No abstract

Cell-free biosensors are powerful platforms for monitoring human and environmental health. Here, we expand their capabilities by interfacing them with toehold-mediated strand displacement circuits, a dynamic DNA nanotechnology that enables molecular computation through programmable interactions between nucleic acid strands. We develop design rules for interfacing a small molecule sensing platform called ROSALIND with toehold-mediated strand displacement to construct hybrid RNA–DNA circuits that allow fine-tuning of reaction kinetics. We use these design rules to build 12 different circuits that implement a range of logic functions (NOT, OR, AND, IMPLY, NOR, NIMPLY, NAND). Finally, we demonstrate a circuit that acts like an analog-to-digital converter to create a series of binary outputs that encode the concentration range of the molecule being detected. We believe this work establishes a pathway to create ‘smart’ diagnostics that use molecular computations to enhance the speed and utility of biosensors.

Tracking progress towards Target 6.1 of the United Nations Sustainable Development Goals, "achieving universal and equitable access to safe and affordable drinking water for all", necessitates the development of simple, inexpensive tools to monitor water quality. The rapidly growing field of synthetic biology has the potential to address this need by isolating DNA-encoded sensing elements from nature and reassembling them to create field-deployable "biosensors" that can detect pathogenic or chemical water contaminants. Here, we describe current water quality monitoring strategies enabled by synthetic biology and compare them to previous approaches used to detect three priority water contaminants (i.e., fecal pathogens, arsenic, and fluoride), as well as explain the potential for engineered biosensors to simplify and decentralize water quality monitoring. We conclude with an outlook on the future of biosensor development, in which we discuss their adaptability to emerging contaminants (e.g., metals, agricultural products, and pharmaceuticals), outline current limitations, and propose steps to overcome the field's outstanding challenges to facilitate global water quality monitoring.

Synthetic biology has enabled the development of powerful nucleic acid diagnostic technologies for detecting pathogens and human health biomarkers. Here we expand the reach of synthetic biology-enabled diagnostics by developing a cell-free biosensing platform that uses RNA output sensors activated by ligand induction (ROSALIND) to detect harmful contaminants in aqueous samples. ROSALIND consists of three programmable components: highly-processive RNA polymerases, allosteric transcription factors, and synthetic DNA transcription templates. Together, these components allosterically regulate the in vitro transcription of a fluorescence-activating RNA aptamer:in the absence of a target compound, transcription is blocked, while in its presence a fluorescent signal is produced. We demonstrate that ROSALIND can be configured to detect a range of water contaminants, including antibiotics, toxic small molecules, and metals. Our cell-free biosensing platform, which can be freeze-dried for field deployment, creates a new capability for point-of-use monitoring of molecular species to address growing global crises in water quality and human health.

Disc fracture of the temporomandibular joint (TMJ) is a little-known pathological condition owing to its extreme rarity. We report two cases of elderly patients who were diagnosed with disc fracture of the TMJ based on MRI, and we review related reports. On physical examination, an incomplete bite and mild joint pain were observed on the affected side in both patients. An MRI showed a complete fracture in the intermediate zone of the articular disc in the TMJ; the posterior fragment was displaced posteriorly, causing occlusal change in the closed position of the condyle and an incomplete bite. Conservative treatment including manual manipulation, physical therapy and oral appliance had no effect on the occlusal abnormality. Although the inciting cause of the disc fracture remained unclear, the degenerative changes in the joint may have been a factor by increasing the brittleness and reducing the elasticity of the disc.