Programming Complex Behavior in DNA-based Molecular Circuits and Robots

Integrated electronic circuits, like those found in cellphones and computers, are ubiquitous in our information-driven society. The success of electronics has, in part, been due its modular architecture that enables individual components to be independently improved while the overall device functionality remains unchanged. Over the last two decades the emerging field of dynamic DNA nanotechnology has been trying to apply the underlying philosophy of electronics to biochemical circuits. DNA nanotechnology employs rationally designed DNA molecules as building blocks of biochemical circuits that can, in principle, enable powerful applications like diagnostics and therapeutics. Researchers in the field of DNA nanotechnology have developed simple elements to construct biomolecular systems with desired functions. They have also developed molecular compilers for defining design principles. The cost of DNA synthesis has decreased by over three orders of magnitude in the past decade. This has lead to a non-trivial number of small scale circuits, like DNA-based logic gates and chemical oscillators, being implemented. However, the scalability of this approach has yet to be clearly demonstrated. n this thesis, we will discuss our main contributions to facilitating the advancement of DNA nanotechnology by developing systematic approaches for constructing modular DNA building blocks. These modules can be used to construct biochemical circuits and molecular robotic systems. The performance of the modules can be individually tuned and integrated into large-scale systems. Using automated circuit-design software and cheap unpurified DNA, we demonstrated the design and construction of a complex synthetic biochemical circuit consisting of 78 distinct DNA species. The circuit is capable of computing the transition rules of a cell updating its state based on its neighboring cells, defined in a classic computational model called cellular automata. Using a bottom-up approach, we first characterized the component necessary for basic Boolean logic computation. We then systematically integrated more circuit elements and eventually constructed the full circuit. By developing a systematic procedure for building DNA-based circuits using unpurified components, we significantly simplified the experimental procedure. By using unpurified DNA components, we reduced the cost and technical barrier for circuit construction, thus making the design and synthesis of complex DNA circuits accessible to even novice researchers. Next we demonstrated a cargo sorting DNA nano-robot, using a simple algorithm and modular building blocks. The DNA robot has a leg and two foot domains for exploring a two-dimensional DNA origami surface, and an arm and hand domain for picking up randomly located cargos and dropping them off at their designated locations. It is completely autonomous and is programmed to perform a random walk without requiring an external energy source. Further, we demonstrated sorting multiple copies of two distinct cargo species on the same origami. Additionally, by compartmentalizing each sorting task on a single origami, we showed that two distinct sorting tasks can be implemented on different origami simultaneously in the same test tube. The recognition of a cargo is embedded in its destination, therefore it is possible to scale up the system simply by having multiple types of cargos. The same robot design can be used for performing multiple instances of distinct tasks in parallel. The different modules can be integrated to perform diverse functions, including applications in time-release targeted therapeutics.</p

Compiler-aided systematic construction of large-scale DNA strand displacement circuits using unpurified components

Biochemical circuits made of rationally designed DNA molecules are proofs of concept for embedding control within complex molecular environments. They hold promise for transforming the current technologies in chemistry, biology, medicine and material science by introducing programmable and responsive behaviour to diverse molecular systems. As the transformative power of a technology depends on its accessibility, two main challenges are an automated design process and simple experimental procedures. Here we demonstrate the use of circuit design software, combined with the use of unpurified strands and simplified experimental procedures, for creating a complex DNA strand displacement circuit that consists of 78 distinct species. We develop a systematic procedure for overcoming the challenges involved in using unpurified DNA strands. We also develop a model that takes synthesis errors into consideration and semi-quantitatively reproduces the experimental data. Our methods now enable even novice researchers to successfully design and construct complex DNA strand displacement circuits

Identifying Vessel Branching from Fluid Stresses on Microscopic Robots

Objects moving in fluids experience patterns of stress on their surfaces determined by the geometry of nearby boundaries. Flows at low Reynolds number, as occur in microscopic vessels such as capillaries in biological tissues, have relatively simple relations between stresses and nearby vessel geometry. Using these relations, this paper shows how a microscopic robot moving with such flows can use changes in stress on its surface to identify when it encounters vessel branches.Comment: Version 2 has minor clarification

Compiler-aided systematic construction of large-scale DNA strand displacement circuits using unpurified components

Biochemical circuits made of rationally designed DNA molecules are proofs of concept for embedding control within complex molecular environments. They hold promise for transforming the current technologies in chemistry, biology, medicine and material science by introducing programmable and responsive behaviour to diverse molecular systems. As the transformative power of a technology depends on its accessibility, two main challenges are an automated design process and simple experimental procedures. Here we demonstrate the use of circuit design software, combined with the use of unpurified strands and simplified experimental procedures, for creating a complex DNA strand displacement circuit that consists of 78 distinct species. We develop a systematic procedure for overcoming the challenges involved in using unpurified DNA strands. We also develop a model that takes synthesis errors into consideration and semi-quantitatively reproduces the experimental data. Our methods now enable even novice researchers to successfully design and construct complex DNA strand displacement circuits

Fractal assembly of micrometre-scale DNA origami arrays with arbitrary patterns

Self-assembled DNA nanostructures enable nanometre-precise patterning that can be used to create programmable molecular machines and arrays of functional materials. DNA origami is particularly versatile in this context because each DNA strand in the origami nanostructure occupies a unique position and can serve as a uniquely addressable pixel. However, the scale of such structures has been limited to about 0.05 square micrometres, hindering applications that demand a larger layout and integration with more conventional patterning methods. Hierarchical multistage assembly of simple sets of tiles can in principle overcome this limitation, but so far has not been sufficiently robust to enable successful implementation of larger structures using DNA origami tiles. Here we show that by using simple local assembly rules that are modified and applied recursively throughout a hierarchical, multistage assembly process, a small and constant set of unique DNA strands can be used to create DNA origami arrays of increasing size and with arbitrary patterns. We illustrate this method, which we term ‘fractal assembly’, by producing DNA origami arrays with sizes of up to 0.5 square micrometres and with up to 8,704 pixels, allowing us to render images such as the Mona Lisa and a rooster. We find that self-assembly of the tiles into arrays is unaffected by changes in surface patterns on the tiles, and that the yield of the fractal assembly process corresponds to about 0.95^(m − 1) for arrays containing m tiles. When used in conjunction with a software tool that we developed that converts an arbitrary pattern into DNA sequences and experimental protocols, our assembly method is readily accessible and will facilitate the construction of sophisticated materials and devices with sizes similar to that of a bacterium using DNA nanostructures

Nanoparticle-induced neuronal toxicity across placental barriers is mediated by autophagy and dependent on astrocytes

The potential for maternal nanoparticle (NP) exposures to cause developmental toxicity in the fetus without the direct passage of NPs has previously been shown, but the mechanism remained elusive. We now demonstrate that exposure of cobalt and chromium NPs to BeWo cell barriers, an in vitro model of the human placenta, triggers impairment of the autophagic flux and release of interleukin-6. This contributes to the altered differentiation of human neural progenitor cells and DNA damage in the derived neurons and astrocytes. Crucially, neuronal DNA damage is mediated by astrocytes. Inhibiting the autophagic degradation in the BeWo barrier by overexpression of the dominant-negative human ATG4BC74A significantly reduces the levels of DNA damage in astrocytes. In vivo, indirect NP toxicity in mice results in neurodevelopmental abnormalities with reactive astrogliosis and increased DNA damage in the fetal hippocampus. Our results demonstrate the potential importance of autophagy to elicit NP toxicity and the risk of indirect developmental neurotoxicity after maternal NP exposure

Impossibility of Sufficiently Simple Chemical Reaction Network Implementations in DNA Strand Displacement

DNA strand displacement (DSD) has recently become a common technology for constructing molecular devices, with a number of useful systems experimentally demonstrated. To help with DSD system design, various researchers are developing formal definitions to model DNA strand displacement systems. With these models a DSD system can be defined, described by a Chemical Reaction Network, simulated, and otherwise analyzed. Meanwhile, the research community is trying to use DSD to do increasingly complex tasks, while also trying to make DSD systems simpler and more robust. I suggest that formal modeling of DSD systems can be used not only to analyze DSD systems, but to guide their design. For instance, one might prove that a DSD system that implements a certain function must use a certain mechanism. As an example, I show that a physically reversible DSD system with no pseudoknots, no effectively trimolecular reactions, and using 4-way but not 3-way branch migration, cannot be a systematic implementation of reactions of the form A⇌B that uses a constant number of toehold domains and does not crosstalk when multiple reactions of that type are combined. This result is a tight lower bound in the sense that, for most of those conditions, removing just that one condition makes the desired DSD system possible. I conjecture that a system with the same restrictions using both 3-way and 4-way branch migration still cannot systematically implement the reaction A+B⇌C