This paper describes the fabrication and the performance of microfluidic paper-based electrochemical sensing devices (we call the microfluidic paper-based electrochemical devices, μPEDs). The μPEDs comprise paper-based microfluidic channels patterned by photolithography or wax printing, and electrodes screen-printed from conducting inks (e.g., carbon or Ag/AgCl). We demonstrated that the μPEDs are capable of quantifying the concentrations of various analytes (e.g., heavy-metal ions and glucose) in aqueous solutions. This low-cost analytical device should be useful for applications in public health, environmental monitoring, and the developing world.

Herein, we demonstrate the controlled formation of two-dimensional periodic arrays of ring-shaped nanostructures assembled from CdSe semiconductor quantum dots (QDs). The patterns were fabricated by using an evaporative templating method. This involves the introduction of an aqueous solution containing both quantum dots and polystyrene microspheres onto the surface of a planar hydrophilic glass substrate. The quantum dots became confined to the meniscus of the microspheres during evaporation, which drove ring assembly via capillary forces at the polystyrene sphere/glass substrate interface. The geometric parameters for nanoring formation could be controlled by tuning the size of the microspheres and the concentration of the QDs employed. This allowed hexagonal arrays of nanorings to be formed with thicknesses ranging from single dot necklaces to thick multilayer structures over surface areas of many square millimeters. Moreover, the diameter of the ring structures could be simultaneously controlled. A simple model was employed to explain the forces involved in the formation of nanoparticle nanorings.

[29] The Hall voltage was below the sensitivity limit of our measurement apparatus.[30] The diode factor is somewhat larger than the theoretical value for the recombination-limited case (2.0). This may be related to the electronic structure of the heterojunction used here. As the electron affinities of a-ZnOŔ h 2 O 3 and a-InGaZnO 4 are different, the heterojunction is thought to have a conduction band offset of~1.7 eV, forming a Schottky-type barrier. Therefore the electron injection at a forward bias condition is also affected by space charge±limited current, increasing the apparent diode factor.[31] N. Uekawa, T. Suzuki, S. Ozeki, K. Kaneko, Langmuir 1992, 8, 1.[32] T. Nakamura, T. Shimura, M. Ito, Y. Takeda, J. Solid State Chem. 1993, 103, 523. Versatile Nanopatterned Surfaces Generated via Three-Dimensional Colloidal Crystals** By Xin Chen, Zhimin Chen, Na Fu, Guang Lu, and Bai Yang* A surface possessing patterned self-assembled monolayers (SAMs) and having a desired morphology is nowadays an essential component of many areas of modern science and technology. Existing fabrication approaches, typically involving microcontact printing and soft lithography, [1,2] self-assembly, [3,4] and laser-assisted directed imprinting, [5] have been applied to many patterned surfaces.[6±8] A substantial amount of research focuses on the fabrication of nanoscale-patterned surfaces as a first step or a prerequisite in controlling crystallization, [9,10] fabricating biological and chemical sensors, [11,12] and engineering microelectronic and optoelectronic devices. [13,14] Therefore, to achieve two-dimensional (2D) nanopatterned SAMs and the desired morphologies on a substrate remains a promising challenge and receives a great deal of attention in establishing parallel nanofabrication techniques.Here we describe an alternative approach, namely the use of ªcolloidal crystal-assisted capillary nanofabricationº (CCACN), to fabricate a surface possessing nanostructured 2D arrays and SAMs with the assistance of confined three-dimensional (3D) colloidal crystals. Recently, 3D colloidal crystals have been used to prepare 3D photonic bandgap and multiporous materials due to their ease of use as templates or scaffolds when infilled with organic or inorganic components. [15,16] However, to our knowledge, 3D colloidal crystals have not been intentionally utilized to produce a surface with 2D nanoscale arrays, especially to pattern nanostructured SAMs on a substrate. On the other hand, the CCACN approach that we introduce here uses 3D colloidal crystals to generate a patterned surface with nanostructured arrays and SAMs and to develop a parallel surface-nanofabrication technique. We used the interstices of the confined 3D colloidal crystals and the space between two close substrate surfaces to guide the desired species and to thus fabricate arrays and SAMs with submicrometer and even nanometer control by combining delicate template technique and controllable capillary and dewetting approaches. Similar principles have been succ...

The fabrication of ordered microstructures is of importance to much of modern science and technology, which thus actively drives the development of various patterning technologies besides photolithography. Soft lithography, [1] encompassing many flexible methods, has become one of the most robust and versatile non-photolithographic routes to ordered microstructures. The success of soft lithography relies on the use of a poly(dimethylsiloxane) (PDMS) elastomer as a stamp, mold, or mask, which ensures the conformal contact between surfaces of the PDMS and substrates of interest and the easy release without destroying the formed microstructures. By flexibly applying different methods of soft lithography, a variety of materials (such as organic molecules, [2] proteins, [3] colloids, [4] metals, [5] and polymers [6] ) could not only be transferred from the surface of a PDMS stamp to the specific area of a substrate, but also be selectively removed from the substrate surface to the PDMS stamp surface using a lift-up process. [7] Colloidal crystals made of polymer or inorganic microspheres have attracted extensive interest due to their potential applications as sensing, [8] optical, [9] and photonic bandgap materials, [10] and for the creation of highly ordered macroporous materials [11] and high-strength ceramics.[12] Usually, specific microstructures are anticipated in colloidal crystals for their device applications, [13] e.g., chemical and biochemical sensors, and photonic chips. Based on photolithography and soft lithography technologies, a large number of solid surfaces could be patterned into nano-or micrometer-sized relief structures, [14] or areas with different properties, such as wettability, [15] charged nature, [16] or current density. [17] These patterned surfaces could be subsequently used to direct the self-assembly of microspheres for creating colloidal crystals with defined crystalline orientations, shapes, and sizes. Most of these methods are commonly based on the strategy of the confined selfassembly of microspheres, in which the patterning and formation of colloidal crystals take place simultaneously. In this communication, we report a complementary soft lithography technique to pattern the obtained colloidal crystals using a lift-up process. Because this method is based on the selective transfer of a single layer of close-packed microspheres from the crystal film to the PDMS stamp surface, it is possible to realize fine control over the microstructures of colloidal film using a layer-by-layer lift-up process. Figure 1 outlines the procedure used to pattern colloidal crystals using the lift-up soft lithography. Monodisperse silica microspheres were assembled into colloidal crystals on the silicon wafer by the evaporation of suspension (see Experimental). A PDMS stamp with patterned features was brought into conformal contact with the surface of the crystal film under a certain pressure. After the sample was heated at 100 C for 3 h and the PDMS stamp was carefully peeled away, a single layer ...

As the most widely used TCFs, indium tin oxide (ITO) can support high transparency (>90%) and low film resistance (<25 Ω sq −1 ). However, the inherent brittleness makes ITO easy to cracking. Meanwhile, conventional sputtering techniques and the limited reserves of indium also result in high material and processing costs. Therefore, it is quite challenging for ITO to adapt to the low-cost, flexible, and wearable applications.Several emerging conductive materials, including metal nanowires, metal grids, graphene, carbon nanotubes, and conductive polymers, have become potential substituents for the fabrication of high-performance TCFs. [12][13][14] Among them, silver nanowires (Ag NWs) have been regarded as the most promising alternative for replacing ITO, because of their good conductivity, high transparency, and especially excellent mechanical flexibility. [15] Comparable or even superior photoelectric properties have been achieved for Ag NW-based TCFs as compared to ITO. [16,17] The commonly used film deposition methods associated with the use of Ag NWs involve spin-coating, rodcoating, dip-coating, spraying techniques, etc. [18][19][20] The limited throughput and abundant material waste are the major challenges toward low-cost and large-scale mass production. It is therefore urgently needed to develop scalable solution processing techniques compatible for manufacturing Ag NW-based TCFs with limited material waste and good cost-effectiveness.Screen printing, as a technique for creating 2D patterns, represents an important step forward for manufacturing highperformance TCFs. [21] However, there exist many crucial challenges for making up printable Ag NW inks, such as complex formulation, environmental hazard (e.g., the use of fluorosurfactant as the binder/additive), and insufficient length of Ag NWs, which would largely limit the practical mass production and the conductivity as well as the flexibility of the resulting TCFs. [22,23] In general, long Ag NWs are preferred for obtaining high-conductive patterns with good flexibility. A high bonding strength between Ag NW patterns and flexible substrates is also critical for achieving stable photoelectric properties under mechanical deformations. Thus, a new type of environmentally friendly printable Ag NW ink with simple formulation, high conductivity, and good compatibility with flexible substrates is highly demanded for manufacturing high-performance Printable silver-nanowire (Ag NW) inks with simple formulation, low cost, and high conductivity are developed and screen printed on flexible poly(ethylene terephthalate) substrates. By using ultralong Ag NWs (≈75 µm in length) as the conductor, the screen-printed Ag NW patterns exhibit exceptional conductivity (up to 8.32 × 10 3 S cm −1 ) and excellent mechanical robustness. Rheological behavior suitable for screen printing is achieved by adjusting the formulation of the inks, which assures neat and smooth screen-printed lines with resolution as high as 100 µm. Uniform and honeycomb-structured Ag NW transparent condu...