Custom-made pencils containing reagents dispersed in a solid matrix were developed to enable rapid and solvent-free deposition of reagents onto membrane-based fluidic devices. The technique is as simple as drawing with the reagent pencils on a device. When aqueous samples are added to the device, the reagents dissolve from the pencil matrix and become available to react with analytes in the sample. Colorimetric glucose assays conducted on devices prepared using reagent pencils had comparable accuracy and precision to assays conducted on conventional devices prepared with reagents deposited from solution. Most importantly, sensitive reagents, such as enzymes, are stable in the pencils under ambient conditions, and no significant decrease in the activity of the enzyme horseradish peroxidase stored in a pencil was observed after 63 days. Reagent pencils offer a new option for preparing and customizing diagnostic tests at the point of care without the need for specialized equipment.

Standard addition assays conducted on paper-based microfluidic devices are introduced as an alternative to external standards for calibrating quantitative tests. To demonstrate this technique, a colorimetric, paper-based, standard addition assay was optimized for the determination of glucose concentrations in the range of 0 to 5 mM. Comparable results were obtained from the assay via digital image colorimetry under three different lighting conditions.

Polycyclic aromatic hydrocarbons (PAHs) are used as adhesives that can be removed on-demand by sublimation without application of solvent or mechanical force. These adhesives are polycrystalline solids that enable bonding of glass, metal, and plastic with lap shear forces ranging from 5 to 50 N cm −2 . Systematic examination of factors governing bonding suggests that favorable chemical interactions between bonded surfaces and PAHs, and structural features at the surface of the substrate influence both the lap shear force and the mechanism of failure. Utilizing sublimable PAHs enables sequential bonding and release of substrates, as well as control of actuation of electronic systems through mechanical work.

Crystal engineering of temporary adhesion is important in diverse fields ranging from healthcare to manufacturing. Molecular solidsa broad class of crystalline materials characterized by discrete molecules with well-defined chemical and crystal structurescan be utilized as sublimable adhesives to achieve rapid adhesion, strong mechanical bonding, and facile on-demand release of surfaces. Through systematic investigation of the interfacial and bulk properties of molecular solids, this paper shows that this class of materials can exhibit remarkable mechanical strength (resistance to shear stress up to 2100 kPa and shear strain up to 37, as well as shear moduli up to 1000 kPa) yet enable on-demand (within minutes) release from adhesion through controlled sublimation without the application of solvents and/or mechanical force. Intermolecular interactions heavily influence the mechanical performance via preferential orientation of the solid relative to surfaces during the melt-bonding process. This research quantifies how chemical and crystal structures inform macroscopic mechanical properties of polycrystalline solids.