More Like this

1. Merging Electric Bacteria with Paper

   https://doi.org/10.1002/admt.201800118  

   Gao, Yang; Choi, Seokheun (July 2018, Advanced Materials Technologies)

   Abstract Paper‐based electronics (papertronics) are recently considered as one of the most exciting device platforms because of their flexibility, sustainability, eco‐friendliness, and low cost as well as their excellent mechanical, dielectrical, and fluidic properties. Now, innovative structure engineering techniques can manipulate diameters of the cellulose fibers of paper, smoothing the roughness and controlling the transparency for numerous device applications. Novel functionalization techniques of paper with organic, inorganic, and biological entities enable many engineering possibilities, revolutionizing papertronics for the next generation of electronics. Among those techniques for new functionalities, integrating electric bacteria into paper has attracted considerable interest as a new energy technique for papertronics. Paper has unique synergistic characteristics including a porous and hydrophilic environment for bacterial viability, a high surface area for bacterial accumulation, and sustainability even in resource‐limited settings. In this work, comprehensive analytical and experimental approaches to provide a novel but realistic and accessible power source from bacteria loaded into paper are pursued. This report provides new approaches to revolutionarily activate the biobattery and significantly improve its shelf life. Furthermore, for the first time the practical efficacy of the explored technique is ensured, generating on‐demand energy even in resource‐limited environments. 

   more » « less
2. Superomniphobic Papers for On‐Paper pH Sensors

   https://doi.org/10.1002/admi.201900232  

   Movafaghi, Sanli; Cackovic, Matthew_D; Wang, Wei; Vahabi, Hamed; Pendurthi, Anudeep; Henry, Charles_S; Kota, Arun_K (May 2019, Advanced Materials Interfaces)

   Abstract Paper‐based superomniphobic surfaces are of great interest because paper is flexible, inexpensive, lightweight, breathable, and recyclable. Prior reports on paper‐based superomniphobic surfaces have failed to demonstrate high mobility with low surface tension liquids. In order to overcome this issue, in this work, superomniphobic papers are developed through growth of nanofilaments on inherent microfibers of papers without noticeably altering their microscale features (i.e., diameter and distance of the microfibers). These superomniphobic papers display very low roll‐off angle, indicative of ultra‐high droplet mobility, even with low surface tension liquids. Here, a facile method is also developed to control the motion and adhesion of the droplets on the superomniphobic paper. Utilizing such liquid mobility in a controlled manner on these superomniphobic papers, a simple on‐paper pH sensor is fabricated. It is anticipated that this on‐paper, simple, and rapid detection methodology can also be extended to the colorimetric sensing of protein and chemical assays. Further, these superomniphobic papers have potential applications in water–oil separation and enhanced weight‐bearing capacity. 

   more » « less
3. A Paper-Based Biological Solar Cell

   https://doi.org/10.1177/2472630319875403  

   Liu, Lin; Choi, Seokheun (September 2019, SLAS TECHNOLOGY: Translating Life Sciences Innovation)

   A merged system incorporating paperfluidics and papertronics has recently emerged as a simple, single-use, low-cost paradigm for disposable point-of-care (POC) diagnostic applications. Stand-alone and self-sustained paper-based systems are essential to providing effective and lifesaving treatments in resource-constrained environments. Therefore, a realistic and accessible power source is required for actual paper-based POC systems as their diagnostic performance and portability rely significantly on power availability. Among many paper-based batteries and energy storage devices, paper-based microbial fuel cells have attracted much attention because bacteria can harvest electricity from any type of organic matter that is readily available in those challenging regions. However, the promise of this technology has not been translated into practical power applications because of its short power duration, which is not enough to fully operate those systems for a relatively long period. In this work, we for the first time demonstrate a simple and long-lasting paper-based biological solar cell that uses photosynthetic bacteria as biocatalysts. The bacterial photosynthesis and respiration continuously and self-sustainably generate power by converting light energy into electricity. With a highly porous and conductive anode and an innovative solid-state cathode, the biological solar cell built upon the paper substrates generated the maximum current and power density of 65 µA/cm²and 10.7 µW/cm², respectively, which are considerably greater than those of conventional micro-sized biological solar cells. Furthermore, photosynthetic bacteria in a 3-D volumetric chamber made of a stack of papers provided stable and long-lasting electricity for more than 5 h, while electrical current from the heterotrophic culture on 2-D paper dramatically decreased within several minutes. 

   more » « less
4. Ramsey, Paper, Scissors

   https://doi.org/10.1002/rsa.20950  

   Fox, Jacob; He, Xiaoyu; Wigderson, Yuval (July 2020, Random Structures & Algorithms)

   We introduce a graph Ramsey game called Ramsey, Paper, Scissors. This game has two players, Proposer and Decider. Starting from an empty graph onnvertices, on each turn Proposer proposes a potential edge and Decider simultaneously decides (without knowing Proposer's choice) whether to add it to the graph. Proposer cannot propose an edge which would create a triangle in the graph. The game ends when Proposer has no legal moves remaining, and Proposer wins if the final graph has independence number at leasts. We prove a threshold phenomenon exists for this game by exhibiting randomized strategies for both players that are optimal up to constants. Namely, there exist constants 0 < A < Bsuch that (under optimal play) Proposer wins with high probability if, while Decider wins with high probability if. This is a factor oflarger than the lower bound coming from the off‐diagonal Ramsey numberr(3,s). 

   more » « less
5. Paper-Based Supercapacitive Mechanical Sensors

   https://doi.org/DOI:10.1038/s41598-018-34606-1  

   Zhang, Ye; Sezen, Serdar; Ahmadi, Mahdi; Cheng, Xiang; Rajamani, Rajesh (January 2018, Scientific reports)

   Paper has been pursued as an interesting substrate material for sensors in applications such as microfuidics, bio-sensing of analytes and printed microelectronics. It offers advantages of being inexpensive, lightweight, environmentally friendly and easy to use. However, currently available paper-based mechanical sensors suffer from inadequate range and accuracy. Here, using the principle of supercapacitive sensing, we fabricate force sensors from paper with ultra-high sensitivity and unprecedented configurability. The high sensitivity comes from the sensitive dependence of a supercapacitor’s response on the contact area between a deformable electrolyte and a pair of electrodes. As a key component, we develop highly deformable electrolytes by coating ionic gel on paper substrates which can be cut and shaped into complex three-dimensional geometries. Paper dissolves in the ionic gel after determining the shape of the electrolytes, leaving behind transparent electrolytes with micro-structured fissures responsible for their high deformability. Exploiting this simple paper-based fabrication process, we construct diverse sensors of different configurations that can measure not just force but also its normal and shear components. The new sensors have range and sensitivity several orders of magnitude higher than traditional MEMS capacitive sensors, in spite of their being easily fabricated from paper with no cleanroom facilities. 

   more » « less