We introduce a simple, scalable, and portable electrochemical aptamer-based system for detection of the SARS-CoV-2 spike protein in saliva with attomolar sensitivity.

We report on the graphene-assisted growth, crystallization, and phase transition of zinc phthalocyanine (ZnPc) vertically oriented single crystal nanopillars. Postcrystallization thermal annealing of the nanostructures results in a molecular packing change while maintaining the vertical orientation of the single crystals orthogonal to the underlying substrate. Grazing incidence X-ray diffraction and high-resolution TEM studies characterized this phase transition from a metastable crystal phase to the more stable β-phase commonly observed in bulk crystals. These vertical arrays of crystalline nanopillars exhibit a high-surface-to-volume ratio, which is advantageous for applications such as gas sensors. We fabricated chemiresistor sensors with ZnPc nanopillars grown on graphene and demonstrated its selectivity for ammonia vapors, and improvement in sensitivity in the β-phase crystal packing pillars due to their molecular orientation increasing the exposure of the Zn ion to the ammonia analyte. This work highlights the first morphology-retentive phase transition in organic single crystal nanopillars through simple postprocessing thermal annealing. This study opens up the possibility of molecular packing control without large variations in morphology, a necessity for high-performance devices and establishing structure-property relations.

surface area. [12,13] To overcome this issue, nanostructured electrodes with small geometric footprints have been fabricated to achieve higher surface area than their planar counterparts. [14][15][16][17] Wearable sensors in particular should be biocompatible and withstand physiological strains due to motion and deformation of human skin, which is ≈30%. [18,19] Stretchable gold electrodes have been evaluated as glucose detection platforms. Chan et al. demonstrated stability at strains up to 230% with their solution-processed wrinkled gold glucose sensor, with a limit of detection (LOD) of 1 × 10 −3 m in artificial sweat. [20] Zhai et al. reported gold nanowire-based electrodes functionalized with glucose oxidase that were stretched to 20% strain to detect glucose concentrations of 1 × 10 −5 m in a solution of NaOH, while Zhao et al. demonstrated a gold-fiber based sensor functionalized with glucose oxidase capable of detecting 6 × 10 −6 m glucose in phosphate-buffered solution (PBS) under strains up to 200%. [21,22] It is critical to have low detection limits and high sensitivity due to lower concentration of glucose in sweat in comparison with other biological fluids. In this work, we introduce a highly stretchable electrode with the lowest limit of detection to the best of our knowledge for flexible enzyme-free glucose sensing at physiological pH.We introduce stretchable wrinkled electrodes for electrochemical sensing by depositing thin gold metal thin film on polyolefin (PO), which shrinks to 5% of its original area. During the shrinking process, the stiffness mismatch between the polymer and the gold thin film leads to buckling of the gold and results in hierarchical, wrinkled structures. The shrinking factor (the ratio of the average unshrunk electrode's geometric area to that of the processed electrode) of the prestressed thermoplastic PO is 21.8. The wrinkled thin film is then transferred to an elastomer. The transfer of the electrode from shape-memory polymer to elastomer results in additional shrinking due to lift-off process, with a total shrinking factor of 33.4 (Figure 1a). The transferred electrodes retain the wrinkled structures (Figure 1b-d) and upon application of strain, the wrinkles stretch and separate from each other as cracks are sustained in the gold thin film (Figure 1e-g).Electrochemical properties of the wrinkled electrodes were characterized by measuring the electrochemical active surface area (EASA) in different solutions. The wrinkled structures contribute to high surface area, which directly correlates Biosensors that detect analytes in sweat face the challenge of maintaining sensitivity upon miniaturization. Various materials and processes have been developed to create nanostructured electrodes with high surface areas to mitigate this issue. The need remains, however, for biocompatible materials that can be scalably integrated into wearable devices. This paper details a gold thin-film electrode fabricated using a thermoplastic shape memory polymer to create hierarchical wrinkled stru...