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Paper-based analytical devices, or μPADs, have proven to be valuable bioanalytical tools for a broad range of applications. New methods for μPAD fabrication are needed, however, to facilitate their mass production at a competitive cost. To address this need, we report the use of a boronic acid-containing siloxane polymer (BorSilOx) for patterning hydrophobic barriers for μPADs. This material functions by covalently binding to hydroxyl groups in the paper substrate. It is compatible with inkjet printing or roll-to-roll (stamping) processes, as demonstrated here using three different deposition methods. BorSilOx is able to render a broad range of cellulosic materials (from paper towels to wood) hydrophobic, with contact angle measurements demonstrating superhydrophobicity in many cases. We further demonstrate the utility of the polymer in μPADs via assays for pH and glucose.

Many (if not most) biosensors rely on functional silane coatings as a first step toward covalent immobilization of specific capture molecules. While methods for silanization of silica (SiO 2 ) surfaces are very well developed, less has been done to develop and characterize silanization methods for alternative substrates, such as alumina (Al 2 O 3 ). In particular, the behavior of Al 2 O 3 coatings grown on aluminum under ambient conditions has not been studied. To address this issue, we have tested solution-phase deposition of two silanes on Al 2 O 3 (3-aminopropyl triethoxysilane and 3-triethoxysilyl)propylsuccinic anhydride) and their applicability to analyte-specific biosensing. Contact angle measurements and imaging via Scanning Electron Microsopy (SEM) were employed to characterize surfaces. We find that 3-aminopropyl triethoxysilane produces well-behaved films and demonstrate that this surface can undergo further reaction with glutaraldehyde followed by an anti- Bacillus subtilis antibody to yield functionalized Al 2 O 3 surfaces capable of specific capture of B. subtilis spores (a model of B. anthracis , the causative organism of Anthrax). In contrast, 3-triethoxysilyl)propylsuccinic anhydride did not behave well with Al/Al 2 O 3 under the reaction conditions tested. In addition to providing specific protocols for Al/Al 2 O 3 functionalization, this work highlights the importance of surface chemistry assessment in the development of new sensors.

Detection of antibodies to upper respiratory pathogens is critical to surveillance, assessment of the immune status of individuals, vaccine development, and basic biology. The urgent need for antibody detection tools has proven particularly acute in the COVID-19 era. We report a multiplex label-free antigen microarray on the Arrayed Imaging Reflectometry (AIR) platform for detection of antibodies to SARS-CoV-2, SARS-CoV-1, MERS, three circulating coronavirus strains (HKU1, 229E, OC43) and three strains of influenza. We find that the array is readily able to distinguish uninfected from convalescent COVID-19 subjects, and provides quantitative information about total Ig, as well as IgG- and IgM-specific responses., (Copyright © 2020 Elsevier B.V. All rights reserved.)