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The realization of microfluidic platforms with liquid pumping and fluid transport independent on external power sources is the goal of a major part of research in the lab-on-chip (LOC) field. Autonomous pumping, indeed, has a strong impact on the cost, usability and portability of LOCs. In this context, power-free pumping is exploited herein by the use of chemically-responsive flexible thin membranes (TMs) as tool to push liquids inside the microchannels of a LOC platform. The assembled device consists of a closed poly(dimethylsiloxane) (PDMS) micro-chamber in which H2O2 dismutation occurs by an artificial catalase (ACat) system, evolving oxygen and generating a pressure gradient. This pressure is then used to push a liquid contained within an upper chamber and inject it into a tailored microfluidic channel. The two chambers are overlapped and separated by a PDMS TM, whose flexibility allows the conversion of the chemical energy into mechanical forces. Thanks to the fine-tuning of the reaction conditions by modulating the ACat catalyst and/or reagents concentrations, a precise control over the injection time and forces of the liquid can be achieved.

Liquid flow in microchannels is completely laminar and uniaxial, with a very low Reynolds number regime and long mixing lengths. To increase fluid mixing and solubility of reactants, as well as to reduce reaction time, complex three-dimensional networks inducing chaotic advection have to be designed. Alternatively, turbulence in the liquid can be generated by active mixing methods (magnetic, acoustic waves, etc.) or adding small quantities of elastic materials to the working liquid. Here, polyelectrolyte multilayer capsules embodying a catalytic polyoxometalate complex have been suspended in an aqueous solution and used to create elastic turbulence and to propel fluids inside microchannels as an alternative to viscoelastic polymers. The overall effect is enhanced and controlled by feeding the polyoxometalate-modified capsules with hydrogen peroxide, H2O2, thus triggering an on-demand propulsion due to oxygen evolution resulting from H2O2 decomposition. The quantification of the process is done by analysing some structural parameters of motion such as speed, pressure, viscosity, and Reynolds and Weissenberg numbers, directly obtained from the capillary dynamics of the aqueous mixtures with different concentrations of H2O2. The increases in fluid speed as well as the capsule-induced turbulence effects are proportional to the H2O2 added and therefore dependent on the kinetics of H2O2 dismutation.

We report a widely applicable and highly controlled approach, based on electron beam lithography (EBL), to interconnect single nano-objects, previously immobilized onto solid surfaces, and to investigate the transport properties at the level of single nanostructures. In particular, a three-step EBL-procedure was used for this purpose by patterning two planar contacts on the sides of an individual nano-object. To demonstrate this approach, we use two different kinds of active elements: a semiconductor nanocrystal (tetrapod) and a thin triangular gold nanoprism (NT). (c) 2007 Elsevier B.V. All rights reserved.

In this work we demonstrate the possibility of obtaining a significant increase of the photoluminescence of colloidal semiconductor nanocrystals (NCs) by means of metallic nanopatterns. Highly ordered triangular-shaped gold nanopatterns (typical dimensions 200 nm) were fabricated on planar substrates by electron beam lithography (EBL). Colloidal semiconductor nanocrystals (core/shell CdSe/ZnS quantum dots or CdSe nanorods) dispersed in a polymer matrix (PMMA) were subsequently deposited on the substrates by spin-coating. The coupling between the surface plasmons (SPs) resonance band of the metallic nanostructures and the excitation/emission bands of the nanocrystals resulted in a strong enhancement of the fluorescence from the quantum emitters, as probed by confocal microscopy analyses. Importantly, the proposed approach allows a precise control of the shape and dimensions of the single metallic nanostructure (and consequently of the SPs resonances), thanks to the nanometer resolution of the EBL. Moreover, the concentration of the NCs dispersed in the blend, as well as the thickness of the active layer, can be finely tuned. These results may open interesting perspectives for a wide range of applications, such as photonic devices, LEDs, sensor technology, microarrays, single/few molecules experiments, and biochemical/biophysical investigations. (C) 2006 Elsevier B.V. All rights reserved.

Electrical conduction in solid state disordered multilayers of non-redox proteins is demonstrated by two-terminal transport experiments at the nanoscale and by scanning tunneling microscopy (STM/STS experiments). We also show that the conduction of the biomolecular films can be modulated by means of a gate field. These results may lead to the implementation of protein-based three-terminal nanodevices and open important new perspectives for a wide range of bioelectronic/biosensing applications. (c) 2006 American Institute of Physics.

The authors report a highly controlled approach, based on electron-beam lithography, to interconnect individual nano-objects for transport experiments. The process is based on a three-step procedure, consisting of fabrication of four alignment markers, localization of the nano-object after its immobilization onto functionalized surfaces, and interconnection of the single nanostructure by patterning two nanoelectrodes on its sides. The approach is highly reproducible and widely applicable and allows an alignment accuracy of 15-20 nm. Here they demonstrate the reliability of such technique by using a thin triangular gold nanoprism as the active element and show the I-V characteristics of the single nanostructure. © 2006 American Vacuum Society.