Increasing the packing density of assays in paper-based microfluidic devices.

Paper-based devices have a wide range of applications in point-of-care diagnostics, environmental analysis, and food monitoring. Paper-based devices can be deployed to resource-limited countries and remote settings in developed countries. Paper-based point-of-care devices can provide access to diagnostic assays without significant user training to perform the tests accurately and timely. The market penetration of paper-based assays requires decreased device fabrication costs, including larger packing density of assays (i.e., closely packed features) and minimization of assay reagents. In this review, we discuss fabrication methods that allow for increasing packing density and generating closely packed features in paper-based devices. To ensure that the paper-based device is low-cost, advanced fabrication methods have been developed for the mass production of closely packed assays. These emerging methods will enable minimizing the volume of required samples (e.g., liquid biopsies) and reagents in paper-based microfluidic devices.

Flame retardant and hydrophobic coatings on cotton fabrics via sol-gel and self-assembly techniques.

Nanocoatings consisting of ammonium polyphosphate (APP), sodium montmorillonite (MMT), and vinyltrimethoxysilane (VTMS) were prepared via self-assembly and in situ sol-gel techniques and applied onto cotton fabrics to achieve both flame retardancy and hydrophobicity. The impacts of APP concentration on the hydrophobicity and fire resistance of the coated fabrics were investigated. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) characterization results verified the hydrolysis-condensation reaction of VTMS and the formation of Si-O-Si network structure. X-ray diffraction (XRD) proved the formation of a layered structure based on MMT nanosheets in the coatings. Both vertical flame test (VFT), limiting oxygen index (LOI), thermogravimetric analysis (TGA) and microscale combustion calorimeter (MCC) characterization were conducted to evaluate the flame retardancy, thermostability and heat release behavior of the coated cotton fabrics, respectively. The results suggested that a higher concentration of APP is beneficial for both hydrophobicity and flame retardancy of the coated substrates. Overall, our research provides a facile and very effective approach to prepare flame retardant and hydrophobic multifunctional coating for cotton fabric and other substrates.