distinct 2D layer {[Cu(tatrz)2(NO3)2]·4.4CH3OH·0.6H2O}n (1c) was isolated. Interestingly, the solvent-exchange conversion is also invertible between 1 and 1c, which exhibits spongelike dynamic behavior with retention of crystalline integrity. If the 2-fold interpenetrating three-dimensional (3D) framework 2 is selected, it can be transformed into another 2-fold interpenetrating 3D framework {[Cu(tatrz)2(H2O)2](ClO4)2·5.56H2O}n (2a) in a reversible SC-SC transformation fashion. However, when the light yellow crystals of mononuclear complex 3 were exposed to trichloromethane containing aromatic organic anthracene (atan), through our careful observation, the crystals of 3 were dissolved and reassembled into dark brown crystals of 2D crystalline coordination framework {[Mn(tatrz)2(SCN)2]·(atan)}n (3a). X-ray diffraction revealed that in 3a, atan acting as an organic template was encapsulated in the confined space of the 2D grid. Luminescent measurements illustrate that 3a is the first report of multidimensional polymers based on triazole derivatives as luminescent probes of Mg(2+).