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This communication describes a simple method for printing aqueous solutions with millimeter-scale patterns on a variety of substrates using an easily fabricated, paper-based microfluidic device (a paper-based “stamp”) as a contact printing device. The device is made from inexpensive materials, and it is easily assembled by hand; this method is thus accessible to a wide range of laboratories and budgets. A single device was used to print over 2500 spots in less than three minutes at a density of 16 spots per square centimeter. This method provides a new tool to pattern biochemicals—reagents, antigens, proteins, and DNA—on planar substrates. The accuracy of the volume of fluid delivered in simple paper-to-paper printing is low, and although the pattern transfer is rapid, it is better suited for qualitative than accurate, quantitative work. By patterning the paper to which the transfer occurs using wax printing or an equivalent technique, accuracy increases substantially., Chemistry and Chemical Biology

The combination of simple Electrochemical Micro-Paper-based Analytical Devices (E\(\mu\)PADs) with commercially available glucometers allows rapid, quantitative electrochemical analysis of a number of compounds relevant to human health (e.g., glucose, cholesterol, lactate, and alcohol) in blood or urine., Chemistry and Chemical Biology

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., Chemistry and Chemical Biology

This account reviews the use of templates, fabricated by patterning paper, for the delivery of aqueous solutions of reactants (predominantly, ions) in the preparation of structured, thin materials (e.g., films of ionotropic hydrogels). In these methods, a patterned sheet of paper transfers an aqueous solution of reagent to a second phase—either solid or liquid—brought into contact with the template; this process can form solid structures with thicknesses that are typically ≤1.5 mm. The shape of the template and the pattern of a hydrophobic barrier on the paper control the shape of the product, in its plane, by restricting the delivery of the reagent in two dimensions. The concentration of the reagents, and the duration that the template remains in contact with the second phase, control growth in the third dimension (i.e., thickness). The method is especially useful in fabricating shaped films of ionotropic hydrogels (e.g., calcium alginate ) by controlling the delivery of solutions of multivalent cations to solutions of anionic polymers. The templates can also be used to direct reactions that generate patterns of solid precipitates within sheets of paper. This review examines applications of the method for: (i) patterning bacteria in two dimensions within a hydrogel film, (ii) manipulating hydrogel films and sheets of paper magnetically, and (iii) generating dynamic 3-D structures (e.g., a cylinder of rising bubbles of O\(_2\)) from sheets of paper with 2-D patterns of a catalyst (e.g., Pd\(^0\)) immersed in appropriate reagents (e.g., 1% H\(_2\)O\(_2\) in water)., Chemistry and Chemical Biology

Although self-assembly (SA) in two dimensions (2D) is highly developed (especially using surfaces as a templates), SA in three dimensions (3D) has been more difficult. This paper describes a strategy for SA in 3D of diamagnetic plastic objects (mm- to cm-sized in this work, but in principle in sizes from [similar]10 μm to m) supported in a paramagnetic fluid by a non-uniform magnetic field. The magnetic field and its gradient levitate the objects, template their self-assembly, and influence the shape of the assembled cluster. The structure of the 3D assembling objects can be further directed using hard mechanical templates—either the walls of the container or co-levitating components—which coincide spatially with the soft template of the magnetic field gradient. Mechanical agitation anneals the levitating clusters; the addition of photocurable adhesive, followed by UV illumination, can permanently fuse components together., Chemistry and Chemical Biology