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Elevated levels of ammonia in breath can be linked to medical complications such as chronic kidney disease (CKD) that disturb the urea balance in the body. However, early-stage CKD is usually asymptomatic and mass screening is hindered by high instrumentation and operation requirements, accessible and reliable detection methods for CKD biomarkers, such as trace ammonia in breath. Enabling methods would have significance in population screening for early-stage CKD patients. We herein report a method to effectively immobilize transition metal selectors in close proximity to single-walled carbon nanotube (SWCNT) surface using pentiptycene polymers containing metal-chelating backbone structures. The robust and modular nature of the pentiptycene metallopolymer/SWCNT complexes create a platform that accelerates sensor discovery and optimization. Using these methods, we have identified sensitive, selective, and robust copper-based chemiresistive ammonia sensors displaying low parts per billion detection limits. We have added these hybrid materials into the resonant radio frequency circuits of commercial near-field communication (NFC) tags to achieve robust wireless detection of ammonia at physiologically relevant levels. The integrated devices offer a non-invasive and cost-effective approach for early detection and monitoring of CKD. 

Chemical sensing has a vital role in promoting security and welfare. Functionalized carbon nanotubes (CNTs) possess unique electronic, mechanical and chemical properties, rendering them as exceptional transducers for developing highly sensitive, selective and robust chemical sensors. In this Primer, we discuss the progress and challenges associated with chemiresistive sensing using functionalized CNTs, providing an introductory overview, spanning from theoretical to experimental aspects. Various covalent and non-covalent CNT functionalization strategies that contribute to enhancing the sensitivity and selectivity of chemiresistive sensors are discussed, along with their respective merits and drawbacks. Additionally, this Primer focuses on the critical facets of experimental design, including material selection, device architecture and fabrication and best practices for sensor testing. This Primer also discusses the significance of rigorous data interpretation, analysis and reporting, ensuring reproducibility and reliability. Finally, this Primer highlights the existing limitations of CNT-based chemiresistive sensors and investigates potential strategies for enhancing sensor selectivity and sensitivity that may broaden their applicability in diverse fields, from environmental monitoring to biomedical diagnostics. By emphasizing the need to understand the molecular interactions between the sensor and target analyte to improve selectivity, this Primer aims to offer a comprehensive understanding of the current state of CNT-based chemiresistive sensing. 

Phenanthracene nanotubes with arylene-ethynylenebutadiynylene rims and phenanthracene walls are synthesized in a modular bottom-up approach. One of the rims carries hexadecyloxy side chains, mediating the affinity to highly oriented pyrolytic graphite. Molecular dynamics simulations show that the nanotubes are much more flexible than their structural formulas suggest: In 12, the phenanthracene units act as hinges that flip the two macrocycles relative to each other to one of two possible sites, as quantum mechanical models suggest and scanning tunneling microscopy investigations prove. Unexpectedly, both theory and experiment show for 13 that the three phenanthracene hinges are deflected from the upright position, accompanied by a deformation of both macrocycles from their idealized sturdy macroporous geometry. This flexibility together with their affinity to carbon-rich substrates allows for an efficient host−guest chemistry at the solid/gas interface opening the potential for applications in single-walled carbon nanotube-based sensing, 

Abstract In contemporary organic synthesis, substances that access strongly oxidizing and/or reducing states upon irradiation have been exploited to facilitate powerful and unprecedented transformations. However, the implementation of light-driven reactions in large-scale processes remains uncommon, limited by the lack of general technologies for the immobilization, separation, and reuse of these diverse catalysts. Here, we report a new class of photoactive organic polymers that combine the flexibility of small-molecule dyes with the operational advantages and recyclability of solid-phase catalysts. The solubility of these polymers in select non-polar organic solvents supports their facile processing into a wide range of heterogeneous modalities. The active sites, embedded within porous microstructures, display elevated reactivity, further enhanced by the mobility of excited states and charged species within the polymers. The independent tunability of the physical and photochemical properties of these materials affords a convenient, generalizable platform for the metamorphosis of modern photoredox catalysts into active heterogeneous equivalents. 

Human-in-the-loop experimentation enables interactive machine learning for continuous flow chemistry reaction planning and optimization.